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 

Blog post by Dr. Caroline Wood

The UCL Institute for Risk and Disaster Reduction held an evening event on Thursday 1^st November 2018 to celebrate the launch of its newest transdisciplinary venture: the UCL IRDR Centre for Digital Public Health in Emergencies (dPHE). The event was attended by more than 120 people, including UCL senior managements, academics, researchers, students, industry specialists, entrepreneurs and policymakers from across a broad range of sectors and specialisms.

The evening started with a welcome address by Professor David Price (UCL Vice Provost for Research) outlining UCL’s Grand Challenges concept of bringing together academic expertise across disciplines to address the issues facing the society and the planet. Professor Peter Sammonds (Director of the UCL Institute for Risk and Disaster Reduction) gave an overview of the IRDR vision and highlighted how the new Centre forms a vital part of the UCL Faculty for Maths and Physical Sciences strategic 5-year development plan.

The Keynote Speaker Professor Virginia Murray (Head of Global Disaster Risk Reduction, Public Health England) kicked off the evening talks with an eye-opening keynote on global response to disasters and emergencies and the potential for science and digital health technologies to contribute. She illustrated her talk with reference to the United Nations Office for Disaster Risk Reduction (UNISDR) Sendai Framework for Disaster Risk Reduction (2015-2030); a tool developed to structure response and protect nations when disasters occur, and stressed the importance of improving accessibility and availability to key data.

The evening continued with Dr. Patty Kostkova (Director of the UCL IRDR Centre for Digital Public Health in Emergencies) outlining the history and vision of the Centre. She emphasised the Centre’s central mission to break down the limits of current health care systems’ capacity and communities’ resilience to improving health and wellbeing at national and international levels. A key part of the Centre’s research agenda will be to explore how use of digital technologies and improving access to data can build the ‘bridge’ between efficient emergency response, emergency activities and improved healthcare systems capacity and routine surveillance. The Centre will also seek to change the current dynamic of knowledge transfer and exchange between academia and policy, directly responding to the main global public health challenges identified by policy but also proactively bringing challenges to policy agendas.

With representation spanning five UCL faculties, involving multiple disciplines and chaired by Professor Ibrahim Abubakar (Director of the UCL Institute for Global Health, Faculty of Population Health Sciences), a panel then discussed the challenges faced by the global public health and potential ways in which digital technologies and community engagement could seek to address them. Professor Julio Davila (UCL Development Planning Unit, Faculty of the Built Environment) proposed that key challenges stem from the world’s continuing ambition to urbanise and from rapid increases in urban sprawl on a global level. He argued that improving infrastructure for capacity building is therefore crucial to efficient global public health response to disasters and emergencies.

Professor Kate Jones (UCL Centre for Biodiversity and Environmental Research, Faculty of Life Sciences) stressed that we need to better realise the state of our global ecosystems and the decreasing environmental diversity. Professor Jones proposed that digital technologies incorporating real-time prediction and big data would enable us to more fully understand links between ecosystem decline and human health. Major challenges surrounding data sharing, ownership and translation between sectors, organisations and disciplines were raised as significant barriers to more efficient ways of working by Professor Muki Haklay (UCL Extreme Citizen Science, Faculty of Social and Historical Sciences) and Dr. Patty Kostkova (UCL IRDR dPHE) stressing the opportunity to enhance big data-driven predictive disease analytics with routine surveillance data collected via mobile technology. Professor Haklay posited that citizen science has a large role to play in ensuring provision of digital tools direct to communities to improve data collection and guide usage of data for better public health response.

Professor Abubakar brought the panel to a close by stressing that it would be a crime not to exploit opportunities for addressing global public health using innovative digital technologies – especially given their growing global penetration, even in low to middle income countries (LMIC). He highlighted the importance of the IRDR Centre for dPHE’s role in bringing different disciplines and sectors together to address the bigger public health challenges and assess how to effectively drive innovation to global change. The role of human computer interaction science, behavioural science and education were specifically mentioned as being key disciplines in helping global public health to better understand how people interact with digital technologies and addressing how best to encourage uptake in communities. Initiatives expanding dPHE to more UCL Faculties beyond the core five represented at the panel were agreed at the event.

Professor David Lomas (UCL Vice Provost for Health) gave the closing address for the event reiterating cross Faculty and the UCL School of Life and Medical Sciences’ (SLMS) support for the new Centre and its importance in maintaining UCL’s role as a leader in improving global public health. A celebratory drinks and networking event showcasing several of the Centre’s collaborative research projects then took place in the Roberts Building Foyer.

Further coverage of the event can be accessed via the dPHE Twitter account @UCL_dPHE or via the hashtag: #dPHELaunch. Recording of the event including the panel discussion will be available to view week beginning Nov 19th. Images with thanks to Dr. Ilan Kelman.

About the UCL Centre for Digital Public Health in Emergencies

The UCL IRDR Centre for Digital Public Health in Emergencies brings together experts from UCL and external stakeholders to lead on interdisciplinary research, training and policy advice to improve global public health through use of digital technologies and data systems.

Recent health emergencies – including the SARS, Zika and Ebola outbreaks, and the Haiti and Nepal earthquakes – have unnecessarily taken thousands lives and cost the global economy billions. These events have shown the limits of current health systems’ capacity and communities resilience to respond to emergencies at local, national and international levels.

The dPHE seeks to:

• Strengthen response to public health challenges and emergencies
• Lead cutting-edge research into mobile technologies, data science and policy
• Harness expertise across sectors to strengthen national and international collaboration
• Cultivate the next generation of experts through evidence-based teaching and training

Established in 2018 as part of the UCL Faculty of Maths and Physical Sciences five-year strategic plan, the vision is to develop the dPHE into a renowned and world-leading Centre in digital public health in emergencies to improve global capacity, preparedness and response to health emergencies.

Contact:  irdr.dphe@ucl.ac.uk

Office location:  Institute for Risk and Disaster Reduction, Wilkins South Wing – 2^nd Floor, University College London, Gower Street, London WC1E 6BT

@UCL_dPHE

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.