I perform various statistical analyses to understand the spatiotemporal behavior of seismicity. These include mapping frequency-magnitude distribution, b-value, and seismic energy released at local and regional scales and investigating their relationships with pre-pressure changes, plate motion, strain rate, fault mechanisms, gravity measurements, crustal structure, and attenuation.
Mousavi, S. M., (2017). Spatial variation in the frequency-magnitude distribution of earthquakes under the tectonic framework in the Middle East, Journal of Asian Earth Science.
Spatial variations of seismic energy released and b-value over the Middle East region are investigated based on a seismicity catalog from 1995 to 2007. The goal is to use these seismic parameters and based on other geodetic and geophysical observations, such as GPS measurements, strain rate model, fault distribution, focal mechanism, crustal model, Q model, and gravity measurements, etc., to uncover spatial patterns that seem anomalous. Areas of high energy released (cumulative) seem to correspond to the areas of relatively high b-values. Areas of high energy released and high b-values seem to correspond very well with the location of continental collision where earthquake activities are high. The divergent boundary between Arabia and African plates and the subduction zone at Makran seem to correspond to low to moderate energy release. Northern Pamir, Azerbaijan-Caucasus, the lower part of the Zagros Mountains, eastern Turkey, Owen Fracture Zone, Strait of Bob-el-Mandeb, and south of the Sulaiman Shear Zone seem to correspond to high cumulative energy-released, high strain rate, high b-values, and high fault density. While, central and eastern Iran, southern Zagros, northern Pakistan, Gulf of Aden, Alborz, southwest of the Caspian Sea, western Caucasus, and Kopeh-Dagh seem to correspond with lower b-values. The cross-section map for Hindu-Kush shows a general decrease of the b-values with depth, however, a region of high b-value is observed underneath Pamir at depths from 170 to 230 km. This anomaly region can be due to dehydration of the Pamir crustal slab at depth.
Mousavi, S. M., Horton, S., Ogwari, P., Langston, C. A., (2017). Spatio-temporal Evolution of Frequency-Magnitude Distribution during Initiation of Induced Seismicity at Guy-Greenbrier, Arkansas, Physics of the Earth and Planetary Interiors.
In this study, we carry out detailed analyses of the spatiotemporal variations of seismic b-value during the onset of the potentially induced-earthquake sequence between Guy and Greenbrier, Arkansas, to investigate correlations with pore-pressure change. The range of b-values suggests that the seismicity in the Guy-Greenbrier area is mostly a result of the activation of pre-existing faults. The spatial distribution of the b-value correlates with modeled pore-pressure changes. In the northern segment of the fault, the b-value increases with depth due to large pore-pressure changes and opening of new fractures in the deeper part, and stress relaxation in the shallower parts. Whereas, in the southern segment, the shallower part shows higher b-values due to higher pore-pressure fluctuations but the deeper part in the crystalline basement has a low b-value due to higher confining stress. The correlation between the temporal variation of the b-value and hypocentral depth explains a previously observed temporal drop of the b-value. This suggests that temporal variations should be interpreted along with spatial variations. An estimation of the seismogenic indices for the Guy-Greenbrier fault is provided. Our analysis suggests that monitoring changes in b-value and seismogenic indices during an injection period might be used to avoid the occurrence of significant events if injection volume is reduced at critical times.
Mousavi, S. M., (2017). Mapping Seismic Moment and b-value within Continental Collision Orogenic Belt Region, the Iranian Plateau, Journal of Geodynamics.
In this paper, a high-resolution map of the Gutenberg–Richter b-value and seismic moment-release are provided for the Iranian Plateau using the unified and homogeneous part of the seismicity record of the region (January 1995–July 2016). We use these parameters as stress meters and qualitatively explore their correlations with the GPS velocity field, strain rate, faulting mechanism, attenuation, and structure of the region. Our goal is to reveal the correlations and anomalous patterns that can help to better understand the seismotectonic and the state of present-day crustal stress within the region. A negative correlation between the b-value and seismic moment release as well as convergence rates is found. Correlation between geodetic measurements and seismic observations might indicate the existence of a strong mechanical coupling between the basement and the sediment cover across Zagros. High geodetic strain rates east of the Hormuz strait, southern central Alborz, and along the north Tabriz fault correspond to low b-value anomalies in these areas. A strong low b-value anomaly is observed at the major tectonic discontinuity between the Zagros continental collision and the oceanic Makran subduction.
Mousavi, S. M., (2017). Comment on “Recent developments of the Middle East catalog” by Zare et al., Journal of Seismology.
In a study by Zare et al. (2014), a new earthquake catalog of the Middle East region has been developed consisting of historical, early, and modern instrumental events recorded between 1250 B.C. and 2006. This valuable effort was undertaken under the framework of the global earthquake model (GEM) and the earthquake model of the Middle East (EMME) projects. The final goal was to establish a unified catalog of seismicity by incorporating regional and international data to be used for a homogeneous estimate of seismic hazards in the region (Erdik et al. 2012). However, observations show that magnitude of completeness (Mc) is not temporally and spatially homogeneous throughout the catalog. My goal in this commentary is to provide more insights into this important characteristic of the catalog and some suggestions on the selection of homogeneous parts of the catalog. This can further aid users in using the catalog for different purposes.