IMAGING STRUCTURE OF THE WESTERN MAKRAN SUBDUCTION ZONE BY RECEIVER FUNCTIONS ANALYSIS

We applied the P and S receiver functions methods to new data from a temporary seismic network of IASBS deployed in the western Makran region to image the geometry of the subducting and overriding plates the subduction zone. IASBS temporary seismic network, consisting of 29 braodband stations, has been deployed in the western Makran in the past three years (Figure 1). For each station, receiver functions were computed from teleseismic events with epicentral distance between 30˚ and 90˚, and magnitude larger than 5.5. Additionally, we computed receiver functions for two permanent broadband stations CHBR and ZHDN belonging to the Iranian National Seismic Network (INSN).The iterative deconvolution method (Ligorria & Ammon, 1999) was used for constructing the P receiver functions. For the deconvolution process, a time window of 90 s and Gaussian filter width of 5 Hz were selected. For constructing S receiver function, a time-domain maximum entropy deconvolution of the vertical component by the radial method (Chen et al., 2008) were applied. To provide an image of the slab geometry, we selected two profiles, AA’ and BB’, perpendicular to the slab strike (Figure 1). We stacked the receiver functions using the Common Conversion Point technique (Zhu, 2000) along the two profiles (Figure 2). Our receiver function profiles delineate the geometry of the subducting slab (the subduction interface marked as black dashed line that follows the converted Ps phase amplitudes in Figure 2). The slab has a shallow dip. From the coast to the Jaz Murian margin it is relatively flat (6˚). The dip angle increases to 12.5˚ from Jaz Murian to near Bazman volcano, and to 27˚ from Bazman volcano to the north of Taftan volcano at the end of BB’ profile. We projected the seismicity on the profiles. Brown circles show the earthquakes along the subduction zone (Figure 2). There is a very close correlation between the top of the slab and the loci of the earthquakes. The depth to the oceanic Moho is 30 km in the coast region. It increases to 60 km beneath the Jaz Murian depression in profile AA’ and to 120 km beneath Taftan volcano in BB’ profile. At stations near the coast, a clear interface can be observed at 10 km depth which indicates base of the sedimentary wedge. The continental Moho of the overriding plate has a clear signal along profile BB’ (marked red dashed line in Figure 2). The thickness of the continental crust in profile BB' is between 40 to 50 km and it gradually decreases southward in profile AA'. These interfaces are also obvious in the S receiver functions depth section.

کلیدواژه ها:

Subduction ، Receiver function ، Makran ، Moho ، Slab