Seismicity and seismotectonics of the Red Sea Region

Abstract

The historical seismicity of the Red Sea region between latitudes 13 and 30°N and longitudes 32 and 46°E has been revised. It is found that during the last 1400 years, some 88 historical earthquakes have occurred with magnitudes M≥ 5.6. Only two M=7.0 are reported, one in each of the northern and southern Red Sea regions, followed by two and one 6.8 in the northern and southern regions, respectively. During the period 1960-2010, some 1310 instrumental earthquakes have occurred in the region with M≥4.0. The largest (M=7.1) occurred in the Gulf of Aqaba, followed by a 6.9 in the entrance of the Gulf of Suez, followed by a 6.7 and a 6.4 that occurred in the southern Red Sea region. All others had M≤6.2. More than 90 % of the seismicity has occurred in the form of sequences and swarms and are believed to be volcanic related. Thus, the seismic hazard of the study region remains quite limited. Both northern and southern parts of the Red Sea region are of comparable seismic activities, while that of the central part is of lower activity. The historical and instrumental seismicity data show excellent correlation with the general tectonics of the study region. These also show that earthquake activity has fluctuated with time from one region to the other. In the Red Sea proper, more than 83 % of the seismic moment is associated with the regional faults of the axial trough with noticeable concentration of activity where the NE trending strike-slip faults cross this trough. Published fault plane solutions for the largest instrumental earthquakes of the last few decades show that both normal and strike-slip faults are active in support of a divergent environment between the Arabian and African plates. Shallow seismicity is a characteristic feature of this region. The data indicates that lithospheric deformations beneath the gulfs area are restricted to the upper part of the crust, while beneath the Red Sea south of latitude 27.8°, these appear to concentrate partially within the crust down to 10 km depth and much more within the uppermost mantle, mostly from 20.1 to 40 km depths. Very little earthquakes occur at depths deeper than 60 km. Frequency-magnitude results of both historic and instrumental data gave the expected b value close to 1.0. The calculated recurrence periods for earthquakes with M=6, 6.5 and 7 are 30±2 years, 150± 10 years and 600±20 years, respectively. The data show that the threshold magnitude for the study region is 4.0, and slightly more for the axial trough.

Lithospheric Structure of the Red Sea Based on 3D Density Modeling: A Contrasting Rift Architecture

“…Changes of lithospheric structure along the axis of the Red Sea have also been inferred from earthquake hypocentral analyses (e.g., El‐Isa, 2015; Mitchell & Stewart, 2018). The northern region of the rift shows a decrease in seismicity rates compared to the central‐southern regions, with an abrupt drop in the occurrence of earthquakes at a transition zone around 21° to 23°N.…”

A First Reliable Gravity Tidal Model for Lake Nasser Region (Egypt)

“…The LCR_D-128 was also used for about 1 year from February 2008 to February 2009 in Hurgada (Red Sea) to characterise the crustal response to tidal force and to determine a reliable tidal model for the region (Hassan et al, 2010c). The Red Sea is classified among the areas of highest seismic potential in Egypt and is of primary geodynamic interest being a rift that represents the locus of sea floor spreading and a divergent environment between the two major African and Arabian plates (El-Isa, 2015).…”

The First Network of Ocean Bottom Seismometers in the Red Sea to Investigate the Zabargad Fracture Zone

“…tectonic mapping on Zabargad island (Marshak et al, 1992). Furthermore, historical catalogs (El-Isa, 2015;Rehman et al, 2017), while limited, highlight the seismogenic potential of the ZFZ by including reports on two earthquakes of magnitude that could have been as large as M w 6. Moderate-to-large earthquakes within the ZFZ would threaten neighboring coastal communities on both sides of the Red Sea (Figure 1), in particular on the more populated Saudi coast, e.g., the city of Yanbu with its large petrochemical facilities, the town of Umm Lujj, and Red Sea Global, a major tourist destination under development mostly within the Al Wajh lagoon/platform (Figure 1).…”