Short term earthquake forecasts at Koyna, India

Abstract

Earthquake activity is monitored in real time at the Koyna reservoir in western India, beginning from August 2005 and successful short term forecasts have been made of M ~ 4 earthquakes. The basis of these forecasts is the observation of nucleation that precedes such earthquakes. Here we report that a total of 29 earthquakes in the magnitude range of 3.5 to 5.1 occurred in the region during the period of August 2005 through May 2010. These earthquakes could broadly be put in three zones. Zone-A has been most active accounting for 18 earthquakes, while 5 earthquakes in Zone-B and 6 in Zone-C have occurred. Earthquakes in Zone-A are preceded by well defined nucleation, while it is not the case with zones B and C. This indicates the complexity of the earthquakes processes and the fact that even in a small seismically active area of only 20 km x 30 km earthquake forecast is difficult.

Investigations related to scientific deep drilling to study reservoir-triggered earthquakes at Koyna, India

“…4). Significantly, the thickness of the Deccan Traps is consistent with the inference from recent broadband seismic monitoring in the area that shows a conspicuous absence of earthquakes in the top ~1 km (Gupta et al 2011a). Cores recovered from the borehole have revealed a flood basalt pile comprising up to 25 lava flows of variable thicknesses, with each flow characterized by a vesicular and/or amygdaloidal layer underlain by fine grained massive basalt.…”

“…The entire seismic activity is restricted to ~30 km × 20 km area, and there is no other earthquake source within ~50 km of the Koyna Dam. The depth of these earthquakes is limited to about 10 km, with almost 80 % occurring between 1 and 6 km depths Gupta 1992Gupta , 2002Talwani 1997a preceded by well-defined nucleation, and real-time identification of nucleation has led to short-term forecasts (Gupta et al 2006(Gupta et al , 2007(Gupta et al , 2011a. Over the years, a considerable shift in the seismic activity to the south has been observed.…”

Detection of Quarry Blasts in the Koyna-Warna Region, Western India

“…Previously, [6] reported the association of earthquakes of magnitude exceeding 3 with these seismic clusters. The zone further south-east of the Warna reservoir was also documented based on events detected with a sparse data set [10].…”

“…The ground velocity spectra over a time window of 8 s duration of the vertical component seismograms at the 2 selected seismic stations, after applying butter worth band-pass filter (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15), are shown in Figure 7. Comparable magnitudes of the order of M L ~2 are considered for spectral discrimination.…”

“…Since August 2005, a closely spaced network with near real time monitoring has been set up. This has enabled identification of a nucleation that precedes moderate earthquakes of magnitude 4.0 to 5.0 [5] [6].…”