Frictional properties and fracture energy constrained from frequency-dependent coseismic radiations of great earthquakes
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AbstractRupture process is one of the key components in earthquake physics and has been investigated extensively using the back projection method. Recent studies have suggested that coseismic radiations of a few megathrust earthquakes have clearly shown frequency-dependent phenomenon, e.g. the 2015 Mw8.3 Illapel and the 2015 Mw7.8 Nepal earthquakes. Low-frequency contents are concentrated at shallower depth while high-frequency radiations are originated from deeper portion of the seismogenic fault, and such feature has been attributed to systematic down-dip changes of frictional properties. However, it remains unknown what properties are changing and what the controlling factors are. Here we conduct a series of numerical experiments to simulate the dynamic rupture processes of the 2015 Illapel and Nepal earthquakes. We first validate our slip models with the finite fault models and find good agreement. We then extract the slip rate and calculate slip acceleration, which is corresponding to far-field ground velocities. By comparison of radiated energy in different frequency bands, we find that such frequency-dependent coseismic radiations are associated with the critical slip-weakening distance d0 and thus the fracture energy (G, half of the product of the dynamic stress drop and d0). In order to impede high-frequency radiation at the shallow depths, the slip-weakening rate w (dynamic stress drop divide d0) needs to be smaller than 2-3 MPa/m, which at deeper portion w could be larger than >8 MPa/m to emit high-frequency energy radiation comparable with observations. In addition, we find that the fracture energy is , where u is the slip on the fault. Our results show that the critical slip-weakening distance d0 and thus the fracture energy G may decrease with depth, which could be a result of reduction in the thickness of the fault gouge.
Acceptance Date04/10/2016
All Author(s) ListHongfeng Yang, Huihui Weng
Name of Conference2016 AGU Fall Meeting
Start Date of Conference12/12/2016
End Date of Conference16/12/2016
Place of ConferenceSan Francisco
Country/Region of ConferenceUnited States of America
LanguagesEnglish-United States

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