A. Deif

Efficiency of horizontal-to-vertical spectral ratio (HVSR) in defining the fundamental frequency in Muscat Region, Sultanate of Oman: a comparative study

Muscat region is the most important political, economic, and densely populated region in the Sultanate of Oman. The proximity of Muscat region to the Oman Mountains and Makran subduction zones controls the earthquake hazard for Muscat. Evidences indicate the occurrence of a nearby historical earthquake with moderate magnitude MS = 5.5 in 1883. This event led to the damage of some villages near Nizwa City. The main objective of the current study is to compare the site characteristics of the region of interest in terms of the fundamental frequency using microtremors measurements with the numerical analysis results using one-dimensional (1-D) shear wave profiles. The microtremor measurements were performed at 99 sites distributed over the study region in order to calculate the horizontal-to-vertical spectral ratio (HVSR). The numerical modeling of horizontal shear (SH) waves in soil at the selected 99 sites are assessed by carrying out 1-D ground response analysis using the program SHAKE91. The required shear wave velocity profiles for the numerical modeling of SH-waves were derived using multichannel analysis of surface waves profiles. The amplification spectra have been evaluated for the soil column at each site location and the fundamental frequency obtained using SHAKE91 and HVSR are compared. Results were found to be compatible with the general surface geology of the region of interest and in most cases the HVSR is proved to be suitable for calculating the fundamental frequency in Muscat region.

Determination of a local earthquake magnitude scale for the Sultanate of Oman

Determination of earthquake magnitude is of great importance for quantitative seismological hazard studies. Since no local magnitude scale has been developed for the seismic network of the Sultanate of Oman, the present work is aiming towards developing the first local magnitude scale for earthquakes that occur in and around the Sultanate of Oman. Currently, the Earthquake Monitoring Center (EMC) in Oman uses the Southern California formula for ML calculations; the calculated values of local magnitudes are not comparable to the average magnitude calculated by the international centers (e.g., ISC and NEIC). In many cases, they show clear underestimation in magnitude for the local and regional distance events compared with magnitude values published by the international centers. A database of 424 simulated Wood–Anderson horizontal amplitudes of 55 events recorded by 9 very broadband stations, available since 2011, is built. All of the available events are located in northern Oman region. The attenuation function together with the magnitudes and the station corrections are determined using a multistep inversion process based on the application of the genetic algorithm. The computation provided the values of the empirical coefficients for geometrical spreading (n) and anelastic attenuation coefficient (k) to be 0.95 and 0.001, respectively. Station corrections for the used nine stations are calculated and found to be in the range of ±0.2 magnitude units. Great improvement regarding the local magnitude calculation is achieved as demonstrated by the better correlation with the provided ISC/NEIC magnitude values.

Development of ground-shaking maps for the Sultanate of Oman

This study presents research toward the development of ground-shaking maps after a real earthquake, or for scenario earthquakes originating from seismic sources within and around the Sultanate of Oman. Major important earthquake sources that are important for the Sultanate of Oman are the Makran zone, the Zagros zone, the Zendan-Minab system, the Oman Mountain zone, the Owen fracture zone and the Gulf of Aden zone. The earthquakes that take place on these zones, particularly those from Makran, already resulted and are likely to result in ground-shaking levels that may be significant for the country. The hazard module of software package ELER was customized for use in the development of shake maps in the Sultanate of Oman. For this purpose, (1) major active faults and systems within and around Oman were defined and implemented; (2) ground-motion prediction equations suitable for use and representative of tectonic conditions in Oman were identified and implemented; (3) the effect of local site conditions in resulting ground-shaking levels was attended by implementing the Vs30 maps into ELER methodology; and (4) scripts were developed for the consideration of ground-motion data coming from strong motion stations and from seismometers in and around Oman. They were used in the adjustment of ground-motion distribution maps, such as peak ground acceleration, peak ground velocity and spectral acceleration maps produced using ground-motion prediction equations. Example runs of different scenarios reflecting the use of newly adopted information are presented.

Developing a seismic source model for the Arabian Plate

A seismic source model is developed for the entire Arabian Plate, which has been affected by a number of earthquakes in the past and in recent times. Delineation and characterization of the sources responsible for these seismic activities are crucial inputs for any seismic hazard study. Available earthquake data and installation of local seismic networks in most of the Arabian Plate countries made it feasible to delineate the seismic sources that have a hazardous potential on the region. Boundaries of the seismic zones are essentially identified based upon the seismicity, available data on active faults and their potential to generate effective earthquakes, prevailing focal mechanism, available geophysical maps, and the volcanic activity in the Arabian Shield. Variations in the characteristics given by the above datasets provide the bases for delineating individual seismic zones. The present model consists of 57 seismic zones extending along the Makran Subduction Zone, Zagros Fold-Thrust Belt, Eastern Anatolian Fault, Aqaba-Dead Sea Fault, Red Sea, Gulf of Aden, Owen Fracture Zone, Arabian Intraplate, and a background seismic zone, which models the floating seismicity that is unrelated to any of the distinctly identified seismic zones. The features of the newly developed model make the seismic hazard results likely be more realistic.