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Article | WTW Research Network Newsletter

Mind the aftershocks – the 2019 Ridgecrest earthquake sequence and implications for the San Andreas fault

By Tim Edwards , Crescenzo Petrone , Myrto Papaspiliou and Hélène Galy | July 13, 2020

Willis Re can condition catastrophe models to quantify the potential impact of the July 2019 Ridgecrest sequence on current and future earthquake risk
Willis Research Network
Climate Risk and Resilience

Non-stationarity is not only a characteristic of climate-related hazards. Local earthquake risk is also thought to change spatially and temporally following recent activity in a region. For the purposes of underwriting and risk management, knowing where risk increases or decreases is useful in order to manage earthquake accumulation and underwriting strategy.

In light of a potentially ongoing earthquake sequence, from the 4th to the 6th of July 2019 around 150 miles north of Los Angeles, we have been considering the potential change in earthquake hazard for the region, to better support and advise clients with exposure in this area.

Willis Re leverages collaborations with academic partners through the Willis Research Network (WRN) to address such complex questions, in order to react to such industry challenges in an independent and rapid fashion.

Coulomb stress methodology – a background

Temblor Inc and Tohoku University have long worked to estimate the impact of current earthquake activity on surrounding faults, indicating future changes in the likelihood of events. Temblor is the only model vendor that has a service which tracks dynamic earthquake hazard, which they call Realtime Risk. They build Realtime Risk into their stochastic event sets, hazard curves, and in loss calculations. Coulomb stress transfer has been a well-recognised mechanism that can promote or inhibit subsequent earthquakes through stress changes in proximity to a ruptured fault.

Earthquakes impart stress to their immediate surroundings, not least via aftershocks, which generally occur where stress promotes additional shaking. A recent example was the 2012 Emilia sequence in Italy, where aftershocks contributed the majority of shaking damages.


Regional Director - Head of Catastrophe Analytics
Globals at Willis Re

Tim joined Willis Re in 2011 and has responsibility for overseeing catastrophe analytics for Global clients, Willis Re’s Model Research & Evaluation also Willis Research Network functions. Tim has 17 years’ experience, starting out at a Lloyd’s syndicate where he led part of the response and reporting to the ’04 and ’05 hurricane seasons. Thereafter, Tim worked at RMS within the team that, for instance, built the 2007 UK flood model that many UK insurers still use today. Tim brings a wealth of UK and global flood modelling knowledge from his work with leading UK and European insurers, in addition to his experience working to support various international catastrophe pools. An economist by background, Tim is ACII qualified and has achieved CFA level 1.

Head of Southern Europe Catastrophe Analytics

An earthquake specialist at Willis Re, Crescenzo develops risk solutions to help clients accurately understand and mitigate their own risk.

Lead Earthquake Specialist
Willis Re International

Myrto is an Earthquake Specialist in the Model Research & Evaluation team for Willis Re International. The team is in charge of developing the Willis Re view of risk by assessing, comparing and adjusting catastrophe model vendors for all perils/territories in the international business. Myrto has been responsible for the co-ordination and delivery of earthquake catastrophe models evaluations for more than 30 territories around the world. Her areas of focus include technical evaluations, supporting clients in developing their view of risk and communicating study outputs with reinsurers. Myrto holds a PhD on Earthquake Engineering and prior to joining Willis in 2012 she worked as an earthquake engineer in a leading engineering consulting company.

Head of People Risks Research
Managing Director of WTW Research Network.

Hélène joined Willis in 1998, specialising in natural hazard modelling and reinsurance optimisation. Since 2001, she has been leading multi-disciplinary teams, who research, design and develop analytical solutions and insights for risk identification, quantification and management. She currently leads the Willis Research Network, an award-winning public-private partnership, which harnesses over 60 science partners to form innovative long-term collaborations, improving our understanding of risks (natural hazards, technological risks, geopolitical drivers of risk) for the benefit of clients and society: using science to support resilience.

Hélène has extensive experience in spatial modelling, design of innovative solutions, and applying science to business challenges. Her current focus is on Climate advisory services (advising corporates on how leading-edge climate research can help them quantify their exposure to climate variability and climate change; exploring the links between climate change and national security) and on People Risks (how people can increase vulnerability or improve resilience: terrorism, societal resilience to systemic risks, including pandemics).

She holds a BSc in Economics & Political Science (Sciences Po), and an MSc in Environmental Economics (UCL).

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Executive Vice President
Willis Re North America

Paul Welsh
Head of Willis Re Specialty Catastrophe Analytics
Willis Re Specialty

Crescenzo Petrone
Divisional Director - Earthquake Specialist
Willis Re International

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