Radiated Energy from the 16 October 1999 Hector Mine Earthquake: Regional and Teleseismic Estimates

189

161

We investigate the relation between a static scaling relation, M 0 (seismic moment) versus f 0 (spectral corner frequency), and a dynamic scaling relation between M 0 and E R (radiated energy). These two scaling relations are not independent. Using the variational calculus, we show that the ratio ẽ ‫ס‬ E R /M 0 has a lower bound, w 10 able data on these scaling relations. We note that the scaling relation, Dr s V 3 ϰ , suggests that even if ẽ is scale independent and M 0 ϰ (i.e., e ‫ס‬ 0),

Section: ‫3מ‬mentioning

confidence: 99%

“…Recent improvements in data quality and methodology have significantly improved the accuracy of E R determination for large earthquakes (e.g., M w Ͼ6) (e.g., Boatwright and Choy, 1986;Boatwright et al, 2002;Venkataraman et al, 2002). For small earthquakes, it is still difficult to correct for the propagation effects.…”

Section: Energy-moment Relationmentioning

confidence: 99%

Static and Dynamic Scaling Relations for Earthquakes and Their Implications for Rupture Speed and Stress Drop

Kanamori¹

2004

189

161

“…It is based on the assumptions that the mainshock and aftershock locations and focal mechanisms are similar. This method was applied by Venkataraman et al (2002) to the regional recordings of the Hector Mine, California, earthquake of 16 October 1999 (M w ‫ס‬ 7.1). The estimated E R values were tightly clustered over distance and over different aftershocks used as EGFs.…”

Section: Estimation Of Radiated Seismic Energymentioning

confidence: 99%

A Source Study of the Bhuj, India, Earthquake of 26 January 2001 (Mw 7.6)

Singh¹

2004

We study the source time function (STF) and radiated seismic energy (E R ) of the M w 7.6 Bhuj earthquake using the empirical Green's function (EGF) technique. Our estimations of the STF and E R are based on teleseismic P waves and regional seismograms, respectively. We find that the STFs as a function of azimuth have a similar shape and nearly constant duration of 18 sec. This suggests that the rupture propagation was essentially radial. The STFs show a sharp rise in the first 6 sec. The E R estimated from the EGF technique is 2.1 ‫ן‬ 10 23 erg. We find that E R 's computed from integration of corrected velocity-squared spectra of teleseismic P waves and regional seismograms are in excellent agreement with the E R obtained from the EGF technique. Since the seismic moment, M 0 , is 3.4 ‫ן‬ 10 27 dyne cm, we obtain E R /M 0 ‫ס‬ 6.2 ‫ן‬ 10 ‫5מ‬ . The radiation efficiency, g R , during the Bhuj earthquake was low, about 0.23. The sharp rise of the STFs and g R ‫ס‬ 0.23 can be explained by Sato and Hirasawa's (1973) quasi-dynamic, circular source model with an effective stress of ϳ300 bar and the ratio of rupture to shear-wave velocity, V R /b, of ϳ0.5. The corresponding estimate of slip velocity at the center of the fault is 156 cm/sec. V R /b ϳ 0.5 is in reasonable agreement with the duration of the STF and the reported dimension of the aftershocks, as well as with the results of inversion of teleseismic body waves.The observations may also be explained by a frictional sliding model, with gradual frictional stress drop and significant dissipation of energy on the fault plane. This model requires an average dynamic stress drop of about 120 bar and V R /b ϳ 0.7 to explain both the rapid rise in the first 6 sec of the STFs and, along with a static stress drop of 200 bar, the observed E R /M 0 . High static stress drop is a common feature of most crustal earthquakes in stable continental regions. An examination of the available data, however, does not suggest that most of them also have relatively low radiation efficiency.

“…The Hector Mine earthquake in 1999 provided a good regional and teleseismic dataset to address this problem for a shallow strike-slip event. Venkataraman et al (2002) used empirical Green's function deconvolution to obtain the source spectrum, then used this source spectrum to estimate the seismic energy. Boatwright et al (2002) estimated the seismic energy of the same event from the integral of the squared velocity spectrum, but in contrast to other studies, used a geometrical spreading correction that is both frequency and distance dependent.…”

Section: Introductionmentioning

confidence: 99%

Reconciling Teleseismic and Regional Estimates of Seismic Energy

Pérez‐Campos¹

2003

Estimates of the radiated seismic energy based on teleseismic and regional data often differ by up to an order of magnitude, with a tendency for regional estimates to be larger than teleseismic estimates for the same event. In this study we compare the velocity spectrum determined from teleseismic data after correction for radiation pattern and propagation effects, with the velocity spectrum determined from regional data, after the corresponding corrections, for nine earthquakes in the Middle America subduction zone of Mexico. This comparison of the corrected spectra is used to identify and reduce the sources of the regional versus teleseismic energy discrepancy, which is about an order of magnitude for these events. We find that the teleseismic attenuation operator needs to be calibrated. In our case, for the tectonic environment of the Mexican subduction zone, we need a teleseismic attenuation operator that is stronger at high frequencies than the global average. A larger factor, however, is the correction needed to account for site amplification. This correction has an impact on both regional and teleseismic data, but it has a larger influence on the regional estimates because the angle of incidence for teleseismic waves is steep and the stations are located on more competent rock. By modifying the teleseismic attenuation operator and applying site corrections based on a generic site model, we essentially eliminate the order-of-magnitude discrepancy between teleseismic and regional estimates of the radiated seismic energy for these events.