Correlation Between Local Slip Rate and Local High-frequency Seismic Radiation in an Earthquake Fault

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, q 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 q = 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 q 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 q 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.