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- Absolute shear-wave velocity (1)
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- Receiver functions (1)
- Subduction zone structure (1)
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Institute
In this receiver function study, we investigate the structure of the crust beneath six seismic broadband stations close to the Sunda Arc formed by subduction of the Indo-Australian under the Sunda plate. We apply three different methods to analyse receiver functions at single stations. A recently developed algorithm determines absolute shear-wave velocities from observed frequency-dependent apparent incidence angles of P waves. Using waveform inversion of receiver functions and a modified Zhu and Kanamori algorithm, properties of discontinuities such as depth, velocity contrast, and sharpness are determined. The combination of the methods leads to robust results. The approach is validated by synthetic tests. Stations located on Malaysia show high-shear-wave velocities (V (S)) near the surface in the range of 3.4-3.6 km s (-aEuro parts per thousand 1) attributed to crystalline rocks and 3.6-4.0 km s (-aEuro parts per thousand 1) in the lower crust. Upper and lower crust are clearly separated, the Moho is found at normal depths of 30-34 km where it forms a sharp discontinuity at station KUM or a gradient at stations IPM and KOM. For stations close to the subduction zone (BSI, GSI and PSI) complexity within the crust is high. Near the surface low V (S) of 2.6-2.9 km s (-aEuro parts per thousand 1) indicate sediment layers. High V (S) of 4.2 km s (-aEuro parts per thousand 1) are found at depth greater than 6 and 2 km at BSI and PSI, respectively. There, the Moho is located at 37 and 40 km depth. At station GSI, situated closest to the trench, the subducting slab is imaged as a north-east dipping structure separated from the sediment layer by a 10 km wide gradient in V (S) between 10 and 20 km depth. Within the subducting slab V (S) a parts per thousand aEuro parts per thousand 4.7 km s (-aEuro parts per thousand 1). At station BSI, the subducting slab is found at depth between 90 and 110 km dipping 20A degrees +/- 8A degrees in approximately N 60A degrees E. A velocity increase in similar depth is indicated at station PSI, however no evidence for a dipping layer is found.
The northward movement and collision of the Arabian plate with Eurasia generates compressive stresses and resulting shortening in Iran. Within the Alborz Mountains, North Iran, a complex and not well understood system of strike-slip and thrust faults accomodates a fundamental part of the NNE-SSW oriented shortening. On 28th of May 2004 the Mw 6.3 Baladeh earthquake hit the north-central Alborz Mountains. It is one of the rare and large events in this region in modern time and thus a seldom chance to study earthquake mechanisms and the local ongoing deformation processes. It also demonstrated the high vulnerability of this densily populated region.