SUMMARY In the Gulf of California, Mexico, the relative motion across the North America–Pacific boundary is accommodated by a series of marine transform faults and spreading centres. About 40 M> 6 earthquakes have occurred in the region since 1960. On 2009 August 3, an Mw 6.9 earthquake occurred near Canal de Ballenas in the region. The earthquake was a strike-slip event with a shallow hypocentre that is likely close to the seafloor. In contrast to an adjacent M7 earthquake, this earthquake triggered a ground-motion-based earthquake early warning algorithm being tested in southern California (∼600 km away). This observation suggests that the abnormally large ground motions and dynamic strains observed for this earthquake relate to its rupture properties. To investigate this possibility, we image the rupture process and resolve the slip distribution of the event using a P-wave backprojection approach and a teleseismic, finite-fault inversion method. Results from these two independent analyses indicate a relatively simple, unilateral rupture propagation directed along-strike in the northward direction. However, the average rupture speed is estimated around 4 km s−1, suggesting a possible supershear rupture. The supershear speed is also supported by a Rayleigh wave Mach cone analysis, although uncertainties in local velocity structure preclude a definitive conclusion. Themore »
Using teleseismic backprojection and InSAR to obtain segmentation information for large earthquakes: a case study of the 2016 M w 6.6 Muji earthquake
A good understanding of earthquake rupture segmentation is important to characterize fault geometries at depth for follow-up tectonic, stress-field or other analyses. We propose a data-driven strategy and develop pre-optimization methods to support finite fault inversions with independent prior estimates on earthquake source parameters. The first method we develop is a time-domain, multi-array and novel multiphase backprojection (BP) of teleseismic data. This method infers the spatio-temporal evolution of the rupture process, including a potential occurrence of rupture segmentation. Secondly, we apply image analysis methods on InSAR surface displacement maps to infer rupture characteristics (e.g. strike and length) and the number of potential segments. Both methods can provide model-independent constraints on fault location, dimension, orientation and rupture timing, applicable to form priors of model parameters before detailed modelling. We demonstrate and test our methods based on synthetic tests and an application to the 25.11.2016 Muji Mw 6.6 earthquake. Our results indicate segmentation and bilateral rupturing for the 2016 Muji earthquake. The results of the BP of the Muji Mw 6.6 earthquake using high-frequency filtered teleseismic waveforms in particular shows the capability to illuminate the rupture history with the potential to resolve the start and stop phases of individual fault segments.
- Publication Date:
- NSF-PAR ID:
- 10379444
- Journal Name:
- Geophysical Journal International
- Volume:
- 232
- Issue:
- 3
- Page Range or eLocation-ID:
- p. 1482-1502
- ISSN:
- 0956-540X
- Publisher:
- Oxford University Press
- Sponsoring Org:
- National Science Foundation
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