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Microearthquake distribution in the Lake Aswan area, Egypt

100%

Hassoup A.

Acta Geophysica Polonica

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2001

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tom Vol. 49, nr 3

317-330

EN

The temporal evolution of the Lake Aswan seismicity in Egypt over a 13-year period, from 1982 to 1995, is characterized by two separate sequences which occurred in August 1982 and June 1987 and a nearly continuous low-level activity over the remainder of the period. This study presents details of the space-time analyses of the two sequences. A nonlinear inversion method was used to relocate 200 events. The distribution of August 1982 foci exhibits asperity deformation; its center is located at 23.58°N, 32.57°E and 17 km depth. The foci distribution forms a zone dipping generally to the southwest. The June 1987 foci are distributed in a nearly vertical zone between 5 and 11 km depth, with epicentral coordinate centered at 23.57°N and 32.68°E. The August 1982 sequence is of foreshock-mainshock-aftershock type with a b-value of 0.8 and an aftershock decay rate of 0.78. The June 1987 activity is characterized by a b-value of 0.6 and is made up of two successive swarm bursts, which took place on June 17 and 19. The aftershock decay rates of these bursts are calculated as 1 and 0.99, respectively. The August 1982 cluster is of small amplitude and associated with a high background level. The June 1987 anomaly is of larger amplitude originating in a nearly zero background level. Our results suggest the Lake Aswan seismicity consists of the seismic zones with different characteristics.

2

Attenuation of intensity in the northern part of Egypt associated with The May 28, 1998 Mediterranean earthquake

63%

Hassoup A. , Tealeb A.

Acta Geophysica Polonica

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2000

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tom Vol. 48, nr 1

79-92

EN

On May 28, 1998, a moderate size earthquake of magnitude 6 occurred at lat, 31.45°N; long. 27.63°E. It was strongly kit in the northern part of Egypt. This study presents its intensity distribution based on the field observations and 280 MMI questionnaires describing the situation in the northern part of Egypt immediately after the mainshock. These reports indicate that this earthquake caused a strong shaking in Cairo and in many localities along the Nile Delta area. Cracks on buildings were observed in several places in Mersa-Matruh province, the western area of the Mediterranean Sea coast in Egypt, but cracks on ground were only observed on the sea beach area of Ras E1-Hekma village. Based on these data, the intensity-distribution map is presented here; its isoseismals are of non uniform distribution. The attenuation of MM intensity (I) with epicentral distance (D in km) of the studied shock is determined using a simple relation of type log I = log Io - mD, where Io is the epicentral intensity and m is constant. According to the variation in m constant, the isoseismal map of the studied area is divided into two zones, (a) and (b) of which zone-a is characterized by a higher m. The interpretation of the remarkable change in the m-value is attributed to the obvious variations in geological structures between zone-a and zone-b.

3

Temporal distribution, source parameters, and depth discrimination of earthquakes from the Abu Dabbab region, Egypt

51%

Hassoup A. , Niewiadomski J. , Gibowicz S.

Acta Geophysica Polonica

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2003

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tom Vol. 51, nr 2

135-146

EN

Records of earthquakes from the Abu Dabbab region in Egypt, situated about 25 km west of the Red Sea coast, were collected from the Aswan Seismograph Network (ASN). The temporal distribution of these events shows several sequences of the foreshock-main shock-aftershock type. Four such sequence occurred in 1984 and 1985. the slope of the frequency-amplitude relation (b-value) for the four sequences ranges form 1.8 to 2.4, reflecting co-seismic deformation with time in the vicinity of the source area. Source parameters were estimated for ten events from the same area, which occurred between 1998 and 2001 and had magnitude ranging from 3.0 to 4.2.the spectral plateau, corner frequency, seismic moment, source dimension, and stress drop were calculated. A good correlation is found between the logarithm of seismic moment and the local duration magnitude determined by the ASN. The stress drop is not uniform and ranges between 0.1 and 6.8 MPa. In addition, the relative decay of the amplitude of S waves from the Abu Dabbab earthquakes with the epicentral distance is examined from the records of various stations of the ASN. It was found the rater of decay can be divided into two distinct types, related to different paths between the hypocenters and the stations, which in turn indicate different depths of the studied events.

4

Seismicity of the Lake Aswan area, Egypt, between 1991-1999

51%

Hassoup A. , Hasseb G. , Dahy S.

Acta Geophysica Polonica

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2002

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tom Vol. 50, nr 3

361-372

EN

The data described here form a part of continuous observations of the earthquake activity and water level variation in Lake Aswan area in Egypt. The earthquake hypocenters from the 1991-1999 period are distributed in four seismic zones (A, B, C and D), trending in the E-W and N-S directions. The hypocenters concentrate within the shallow part of the crust. The number of deeper events, with focal depths between 10 and 30 km, is small. The temporal distribution of seismicity in the 1991-1999 period correlates with water level changes in the lake. This well observed correlation indicates that the water level variation is effective in the Lake Aswam area, and suggests that the 1991-1999 earthquake activity may be classified as reservoir-triggered seismicity. The composite fault plane solution is considered for the earthquakes of magnitude greater than 2. Nine solution were obtained, representing the four epicentral zones. The strike-slip and strike-slip with normal component focal mechanism are dominant in the study area. This result is consistent with the interpretation of tectonics in the Aswan region. The focal mechanism with normal component is found only in zone C. This observation may be related to an effect produced either from the change in water load due to the water level variation or from tectonic characteristics of zone C.