A Special Type of Georesistivity Variation before Some Larger Earthquakes

Abstract:

Abstract: According to a detailed analysis of georesistivity data recorded from 2004 to 2011 by the PS100 geoelectric stations, a number of georesistivity pulses which appeared a couple of months to a couple of days before large earthquakes (eg., Wenchuan earthquake, Ms8.0, 2008; Yushu earthquake, Ms7.3, 2010) are reported in this study. These pulses may be responses of the wave related to tidal force and the wave may generate in the earthquake source region for the following reasons: Firstly, statistics indicate that the duration time of these pulses ranges from 8 to 22 hours and concentrate on about 13 hours which is roughly in agreement with the period of the tidal force M₂ (12h25min); Secondly, time delays (T, unit: hour) exist between the arrival time of the pulses’ minima and gravity tide maxima and they differ from the distance (d, unit: km) between the earthquake epicenter and PS100 stations, but what’s may be more interesting is that the distance and time delays satisfy the formula of d=41.47T, suggesting that this kind of pulses shows some wave-like properties. Further investigations reveal that the wave may be the result of perturbation of the mass beneath the earthquake source region in the critical stage of earthquake when the crust is weakened on a large scale and it will be useful for earthquake prediction.

Key words: Tidal force, Georesistivity pulses, Wenchuan earthquake, Yushu earthquake, Sumatra earthquake