Exploring the relation between backprojection images and earthquake
source processes
Abstract
Backprojection (BP) of teleseismic P waves is a widely-used method to
study the evolution of earthquake radiation and is particularly
effective for large earthquakes. We can harness key information on the
spatiotemporal evolution during the rupture process from waveform
similarity or coherency. Understanding the relation between earthquake
physics and the spatiotemporal evolution from BP imaging, which are
usually obtained from high frequency seismic waveforms, is of great
importance. Theoretical studies indicate that the high-frequency bursts
can be related to abrupt changes in rupture velocity (e.g. stopping of
rupture or kinks on the fault). Moreover, the BP images are thought to
be equivalent to either slip or slip rate on the fault, provided that
the Green’s functions from the sources to the receivers are incoherent
delta functions. Furthermore, recent studies propose that the frequency
dependent features of BP results can reflect the stress status,
frictional and/or geometrical heterogeneity on the fault surface. It is
promising that we can obtain more observational constraints and
information about the earthquake dynamic source from the backprojection
results combined with other independent techniques. In this study, we
attempt to figure out the relation between the BP results and earthquake
source process by testing both kinematic and dynamic source models. With
these source models, we can synthesise the seismic waveforms and trace
them back to the fault surface using the BP method. Therefore, we can
directly compare the BP results with the already-known earthquake
sources and further explore the possible relation to the source
properties by varying our source models such as the friction laws, fault
geometries. To simplify our problem and exclude the potential effects
from complex earth structure, our tests are carried out in a purely
elastic medium, whole space, allowing us to solve analytically for the
far-field body waves. From these systematical tests and comparisons, we
aim at building a comprehensive relation between the BP images and
various source properties. Moreover, our results can provide significant
help to better understand the physics of earthquake source process from
seismic observations.