Double-Corner Source Spectrum Explains Earthquake Duration, Energy and High-Frequency Ground Motion

Date: 4/25/2019

Time: 09:00 AM

Room: Pine

We show that a double-corner source spectrum can reproduce the peak ground acceleration (PGA) and peak ground velocity (PGV) of the NGA West-2 data set for 5.3 ≤ M_W ≤ 7.7. Earlier–Archuleta and Ji, GRL 2016–we found an apparent moment rate function that reproduced PGA, PGV and PWA (peak Wood Anderson displacement) for M_W ≤ 5.3. This apparent moment rate also had two-corner spectrum. For M_W ≤ 5.3, the two corners scale with magnitude; however, the scaling is different for magnitudes above and below 5.3. For M_W ≥ 5.3. The two corners f_c1 and f_c2 scale as Log(f_c1) = 1.754 – 0.5Mand Log(f_c2) = 3.250 – 0.5M. Both corners are proportional to f indicating self-similar scaling with seismic moment. The lower corner f_c1 is within 18% of the corner one would observe from the global CMT catalog, i.e., it’s inverse 1/(πf_c1) corresponds to the duration of earthquakes found worldwide. Thus, the lower corner would be consistent with the average stress drop found for global earthquakes. Between f_c1 and f_c2 the acceleration spectrum is proportional to f. The acceleration spectral level at frequencies greater than f_c2 is consistent with PGA and PGV for earthquakes in the NGA West-2 data. This high-frequency spectral level is proportional to the stress parameter used in time domain stochastic predictions of PGA and PGV. We find that the predicted radiated energy and the apparent stress agree with global estimates of these parameters for the same magnitude range. We will incorporate this two-corner spectrum into the UCSB method for broadband ground motion prediction.

Presenting Author: Ralph J. Archuleta

Authors