How well do we really understand earthquake potential?

The last decade has seen some of the most devastating earthquakes to society, with some 630,000 lives lost since 2000 due to earthquakes and corresponding cascading hazards like tsunamis and landslides—and economic losses of over US$ 500 billion. This could be even worse in the future with the increase in exposure through urban expansion, and vulnerability through building codes enforcement.

New faults

Apart from earthquake-prone areas in subduction zones, there have been in the last decade some devastating continental earthquakes (e.g., 2010 M7.0 Haiti) that have occurred in faults previously unknown to scientists.

Giant earthquakes occurring on collision zone megathrusts are among the deadliest natural hazards

Additionally, half of humanity lives close to elevated collisional mountain ranges that supply drinking water, industry, food, energy production—and hosts 20% of the known hydrocarbon reserves. Giant earthquakes occurring on collision zone megathrusts (such as the 1999 M~7.6 Chichi earthquake in Taiwan) are among the deadliest natural hazards. During the last decade, such events killed nearly 200,000 people, the most devastating being the 2008 M7.9 Sichuan earthquake in China (with an estimated economic cost of about 130 billons €), and the recent 2015 M~7.8 Gorkha earthquake in Nepal.

New questions

For decades, earthquake scientists have been working in close collaboration with private and public partnerships around the world to produce technologically advanced models to improve preparedness and resilience of communities and infrastructures in earthquake-prone regions. However, according to scientists, the 2011 M 9.0 Tohoku earthquake greatly exceeded previous scientific estimates of magnitude potential, killing 20,000 in its tsunamogenic aftermath.

This and previous devastating events have prompted rethinking of whether we fully understand the earthquake potential of specific parts of subduction zones, and whether there are larger and more devastating earthquakes yet to be observed.

The uncertainties surrounding the occurrence of an earthquake go beyond the event itself, often raising questions about possible future events. The magnitude M7.8 Kaikoura quake on November 13th 2016 has raised questions about whether the event has caused an increase on the stress in Wellington and Wairarapa faults and therefore presaging a larger and more catastrophic event. Often, foreshocks (earthquakes that occur before a main shock in the same area) are not known to be such until the mainshock happens.

Post-event studies following the Kaikoura event included Coulomb stress transfer, clustering, pairing of events, dynamic triggering and even techniques such as 3D velocity modelling of earthquake wave propagation, to try and understand the damage and future consequences of this earthquake.

So, is the Big One yet to happen?

Earthquakes communicate with each other through the transfer of stress, which can be static or dynamic

How do we know if the world’s biggest-ever mega-earthquake is yet to be observed? Is there a theoretical limit to what is physically possible? Would this create a truly market changing mega-event beyond those which we have not seen or anticipated to date?

If we don´t fully understand the earthquake potential of certain subduction and collision zones, we may also be underestimating the associated risk. To answer the above we need to go deeper into the science of earthquakes and better understand how they work and interconnect with each other in time and space. What research directions (if any) could help answer these and related questions?

How earthquakes converse

An earthquake occurs when plates grind and scrape against each other. In a nutshell, an earthquake is caused by a sudden slip on a fault. Stresses in the Earth’s outer layer push the sides of the fault together. Stress builds up and the rocks slip suddenly, releasing energy in waves that travel through the Earth’s crust and cause the shaking that we feel during an earthquake.

Aftershocks (earthquakes that occur after a main shock in the same area) can sometimes be larger or more damaging than their mainshock (e.g, Kumamoto and Christchurch).

Earthquakes communicate with each other through the transfer of stress, which can be static or dynamic. Static stress triggers act over short distances (generally less than <200 km) and time periods from minutes to decades.

The above image shows a classic example of static stress triggering: The 1992 M7.3 Landers earthquake was followed by the M6.5 Big Bear event 3 hours later in one trigger lobe, and the M7.1 Hector Mine quake after 7 years in another trigger lobe. Failure is promoted in stress trigger zones (red); failure is inhibited in stress shadows (blue).

In addition, recent research on dynamic stress triggering has found new evidence on how earthquakes interact over long distances. Could this mean earthquakes can be linked many thousands of kilometres apart? This may present a challenge to the reinsurance assumption that globally distributed earthquakes are independent.

There is on-going research to show if dynamic stress transfer could trigger an aftershock several kilometres apart from its mainshock.

In short

There are many questions still to answer if we are to better manage seismic risk.

  • If the largest and most devastating earthquake is yet to happen, what areas are most likely to be affected?
  • How do we recognize a time and space clustering sequence?
  • Can a large earthquake in Nepal trigger another one in Japan in a matter of seconds?
  • Can Static stress transfer be quantified via Coulomb stress and used to better assess how earthquakes “talk” to each other?
  • Can pioneering techniques to simulate wave propagation using 3D velocity models help understand and assess the potential damage from large earthquakes?

These questions show that more pioneering research is needed to understand, monitor and document earthquakes, as well as their effects on our intertwined societies, in order to increase resilience and improve preparedness.

WRN Seismic Seminar in London February 23rd

If you are interested in finding out more about the science behind earthquakes, we will be discussing trending topics on seismic hazard and risk, as part of a WRN-hosted seminar in London on the 23rd of February. The aim will be to highlight research directions that could trigger major advances and improve the way seismic hazard and risk is perceived, assessed and quantified in the Re/Insurance industry.

Professor Ross Stein, CEO and co-founder of Temblor.net, USGS Scientist Emeritus and Adjunct Professor of Geophysics at Stanford University, will discuss the cutting edge of static (Coulomb) stress triggering methodologies and real-time aftershock forecasting.

Tom Parsons, from USGS, Menlo Park, CA and Emily Brodsky, from University of California, Santa Cruz, continue to pioneer research in the field of dynamic stress triggering. They will present the state of art and latest developments, as well as clear influences of global interactions on earthquake occurrence rates in specific regions.

The latest advances in computing now allow for 3D simulation of wave propagation; techniques simply not available to us previously. This will allow us to better understand the rupture of the largest earthquakes and in greater detail. How can this new method be used to better assess earthquake impact? Kim Olsen, from San Diego State University, CA, will be presenting this pioneering technique with applied examples for the USA (CA – Los Angeles, UT – Salt Lake City, Cascadia subduction).

Karl Jones and Myrto Papaspiliou will also present on how we can apply this kind of science to our everyday risk management practices. There is still time to register:

  • The Willis Research Network: Managing risk and delivering resilience into the re/insurance industry
  • Time and Date: 13:30 – 17:00, February 23rd followed by drinks
  • Location: Willis Towers Watson Auditorium, 51 Lime Street, London, EC3M 7DQ
  • To register: Email: wrn@willis.com

If this is of interest to your business, please come along for the afternoon of discussion, followed by an opportunity to network and chat to the scientists.

About Rosa Sobradelo

Rosa Sobradelo is part of the Willis Research Network where she coordinates research activities in the areas of geo…
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