TY  - JOUR
ID  - epos1349
UR  - http://dx.doi.org/10.1016/j.tecto.2006.11.010
IS  - 1-2
A1  - Chadha, Rajender Kumar
A1  - Kuempel, Hans Joachim
A1  - Shekar, M.
N2  - Water level fluctuations in twenty-one observation wells have been monitored for the last 10 years around the seismically active Koyna?Warna
region, western India where earthquakes continue to occur even after four decades of the initiation of the seismic activity in the region. Fourteen of
the observation wells act as volume strain meters as their water levels show earth tidal signals. Our analysis suggests three types of response of the
well water levels to seismo-tectonic effects, i) one to local earthquakes, ii) to regional and teleseismic events, and iii) to local fluctuations in rock
strain on regional scale. We observed five cases of co-seismic step-like well water level changes, of the order of few centimeters in amplitude,
related to earthquakes in the magnitude range 4.3?M?5.2. All these earthquakes occurred within the network of wells drilled for the study and
within 25 km distance of the recording wells. In three cases, drop in well levels preceded co-seismic step-like increases, which may be of
premonitory nature. The second type of response is observed to be due to the passing of seismic waves from regional and teleseismic earthquakes
like the M 7.7 Bhuj event on January 26, 2001 and the M 9.3 December 26, 2004 Sumatra earthquake. The third type is a well level anomaly of
centimeter amplitude coherently occurring in several wells. The anomalies are similar in shape and last for several hours to days.
From our studies we conclude that the wells in the network appear to respond to regional strain variations and transient changes due to distant
earthquakes. The two factors which are important to co-seismic steps due to local earthquakes are the magnitude and epicentral distance. From the
limited number of events we found that all local earthquakes exceeding M?4.3 have produced co-seismic changes. No such changes were
observed for earthquakes below this magnitude threshold.
VL  - 456
TI  - Reservoir Triggered Seismicity (RTS) and well water level response in the Koyna?Warna region, India
AV  - none
EP  - 102
Y1  - 2008///
PB  - Elsevier
JF  - Tectonophysics
KW  - Well water level
KW  - Hydrological precursors
KW  -  Koyna?Warna area
SN  - 0040-1951
SP  - 94
ER  -