Study of the tectonic and reservoir-triggered seismogenic processes in the Aswan area (Egypt)

Project leaders

Vincenzo Lapenna, Raafat El-shafei Fat-helbary

Agreement

EGITTO - ASRT - Academy of Scientific Research and Technology

Call

CNR-ASRT 2016-2017

Department

Earth system science and environmental technologies

Thematic area

Earth system science and environmental technologies

Status of the project

New

Research proposal

It has long been known that water reservoirs are capable of triggering seismicity. The magnitude 6.3, 1967 earthquake occurred in the Koyna-Warna Region in India following the impoundment of a large water reservoir, is the most emblematic case. To date many worldwide cases of reservoir-triggered seismicity have been reported in literature, in Nurek Reservoir, Tadjikistan (Simpson and Negmatullaev 1981), in the reservoirs LG3 and Manic 3, Quebec, Canada (Anglin and Buchbinder 1985; Leblanc and Anglin 1978), in Govind Ballav Pant reservoir, India (Gahalaut et al. 2007), just to mention some cases.
Reservoir-triggered seismicity is characterized by features that discriminate them from normal seismic events, like higher b-value, larger magnitude ratio of the largest aftershock to the mainshock, increase of seismicity rate with the increase of water level.
It is generally assumed that ground water plays an important role in reservoir-triggered seismicity: water pore pressure reduces the normal stress within a rock while not changing the shear stress, and an increase in water pore pressure could make the critical value of shearing stress arbitrarily low, triggering an earthquake. For large reservoirs, the oscillation of the gravitational loading can also affect the fault stability, which is dependent on (a) the location of the reservoir with respect to the faults, (b) the fault orientation, and (c) the stress field (Roeloffs, 1988; Talwani, 1997).
Even if the basic mechanisms that can trigger earthquakes are presently well understood, models to predict the size and location of earthquakes in response to water reservoir perturbations are compromised in large part due to the lack of basic data on the interactions among rock, faults, and fluid as a complex system. Therefore, reservoir-triggered seismicity is still at a pioneering stage and represents a topic still debated by the scientific community, due to the strong social impact and to its implications for seismic hazard and risk.
The activity to be developed in this project is addressed to the application of advanced methodologies for studying seismic source processes and clustering in the Aswan area (Egypt), which represents one of the most interesting seismic areas in the world due to the possible reservoir-related earthquake triggering mechanisms linked with the loading/unloading operations of the Lake Nasser. Aswan hosts the largest dam in Egypt, "The high Dam", which is 111 m high, a crest length of 3830 m and a volume of 44.3E+6 cubic meters, impounds a reservoir, Lake Nasser, that has a gross capacity of 169 billion cubic meters. The Aswan High Dam hydropower project was constructed in 1970. It is the most important project in Egypt from the social, agricultural and electrical energy production points of view. The importance of this dam comes from the fact that it is a unique case in the world where one single dam controls almost whole nation in its downstream. Protection of this structure from all kinds of hazard, particularly earthquakes, is actually a conservation of Egypt in the present and the future. Indeed, the area is known to be seismically active since the occurrence of the Mw 5.8, November 1981 Aswan earthquake. Detailed geological and geophysical surveys in the area confirm the existence of few active faults to the southwest of the Aswan High Dam (e.g. Kalabsha, Khor El-Ramla and Kurkur faults). The seismic activity in this area might be related to both tectonic activities along these active faults and/or reservoir induced seismicity due to the Aswan Lake construction. Therefore, a regional seismological network was established since 1982 around the northern part of the Lake Nasser to monitor all earthquake activity and recently, on 2007, the National Research Institute of Astronomy and Geophysics (NRIAG) have started the upgrading of this network by using broad band stations that send data in real time to the main data centre at Aswan using satellite communication.
In order to study the natural and reservoir-related processes associated with the triggering of earthquakes, earthquake clustering, and earthquake migration in the Aswan area, our project is aimed at clarifying the links among the different physical, mechanical and geological parameters involved in the triggering processes with the size and location of seismic events. Particular attention will be paid to better understand the links between the water level fluctuations of the reservoir and the earthquake occurrence. Therefore, spatial and temporal pattern of seismicity, stress field and modelling of the pore pressure diffusion due to seasonal variations of the water level in Aswan Lake will be studied. The proposal is also aimed at providing the scientific community with new elements and data for a better understanding of the phenomenon and a more accurate seismic hazard assessment and risk mitigation of the Aswan area.
To perform such activities the available resources for the project are: 1) Detailed geological setting based on the detailed studies performed by Woodward Clyde Consultants (WCC, 1985); 2) Detailed crustal structure provided from passive and active seismic studies previously performed by NRIAG researchers; 3) Previous geophysical studies performed by NRIAG researchers; 4) Revised regional and local earthquakes catalogue for Aswan area from 1981-2015; 5) Water level data from 1964-2015; 6) Digital waveform data of events recorded by the seismic network.
The Egyptian and Italian groups will share their experience and competence in seismic data analysis, seismic measurements, seismological network design and installation; and they will carry out the project in terms of knowledge transfer, data and methodologies sharing for a better understanding of seismic processes, acquisition of co-operation procedures and sharing of human resources, to be exploited for a future continuation of joint research/education activities.

Research goals

The general aim of the project is to better understand the processes associated with the triggering of earthquakes and earthquake migration in the Aswan area, to find possible interactions among the clusters, to better assess correlations with water level fluctuations of the Lake Nasser, and to track the small-scale variability of faulting style, stress and strength of active faults. The specific objectives are: 1) To perform accurate earthquake location and estimation of seismic source parameters of recorded seismicity at Aswan area. 2) To study similarities and differences between natural and reservoir-triggered seismicity in Aswan area. 3) To study the space-time evolution of the seismicity at Aswan area and to analyze the space-time relationship of the triggered seismicity with the water level of the reservoir, the local stress field and the geological settings. 4) To investigate and understand the processes involved in the reservoir-triggered seismicity. 5) To develop a hydromechanical model for the Aswan area and to estimate the hydraulic diffusivity of the area also from the space-time evolution of reservoir-triggered events. 6) To provide an assessment of the seismic hazard of the area on the base of the results obtained through the analysis of the seismological and geophysical parameters measured in the area. 7) To disseminate the preliminary and final results of the project in international conferences, publications, and in a project-oriented internet website.

Last update: 24/04/2024