Size and duration of the high-frequency radiator in the source of the 2004 December 26 Sumatra earthquake

Abstract

We recover the gross space–time characteristics of high-frequency (HF) radiator of the great Sumatra-Andaman islands earthquake of 2004 December 26 (M w = 9.1–9.3) using the time histories of the power of radiated HF P waves. To determine these time histories we process teleseismic P waves at 36 BB stations, using, in sequence: (1) bandpass filtering (four bands: 0.4–1.2, 1.2–2, 2–3 and 3–4 Hz); (2) squaring wave amplitudes, making ‘power signals’ for each band and (3) stripping the propagation-related distortion (P coda, etc.) from the power signal and thus recovering source time function for HF power. In step (3) we employ an inverse filter constructed from an empirical Green’s function, which is estimated as the power signal from an aftershock. For each ray we thus obtain signals with relatively well-defined end and no coda. From these signals we extract: total duration (joint estimate for all four bands) and temporal centroid of signal power for each band. Through linear inversion, the set of duration values for a set of rays delivers estimates of the rupture stopping point and stopping time. Similarly, the set of temporal centroids can be inverted to obtain the position of the space– time centroid of HF energy radiator. The quality of inversion for centroid is acceptable for lower-frequency bands but deteriorates for higher-frequency bands where only a fraction of stations provide useful data. For the source length and duration the following joint estimates were obtained: 1241 ± 224 km, 550 ± 10 s. The estimated stopping point position corresponds to the northern extremity of the aftershock zone. Spatial HF radiation centroids are located at distances 350–700 km from the epicentre, in a systematic way: the higher is the frequency, the farther is the centroid from the epicentre. Average rupture propagation velocity is estimated as 2.25 km s–1

Long-period spectral features of the Sumatra-Andaman 2004 earthquake rupture process

“…Summarizing these results, and relying on the fact that the size of the source is constrained by HF P‐wave energy radiation (Lomax 2005; Ishii et al 2005; Ni et al 2005; Kanamori 2006; Gusev et al 2007), HF T‐waves (DeGroot‐Hedlin 2005), and very long‐period data (normal modes, tsunami) (Ammon et al 2005; Lay et al 2005; Park et al 2005; Fujii & Satake 2007; Piatanesi & Lorito 2007), we propose that the Northern part of the Sumatra‐Andaman fault (to the North of 8°) radiated very long period seismic energy and did not radiate long period seismic energy at periods shorter than 650 s. We show that simple dynamic modeling can reproduce this feature as long as effective viscous faulting effects are introduced.…”

“…In the case of the Sumatra–Andaman earthquake, the size of the source is constrained by both HF P ‐wave energy radiation (e.g. Lomax 2005; Ishii et al 2005; Ni et al 2005; Kanamori 2006; Gusev et al 2007), T waves (e.g. DeGroot‐Hedlin 2005), and very long‐period data (normal modes, tsunami) (e.g.…”

The 2010 Qinghai, China, Earthquake: A Moderate Earthquake with Supershear Rupture

“…We apply a highfrequency (0.2-2 Hz) P-wave envelope inversion using empirical Green's functions to locate the centroids of highfrequency energy (Gusev et al, 2007). We used data from two arrays at similar distances (62.5°-64.0°) that are located in the forward (Warramunga Array in Australia) and backward (Graefenberg Array in Germany) directions of the rupture.…”

“…Then, we analyze teleseismic data with a highfrequency P-wave (0.2-2 Hz) envelope inversion using an empirical Green's function event to investigate the sources of high-frequency radiation (Gusev et al, 2007).…”

Temporal characteristics of high band-pass filtered teleseismic P-waveforms from large shallow earthquakes

“…3 and 4 imply that the high-frequency energy radiation is weak in the vicinity of rupture starting regions. The systematic determination of spatial and temporal distributions of high-frequency energy radiation for a set of earthquakes considering seismic wave propagation and site effects using techniques such as the empirical Green's function method (e.g., Gusev et al, 2007) will be an interesting issue to be studied in future research.…”