Earthquake Monitoring in Southern California for Seventy-Seven Years (1932-2008)

Abstract

The Southern California Seismic Network (SCSN) has produced the SCSN earthquake catalog from 1932 to the present, a period of more than 77 yrs. This catalog consists of phase picks, hypocenters, and magnitudes. We present the history of the SCSN and the evolution of the catalog, to facilitate user understanding of its limitations and strengths. Hypocenters and magnitudes have improved in quality with time, as the number of stations has increased gradually from 7 to ∼400 and the data acquisition and measuring procedures have become more sophisticated. The magnitude of completeness (M c ) of the network has improved from M c ∼3:25 in the early years to M c ∼1:8 at present, or better in the most densely instrumented areas. Mainshock-aftershock and swarm sequences and scattered individual background earthquakes characterize the seismicity of more than 470,000 events. The earthquake frequency-size distribution has an average b-value of ∼1:0, with M ≥ 6:0 events occurring approximately every 3 yrs. The three largest earthquakes recorded were 1952 M w 7.5 Kern County, 1992 M w 7.3 Landers, and 1999 M w 7

Computing a Large Refined Catalog of Focal Mechanisms for Southern California (1981-2010): Temporal Stability of the Style of Faulting

“…We used polarities that were picked and reviewed by data analysts of the SCSN and archived at the Southern California Earthquake Data Center (SCEDC; Hutton et al, 2010). For stations with reverse polarities, we documented the reverse periods using teleseismic earthquakes and corrected the polarities before calculation.…”

“…With the progressive improvement of the SCSN network, station density has been increasing gradually, and the number of polarities per event has remained stable with a mean value of nine per event. In comparison, the mean number of S/P ratios per event increased in two steps: (1) increasing from zero in the 1980s to around 0.43 in the 1990s because of the first introduction of three-component broadband digital seismometers of the TERRAscope project in 1987 (Kanamori et al, 1993); and (2) increasing to an average of 6.4 per event since 2003 because of a major upgrade to the SCSN during 1997SCSN during -2002, when most single-component seismometers were replaced with three-component seismometers Hutton et al, 2010).…”

Testing Waveform Predictions of 3D Velocity Models against Two Recent Los Angeles Earthquakes

“…Figure 2 gives the locations and source mechanisms determined by SCSN from first motions and centroid moment tensor (CMT) waveform inversions using the 1D crustal model of Dreger and Helmberger (1993) (e.g., Clinton et al, 2006;Hutton et al, 2010).…”

Determination of Mmax from Background Seismicity and Moment Conservation

“…For example, different studies of the seismicity of California report values of 0.9 (Bakun, 1999), 0.95 (Tormann et al, 2010), 1:02 0:11 (Felzer, 2008), 1:03 0:12 (Page and Felzer, 2015), and 1.05 (Marsan and Lengliné, 2008). A value of about 1 was also determined from both historical and instrumental catalogs (Felzer et al, 2004;Wang et al, 2009;Hutton et al, 2010;Field et al, 2014). These regional b-values are close to the b-values obtained from individual earthquake sequences; for example, the value was 1:09 0:9 for the Landers aftershocks (Felzer et al, 2002).…”

“…Though there are some variations, b-values from different studies average around 1 in California for both the instrumental and historical records (Felzer, 2008;Wang et al, 2009;Hutton et al, 2010). We compare the results with historical earthquakes (Stover and Coffman, 1993;National Geophysical Data Center [NGDC], 2016) within 20 km of the fault trace (wider than the 10 km we use for the recent instrumental data to allow for larger location errors in the historical catalog), as shown in Figure 4.…”