EFFECTS OF THE JANUARY 30, 2016, Mw=7.2 ZHUPANOVSKY EARTHQUAKE ON THE WATER LEVEL VARIATIONS IN WELLS YUZ-5 AND E-1 IN KAMCHATKA

Abstract

This paper describes the water level variations in wells YuZ-5 and E-1 in Kamchatka during the Zhupanovsky earthquake that occurred on January 30, 2016 (Mw=7.2, Н=180 km). The distances from the Zhupanovsky earthquake epicenter to wells E-1 and YuZ-5 were 70 and 80 km, respectively. In well YuZ-5, the water level raised by 9.4 cm during 45 minutes after the seismic wave arrival. This effect was caused by a combination of a co-seismic rise in the water level due to the volumetric compression of the water-bearing rocks during fracturing in the earthquake source and an impulse increase in the fluid pressure near the wellbore during the seismic shocks. We estimated the amplitude of the coseismic water level increase (h=7.3 cm) and the strain value resulting from the volumetric compression of the water-bearing rocks, which is consistent with the estimated value of the coseismic volumetric deformation in the area of the well at the depth of 500m: D1 =-4.510-8. This estimation was based on the model of the dislocation source in the homogeneous isotropic elastic half-space with the parameters of the Zhupanovsky earthquake focal mechanism. After the earthquake, the water level dropped for three months at an amplitude of about ~40 cm. In order to estimate the radius of the well sensitivity to the pressure drop source, we used the model of water level lowering that followed the pressure drop in the aquifer at a distance to the well as a result of the improved filtration properties of the water-bearing rocks after the seismic shocks. The estimated radius of the well sensitivity, R is 450 m. For 3.5 months before the Zhupanovsky earthquake, ~20 cm increase in the water level was observed, which is anomalous in comparison with the average seasonal variations of the water level, as shown by the long-term observations. In our opinion, such a rise in the water level occurred in the process of the earthquake preparation, and can thus be viewed as its precursor. In well E-1, a sequence of water level changes manifested a hydrogeodynamic precursor: the water level dropped at an increased rate for 21 days before the earthquake, and raised at an amplitude of 3.7 cm during one month after the earthquake. The hydrogeodynamic precursor detected in real time gave grounds for forecasting a highly probable strong earthquake at a distance of up to 350 km from wells E-1 within a month. This forecast was reported to the Kamchatka Branch of the Russian Expert Council (KB REC) on January 21, 2016. The Zhupanovsky earthquake occurred on January 30, 2016, and its magnitude, time and location correlated with the prediction. The case of this earthquake shows that the Kamchatka Branch of the Federal Research Center 'Geophysical Survey of RAS' has the system of water level observations and data processing, which is capable of diagnosing (close to real time and retrospectively) different types of hydrogeoseismic variations in the water level in wells in case of strong seismic events, and detecting the hydrogeodynamic precursors of strong earthquakes.

Statistical Analysis of Precision Water Level Data from Observations in a Seismoactive Region: Case Study of the YuZ-5 Well, Kamchatka

“…Water level changes demonstrated an intraannual seasonal character with an amplitude of up to 50 cm (Boldina and Kopylova, 2017), as well as barometric and tidal variations (Kopylova, 2006a). Local strong earthquakes cause coseismic and postseismic variations in water level changings.…”

“…Local strong earthquakes cause coseismic and postseismic variations in water level changings. The hydrogeodynamic precursors were retrospectively distinguished in water level variations before the Kronotskoye (December 5, 1997, М w = 7.8) and Zhupanovo (January 30, 2016, М w = 7.2) earthquakes (Kopylova, 2006a;Kopylova and Boldina, 2012;Boldina and Kopylova, 2017). The passage of surface seismic waves from the strongest earthquakes with М w of about 8-9 at epicentral distances of hundreds to thousands of kilometers due to water level variations (hydroseisms) with amplitudes of up to 9 cm and durations of several hours to one day.…”

“…The passage of surface seismic waves from the strongest earthquakes with М w of about 8-9 at epicentral distances of hundreds to thousands of kilometers due to water level variations (hydroseisms) with amplitudes of up to 9 cm and durations of several hours to one day. More detailed data on the well structure, elastic and filtering properties of water-saturated rocks, regularities of the hydrogeodynamic regime, and earthquake effects in water level changes are presented in our earlier publications (Kopylova, 2006a;Kopylova and Boldina, 2006;Kopylova et al, 2010Kopylova et al, , 2016Kopylova, 2016, 2017) and in publications by other authors.…”

“…Retrospective analysis revealed that event no. 4 (Table 1) was preceded by an HP in the form of a water level rise by 28 cm over 3.5 months (Boldina and Kopylova, 2017).…”

“…Recent studies in Kamchatka have shown that application of traditional processing methods to water level measurement data (Kopylova, 2001(Kopylova, , 2006a, aimed at distinguishing lowfrequency trends in water level variations, can aid in detecting hydrogeodynamic precursors (HPs) before strong earthquakes. HPs are expressed as water level changes in time reference intervals from a few tens of days to months and years before earthquakes with magnitudes of about 7-8 at epicentral distances of up to a few hundred kilometers from observed wells (Kopylova et al, 2001;Kopylova, 2001Kopylova, , 2006aBoldina and Kopylova, 2017). Examples of successful mid-term predictions of strong earthquakes in Kamchatka using HPs are provided in (Chebrov et al, 2011;Firstov et al, 2016).…”