The b value before the 6th August, 1988 India-Myanmar Border Region Earthquake—a case study

Forecast experiment: Do temporal and spatial b value variations along the Calaveras fault portend M ≥ 4.0 earthquakes?

“…If the seismic b value is inversely proportional to stress [e.g., Scholz , 1968: Main et al , 1992; Amitrano , 2003; Schorlemmer et al , 2005], then the hypothesis behind forecasting with temporal magnitude‐frequency changes is an expectation of lowered b value prior to large earthquakes [e.g., Imoto , 1991; Kebede and Kulhánek , 1994; Sahu and Saikia , 1994; Enescu and Ito , 2001; Cao and Gao , 2002; Ziv et al , 2003; Nuannin et al , 2005]. In this section I discuss whether 24 M ≥ 4.0 earthquakes that happened within seven 5‐km‐radius cylindrical volumes centered on the Calaveras fault were associated with significant changes in b value before their occurrence in a retrospective test.…”

“…Motivated by laboratory experiments [ Scholz , 1968; Amitrano , 2003], theoretical studies [e.g., Main et al , 1992], and observations [ Schorlemmer et al , 2005] showing b values decreasing with increasing stress, investigators have sought temporal and/or spatial b value variations that correlate with earthquake occurrence. Two viewpoints prevail: in the first, time‐varying b values are associated with large earthquakes or moment rate changes [e.g., Imoto , 1991; Kebede and Kulhánek , 1994; Sahu and Saikia , 1994; Enescu and Ito , 2001; Cao and Gao , 2002; Ziv et al , 2003; Nuannin et al , 2005]. In the second, b values are found constant in time, but spatial variations are related to earthquake occurrence and/or likelihood [ Abercrombie and Brune , 1994; Westerhaus et al , 2002; Schorlemmer et al , 2003; Wyss et al , 2004; Schorlemmer et al , 2004; Wyss and Stefansson , 2006].…”

Mapping the <i>b</i>-values along the Longmenshan fault zone before and after the 12 May 2008, Wenchuan, China, <i>M<sub>S</sub></i> 8.0 earthquake

“…In the figure, we adapted the 2-dimensional slip distribution profile into a 1-D distribution of total slip and take the 70% and 50% maximum, respectively, as the first-order measure of the slip distribution or the "effective length". Hinted by previous results of temporal b-value variation before earthquakes (Imoto, 1991;Kebede and Kulhánek, 1994;Sahu and Saikia, 1994;Enescu and Ito, 2001;Cao and Gao, 2002;Ziv et al, 2003;Nuannin et al, 2005), we also try to investigate whether there is any change of b-value before the Wenchuan earthquake. Figure 4b shows the temporal variation of b-value within the polygon.…”

Microearthquake Seismology and Seismotectonics of South Asia

“…A temporal change of b-value, before the August, 1988 Indo-Burma border earthquake (M L 7.5), was studied by Sahu and Saikia (1994). They analysed the data for the period 1976-1987, with a threshold magnitude of earthquake m b 4.5, within the latitude 21°-25°N and longitude 93°-96°E in the Indo-Burma ranges.…”