3-D imaging of the upper crust beneath the Denizli geothermal region by local earthquake tomography, western Turkey

The Denizli basin and its surroundings are one of the regions that have high seismic activity and rich geothermal fields in western Anatolia. In the first half of year 2000, an increasing seismic activity was observed around the Denizli basin without a large mainshock occurrence. A temporary seismic network consisting of 28 stations were deployed to observe the seismic activity in the region by The Scientific and Technological Research Council of Turkey-Marmara Research Center-Earth and Marine Science Institute (TÜBİTAK-MAM-EMSI). In this study, one- and three-dimensional VP and VP/VS structure of the Denizli basin have been determined by using the travel times of the 635 recorded earthquake data. Firstly one-dimensional inversion schema was performed to stabilize initial velocity model and to have more reliable hypocentral locations. Then an iterative and simultaneous three-dimensional inversion procedure was carried out to obtain 3-D high-resolution seismic velocity models. Furthermore to assess the solution quality of our inversion, we conducted a series of resolution tests. We concluded high-resolution 3-D VP and VP/VS seismic velocity models for the upper 20 km of the crust beneath the Denizli basin and surroundings and interpreted the results in the context of known geologic and tectonic units. The resulting 3-D VP models define the geometry of the basin, sediment thickness, and intrusive magmatic bodies as well as regions of anomalous velocity. The VP/VS models help to constrain the location and geometry of the faults, zones of weakness, and gas or fluid saturated formations with high pore pressure zones. All tomographic results show that there is a strong correlation between local seismicity and the high VP and VP/VS anomalies. Consequently, this relationship indicates that the reason of the high seismicity in the Denizli basin depends on activity of hydrothermal system as well as tectonic regime.

► 1-dimensional P- and S-wave velocity structures of the Denizli basin has been determined.
► 3-dimensional VP and VP/VS structures of the region have been modeled.
► Low and high velocity anomalies have been associated with the geology and hydrothermal system in the region.
► A strong correlation has been found between the high VP/VS bodies and the local seismicity in the region.