Correlation Between Local Slip Rate and Local High-frequency Seismic Radiation in an Earthquake Fault |
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| Authors: | Alexander A Gusev Eugenia M Guseva Giuliano F Panza |
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| Institution: | (1) Institute of Volcanology and Seismology, Russian Ac. Sci, 9 Piip Blvd, Petropavlovsk-Kamchatsky, 683006, Russia;(2) Kamchatka Branch, Geophysical Service, Russian Ac. Sci, 9 Piip Blvd, Petropavlovsk-Kamchatsky, 683006, Russia;(3) Department of Earth Sciences, University of Trieste, Via E. Weiss 4, 34127 Trieste, Italy;(4) The Abdus Salam International Centre for Theoretical Physics, SAND Group, Trieste, Italy |
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| Abstract: | For any earthquake, the slipping fault and the source of high-frequency seismic waves, by and large, coincide. On a more local
scale, however, the areas of high seismic slip rate and of increased high-frequency radiation output (seismic luminosity)
need not match. To study in some detail how slip rate and seismic luminosity are interrelated, a systematic study is performed
that uses 251 records of teleseismic P waves from 23 intermediate-depth earthquakes of magnitude 6.8 and above. From a broadband trace we extract two time histories:
(1) displacement and (2) 0.5–2.5 Hz band-passed and squared velocity, or ``HF power', and calculate correlation coefficient,
ρ between the two. To reduce the bias related to formation of P coda, a special procedure is applied to data. We estimated the average value ρ = 0.52 (range of event averages 0.35 to 0.65) for the correlation coefficient between the radiated time histories for displacement
and ``HF power', which is considerably below the ``ideal' value of unity. We argue that the same or even lower value characterizes
the degree of slip rate - seismic luminosity correlation at the fault. Two factors may contribute to the revealed decorrelation:
(1) random fluctuations of observed HF power (inevitable for a signal with a limited bandwidth), and (2) the genuine mismatch
of slip rate and mean luminosity. We show that these factors, acting separately, would result in the ρ values equal to, correspondingly, 0.72 and 0.80. We also show that genuine decorrelation is statistically significant. We
conclude that the observed values of ρ indicate genuine differences between the distributions of the slip rate and the seismic luminosity over the fault area. These
results provide important constraints both for the accurate wide-band simulation of strong ground motion and for theoretical
dynamic source models. |
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| Keywords: | Earthquake fault stochastic high-frequency radiation envelope seismic energy non-coherent strong motion simulation |
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