The main goal of this work is to: (1) argue for the importance of a physically-based probabilistic seismic hazard analysis (pb-PSHA) methodology and show examples to support the argument from recent events, (2) demonstrate the methodology with the ground motion simulations of May 28, 1998, Mw = 5.5 Ras-Elhekma earthquake, north Egypt. The boundaries for the possible rupture parameters that may have been identified prior to the 1998 Ras-Elhekma earthquake were estimated. A range of simulated ground-motions for the Ras-Elhekma earthquake was ''predicted" for frequency 0.5-25 Hz at three sites, where the large earthquake was recorded, with average epicentral distances of 220 km. The best rupture model of the 1998 Ras-Elhekma earthquake was identified by calculated the goodness of fit between observed and synthesized records at sites FYM, HAG, and KOT. We used the best rupture scenario of the 1998 earthquake to synthesize the ground motions at interested sites where the main shock was not recorded. Based on the good fit of simulated and observed seismograms, we concluded that this methodology can provide realistic ground motion of an earthquake and highly recommended for engineering purposes in advance or foregoing large earthquakes at non record sites. We propose that there is a need for this methodology for good-representing the true hazard with reducing uncertainties.
Understanding how sedimentary basins respond to seismic-wave energy generated by earthquake events is a significant concern for seismic-hazard estimation and risk analysis. The main goal of this study is assessing the vulnerability index, K g , as an indicator for liquefaction potential sites in the Nile delta basin based on the microtremor measurements. Horizontal to Vertical spectral ratio analyses (HVSR) of ambient noise data, which was conducted in 2006 at 120 sites covering the Nile delta from south to north were reprocessed using Geopsy software. HVSR factors of amplification, A, and fundamental frequency, F, were calculated and K g was estimated for each measurement. The K g value varies widely from south toward north delta and the potential liquefaction places were estimated. The higher vulnerability indices are associated with sites located in southern part of the Nile delta and close to the branches of Nile River. The HVSR factors were correlated with geologic setting of the Nile delta and show good correlations with the sediment thickness and subsurface stratigraphic boundaries. However, we note that sites located in areas that have greatest percentage of sand also yielded relatively high K g values with respect to sites in areas where clay is abundant. We concluded that any earthquake with ground acceleration more than 50 gal at hard rock can cause a perceived deformation of sandy sediments and liquefaction can take place in the weak zones of K g ! 20. The worst potential liquefaction zones (K g > 30) are frequently joined to the Damietta and Rosetta Nile River branches and south Delta where relatively coarser sand exists. The HVSR technique is a very sensitive tool for lithological stratigraphy variations in two dimensions and varying liquefaction susceptibility.
The large impact of moderate earthquakes in unstable shelf of north Egypt on human society provides a strong motivation to study and understand the systematics of their occurrence. In this study, we examine the correlation of north Egypt unstable shelf earthquakes using five geologic and geophysical data sets: a newly compiled age-province map, Bouguer gravity data, aeromagnetic anomalies, tectonic stress field, and GPS velocity rate measurements. Based on the qualitative and quantitative interpretation of these five data sets, we inferred that (1) although surface features disappeared of unstable shelf crust, Phanerozoic crust shows clear correlation of crustal age and earthquake frequency. (2) The seismic ages are during Precambrian and Paleozoic unstable shelf crust.(3) Seismicity is correlated with the major tectonic events in the geologic history of Egypt. Unstable shelf seismicity mainly (1) follows the NW-SE lineaments and (2) forms clusters at what have been termed stress concentrators (e.g., intersecting faults and igneous intrusions) at EN-WS and E-W structural trends. The correlation of seismicity with NW-SE-oriented lineaments implies that the unstable shelf seismicity is related to the accretion and rifting processes that have formed the Red Sea and Gulf of Suez which still records active rifting. An analysis of hypocentral depths for unstable shelf earthquakes shows that the frequency and moment magnitude of events are nearly uniform for the entire 5-30 km depths over which crustal earthquakes extend. We appreciate that the deep structure of the crust, in particular the existence of deeply penetrating faults, is the controlling parameter, rather than lateral variations in rheology or high pore pressure. We conclude that the distribution of the unstable shelf earthquakes in north Egypt is consistent with the existence of deeply penetrating crustal faults that have been reactivated in the present stress field. Future earthquakes may occur anywhere along the geophysical lineations that we have identified. This implies that seismic hazard is more widespread in the Nile Delta Basin and Cairo province of north Egypt than indicated by the distribution of limited and inaccurate historical seismicity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.