By its very nature Earth is unsettled and in continual motion. Earthquakes and volcanoes are an expression of the convective motions of the planet, and our existence on Earth is a consequence of this tectonic activity. Yet, as humans, we often struggle to understand our role in relation to such unpredictable natural phenomena and use different methods to attempt to find order in nature's chaos. In dwelling on the surface of our “unsettled planet”, we adapt and live with a range of ground vibrations, both natural and anthropogenic in origin. Our project, funded by the University of Bristol's Brigstow Institute, seeks to explore how we perceive and understand the shaky ground we live on, using an interdisciplinary approach that brings together the Earth sciences, the history of art and literature, and performance art. Inspired by historical commentary in the aftermath of large earthquakes, which frequently notes the unscheduled ringing of church bells excited by the shaking around them, we reflect on how these purported unscheduled bell-ringing events were caused not only by near earthquakes but also by distant incidents. To investigate this phenomenon, we installed a state-of-the-art broadband seismometer in the Wills Memorial Building tower to record how Great George (the tower bell) responds to the restless world around him. The installed seismometer has been recording activity around and within the tower on a near-continuous basis between late-March 2018 and January 2019. Here, we present the signals recorded by the seismometer as Great George overlooks the hustle and bustle of the city around him and investigate how connected we are to our unsettled planet, even from our tectonically quiet setting in Bristol. We find that the seismometer not only shows the ebb and flow of activity in and around Bristol but also registers earthquakes from as nearby as Lincolnshire, UK, or as far away as Fiji, halfway around the world. In order to contextualize our findings, our project also considers what determines how people have responded to earth-shaking events, drawing on both historical and recent examples, and looks to contemporary art practice to consider how an awareness of our unsettled planet can be communicated in new ways. The project has led to a number of art installations and performances, and feedback from artists and audiences shows how making art can be used to both investigate our connections with the Earth and to articulate (and even accept) the uncertainties inherent in encountering unstable ground.
People live with the ground shaking on a daily basis but when and why we become aware of this is contextual. To varying degrees, our capacity to dwell on the surface of the Earth is shaped by a learned tolerance of vibrations – sometimes benevolent and commonplace and at other times potentially calamitous – beneath and through our spaces of habitation. From the measurable footfall of humans walking along a pedestrian street in Bristol and the locomotion of individual elephants in Kenya to the co-ordinated motion of a stadium crowd and the combined impact of traffic noise, our world reverberates with the forces generated by human, animal and vehicular activity. The resulting vibrations go largely unnoticed as the ground motion that they produce is relatively small and fades into the hustle of everyday life. More attention grabbing, of course, are the vibrations produced by phenomena such as earthquakes.
Whether large or small, these vibrations provide vital information not only about the settings in which we live but also about the natural world around us and how we react to it. Just as footsteps are easier to discern when made on a creaky floor than they are on solid ground, so too does the setting in which Earth shaking occurs affect our perception of events. The 1985 magnitude-8 earthquake, 350 km away from Mexico City, for example, caused significant damage and loss of life. The extent of the damage was due to the nature of the ground beneath the city (Seed et al., 1988). Centuries earlier, as Nichols (2014) observes of the devastating 1755 Lisbon earthquake, “the historic Baixia area on the north side of the Tagus, the seat of government, with narrow streets and timber-built houses, rested on water-saturated alluvial sediment” that “liquefied during the earthquake and lost its bearing strength during the shock waves. Down the coast, Tavira, sitting on limestone met with few casualties”. Furthermore, human-induced earthquakes in Lancashire – due to hydraulic fracture stimulation (fracking) – register differently in the public consciousness (Williams et al., 2017) than much larger natural earthquakes in more seismically active regions such as Japan. An earthquake can thus be a disaster for one person, slightly worrying for another and barely perceptible for many more. The factors shaping individual responses might be simply determined by proximity to an earthquake but are more often influenced by other considerations including the underlying geology, local culture, collective memory, a familiarity with the associated phenomena, and the inequalities of disaster management. Living on an unsettled planet such as ours is tolerable for most of the time but at other times can be catastrophic.
This paper offers reflections on an interdisciplinary project that explored the relationship between scales of Earth shaking and thresholds of habituation. A response to the theme of “living well with uncertainty” proposed by the University of Bristol's Brigstow Institute, the project brought together a sound artist and researchers from the arts, humanities and earth sciences at the university. We found ourselves particularly interested in how people react to first-hand experiences with the fact that the ground is not stable or firm. At one extreme, this involved thinking about living in earthquake-prone regions, and at the other, it involved considering how someone from the countryside might find it unsettling to live in a city with heavy traffic vibrations. Indeed, as we discovered, thinking about how people live with the ground shaking daily does not just apply to distant places, rich in seismic activity, poised on a fault line, but can also be used to consider our own located positions, which, for the purposes of the project, took in the steep incline of Park Street and the Wills Memorial Building in Bristol: surely, the epitome of solid ground. Even familiar territory, we found, is constantly on the move, impacted by both our own bodies and by seismic events across the world. In the School of Earth Sciences, for example, our conversations took place against a background of heavy traffic vibration caused by buses passing by immediately outside the windows of the Wills Memorial Building: vibrations ultimately equivalent to those that might reach Bristol from a distant earthquake. In combining approaches drawn from geophysics, the humanities and the arts, then, we connected different categories of knowledge-making in order to grasp what is there or what could be there, not only under but also passing through the ground beneath our feet, and made links between what we know and what we imagine. The project focused on the current discourses surrounding controversial issues such as fracking but also looked at how past perceptions of seismic and volcanic hazards have evolved over time. We specifically aimed to probe the effects of seismic vibrations from regions of the Earth that are both near to and far from our relative haven in Bristol and to reflect on how those events are perceived by those around us. Our group aim was to engage with the sounding phenomena around us, thus enabling us to perceive the world in a different and more connected way.
Within our interdisciplinary team of co-authors, we found marked differences in our ways of working. It was easy to recognize this methodological range, but its implications were harder to fathom. We could use labels that corresponded to the badges of our professions – earth sciences, literary and historical studies, artistic practice – but the project asked us to think about our default settings and manner of approaching things. Some of us are more attentive to sounds, some of us to words, some to images, some to things, and some to numbers. Some of us think mainly in decades and centuries, while others in minutes or even in millions of years. We did not strain to find common ground; after all, we have a collective interest in the ground beneath our feet. It was always easy to talk, but this involved a particular kind of conversation, which one participant described as “specialists speaking colloquially”. Of course, we are also more than our disciplines. What we each brought to the discussion was dependent on the parts of the Earth's surface with which we are familiar; this was a frame of reference which came partly from professional activities but also personal trajectories, anecdotes, questions, lines from a poem, an image and identities; all of these provided points of connection, but we ultimately found collective stimulus in a bell.
Great George (the bell in the tower of the Wills Memorial Building) became something of an emblem for us in that it offered a fusion of “vibrant matter” and symbolic resonance (Bennett, 2010). As a material object specifically designed and fabricated to resound in a particular way, the bell participates physically in the marking of time but also acts as a reminder of how bells have historically sounded in times of celebration, admonition and mourning. By using the bell as an instrument for registering vibration, whether that caused by the passage of buses on Park Street or that generated by seismic activity a thousand kilometres away, we reflected on technologies of recording, both those designed with a specific purpose in mind and those repurposed and used inventively and creatively. In its capacity to register vibrations, then, the bell's purpose as percussive instrument was revised, using the addition of a seismometer (Fig. 1), to become an instrument of measurement: a transformation that also asked us to think about how solid bodies, including our own, register the unpredictable motion of our unsettled planet. Bells have often been anthropomorphized, i.e. given human names and marked with inscriptions couched in the first person. If the place of Great George in the project lay partly in the rich potential of using a bell as an object to think with, its importance for us also owed something to the fact that it was physically present above us in the building in which we generally met and audible wherever we were in the city. Great George is an object that can be visited, touched and even swung; it is an object that is multi-vocal and expansive, in terms of both its E-flat tone – audible up to 20 km away – and its twitter feed – with a potentially global reach. The material qualities of the historic bell, cast in 1924, became particularly compelling when put into dialogue with modern scientific equipment, which was as exotic and mysterious to some of us as it was familiar to others.
Great George bell
The project also involved encounters with objects that were more familiar to
those of us working in the arts and humanities. A workshop in the Special
Collections of the university library allowed us to look together at printed
material on earthquakes ranging from the sixteenth to the nineteenth
century, drawn mainly from the Eyles Collection (Eyles and Eyles, 1679–1983). Here, the objects of our attention were sometimes fragile books
resting on foam cradles, with pages held down with snake weights, and works with
evocative paragraph-long titles such as “A true and exact relation of the
most dreadful earthquake which happened in the City of Naples and several
parts of that Kingdom, June the 5th, 1688: whereby about forty cities
and villages were either wholly ruin'd or extreamly damnified; eight
thousand persons destroy'd and about eight hundred wounded; of which four
hundred were digg'd out of the ruins, and many others miraculously
preserved, translated from the Italian copy printed at Naples, by an
eye-witness of those miserable ruins” (J. P., 1688). We scrutinized
striking images such as Athanasius Kircher's cross sections of the Earth
(Kircher, 2015), previously met as disembodied images on the web (a very
different experience from turning the pages of
A single-day public colloquium allowed us to share some of our developing ideas with a wider audience and to benefit from the expertise and insights of others. Part of the day adopted a traditional format of short papers. Three invited speakers discussed projects that independently involved dialogue between disciplines and audiences. Stephen Vaughan, a photographer from Bath Spa University, spoke about his work on the impact of earthquakes in Japan and the United States. His focus on earthquake-induced tsunamis encouraged us to include water more fully in our thinking. By exploring how individual seismic events are discernible in the geological and dendrochronological record on both shores of the Pacific, he also gave us another way to think about distance and how seismic activity connects places. Paula Koelemeijer, an Earth scientist then at the University of Oxford, reported on research conducted with Beth Mortimer (Mortimer et al., 2018), a biological scientist at the University of Bristol, bringing animals into the conversation. Not only was this research team able to track the movement of the elephants, differentiate between them and determine the kind of ground they were traversing but they also hypothesized that the elephants themselves were possibly able to communicate in this way, picking up on different frequencies produced by the tread of fellow elephants across distances of tens to hundreds of kilometres. Paul Denton from the British Geological Survey spoke about crowd-generated earthquakes. Since the bulk of conversations about human-induced seismicity surrounds activities such as fracking, it was surprising for many to learn that amassed human footfall during outdoor rock concerts or football games could result in ground vibrations equivalent to those induced by a magnitude 2–3 earthquake a few kilometres away. Low-cost seismometers, e.g. built from Lego and installed in schools, can pick up such vibrations as well as other earthquakes, extending the kinds of possible audience invited to attend to the movement of the unsettled planet.
Within the lecture theatre, charismatic objects from science and artistic practice helped to make ideas concrete. Speakers passed around 3D-printed models of the Earth and a fired-clay disc inscribed with a sound wave in the manner of an LP record. At the edge of the stage, a different kind of speaker – a huge amplifier – formed an intriguing presence, already reminding us of the sonic quality of seismic activity before allowing everyone to hear and feel the movement recorded by Great George the bell. Participants also gained a new awareness of the unsettled ground beneath the building by inhabiting other spaces, heading up the tower to meet Great George himself and look out over his soundscape, and sitting in a van at the base of the tower to listen to the amplified steps of passers-by (Fig. 2).
Workshop participant jumping near geophone set up to record foot traffic near the Wills Memorial Building.
These activities were carried out concurrent with our seismic instrumentation of the bell tower. In the following sections, we describe the setup of our experiment as well as the data that we gathered from the instrument between March 2018 and January 2019. We describe the data gathered in the context of how our bell tower is positioned not only within the interactions of our city but also in a larger global picture.
To quantify the contemporary vibrations of our unsettled planet, we used two
methods to collect seismic data. The bulk of these data were collected in
and around the Wills Memorial Building (WMB). The WMB tower is a neo-Gothic
reinforced concrete structure which stands 65.5 m above the street
level and is 16 m
The first of the two data collection methods utilized a 10 Hz vertical geophone which was embedded in the shallow subsurface outside the WMB (Fig. 2). A geophone is a sensitive instrument that converts ground motion into an electrical signal via a magnet suspended within a coil on small springs. The data collected by the geophone, such as the footsteps of pedestrians on the pavement, were then converted into sound and played back through an audio system in real time. This allowed workshop participants to have both a visual and audio illustration of the vibrations recorded by the geophone.
The second method of data collection involved the installation of a
Nanometrics Trillium 120 PA three-component broadband seismometer, connected to
a Taurus data logger in the WMB tower (Fig. 1), to monitor the response of
Great George not only to the activity in and around the building but also to
signals from much farther distances. Such instruments are routinely deployed
at seismic stations around the world and are used to monitor the Earth's
seismic activity. This station was given the name GT01 and will be referred
to as such in the figures that follow. A broadband seismometer allows for
the accurate recording of seismic data (vibrations) in a broad range of
frequencies, which is ideal for capturing the variety of signals reaching
the tower. The three components of the seismometer record ground velocity in three
orthogonal directions: east–west (HHE), north–south (HHN), and up–down or
vertical (HHZ). The seismometer collected data at a rate of 100 Hz (100 samples s
On most days, Great George rings hourly by the action of an external clapper striking the exterior of the bell. The sound produced by this ringing can be heard as far as 1.6 km (1 mile) away; the maximum distance at which the bell can be heard extends up to 20 km (12 miles) (Ringing For England, 2019) when the internal clapper is used on special occasions. The seismic signal produced by the ringing of the bell stands out from the background activity around the tower, because it is produced by a source that is near the tower seismometer. The signal also contains a distinctive set of frequencies, which gives the bell its recognizable sound.
24 h of continuous seismic data recorded on three channels (HHE, HHN, HHZ) at the seismic station GT01, which is housed in the bell tower of the Wills Memorial Building. The orange box on the HHE (top) trace highlights the bell chimes at 22:00 LT (21:00 UTC). The red box shows the much larger bell-ringing for the Charter Day commemoration on 23 May 2018. Both highlighted signals are explored further in Fig. 4. The numbers in the upper right corner of each trace indicate the absolute maximum amplitude of that trace in counts.
There are a number of ways of visualizing seismic data; commonly, signals are displayed in the time domain where changes in amplitude of the waves are shown as a function of time (e.g. Fig. 3). Another method of visualizing seismic data is to display the signal in the frequency domain – here, the amount of energy in a frequency band is shown as a function of time. Such data are typically presented in a spectrogram as is done in Fig. 4, which represents the energy in each frequency band as a colour: warmer colours indicate stronger energy.
Zoomed-in spectrograms of the signals highlighted in Fig. 3. Panel
Figure 3 shows a day of data recordings on all three components of the
seismometer. These recordings were made on 23 May 2018, the university
Charter Day, when the bell was rung by a group of bell-ringers (see time-lapse video of the bell and Charter Day bell-ringing:
In addition to the signals produced by the ringing bell, three noteworthy
features are striking when looking at a full day of activity near the tower.
First, the station is always recording activity – the area is never quiet.
The tower sits along one of the major thoroughfares into and out of Bristol
city centre, including an often-used route to and from the Bristol Royal
Infirmary (hospital). Second, the data show a marked difference in activity
near the tower during the day as opposed to the night-time. And third, there
are several more hours of overnight activity on the weekends compared to a
typical weeknight; this is somewhat different from the observations of
Díaz et al. (2017), who note generally quieter weekends in their
study. Figure 5 shows 2 d of activity, presented as 1 h of data in
the time domain per line (much like an old-fashioned helicorder). The data
for Thursday (14 June 2018 00:00 UTC to 15 June 2018 00:00 UTC) (Fig. 5a)
show that there are fewer bursts of activity in the early morning hours
than there are later in the day starting at about 05:00 UTC until
Helicorder recordings showing seismic signals
Spectrograms of the time-domain data shown in Fig. 5. The
spectrogram is displayed in the bottom portion of panels:
Figure 6 displays the same data presented in Fig. 5 as a spectrogram. Again, both figures show higher amounts of energy or vibrations recorded during the daytime hours starting at about 06:00 LT and continuing throughout the day until about 22:00 LT at night on a typical weekday. They also show that this period of heightened activity extends almost 24 h on the weekend. This is particularly clear on the condensed seismogram displayed above the two spectrograms. These examples confirm what we already know, namely that there is more activity in a city centre during work hours and also late at night on the weekends; however, the recorded data also evidence the extent to which our cities are never silent, existing as environments continuously animated by ground vibrations. A notable departure from this constant hum of activity comes in the wake of the 2020 Covid-19-related lockdowns. The nearly global stay-at-home orders have resulted in a corresponding global decrease in seismic background noise levels. In Brussels, Belgium, for instance, the reduction in background noise is such that, in some cases, seismic events at the same high-frequency levels as the background noise can be detected and surface stations have the same signal quality as borehole stations buried at depths of 100 m (Gibney, 2020).
During the
When an earthquake occurs, it releases energy in the form of seismic waves
which radiate away from the earthquake source in all directions. This energy
can be picked up by seismometers, because they are highly sensitive
instruments capable of measuring vibrations not only in the immediate
vicinity of the instrument but also from regional and teleseismic
distances. What distinguishes a regional event from a teleseismic event is a bit
arbitrary, but generally, teleseismic events are considered to be those that
occur at distances greater than 1000 km and regional events are closer.
Charles Richter (Richter, 1935) established an empirical magnitude scale for
assessing the size of local seismic events (abbreviated
Lincolnshire earthquake
An example of a local or near-regional earthquake was recorded by the tower seismometer on 9 June 2018. This magnitude-4.3 earthquake occurred near Grimsby, Lincolnshire, UK. Signals from regional (or teleseismic) earthquakes look very different at distant stations than they do at stations near the source (compare the images in Fig. 7). As a seismic wave propagates through the Earth, its signal gets weaker and weaker as the seismic wave spreads out – this is known as spherical divergence or geometrical spreading. Furthermore, the Earth acts as a natural filter, absorbing high-frequency energy. The ability to distinguish these signals from the background noise at distant stations often requires the application of a filter to remove cultural noise like that seen in Fig. 6 in the frequency range of 5–20 Hz. For most of the distant earthquakes recorded in the tower, a filter of 0.1 to 1 Hz was used, which is in a range well below the dominant cultural noise from traffic, people and machinery.
The seismic signal recorded near the Lincolnshire earthquake clearly shows
the onset of the seismic wave train at station LMK, which is located near
Market Rasen, Lincolnshire, England, UK (latitude 53.4573
The Lincolnshire event was relatively small compared to several other large
and devastating earthquakes that occurred in 2018. As indicated above,
Richter's original magnitude scale is only appropriate for local events, so
instead, these large events are reported in the moment magnitude (
Filtered seismic waveform showing some of the seismic phases
visible from the 28 September 2018 Palu, Indonesia, earthquake. The
vertical-component waveform is bandpass filtered between 0.01 and 0.1 Hz to
isolate the signals of interest. The earthquake occurred at a depth of 20 km
and was
Although this earthquake was almost 110
When examining data from distant, large earthquakes, early researchers
(Oldham, 1906; Mohorovičić, 1910; Jeffreys, 1926; Lehmann, 1936)
could identify simple arrivals from P and S waves, but they could also see
other arrivals as seismic energy propagated and reverberated within the
Earth. Some of these additional phases (Pdiff, SP, PKKP, etc.) can be seen
in Figs. 8 and 9. The first signal to arrive at GT01 is the P wave
(Pdiff) that transits the Earth's mantle and diffracts along the core–mantle
boundary, which lies nearly 3000 km below our feet. Others that are visible
include those that interact with the Earth's core – for example, PKKP, is
the P wave that travels through the mantle and outer core, reflecting once
off the underside of the core–mantle boundary before reaching the seismic
station. Figure 9 shows the paths of various seismic phases that travelled
from the site of the earthquake, denoted by the star at 0
Plot showing some of the ray paths that seismic waves travelled on from the source in Indonesia to the seismic station set up in the WMB tower. The star shows the earthquake epicentre, while the pentagon denotes the station location. The inner core is shown in yellow, the outer core in beige, and the mantle in green and brown in the image. The thin crust on which we live is the black outer layer, which is barely visible in the image. The arrivals of these phases are marked on the seismogram in Fig. 8.
Seismic waves travel through the Earth like light travels through a prism;
as the waves cross layers they encounter variations in material properties,
which cause them to bend/refract, reflect or even change phase (e.g. P waves
convert to S waves). Analysis of these changes in the seismic waves
highlights the existence of the main layers within the Earth such as the
solid inner core, the liquid outer core, the mantle and the comparatively
thin crustal layer upon which life exists. The arrivals from an event such
as the Palu earthquake, which occurred at a relatively shallow depth of
Seismic recording of the magnitude-6.8 earthquake that occurred
44 km SW of Mouzaki, Greece, on 25 October 2018. The earthquake occurred at a
depth of 14 km and was
Closer to home, the
The amplitude of the seismic signal is a direct measure of the strength of vibrations affecting the seismometer. Signals that are produced by the horizontal motions of the ground or wind should produce a stronger signal on the horizontal channels (HHE and HHN) than they would on the vertical channel (HHZ). Likewise, signals produced by the vertical movement of the ground beneath the tower should produce a stronger signal on the vertical channel than they do on the horizontal channels. A look at the data from the tower (Fig. 11) shows that many of the signals recorded have higher amplitude on the vertical channel than they do on the horizontal channels. This is somewhat surprising since the expectation prior to the launch of this experiment was that the natural sway of the building, coupled with the impact of strong winds, would have greater effect on the horizontal channels than it would the vertical.
Seismic signals from the Lincolnshire earthquake recorded on one of the seismometers on the first floor of the WMB (beige) overprinted on a waveform of the same event recorded at station GT01 (black) in the WMB tower. The signal from the tower is more than double the amplitude of that recorded on the first floor of the building. Both traces were bandpass filtered between 2 and 10 Hz.
At various points during the period that the seismometer was installed in the tower, there were other seismometers recording in the Wills Memorial Building. Comparison of the data from these seismometers to that recorded on the tower seismometer showed that the signal in the tower was being amplified on all channels. This is not surprising as shaking is expected to be amplified in tall buildings, particularly when they are impacted by low-frequency shaking that matches their resonant frequency. A building's resonant frequency is approximately inversely proportional to its height (Pratt et al., 2017). An example of this signal amplification is shown in Fig. 11; here, the traces are filtered between 2 and 10 Hz to separate the earthquake signal from the background noise. This figure shows a comparison between the signals recorded from the Lincolnshire earthquake discussed above as recorded by a seismic instrument on the first floor (one floor above the street level) and GT01 in the WMB tower. The amplitude of the data recorded in the tower is more than double that recorded on the lower level.
While the day-to-day “seismic” activity around the WMB seems quite vigorous, it goes largely unnoticed by the city's inhabitants. This raises questions of how Bristol's daily seismic activity compares to seismic signals from real earthquakes. Data recorded in the tower of both background noise and the bell peal were compared to seismic data from earthquakes of varying magnitudes recorded at stations in Hawaii. The Hawaiian earthquakes were recorded on seismic stations that were within 1 to 5 km from the earthquake epicentre. As illustrated in Fig. 12, the data from the tower are barely visible against the higher-amplitude signals produced by real earthquakes. The smallest real seismic event on these plots is a magnitude-1 earthquake recorded at a station 1 km from the event. From the zoomed-in view in the inset of Fig. 12, the amplitude of the Bristol data (magenta and green) can be seen to fit neatly within the amplitude of the waveform for the magnitude-1 event (blue waveform). The Bristol data sit well below the vibrational levels of both the magnitude-3 (yellow) and the magnitude-6 (red) events. Placed in this context, it is clear why the activity in the city may go largely unnoticed. The amount of shaking produced by a magnitude-1 earthquake is seldom within the detection threshold of humans. However, as the event magnitude increases, it becomes easier for humans to detect a ground motion event in noisy settings even when the changes in magnitude are relatively small. This is because the commonly used earthquake magnitude scale is a measure of the amplitude of ground displacement and is logarithmic; this means that an increase of 1 in magnitude equates to a 10-fold increase in the amplitude of ground displacement. There is also a multi-fold increase between the energy released by an earthquake and its calculated magnitude. For instance, a magnitude-3 earthquake releases roughly 32 times more seismic energy than does a magnitude-2 earthquake.
Comparison plot of different seismic signals from various sources
recorded at stations in Hawaii (signals labelled
Historical reports of earthquake activity frequently include notes on church
bell peals accompanying ground shaking during an earthquake, even in
situations where the bell is not proximal to the earthquake epicentre. Such
incidents were reported in Charleston, SC, USA, following the 1811 New Madrid
earthquake, which occurred on a fault approximately 977 km away from the
church (LaCapra, 2011). Likewise, the spontaneous ringing of
church bells was heard as far away as Paris following the 1755 Lisbon,
Portugal, earthquake (Penna and Rivers, 2013). Both earthquakes in the
examples above were large, but it is also worth analysing the effect of the
energy released on structures far away from the epicentres. The “modified
Mercalli intensity scale” estimates that bells ring with earthquake
intensities of V to VI, which roughly corresponds to the shaking experienced
in a magnitude-5 earthquake near the epicentre. The relation between
earthquake magnitude and energy can be written as
This calculation shows that there is a large amount of energy released by a magnitude-5 earthquake, but this number only relates to the energy released in the immediate environment of the fault that generated the earthquake. As the seismic energy propagates out from the earthquake epicentre, it dissipates; this is referred to as geometric spreading. The formulae for estimating the relationship between the energy dissipation and earthquake distance are given in Eqs. (2) and (3) for surface waves and body waves (P and S phase), respectively,
The 1811 New Madrid earthquake has an estimated magnitude range of 7.0–8.0 (Johnston, 1996; Hough, 2004; LaCapra, 2011). As an example, we can therefore estimate the amount of seismic energy that arrived in Charleston, SC, USA. The surface wave energy reaching the city was about 6 orders of magnitude larger than the body wave energy but was only equivalent to the energy released by a proximal magnitude-3 earthquake. Magnitude-3 earthquakes are considered weak events that cause little to no structural damage. Therefore, for ringing to occur under these conditions, other factors may have been influential. For instance, church bells are often left in the “ready” position (Woodhouse et al., 2012) in which the bell is placed just beyond its unstable equilibrium position and held in place by a sliding stopper. In the ready position, the inertial forces that must be overcome to swing the bell are greatly reduced, which in turn also reduces the amount of ground shaking necessary to move the bell. In cases where bells are rung by the action of an external clapper, it would likely be easier to move the external clapper during an earthquake than it would be to move the bell and its internal clapper.
A third factor that may have influenced the ringing of the church bells during an earthquake is the amplification effect of the bell tower. Research by Blakeborough (2001) showed that while the ringing of the bell is dependent on the mechanics of the bell and the tower in which it is hung, the peak ground acceleration (PGA) typically required for unplanned ringing needs to exceed the PGA of a magnitude-5 earthquake. From our own experiment, illustrated in Fig. 11, there was at least an order of magnitude increase in amplification between the signals measured on the tower compared to the seismometer on the lower floors of the building. The signal measured in the tower was roughly double that measured on the lower floor but would not be enough to amplify the shaking from a magnitude-3 to a magnitude-5 event. Besides the basic amplification effects of the height of the tower, it is also reasonable to consider how resonance may play a role in the signal amplification. All structures have a natural frequency at which they will vibrate when a force is applied. For buildings, this natural frequency is affected by a number of factors such as building shape and material make-up but is most strongly affected by building height; tall buildings have a lower natural frequency than shorter ones. When incoming seismic waves have the same frequency as the natural frequency of a building, the shaking that that building experiences is amplified; this signal amplification may be up to 4–5 times as strong as the original arriving wave (Arnold et al., 2006). This resonance effect has been noted to cause differential building damage in past earthquakes; for example, during the 1985 Mexico City earthquake, the presence of soft sediments from an old lake bed beneath the city caused certain frequencies of the arriving earthquake wavefront to be amplified even though the city was 250 km away from the earthquake focus; the frequencies of these amplified signals coincided with the natural frequencies of buildings between 6 and 20 stories tall (Seed et al., 1988; Arnold et al., 2006). As such, the damage incurred by buildings in this height range was more severe than buildings outside of it. Therefore, if a similar resonance effect is experienced by a distant bell tower, it is possible that the tower may experience more shaking than other buildings in the area which could potentially result in unscheduled bell-ringing. All the above-mentioned factors may serve to increase the effect of seismic waves arriving from great distances; hence, a number of factors could have contributed to the historical unscheduled ringing of church bells reported following large earthquakes, such as that observed in Charleston following the New Madrid earthquake.
Monitoring ground shaking and earthquake activity is mostly the job of
scientists and researchers, whose areas of expertise connect with the
distant global environment. And for those who live near an area that
directly experiences the Earth's tectonic activities, the contact is only
too real and impacts daily lives. But for many where this impact is not
usually felt or experienced, being made aware of the constant noise and
movement occurring under our feet can be surprising. The creative aspect of
this project thus experimented with performance in order to encourage public
engagement with the energy, force and distant origins of particular sources
of sound; onlookers and audiences could fast track the “scientific
explanations” of the unsettled Earth's activity and instead perceive it in a
direct and visceral way. After hearing recordings captured during the
Artists perform a durational dance piece entitled
We found that the set of vocabularies we have for size, scale, distance and
time needed to be reimagined, processed and reassessed when contemplating
the vastness of the Earth, particularly by those of us not used to thinking
in this way. With this in mind, the third artwork coming from the ideas
raised by this interdisciplinary project dealt with temporality, exploring
the notion of geological time. The birth of planet Earth, its existence, and
its projected demise spans a very different duration compared to our
quotidian experience of the day to day. Shirley Pegna's
The various art installations and performances that have resulted from this
project demonstrate how people view everyday rumblings and vibrations of the
ground beneath our feet, but they also give insights into how we view the more
catastrophic nature of large earthquakes. Audience members were asked for
feedback after the
In general, the projects were well received and stimulated a diverse set of
personal experiences. Nevertheless, there are some common threads through
the remarks. To capture this, a summary of the comments from performers,
participants and audience members is presented through a word cloud (Fig. 14). The most commonly occurring words are
A word cloud formed by counting the occurrence of words in
comments from participants, the audience, and performers in art performances
and installations developed by Shirley Pegna, as part of the Unsettled
Planet project. Performances include the
Another common theme concerns togetherness (or a shared human experience
with planet Earth) and registers an ecological awareness that is
simultaneously both connective and disquieting. As one of the dancers in the
The feedback also demonstrates that how we react to ground motion is a very
personal experience, and it can vary widely between individuals. Some found the
performances comforting: “Love that sound”; “Very comforting”, whilst others found them unsettling:
“Spooky – scary”; “Made me feel ill”. Some found the immediacy of the listening experience exciting:
“Brilliant – noisy isn't it?”, while for others it evoked memories of previous embodied experiences.
Particularly striking is the use of simile – a figure of speech that looks
for resemblance – in the responses to
The projects made people think about the unsettled nature of the Earth and
question its cause (“Was it the trees and the roots (making the sound)?”). As an audience member at the
Through these experiences, audience members and performers could derive a sense of uncertainty associated with experiencing an earthquake (how will I react? how bad will it get?). But their responses also demonstrate some of the challenges inherent in earthquake hazard awareness and preparedness. As one audience member said: “The voyeuristic nature of the performance would break once the performers pushed themselves into the crowd, activating the audience to move or become a part of the performance itself”. In some ways, people are like this with natural disasters. What is initially an interesting or entertaining thing to watch quickly changes when you experience it first-hand and become part of it. This work shows how performance art can be used to better appreciate and communicate our connection with the Earth while also improving our awareness of natural hazards such as earthquakes.
As discussed above, the Earth is constantly moving and vibrating around us, although this motion is a frequently accepted part of our daily lives and often ignored. This general acceptance of ground motion leads to the question of what determines human responses to Earth vibrations. The eventual acceptance of the theory of plate tectonics, some 50 years ago, ushered in a new scientific paradigm that explains the driving forces behind earthquakes (McKenzie, 1977; Oreskes, 1999). The Earth through its frantic effort to cool itself through convection and conduction, has created and destroyed entire tectonic plates many times through its history. However, at various points throughout our human history, earthquakes have played a central role in human thought and development. From early ideas concerning punishment or exercise of divine wrath to the facilitation of dynastic changes to enable modernization, earthquakes have been explained through folklore, religion and philosophy (Winchilsea, 1669; Mallet, 1728; Ponton, 1872). The Great Lisbon earthquake of 1755 is a famous example of an earthquake accelerating divisions between religion and science, leading thinkers and poets to question the benevolence of a divine god. Indeed, as Juengel (2009) summarizes, “Lisbon has of course long loomed as the world historical event that cracked the foundation of Enlightenment optimism, driving Voltaire to abandon Leibniz, Pope, and the rightness of what is and to embrace Bayle's more profound doubt” (see also Nichols, 2014).
For historical earthquakes from the “pre-instrumental era” prior to the last decade of the nineteenth century, the only method of study is to use intensity, which is a number quantifying the degree of shaking at a particular point. In the case of the earthquake of 6 April 1580, for example, which was felt throughout a large portion of England, northern France and the Low Countries, and it is now thought to have had an epicentre in the Strait of Dover. A rich multi-lingual textual record of sources, including letters, new pamphlets, prayers, treatises and even satires, bears witness to the effects of the shock (Neilson et al., 1984). These sources include not only vivid literary responses to the earthquake, all the more fascinating for the different generic and ideological frameworks through which they are presented, but also document the particular effects felt in specific locations: from falling masonry to bells ringing and theatres shaking (Totaro, 2017). In his discussion of the event, the physician and translator Thomas Twyne (1580) wrote of how “the very shaking caused the bells in some steeples to knoll a stroke or twain”, and that “the tops of half a dozen chimneys in London were cast down”. As someone who did not feel the ground moving personally, he was keen to address how not everyone felt the effects of the earthquake equally:
Some that were above in their chambers, commonly judged that some violence
had been done to their houses beneath. Some that remained below, found fault
with tumbling and trampling above. Some imputed the rattling of wainscots to
rats and weasels; the shaking of the beds, tables, and stools to dogs; and the
quaking of their walls to their neighbours rushing on the other side. And as
their opinions were sundry, so were their speeches thereupon diverse, until
a common conference being had, they were resolved upon their common case and
danger. For many not trusting to their own judgement, and partly also moved
with fear, ran out into the streets to know if the like had happened unto
others.
From the perspectives of the humanities, then, responses to the ground
moving can be seen to be determined by how lived experiences are processed
and understood within pre-existing cultural, theological, linguistic,
philosophical and narrative frames. In historical reports it seems to matter
whether the right language can be found to articulate the experience of the
ground shaking, and this can often involve analogy in order to communicate
the precise nature of the sensations experienced, which can then be likened
to a cognate encounter of unsteadiness or vibration. Perhaps more
importantly, the use of literary genre to construct a deliberate
interpretative frame asks us to consider how genre gives shape to different
kinds of temporal relationships and possible endings, owing to how genres
can be used to determine narrative expectations by connecting causality,
action and consequences in particular ways. In Europe, representations of
earthquakes have been historically framed not only by tragic modes which
speak of hubris, divine retribution, and even apocalypse, but also through
providential models, including those of recuperation, where the earthquaking takes on the significance of a divine admonition: calling the
faithful both to repent and to give thanks for their deliverance. These
literary and theological frameworks co-exist in generative ways with local
folklore, eyewitness testimony and the rationalizations of science, which
in Europe, from the late sixteenth century onwards, grew out of the
narrative methods of natural philosophy and drew on the authority of
classical treatments of earthquakes and their causes by writers such as
Aristotle and Lucretius (Prewitt, 1999; Passannante, 2008). In early
modern Europe, ca. 1500–1800, surviving textual responses to natural disasters
also reveal active transnational networks of printed news – an early
version of our contemporary rapid mediation of such phenomena – and the
ways in which environmental events, including floods, volcanoes and
earthquakes, could be used for political ends, prompting the
state-authorized publication of guides for public worship (Mears, 2012;
Caracciolo, 2016). The historical records of natural disasters are also
useful for dating literary works. The composition of William Shakespeare's
To write in response to catastrophe, then, is to engage imaginatively with
the limits of human reasoning and to formulate representational and
aesthetic modes capable of handling epistemological change (Heringman,
2003). As Totaro (2017) observes of the 1580 event, “the earthquake
imprinted the body-mind and altered all other sensory-related terrain
immediately”: a reaction that transformed the event into “a subject of epic
proportion”. To connect the scale of the earthquaking to the epic mode is
perhaps to consider what it takes for a culture to live and rebuild in the
aftermath of natural disaster; yet, for writers of the eighteenth century
responding to the Lisbon earthquake of 1 November 1755, the magnitude of the
destruction was connected to the sublime. As the I can't conceive that “what is, ought to be,” In this each doctor knows as much as me. We're told by Plato, that man, in times of yore, Wings gorgeous to his glorious body wore, That all attacks he could unhurt sustain, By death ne'er conquered, ne'er approached by pain. Alas, how changed from such a brilliant state! He crawls 'twixt heaven and earth, then yields to fate. Look round this sublunary world, you'll find That nature to destruction is consigned.
A similar scaling of response, used to confront the “unthinkable”, is seen
when comparing large earthquakes between regions in modern society. In
general, people living in earthquake-prone areas in developed countries like
Japan tend to be more comfortable with large earthquakes than those living
in developing but earthquake-prone countries like Haiti. This relative
comfort is imparted by confidence in the engineering and disaster management
in place in developed countries (Kahn, 2005). However, this
confidence can potentially be a double-edged sword leading to complacency
which may result in significant loss of life and resources as illustrated in
the aftermath of the 2011 Tohoku earthquake (
In recent years, humans have also become acutely aware that their activities
and interactions with the subsurface of the Earth induce earthquakes, which are
sometimes in magnitude at dangerous levels. However, human acceptance of
such
In contrast, fracking has led to much larger earthquakes in Canada (up to
During the final stages of writing this paper, Covid-19 reached the UK, and we all went into a period of extended lockdown and isolation. As everyone stayed at home, except those providing essential services, the anthropogenic noise in the country dropped to levels not experienced in decades. In addition to traditional journal sources (e.g. Gibney, 2020; Lecocq et al., 2020), seismologists across the world have been sharing on social media visual graphics that illustrate reductions in seismic noise across most seismic networks. Figure 15 is one such example, produced by Stephen Hicks at Imperial College London. It shows the seismic noise on two UK networks (British Geological Survey, BGS, and Raspberry Shake, RS), comparing levels before and after lockdown. It also shows a correlation with UK retail and recreational activity.
The British Geological Survey (BGS) operates a dense network of seismic
stations, using instruments similar to those we deployed in the Wills
Memorial Building. These stations are deliberately deployed in quiet
settings. Nevertheless, a clear drop in background noise is visible starting
in late March 2020 (Fig. 15). In recent years, seismometers have been
deployed that cost a fraction of the price of conventional seismometers, but
with only a slight degradation in instrument sensitivity. The Raspberry
Shake instrument (
The ground beneath our feet may be unusually quiet, then, at this precise
moment of writing; however, a glance at the language of recent headlines
reveals that “seismic shifts” are occurring in other terms and in forms of
activity across all areas of daily life: from consumer habits and corporate
culture to educational practices and the trends of global politics. Indeed,
our cross-disciplinary conversations prompted an increasing awareness of how
we use different vocabularies, with different resonances, to articulate the
phenomena of earthquakes and how these vocabularies resonate within everyday
speech. From a literary perspective, it is striking how some of the most
commonly used vocabularies carry metaphorical currency, having either been
absorbed into colloquial ways of speaking of nonspecific adverse events
or, more complexly, tasked with operating in intrinsically figurative ways
themselves, retaining the memory of an emotional, moral, biological or
physical charge: aftershock, stress-trigger, rift, fault, tremor, swarm,
cascade and shadow zone. The increasingly over-used idiomatic term seismic
shift, for example, used to connote conceptual change across all aspects of
human experience, has been commonplace in our public discourse since the
1980s, as the Google Ngram Viewer (Lin et al., 2012) bears witness (see
graph linked here:
For the duration of the project, we also found ourselves drawn to a set of
vocabularies related to the sonic potential of vibrations, whereby the earth
can be thought to sound like a giant bell: harmonics, tones, fundamental
modes and whispering gallery waves. Indeed, the bell like sonority of the
Earth, our “blue planet”, resembles a resonant chamber where seismic waves
travel through and around its interior. The comparison is made with the
Whispering Gallery in the roof of Saint Paul's Cathedral, where sound waves
are reflected horizontally round the walls circle and bounce around
multiple times because the angles involved are so slight (Fitzgerald,
2016). Interestingly, seismic phases can propagate around the inside of the
planet in a similar fashion, clinging to the underside of the Earth's
core–mantle boundary, some 3000 km beneath our feet. Our data from the Wills
Memorial Building tower at the University of Bristol showed evidence of seismic
waves coming not only from the tower bell, Great George, and local city
impact but also extremely distant impacts travelling to the instrument from
seismic activities on different continents. Our response to the data
realized in sound and vibrations from the WMB tower seismometer could be
described as hearing “music as audible physics” (Young, 1998), where the
waves travelling around the inside of the Earth are described as resounding
and reverberating. Reciprocally, such realizations can also be used to help
scientists interpret seismic data (e.g. Paté et al., 2017).
Transforming earthquake signals into audible sound helps us to better
understand the scale of seismic shifts in the Earth (see, for example,
The technology, namely the seismometers and the geophone used either in (or
within the vicinity of) the WMB tower to “listen in” to the ground,
ultimately acted like bionic extensions to our human ears. Seismic waves
reached the instruments from great distances by travelling through the
ground, and so being able to hear and experience the waves altered our
perception of what goes on under our feet and in our surroundings, by
expanding the reach of our hearing and extending our auditory map further
than the limitation of our anatomy: our planet might be unsettled but we are
implicated in its motion in complex ways, with our own bodies forming part of a
network of sensing instruments. The ear has been described as “half anatomy
and half imagination” by writer and cultural critic Connor (2010), who
describes how our perception of sound enhances our understanding when we can
only imagine a sound's location but cannot see its source. Our technology
also picked up different frequency waves, some audible and others inaudible
to our ears, prompting a thought experiment to imagine what we could not
hear with our human ears when perceiving seismic waves pitched below our
auditory range. Yet, if we could not hear the waves as audible sound, they
could still provide an impression of our surroundings. Musician Evelyn
Glennie, who has a hearing impairment, comments in her
Connor (2010) describes sound and place as being intrinsically linked,
where a “sound is the space in which it occurs” and “sonic essence inheres
in spatial accident”. In our discussions, we became fascinated by extending
the notion that people “site” themselves in place by connecting to sound and to
the idea that attending to vibrations in the Earth requires people not only
to site themselves in relation to their local environment but also to
their global environment. John Luther Adams, for example, in his work
The raw data utilized in this study have been archived
with the National Geoscience Data Centre (NGDC;
With the exception of the data analysis section that was largely written by JMK and OAG, all co-authors contributed equally to the remaining sections of the article. This was done as part of a writing retreat; each of the co-authors wrote a page or more for each of the sections of the paper which was later synthesized to the final version presented in the article.
The authors declare that they have no conflict of interest.
This work was funded and facilitated by the University of Bristol's Brigstow Institute as part of their “Living well with uncertainty” initiative in 2018. Ophelia Ann George and John Michael Kendall were funded by NERC grant NE/R018006/1. We gratefully acknowledge support from the sponsors of the Bristol University Microseismicity Projects (BUMPS). We thank Stephen Hicks for generating the plot in Fig. 15. We are also grateful to Michael Richardson, who facilitated our access to the Special Collections of the University of Bristol's library and to its holdings in our area of interest. We would also like to express gratitude to reviewers Paul Denton and Susanne Maciel for their thorough reviews which helped to make the article stronger.
This research has been supported by the University of Bristol's Brigstow Institute (“Living well with uncertainty” initiative) and NERC (grant no. NE/R018006/1).
This paper was edited by Mirjam Sophia Glessmer and reviewed by Paul Denton and Susanne Maciel.