COMET Webinar: CH Wendy Tsai (University of Oxford) and Aisling O'Kane (University of Cambridge). 24 August 2022

Scott Watson C.S.Watson at leeds.ac.uk
Wed Aug 10 07:00:50 UTC 2022


Dear Colleagues,

COMET (The Centre for Observation and Modelling of Earthquakes, Volcanoes, and Tectonics) invites you to the next instalment of our COMET webinar series with a great line up of two student presenters, viewable from the home office.

Probing the Upper End of Intra-continental Earthquake Magnitude: a Prehistoric Example from the Dzhungarian and Lepsy Faults of Kazakhstan

CH Wendy Tsai (University of Oxford)

Seismotectonics of the NW Himalayas with insights for seismic hazard

Aisling O'Kane (University of Cambridge)

Wednesday 24th August 2022 at 4pm UK time (3pm UTC / 5pm CEST / 8am PDT)

Please register at: https://universityofleeds.zoom.us/webinar/register/WN_Fo8NgKmBQ9W8ryWv-rHGcQ

(After registering, you will receive a confirmation email containing information on how to join the webinar)

Probing the Upper End of Intra-continental Earthquake Magnitude: a Prehistoric Example from the Dzhungarian and Lepsy Faults of Kazakhstan

The study of surface ruptures is key to understanding the earthquake occurrence of faults especially in the absence of historical events. We present a detailed analysis of geomorphic displacements along the Dzhungarian Fault, which straddles the border of China and Kazakhstan. We use digital elevation models derived from structure-from-motion analysis of Pléiades satellite imagery and drone imagery from specific field sites to measure surface offsets. We provide direct age constraints from alluvial terraces displaced by faulting and indirect dating from morphological analysis of the scarps. We find that the southern 250 km of the fault likely ruptured in a single event in the last 4000 years, with displacements of 10-15 m, and potentially up to 20 m at one site. We infer that this Dzhungarian rupture is likely linked with a previously identified paleo-earthquake rupture on the Lepsy Fault through a system of splays in the intervening highlands. Though there are remaining uncertainties regarding consistency in age constraints between the two fault ruptures, most of the sites along the two faults are consistent with a most recent event 2000-4000 years ago. Rupture on the Dzhungarian Fault alone is likely to have exceeded Mw 8, and the combined Lepsy-Dzhungarian rupture scenario may have been up to Mw 8.4. Despite being at the upper end of known or inferred continental earthquake magnitudes, our proposed scenario combining the 375 km of the Dzhungarian and Lepsy ruptures yields a slip-to-length ratio consistent with global averages and so do other historical intra-continental earthquakes in Central Asia.

Seismotectonics of the NW Himalayas with insights for seismic hazard

Large thrust faults accommodate the convergence between India and Tibet along the southern margin of the Himalaya and have a history of producing great earthquakes that cause widespread damage. Along most parts of the Himalaya, there is geomorphological evidence that these thrusts can rupture to the surface in Mw >8 earthquakes. However, in the Himalayan state of Jammu & Kashmir (NW India), the thrust faults are blind and large-scale folding is the only expression of active deformation at the surface, making it difficult to assess the seismic hazard in this region. In this webinar, I will discuss how we used field, satellite, and seismological observations to determine the fault geometry beneath the NW Himalayas, and investigate the relationship between thrust faulting and folding. These results were used to construct seismic wavefield models, to determine earthquake ground motion estimates if the Main Himalayan Thrust in the region were to rupture. I will present our results which show that peak ground velocities are extremely sensitive to minor variations in the fault geometry, with ~3 times larger PGVs generated from ruptures on the buried, shallow part of the locked Main Himalayan Thrust, compared to earthquakes of the same magnitude on its deeper portions. This webinar will highlight why it is important to accurately determine the shallow geometry of thrust faults along the margins of mountain ranges for estimating seismic hazard.



Catch up on past COMET and COMET+ webinars on our YouTube page: https:/www.youtube.com/channel/UCtFDytX1hgjvlS4NH48M2oQ/video<https://www.youtube.com/channel/UCtFDytX1hgjvlS4NH48M2oQ/videos>



Best wishes,

Scott Watson & Qi Ou



COMET - Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics

https://comet.nerc.ac.uk/

@NERC_COMET<https://twitter.com/nerc_comet?lang=en>

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