Capturing broadband spectral characteristics of moderate-sized earthquakes using nearby recordings: Verification

Chen Ji, Ralph J. Archuleta, & Aaron J. Peyton

Published September 8, 2024, SCEC Contribution #13989, 2024 SCEC Annual Meeting Poster #052

We propose to characterize earthquake source spectra with three measures: seismic moment M_0, apparent stress σ_a, and stress parameter 〖Δσ〗_B. We studied 42 moderate-sized (4.0≤M_w≤5.4) Ridgecrest, California earthquakes using 3-component S wave records within 50 km. To explain the distance dependency of σ_a in the time domain, we obtained a crustal attenuation function q(r)=r^(-1) exp⁡[-(k_1+k_2 M_w )r],r^2=Δ^2+h^2 with k_1=0.040, k_2=-0.0026, where Δ and h are epicentral distance and centroid depth, respectively. In the frequency domain, this function is equivalent with a frequency-dependent Q model Q(f)=60f^0.675 for f>1.0 Hz and an r^(-1) geometric decay. Our results reveal that both σ_a and Δσ_B have a dependence on centroid depth. These earthquakes can be divided into “shallow” and “deep” groups with a demarcation depth of 5.5-6 km. The geometric mean σ_a^F and Δσ_B of the “shallow” group are about 4 times smaller than those of the “deep” group. The ratio of Δσ_B and σ_a (3.0) suggests the source spectrum in this magnitude range is close to a single-corner spectral model. We verify these findings with the observations of other moderate-sized earthquakes in Southern California. Our preliminary analysis for 80 3.5≤M_w≤3.9 Ridgecrest earthquakes shows remarkable agreement with the results for earthquakes 4.0≤M_w≤5.4. With the expanded magnitude range, the increase of Δσ_B and σ_a with M_w becomes statistically more significant, though the scaling relations for the “shallow” and “deep” earthquake groups are notably different.

Citation
Ji, C., Archuleta, R. J., & Peyton, A. J. (2024, 09). Capturing broadband spectral characteristics of moderate-sized earthquakes using nearby recordings: Verification. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology