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Earthquake surface measurements reveal new revelations about how faults rupture

Joanna PFaure Walker12 November 2018

PhD student Francesco Iezzi (Birkbeck College), supervised by Prof Gerald Roberts (Birkbeck College) and Dr Joanna Faure Walker (UCL IRDR), has published a paper that could revolutionalise how geologists and seismic hazard modellers use long established scaling relationships between fault lengths and surface rupture parameters.

The paper is freely available to all and can be found here.

What new observations have been made?

For five earthquakes studied, the surface fault slip (the amount the fault surface moved during the earthquake) and the throw (the vertical component of the slip) was higher where there was a bend along the length of the fault.

Following the central Italy August and October 2017 earthquakes that ruptured the ground surface, we made detailed high spatial resolution measurements of surface fault displacement along the length of the surface fault ruptures. A study of the amount of vertical and horizontal displacement that occurred along the length of the fault revealed that the throw and slip that occurred during the earthquakes increased where there are bends in the fault. This result is critical and has not been identified before for individual earthquakes.

Damage in Amatrice from the August 2016 Earthquake. Photograph take during EEFIT fieldwork by Dr Joanna Faure Walker.

Why does this occur?

We hypothesis that this occurs in order to maintain the horizontal strain (change in length relative to the original length) across a fault during an earthquake and the long-term horizontal strain-rate that accumulates from multiple earthquakes over thousands of years.

Are there other examples of this?

We then went back and studied other examples earthquakes where there was enough information to determine whether a similar pattern of higher throw and slip could be seen across bends in the fault. In the three further events studied in USA Basin and Range, Greece, and Mexico, we found the same relationship. So it seems this phenomenon occurs worldwide in normal (extensional) faults.

This was the first time that the change in vertical component of slip during an earthquake has been shown to be predictable. However, the observed relationship of increased throw across fault bends has been identified previously in long-term displacements that have accumulated over 15 thousand years as a result of multiple earthquakes in Italy (Faure Walker et al., 2009, Wilkinson et al., 2015). Before now, it was not known whether this increase was caused by there being more earthquakes across the bends or more movement during individual events.  We now know that there can be more slip during individual events, however we do not know whether this is the only mechanism for creating a long-term higher throw-rate across the bends.

What does this mean for earthquake science?

This paper suggests that slip during an earthquake will change where there is a bend along the length of the fault and this change can be quantified and predicted using the proposed theory. This means that close to the fault, earthquakes may be more damaging near a bend in the fault. This finding suggests that we cannot use fault scaling relationships between fault length and expected slip in earthquakes without consideration of fault geometry. This paper can also explain much of the scatter seen in existing plots of maximum surface slip against fault length because when collecting the data as input for such relationships, consideration was not given about whether the measurements were taken across fault bends or not.

These changes in slip along faults in individual earthquakes related to the fault geometry should be included in probabilistic seismic hazard assessments (PSHA).

What other research in the IRDR relates to this?

This work contributes to the IRDR and colleagues’ work on investigating fault behaviour to improve our understanding of earthquake hazard. Recent papers have demonstrated the importance of including detailed fault geometry and slip-rates in seismic hazard calculations (Faure Walker et al., 2018) and Coulomb stress transfer calculations (Mildon et al., 2016, 2017).

Iezzi et al (2018), Coseismic Throw Variation Across Along‐Strike Bends on Active Normal Faults: Implications for Displacement Versus Length Scaling of Earthquake Ruptures, Journal of Geophysical Research, https://doi.org/10.1029/2018JB016732 

More data needed for better earthquake hazard and risk calculations

Joanna PFaure Walker6 November 2018

New research demonstrates the importance of having detailed measurements at multiple sites along a fault of how fast the fault is moving and how the surface orientation of the fault changes. To access the full paper click here.

Why do we need fault measurements?

Measurements of fault slip rate and the geometry of the fault (it’s 3d orientation) can be used to calculate earthquake recurrence intervals to give probabilities of how likely earthquakes of different magnitudes are to occur. We also need these measurements to model how much ground shaking there will be at given locations. Hazard maps of expected ground shaking can be used to inform building codes and identify where buildings including homes and schools might need retrofitting to improve their resistance to earthquake shaking.

There are other methods available for creating earthquake hazard maps, such as using historical records of earthquake shaking. However, these records unlikely go back far enough in time to capture all faults capable of hosting large earthquakes because some faults will not have hosted earthquake within the time period covered by such records. Therefore, the hazard from some faults would be missing in hazard maps based solely on historical seismicity leading to underestimations in earthquake hazard.

What new insights have been revealed in the research publication?

The paper, entitled “Variable fault geometry suggests detailed fault slip rate profiles and geometries are needed for fault-based probabilistic seismic hazard assessment (PSHA)” demonstrates that relying on only one or a few measurements of how fast the fault is moving along a fault and projecting these measurements along the entire fault may lead to underestimating the uncertainty in the earthquake hazard calculations. Crucially, there may be locations where the hazard is underestimated, meaning people could be at more risk than suggested by simpler models (the converse is also possible). Therefore, earthquake hazard assessments based on fault parameters need to either use detailed measurements including measurements of how fast the fault is moving at multiple sites along the fault or to incorporate how the lack of such data increases the uncertainty in calculated earthquake hazard assessments.

Why are detailed measurements not being already used?

In many regions it is difficult to constrain the fault slip rate (how much the fault has moved in a given time) or throw rate (vertical component of slip rate) along a fault at even one location, let alone several. However, there are regions where this is possible so as more data is collected, this detail should help to improve earthquake hazard assessments both in those regions and worldwide.

Where can I find out more?

Faure Walker J., Visini F., Roberts G., Galasso C., McCaffrey K., and Mildon Z., (2018) Variable fault geometry suggests detailed fault slip rate profiles and geometries are needed for fault-based probabilistic seismic hazard assessment (PSHA), Bulletin of the Seismological Society of America, doi: 10.1785/0120180137

The Fault2SHA Working Group is an ESC (European Seismological Commission) group of researchers in both universities and civil protection authorities collaborating to increase incorporation of fault data in seismic hazard assessments and to improve our understanding of how such data should be used.

Disaster Science is one of five key themes for partnership between UCL and Tohoku University

Joanna PFaure Walker21 October 2018

UCL and Tohoku University signed a Memorandum of Understanding on Thursday 11th October 2018 as part of the kickoff partnership event. President Arthur and President Ohno stated their commitment to continuing research exchange, following the agreement of the previous five years.

President Arthur and President Ohno sign memorandum of understanding Photo source: https://www.tohoku.ac.jp/japanese/2018/10/news20181018-02.html

Workshops for five key themes were held on the 11th and 12th October as part of the event that saw 50 delegates come to UCL from Tohoku University. The five themes were disaster science, data science, neuroscience, higher education and material science and spintronics.

The disaster science delegation (From left to right) Prof. Shinichi Kuriyama Dr Katerina Stavrianaki Dr Ilan Kelman Ms Anna Shinka Dr Tiziana Rossetto Dr Joanan Faure Walker Dr David Robinson Assist. Prof. Shuji Seto Prof Maureen Fordham Ms Miwako Kitamura Prof David Alexander Assoc. Prof. Anawat Suppasri

The disaster science delegation comprised representatives from UCL IRDR, Tohoku University IRIDes (International Research Institute for Disaster Science), and UCL EPICentre. The workshop has helped form new collaboration opportunities building on the existing relationship between these research institutions. Our collaboration cincludes joint publications in earthquake stress transfer (e.g. Mildon et al., 2016), disaster fatalities (Suppasri et al., 2016), and temporary housing (e.g. Naylor et al., 2018). We look forward to the next five years of working with all our colleagues at IRIDeS to enhance the field of disaster science.

Discussions during the disaster science workshop Photo source: https://www.tohoku.ac.jp/japanese/2018/10/news20181018-02.html

The disaster science workshop included the following talks, which prompted discussions of further questions we would like to research together:

  • Assist. Prof. Shuji Seto (IRIDeS)
    • New Research Project on the Fatality Process in the 2011 Tohoku Earthquake for Survival Study from Tsunami Disaster
  • Dr Ilan Kelman (UCL IRDR)
    • Disaster, Health, and Islands
  • Prof. Shinichi Kuriyama (IRIDeS)
    • Challenge of Public Health to Disaster – Using Public Health Approach and Artificial Intelligence Techniques
  • Prof Maureen Fordman (UCL IRDR)
    • Gender and Disasters
  • Ms Miwako Kitamura (IRIDeS)
    • Gender problems as seen from the oral history of the bereaved families of the deceased Tsunami in Otsuchi Town, during the Great East Japan Earthquake
  • Ms Anna Shinka (IRIDeS)
    • A questionnaire study on disaster folklore and evacuation behavior for human casualty reduction – Case of Kesennnuma City, Miyagi Prefecture.
  • Prof Tiziana Rossetto (UCL EPICentre)
    • Building response under sequential earthquakes and tsunami
  • Assoc. Prof. Anawat Suppasri (IRIDeS)
    • Building damage assessment considering lateral resistance and loss estimation using an economic model “Input-Output table”
  • Prof David Alexander (UCL IRDR)
    • A framework for Cascading Disasters
  • Dr Joanna Faure Walker (UCL IRDR)
    • Disaster Warning, Evacuation and Shelter

NHK, the largest broadcaster in Japan, reported the workshop with a focus on Miwako Kitamura and the UCL Gender and Disaster Centre:  NHK report (in Japanese)

Induced earthquakes – how and when they have occurred, and why should anyone care

Joanna PFaure Walker27 September 2018

Despite the high volume of material out there about induced earthquakes, it can be hard to separate fact from opinion. To help explain what induced seismicity is, how it is caused and what the risks are, a group of researchers from UCL Department of Chemical Engineering and Institute for Risk and Disaster Reduction have published “Addressing the risks of induced seismicity in subsurface energy operations”.

What causes “induced seismicity”? Induced earthquakes, those mainly caused by human action, can invoke strong feelings towards the processes that cause them, the most widely known among these is hydraulic fracturing (less favourably known as “fracking”). But hydraulic fracturing for shale gas extraction is not the only cause of induced earthquakes – several industrial activities are capable of inducing or triggering earthquakes, including mining, dams, conventional oil and gas operations, groundwater extraction, CO2 Capture and Storage (CCS), underground waste fluid disposal and the creation of geothermal energy systems. Rightly or wrongly, negative public perception and local public opposition to induced seismicity has led to numerous international projections having been suspended, delayed or curtailed.

How does industrial operation induce earthquakes? The Earth’s crust is believed to be in a state where it is critically stressed and only small stress changes in the right direction can cause an earthquake. Industrial action can alter the stress field in the most shallow part of the Earth’s crust, inducing a seismic event.

Are these events getting more likely? The number of documented cases of man-made earthquakes in different industrial activities is rapidly increasing: In 2017 alone, there were two reported record-breaking magnitude induced seismic events. One of the more well-known areas of induced seismicity is in the United States: The notable increase in seismicity within the last decade in the previously seismically quiet State of Oklahoma has been widely attributed to large scale waste water injection wells connected to the hydrocarbon production industry.

How big are induced earthquakes? Most induced earthquakes are low in magnitude (typically less than magnitude 4). However, even these small events are capable of causing structural damage to properties and evoking widespread fear and anxiety. We say most are small, but there are some examples where large magnitude earthquakes have been alleged to be caused by human activities. For example, in China in 2008, a dam was built that filled a reservoir behind it. A short time later, a magnitude 8 earthquake occurred in the region. Some scientists proposed this large earthquake was caused by the mass loading of the water in the dam and its penetration into rock, affecting the subsurface pressure in an underlying fault line and possibly setting off a series of ruptures that led to the earthquake.

So what is being done about it? Minimising seismic risk should be a high priority for industrial operators. All fluid injection processes should require detailed seismic hazard assessments for imaging and characterising faults prior to operations, with dedicated monitoring systems in addition to existing national seismic monitoring facilities. For assessing the risks, monitoring the operations, and designing mitigation strategies using predictive models that can characterise the spatiotemporal evolution of induced seismicity would be extremely helpful. Examples of best practice approaches show that maintaining a transparent dialogue between operator and the public, while adhering to the regulatory processes can allow safe operations in an atmosphere of public acceptance.

Where can I find out more? With all the controversy around such events, we need to understand what are the risks of induced earthquakes and how can we model them. In the published article in Wiley Interdisciplinary Reviews, Richard Porter, Alberto Atriolo, Haroun Mahgerefteh and Joanna Faure Walker provide a review of several alleged induced seismicity case studies that have occurred in the last 15 years covering a variety of causal mechanisms. We discuss issues relating to public perception and procedures and strategies that could be implemented to help prevent and mitigate future occurrences.

The above work was funded by Horizon 2020 research and innovation programme, Grant/Award Number: 640979

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