Multi-fault ruptures : higher likelihood of larger Californian earthquakes

As I have mentioned in my About section, I am funded by NERC (that’s the Natural Environment Research Council) for my PhD in a DTP, which is like a special training program for PhD students (see here for more information). I would recommend anyone else who is applying for a PhD to try and get one which is a part of one of these programs as it has been great!

Through my DTP, I was rewarded funding to undertake a 2 week internship at a business, in order to get some real-life experience. I think we all know that 2 weeks is not quite long enough to do much, but it is really useful in the sense of forging connections between my own research interests, and industry work. In my case, there were connections with Risk Management Solutions (RMS), who are a company who model catastrophe risk for insurance purposes. Their work ranges from modelling the risks associated with earthquakes (so right up my street) to terrorism risk.

My work entailed looking into multi-fault ruptures in California. Multi-fault ruptures were once thought of as a rare earthquake case of earthquakes ‘jumping’ from fault to fault. However, they are a deadly occurrence, as with multi-faults come larger earthquakes. Cases such as the M7.8 2016 Kaikoura, New Zealand earthquake, show just how massive multi-fault ruptures can be. This particular earthquake is reported as having 21 different fault ruptures, and causing about 180km of surface rupture.

intensity

ShakeMap of the M7.8 2016 Kaikoura earthquake – the red areas are those which experienced the largest shaking intensity (from USGS).

This is probably one of the most complex earthquake cases, as there are just so many faults involved. It also brings up the question: what if there were a similar case in California? It could be deadly.

As our understanding of earthquakes is ever evolving, it is important that earthquake forecast models are inclusive of this information. Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3) is a new earthquake forecast model for the whole of California, which has been developed by a breadth of specialists. It is a highly advanced model, as it estimates magnitude, location, as well as the likelihood of potential earthquakes. UCERF3 is particularly new and innovative, when compared with other models, as it incorporates multi-fault ruptures. From including these types of ruptures in their forecast, the possibility of a larger earthquake (M>7) increased.

The overall likelihood of a magnitude 6.7 (or higher) earthquake occurring within the next 30 years, was calculated by UCERF3, and is shown below. The research done for the UCERF3 model not only shows the increased likelihood of earthquakes in California, but also how interconnected the whole fault system is.

Likelihood that each region of California will have a magnitude 6.7 (or larger) earthquake in the next 30 years.

UCERF3 produced this map of California (white lines define borders) showing the likelihood of a magnitude 6.7 (or higher) earthquake will occur within the next 30 years (from Field, E.H., and 2014 Working Group on California Earthquake Probabilities, 2015, UCERF3: A new earthquake forecast for California’s complex fault system: U.S. Geological Survey 2015–3009, 6p., https://dx.doi.org/10.3133/fs20153009. )

I would recommend checking out UCERF3 if you are interested – it’s fascinating being able to see all the different fault sections and how they are connected to one another.

It’s a shame I only had two weeks to look into this area – hopefully I will get the chance to revisit it again to be able to apply the model myself.

–Roseanne

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