 |
| Titel |
Mach-wave coherence in 3D media with random heterogeneities |
| VerfasserIn |
Jagdish C. Vyas, P. Martin Mai, Martin Galis, Eric M. Dunham, Walter Imperatori |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250129476
|
| Publikation (Nr.) |
 EGU/EGU2016-9597.pdf |
|
|
|
|
|
| Zusammenfassung |
| We investigate Mach-waves coherence for complex super-shear ruptures embedded in 3D
random media that lead to seismic scattering. We simulate Mach-wave using kinematic
earthquake sources that include fault-regions over which the rupture propagates at
super-shear speed. The local slip rate is modeled with the regularized Yoffe function. The
medium heterogeneities are characterized by Von Karman correlation function. We consider
various realizations of 3D random media from combinations of different values of correlation
length (0.5 km, 2 km, 5 km), standard deviation (5%, 10%, 15%) and Hurst exponent (0.2).
Simulations in a homogeneous medium serve as a reference case. The ground-motion
simulations (maximum resolved frequency of 5 Hz) are conducted by solving the
elasto-dynamic equations of motions using a generalized finite-difference method, assuming
a vertical strike-slip fault. The seismic wavefield is sampled at numerous locations within the
Mach-cone region to study the properties and evolution of the Mach-waves in scattering
media.
We find that the medium scattering from random heterogeneities significantly diminishes
the coherence of Mach-wave in terms of both amplitude and frequencies. We observe that
Mach-waves are considerably scattered at distances RJB > 20 km (and beyond) for
random media with standard deviation 10%. The scattering efficiency of the medium for
small Hurst exponents (H <= 0.2) is mainly controlled by the standard deviation of the
velocity heterogeneities, rather than their correlation length, as both theoretical
considerations and numerical experiments indicate. Based on our simulations, we propose
that local super-shear ruptures may be more common in nature then reported, but are very
difficult to detect due to the strong seismic scattering. We suggest that if an earthquake is
recorded within 10-15 km fault perpendicular distance and has high PGA, then inversion
should be carried out by allowing rupture speed variations from sub-Rayleigh to super-shear. |
|
|
|
|
|
|