Three‐dimensional V_P and V_P/V_S structure of the upper crust in the Erzincan basin (eastern Turkey)

Abstract

[1] Using aftershocks of the 13 March 1992 Erzincan earthquake (Ms = 6.8) three dimensional V P and V P /V S velocity structure of the Erzincan basin and its surroundings were modeled by local earthquake tomography. Travel times of body waves, belonging to 1025 selected high-quality events recorded by 58 temporary stations, were inverted iteratively and simultaneously by using the SIMUL2000 algorithm. Synthetic and resolution tests were performed to analyze the sensitivity of tomographic results and model parameterization. The resulting 3-D V P and V P /V S tomographic images show velocity anomalies related to geologic and tectonic structures beneath the Erzincan basin. While low V P anomalies down to 2-3 km depths are associated to thick Neogene sediments deposited in the Erzincan basin, high V P anomalies indicate bed rocks and intrusive magmatic rocks beneath the mountain ranges. V P /V S anomalies are an important indicator of local tectonic structures, and the physical, mechanical, and compositional variations in the rocks. The low V P /V S anomalies ( 1.7) observed at shallow depths (0-4 km) track the main fault systems and thus the weakness zones in the basin. The high V P /V S anomalies (!1.9) located between 4 and 6 km depth in the southeast of the Erzincan basin may correspond to fluid saturation, high pore pressure, and carbonate content in the rock matrix. The high V P /V S ratios play an important role for increasing seismicity in this area because of the fluid saturation and the high pore pressure. Finally, on the basis of the 3-D tomographic images, basement of the Erzincan basin deepens down to about 10 km depth and possesses an irregular and asymmetric shape. The thick and unconsolidated sedimentary layer increases seismic risk to Erzincan and other cities located on the basin as it magnifies ground motion caused by large earthquakes.Citation: Kaypak, B. (2008), Three-dimensional V P and V P /V S structure of the upper crust in the Erzincan basin (eastern Turkey),

High-resolution local earthquake tomography of the southern Dead Sea area

“…Between 35.35°E and 35.55°E the P velocities are up to 25 per cent slower than in the background model. Similarly large differences to the background model are found in other sedimentary basins, for example, in eastern Turkey (Kaypak 2008) and in southern California (Lin et al 2007). The lower boundary of the relatively low velocities is reached at 18 km depth.…”

Crustal structure in the southern part of West Java based on analysis of teleseismic receiver function

“…If the fracture zones are filled by fluid, it will decrease the S wave velocity and increase the Vp/Vs ratio. In other hand, if the fault zones are very porous, they will provide low values in the Vp/Vs ratio [23]. Therefore, the presence of fluid filled fracture zone is another plausible explanation related to high Vp/Vs beneath station SKJI.…”

Crustal Structure Along Sunda-Banda Arc Transition Zone from Teleseismic Receiver Functions

“…The presence of fracture zone containing fluid might increase the Vp/Vs ratio. Conversely, the porous fracture zone might reduce the Vp/Vs ratio (Wang 2012, Kaypak 2008. High Vp/Vs ratios due to the crack fabric have been reported in other regions, for example, by Matsubara et al (2008) and Kodaira et al (2004).…”