An Application of Ambient Seismic Tomography Method to Determine Magma Chamber in the Damavand Region

Tehran, the capital of Iran, is surrounded by many active fault zones, e.g., the Mosha, the North Tehran and the South/North Rey faults and also is situated close to the Damavand quaternary volcano. Currently, our knowledge about the 3D velocity structure of the Damavand region including the magma chamber is limited. Location of the Damavand volcano in a compression region and recently geothermal studies persuades us to study the effect of magma chamber on adjacent faults. Seismic Ambient Noise Tomography (ANT) is often used to delineate velocity anomalies including magma bodies in the crust and upper mantle. In this study, we use continuous data recorded by IRSC (Iranian Seismological Center) network in the Damavand region. The IRSC network is equipped with SS-1 Kinemetrics velocity proportional sensor.The data processing was done following common-low-frequency technique introduced by Bensen et al. (2007). After computation the cross-correlation between vertical-vertical and transverse-transverse component seismograms from station-pairs with matched sensor types, we apply our new stacking method which is based on large RMS values in the time-interval that we expect to receive fundamental mode of the surface waves. Phase velocity dispersion curves are then calculated using modified image transformation technique. Finally, after obtaining 2D phase velocity maps for each period, Vs velocity and anisotropy maps are calculated by applying iterative inversion method.Vs velocity maps reveal anomalous low-velocity anomalies in the subsurface structures which presents magma chamber of the Damavand volcano. Main faults are marked by abrupt transitions between regions of high- to low-velocity regions.

کلیدواژه ها:

Damavand volcano ، ambient seismic noise ، RMS-stacking method ، 2D tomography ، 3D velocity model ، anisotropy