Spatio-Temporal Analysis of Tehran's Historical Earthquakes Trends

Iran is one of the most seismically active regions of the globe. The metropolis of Tehran is located at the southern foothills of the Alborz Mountains that are the northern branch of the Alpine-Himalayan orogeny in Iran. The extremely high density of population concentrated in the Tehran metropolis (with more than 12 million inhabitants) coupled with the fragility of houses and life-lines, highlight the urgency of a reliable assessment of fault activity in this city. Three main active fault zones exist in the vicinity of Tehran: North Tehran fault; Mosha fault; and Eyvanekey-Kahrizak fault. In this paper, a total of 894 historical earthquakes of the study area with magnitudes over 2.5 Richter were collected since 1900. Three scenarios were considered for faults. In each scenario, every earthquake was associated to its relevant fault, spatial and temporal analyses were done to reveal the spatial and temporal trend of fault activities. First the north-south and east-west trends of magnitudes of earthquakes were verified and showed no meaningful trends. Spatial dependence of magnitudes of earthquakes was described in terms of global Moran's I and general G. The indices showed that the magnitudes of earthquakes were not clustered or spatially correlated. Ripley's K function determined that earthquakes are clustered at multiple distances. The temporal analyses were used to extract temporal trends in each scenario. The results showed that eastern sections of all faults are more active and the majority of large earthquakes have occurred in the middle sections of the faults. It is also anticipated that the eastern section of the Mosha fault is more capable of generating large earthquakes than the other faults in the Tehran region. The results of this paper can be useful for extracting hazardous areas and risk zonation or forecasting earthquakes.