Role of fluids in the earthquake occurrence around Aswan reservoir, Egypt

Abstract

.[1] Continuing seismicity for about 30 years near a large western embayment of the Lake Nasser, about 50 km from the Aswan High Dam in Egypt, has led to a debate about the possibility of its relation with the reservoir impoundment. The largest event in the region occurred on 14 November 1981 (M 5.3), 20 km beneath the Wadi Kalabsha embayment, a westward extension of the Lake Aswan. Since then, continuous monitoring of seismic activity has given an excellent opportunity to study the spatiotemporal distribution of seismicity in the area. Most of the immediate aftershocks of the 1981 main shock were located in the Gebel Marawa area at depths between 15 and 30 km. Depths of almost all earthquakes away from this zone were shallower than 12 km. To quantify the effect of the reservoir impoundment on the seismicity of the Aswan area, we calculated changes in stress and pore pressure due to the reservoir impoundment using Green's function approach. The change in Coulomb stress (DS) is calculated on the fault planes responsible for majority of the seismicity of the region. We found that for all the seismogenic faults, DS is negative, i.e., stabilizing, when we consider the effect of the reservoir load only, whereas it is positive, i.e., destabilizing, when we include pore pressure. For example, at the hypocenter of the main earthquake, shear stress, normal stress, and pore pressure due to reservoir operation are estimated as 5.5, 13.2, and 13.5 kPa, respectively, which suggest that DS is À3.1 kPa when we do not consider the effect of pore pressure and 5.7 kPa when contribution from pore pressure is considered. Hence, the seismicity in the Aswan lake region is driven by the pore pressure due to reservoir impoundment.

Monsoon-induced earthquake activity in Talala, Gujarat, India

“…To calculate the reservoir-related stress variations, we follow the calculations of Gahalaut & Hassoup (2012) assuming an uniform and isotropic half-space. The total pressure change p related to a reservoir is the sum of p c and p d , which are the change in pore pressure due to the instant compression caused by the reservoir load, and the change in pore pressure due to the diffusion of reservoir water load, respectively (Roeloffs 1988).…”

“…Triggering of earthquakes is evident for fluid injections in wells, for example (Zoback & Harjes 1997;Shapiro et al 2003;Fischer et al 2008), where engineering data are available and dense monitoring systems are installed. Furthermore, it is known that the filling as well as seasonal variations of reservoirs can trigger local earthquakes, for example (Talwani 1997;Gahalaut & Hassoup 2012). A less-known source of hydroseismicity is rainfall, which leads to pore-pressure changes in the crust due to the infiltration of water in the ground.…”

Influence of the impoundment of the Three Gorges Reservoir on the micro-seismicity and the 2013 M5.1 Badong earthquake (Yangtze, China)

“…It is also used in the analysis of tidal triggering (Heaton, 1975;Perfettini and Schmittbuhl, 2001) and reservoir triggering (Cheng et al, 2012;Gahalaut and Hassoup, 2012;Ge et al, 2009). As limited by lacking of reliable measurement techniques of full stress in earth's crust, the tectonic stress field of the crust beneath the reservoir cannot be determined in advance.…”

The implications of regional microseismic activities: A lesson from 2008 Ms. 8.0 Wenchuan earthquake

“…Post-seismic change of seismicity following the major event is a direct and visible indicator of regional stress migration which can directly reflect the aftershock nucleation or triggering of the future events (Brodsky and Lay, 2014;Gahalaut and Hassoup, 2012;King et al, 1994;Stein et al, 1992). With the help of broadband seismicity observations and statistical methods in recent decades, studies in statistical seismology have been making considerable progress.…”

“…Thus, these models mentioned above can only adopt the Coulomb failure stress change (∆CFS) to quantitatively evaluate the influence of the major event on the post-seismic nucleation and its triggering mechanism. According to the Mohr-Coulomb theory and the Hook-Brown strength criteria (Gahalaut and Hassoup, 2012;King et al, 1994;Stein et al, 1992), ∆CFS on the existing fault plane is …”