Variation of seismicity parameters and its link to tectonic features of the central portion of the Zagros Fold-Thrust Belt, Iran

Abstract

: The Zagros Fold-Thrust Belt is one of the most tectonically active regions in the world. The seismicity of this belt is affected by various factors and has certain complexities. This paper provides the results of assessment of temporal and spatial seismicity variations of the central portion of the belt in Fars and Bushehr provinces and their link to regional tectonic properties. Relatively, everywhere in the belt, the geometry of the folds has been mainly affected by thrusts and basement faults. There is a meaningful link between seismic activity and folding in the belt. The most abundant types of folds are detachment folds, fault bend and fault propagation folds. They play an important role in the spatial seismicity of the area. The maximum number of seismic events have medium magnitude which ranges between 2.5 and 3. There is a decreasing trend of a and b parameters from south-west to north and north-east where the occurrence of higher ­magnitude­earthquakes­is­expected.­Temporal­analysis­of­seismicity­shows­that­earthquakes­with­magnitude­≥ 6.5­have­ a ten-year return period in the region. The occurrence of several earthquake groups in the belt was in the form of swarms showing point or linear spatial distribution. Some of these possible swarms are around transverse faults, salt domes and some are related to blind faults, which indicate the complexity of the seismicity in this belt. Spatial distribution of low magnitude seismic clusters is also influenced by two other factors (1) existence of frequent salt domes many of which might be active and their spatial links to major faults and (2) human-related