TY - JOUR A1 - Weber, Michael H. A1 - Wicks, Charles A1 - Le Stunff, Yves A1 - Romanowicz, Barbara A1 - Krüger, Frank T1 - Seismic evidence for a steeply dipping reflector-stagnant slab in the mantle transition zone JF - Geophysical journal international N2 - Studies of seismic tomography have been highly successful at imaging the deep structure of subduction zones. In a study complementary to these tomographic studies, we use array seismology and reflected waves to image a stagnant slab in the mantle transition zone. Using P and S (SH) waves we find a steeply dipping reflector centred at ca. 400 km depth and ca. 550 km west of the present Mariana subduction zone (at 20N, 140E). The discovery of this anomaly in tomography and independently in array seismology (this paper) helps in understanding the evolution of the Mariana margin. The reflector/stagnant slab may be the remains of the hypothetical North New Guinea Plate, which was theorized to have subducted ca. 50 Ma. KW - Mantle processes KW - Composition of the mantle KW - Seismic tomography KW - Wave scattering and diffraction KW - Subduction zone processes KW - Volcanic arc processes KW - Continental margins: convergent KW - Pacific Ocean Y1 - 2015 U6 - https://doi.org/10.1093/gji/ggu438 SN - 0956-540X SN - 1365-246X VL - 200 IS - 2 SP - 1235 EP - 1251 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Ramos, C. A1 - Mechie, James A1 - Feng, M. T1 - Shear wave velocity and Poisson's ratio models across the southern Chile convergent margin at 38°15′S JF - Geophysical journal international N2 - Using active and passive seismology data we derive a shear (S) wave velocity model and a Poisson's ratio (σ) model across the Chilean convergent margin along a profile at 38°15′S, where the Mw 9.5 Valdivia earthquake occurred in 1960. The derived S-wave velocity model was constructed using three independently obtained velocity models that were merged together. In the upper part of the profile (0–2 km depth), controlled source data from explosions were used to obtain an S-wave traveltime tomogram. For the middle part (2–20 km depth), data from a temporary seismology array were used to carry out a dispersion analysis. The resulting dispersion curves were used to obtain a 3-D S-wave velocity model. In the lower part (20–75 km depth, depending on the longitude), an already existent local earthquake tomographic image was merged with the other two sections. This final S-wave velocity model and already existent compressional (P) wave velocity models along the same transect allowed us to obtain a Poisson's ratio model. The results of this study show that the velocities and Poisson's ratios in the continental crust of this part of the Chilean convergent margin are in agreement with geological features inferred from other studies and can be explained in terms of normal rock types. There is no requirement to call on the existence of measurable amounts of present-day fluids, in terms of seismic velocities, above the plate interface in the continental crust of the Coastal Cordillera and the Central Valley in this part of the Chilean convergent margin. This is in agreement with a recent model of water being transported down and released from the subduction zone. KW - Controlled source seismology KW - Seismic tomography KW - Computational seismology KW - South America Y1 - 2016 U6 - https://doi.org/10.1093/gji/ggv541 SN - 0956-540X SN - 1365-246X VL - 204 SP - 1620 EP - 1635 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Pesicek, J. D. A1 - Engdahl, E. R. A1 - Thurber, C. H. A1 - DeShon, H. R. A1 - Lange, Dietrich T1 - Mantle subducting slab structure in the region of the 2010 M8.8 Maule earthquake (30-40 degrees S), Chile JF - Geophysical journal international N2 - We present a new tomographic model of the mantle in the area of the 2010 M8.8 Maule earthquake and surrounding regions. Increased ray coverage provided by the aftershock data allows us to image the detailed subducting slab structure in the mantle, from the region of flat slab subduction north of the Maule rupture to the area of overlapping rupture between the 1960 M9.5 and the 2010 M8.8 events to the south. We have combined teleseismic primary and depth phase arrivals with available local arrivals to better constrain the teleseismic earthquake locations in the region, which we use to conduct nested regionalglobal tomography. The new model reveals the detailed structure of the flat slab and its transition to a more moderately dipping slab in the Maule region. South of the Maule region, a steeply dipping relic slab is imaged from similar to 200 to 1000 km depth that is distinct from the moderately dipping slab above it and from the more northerly slab at similar depths. We interpret the images as revealing both horizontal and vertical tearing of the slab at similar to 38 degrees S to explain the imaged pattern of slab anomalies in the southern portion of the model. In contrast, the transition from a horizontal to moderately subducting slab in the northern portion of the model is imaged as a continuous slab bend. We speculate that the tearing was most likely facilitated by a fracture zone in the downgoing plate or alternatively by a continental scale terrane boundary in the overriding plate. KW - Seismicity and tectonics KW - Seismic tomography KW - Subduction zone processes Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-246X.2012.05624.x SN - 0956-540X VL - 191 IS - 1 SP - 317 EP - 324 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Muksin, Umar A1 - Haberland, Christian A1 - Bauer, Klaus A1 - Weber, Michael H. T1 - Three-dimensional upper crustal structure of the geothermal system in Tarutung (North Sumatra, Indonesia) revealed by seismic attenuation tomography JF - Geophysical journal international N2 - The geothermal potential in Tarutung is controlled by both the Sumatra Fault system and young arc volcanism. In this study we use the spatial distribution of seismic attenuation, calculated from local earthquake recordings, to image the 3-D seismic attenuation of the area and relate it with the temperature anomalies and the fluid distribution of the subsurface. A temporary seismic network of 42 stations was deployed around Tarutung and Sarulla (south of Tarutung) for a period of 10 months starting in 2011 May. Within this period, the network recorded 2586 local events. A high-quality subset of 229 events recorded by at least 10 stations was used for the attenuation inversion (tomography). Path-average attenuation (t(p)*) was calculated by using a spectral inversion method. The spread function, the contour lines of the model resolution matrix and the recovery test results show that our 3-D attenuation model (Q(p)) has good resolution around the Tarutung Basin and along the Sarulla graben. High attenuation (low Q(p)) related to the geothermal system is found in the northeast of the Tarutung Basin suggesting fluid pathways from below the Sumatra Fault. The upper part of the studied geothermal system in the Tarutung district seems to be mainly controlled by the fault structure rather than by magmatic activities. In the southwest of the Tarutung Basin, the high attenuation zone is associated with the Martimbang volcano. In the Sarulla region, a low-Q(p) anomaly is found along the graben within the vicinity of the Hopong caldera. KW - Seismicity and tectonics KW - Body waves KW - Seismic attenuation KW - Seismic tomography Y1 - 2013 U6 - https://doi.org/10.1093/gji/ggt383 SN - 0956-540X SN - 1365-246X VL - 195 IS - 3 SP - 2037 EP - 2049 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Bräuer, B. A1 - Asch, Günter A1 - Hofstetter, Rami A1 - Haberland, Christian A1 - Jaser, D. A1 - El-Kelani, R. A1 - Weber, Michael H. T1 - High-resolution local earthquake tomography of the southern Dead Sea area JF - Geophysical journal international N2 - Local earthquake data from a dense temporary seismological network in the southern Dead Sea area have been analysed within the project DESIRE (Dead Sea Integrated Research Project). Local earthquakes are used for the first precise image of the distribution of the P-wave velocity and the vP/vS ratios. 65 stations registered 655 local events within 18 months of observation time. A subset of 530 well-locatable events with 26 730 P- and S-arrival times was used to calculate a tomographic model for the vP and vP/vS distribution. Since the study area is at first-order 2-D, a gradual approach was chosen, which compromised a 2-D inversion followed by a 3-D inversion. The sedimentary basin fill is clearly imaged through high vP/vS ratios and low vP. The basin fill shows an asymmetric structure with average depth of 7 km at the western boundary and depth between 10 and 14 km at the eastern boundary. This asymmetry is reflected by the vertical strike-slip eastern border fault, and the normal faulting at the western boundary, caused by the transtensional deformation within the last 5 Myr. Within the basin fill the Lisan salt diapir is imaged through low vP/vS ratios, reflecting its low fluid content. The extensions were determined to 12 km in EW and 17 km in NS direction while its depth is 56 km. The thickness of the pre-basin sediments below the basin fill cannot be derived from the tomography datait is estimated to less than 3 km from former investigations. Below the basin, down to 18 km depth very low P-wave velocities and low vP/vS ratios are observedmost likely caused by fluids from the surrounding crust or the upper mantle. KW - Seismic tomography KW - Continental margins: transform KW - Continental tectonics: strike-slip and transform Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-246X.2012.05668.x SN - 0956-540X VL - 191 IS - 3 SP - 881 EP - 897 PB - Wiley-Blackwell CY - Hoboken ER -