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Towards a new global earthquake catalogue - Full waveform constraints on earthquake mechanisms and their uncertainty

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If you have a question about this talk, please contact Alistair Boyce.

For any given moderate magnitude (5.8 – 7.0 Mw) earthquake there are multiple constraints on the earthquake source parameters provided by various global and regional earthquake monitoring agencies. While the broad characteristics of the location and mechanisms are often in agreement, there is still a large range of depths, focal mechanisms and even epicentres reported for the same earthquake. In this talk I will outline a new procedure developed in collaboration between Oxford seismology group and the International Seismological Centre (ISC) to constrain the moment tensor, source time function and depths of moderate magnitude earthquakes, along with the uncertainty in these source parameters.

We use a Bayesian inversion scheme to provide an ensemble of point source earthquake models that give an indication of the potential variability of the earthquake mechanism and depth. We show that by jointly inverting for the earthquake source time function, moment tensor and depth we can improved resolution to the earthquake depth, as well as a measure of the uncertainty in the earthquake mechanism, source time function and depth. The increased depth resolution that is seen particularly for shallow events is achieved by accounting for the surface reflected depth phases. For intermediate depth earthquakes (70 – 300 km depth) it is well understood that these phases are strongly depth dependent, but for shallow events they are often subsumed within the source time function, and are therefore unobservable. By jointly solving for the earthquake depth and the source time function, we are able to assess the likelihood of a shallow earthquake occurring at a range of depths.

We hope that this method will offer a new ISC product, in the form of source time functions for moderate magnitude earthquakes, as well as improving the depth determination for shallow earthquakes in remote and un-instrumented parts of the world.

This talk is part of the Bullard Laboratories Wednesday Seminars series.

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