ALBERT

Description: The Pamir plateau protrudes ∼300 km between the Tajik- and Tarim-basin lithosphere of Central Asia. Whether its salient location and shape are caused by forceful indentation of a promontory of Indian mantle lithosphere is debated. We present a new local-seismicity and focal-mechanism catalog, and a P-wave velocity model of the eastern part of the collision system. The data suggest a south-dipping Asian slab that overturns in its easternmost segment. The largest principal stress at depth acts normal on the slab and is orientated parallel to the plate convergence direction. In front (south) of the Asian slab, a volume of mantle with elevated velocities and lined by weak seismicity constitutes the postulated Indian mantle indenter. We propose that the indenter delaminates and overturns the Asian slab, underthrusts the Tarim lithosphere along a compressive transform boundary, and controls the location and shape of the Pamir plateau.

Description: We present a new seismic tomography model for the crust and upper-mantle beneath the Central Andes based on multi-scale full seismic waveform inversion, proceeding from long periods (40–80 s) over several steps down to 12–60 s. The spatial resolution and trade-offs among parameters are estimated through the multi-parameter point-spread functions. P and S wave velocity structures with spatial resolution of 30–40 km for the upper mantle and 20 km for the crust could be resolved in the central study region. In our study, the subducting Nazca slab is clearly imaged in the upper mantle, with dip-angle variations from the north to the south. Bands of low velocities in the crust and mantle wedge indicate intense crustal partial melting and hydration of the mantle wedge beneath the frontal volcanic arc, respectively and they are linked to the vigorous dehydration from the subducting Nazca plate and intermediate depth seismicity within the slab. These low velocity bands are interrupted at 19.8°–21°S, both in the crust and uppermost mantle, hinting at the lower extent of crustal partial melting and hydration of the mantle wedge. The variation of lithospheric high velocity anomalies below the backarc from North to South allows insight into the evolutionary foundering stages of the Central Andean margin. A high velocity layer beneath the southern Altiplano suggests underthrusting of the leading edge of the Brazilian Shield. In contrast, a steeply westward dipping high velocity block and low velocity lithospheric uppermost mantle beneath the southern Puna plateau hint at the ongoing lithospheric delamination.

Description: A sequence of three strong (M W 7.2–6.4) and several moderate (M W 4.4–5.7) earthquakes struck the Pamir Plateau and surrounding mountain ranges of Tajikistan, China, and Kyrgyzstan in 2015–2017. With a local seismic network in operation in the Xinjiang province since August 2015, an aftershock network on the Pamir Plateau of Tajikistan since February 2016, and additional permanent regional seismic stations, we were able to record the succession of the fore-, main-, and aftershock sequences at local distances with good azimuthal coverage. We located 11,784 seismic events and determined the moment tensor for 33 earthquakes. The seismicity delineates the major tectonic structures of the Pamir, i.e., the thrusts that absorb shortening along the plateau thrust front, and the strike-slip and normal faults that dissect the Plateau into a westward extruding and a northward advancing block. Fault ruptures were activated subsequently at increasing distances from the initial M W 7.2 Sarez. All mainshock areas but the initial one exhibited foreshock seismicity which was not modulated by the occurrence of the earlier earthquakes. The tabular ASCII data of the seismic event catalog consist of origin date, time, location, depth and magnitude of the events, along with the quality measures: number of P- and S-wave arrival time picks, location root-mean-square misfit and localization method. The tabular ASCII data of the moment tensor catalog consist of origin date, time, location, the six independent components of the moment tensor, the moment magnitude, and the orientation of the preferred fault plane parameterized as fault strike, dip and rake.

Description: This data publication includes geochronological and fission track data used to derive the provenance and pressure-temperature-time-deformation evolution of Indian crust in central Myanmar (results from U/Th-Pb igneous zircon, monazite and titanite dating, U/Th-Pb detrital zircon dating, 40Ar/39Ar dating, Rb-Sr dating, zircon (U,Th)/He dating and zircon and apatite fission-track dating. The data are supplementary material to Min et al. (2022). The data are presented as Excel tables and further decribed by a README (pdf). LA-ICP-MS data fiollows the Community-Derived Standards for LA-ICP-MS U-(Th-)Pb Geochronology by Horstwood et al. (2016) and Ar/Ar geochronology was described in Schaen et al. (2020). The data format is ready to be read by Isoplot (Ludwig, 2008ff).

Description: The Pamir plateau protrudes ~300 km between the Tajik- and Tarim-basinlithosphere of Central Asia. We present a new local-seismicity catalog, a focal-mechanism catalog, and a P-wave velocity model of the of the collision system between the Pamir plateau and the Tarim basin. The data suggest a south-dipping Asian slab that overturns in its easternmost segment. The largest principal stress at depth acts normal on the slab and is orientated parallel to the plate convergence direction. In front (south) of the Asian slab, a volume of mantle with elevated velocities and lined by weak seismicity constitutes the postulated Indian mantle indenter. The data set consists of an earthquake catalog, an earthquake focal mechanism catalog and a subsurface P-wave velocity model of the central and eastern Pamir plateau and the adjacent north-western Tarim basin; between 36.8–40.0 °N and 72.2–78.0 °E. It was collected to identify the deep tectonic structures that determine the lithospheric architecture of the Pamir plateau. Earthquakes were recorded by two temporary seismic deployments. Earthquakes that occurred between 1st August 2008 and 6th June 2010 were primarily recorded by the TIPAGE network (Yuan et al., 2008); those, between 3rd August 2015 and 23rd June 2017 by the East Pamir and Sarez aftershock networks (Yuan et al., 2018a, b). The earthquake catalog contains 1,493 seismic events at depth 〉50 km. They were localized in the present 3-D velocity model. Some events were re-located with hypoDD. The focal mechanism catalog consists of double-couple fault-slip parameters for 38 events, 29 of which are newly determined using the HASH algorithm and 9 are moment tensors from Kufner et al. (2016). The P wave-velocity model has been determined using simulps from 2,264 seismic events with well-constrained P- and S-wave arrivals. It is parameterized as velocity gradients between nodes with a horizontal and vertical spacing of 40 and 15 km, respectively. Unresolved nodes were masked using a checkerboard resolution test. The full description of the methods is provided in the data description file.

Description: The present dataset is a comprehensive earthquake catalogue for the Northern Chile subduction zone forearc covering the period 2007-2021, determined from IPOC seismic station data (GFZ and CNRS-INSU 2006; https://doi.org/10.14470/pk615318) plus some auxiliary stations (IPOC = Integrated Plate Boundary Observatory Chile; http://www.ipoc-network.org). The method of automatized earthquake catalogue retrieval, the different relocation steps as well as the different earthquake class labels, and the structures outlined by the seismicity are described in detail in Sippl et al. (2023). The catalogue builds on the one from Sippl et al. (2018; https://doi.org/10.5880/GFZ.4.1.2018.001), but uses a slightly deviating parameter set and a new event category. The columns of the data files are: year, month, day, hour, minute, second, latitude [dec. degrees], longitude [dec. degrees], depth [km], magnitude [ML], identifier The identifier term provides a first-order spatial classification of the seismicity, an explanation is given in Sippl et al. (2023).

Description: Mejillones peninsula located in the north of Chile is considered a potential seismic barrier. Two major earthquakes have occurred south and north of it: The M8.1 1995 Antofagasta and the M7.8 2007 Tocopilla earthquakes. Slip and aftershock distribution show the central axis of this peninsula as the limit. We use travel time data of earthquakes recovered by three networks, overlapping in space but not in time, including offshore stations (CINCA network 1995; TaskForce 2007, and MEJIPE 2013-2015). A three-dimensional local tomographic inversion was performed using ~4000 events. The resolution of tomographic images was analysed by the model resolution matrix and numerical tests. Vp velocity and Vp/Vs ratio images are capable of resolving main tectonic units up to 80 km depth. Our work shows the presence of two basal possible underplating structures: The first is located below the peninsula with similar dimensions of it (~60 km) found at depths 〉 35 km and a second structure of smaller dimensions is located to the north where the Tocopilla earthquake nucleated. This evidence justifies the possible segmentation in the rupture zones of both earthquakes in the north of Chile.

Description: Subduction zone forearcs deform transiently and permanently due to the frictional coupling with the converging lower plate. Transient stresses are mostly the elastic response to the seismic cycle. Permanent deformation is evidenced by forearc topography, upper plate faulting, and earthquakes; its relation to the megathrust seismic cycle is debated. Here we study upper plate seismicity in the northern Chile subduction zone as a proxy for forearc brittle deformation. We find that seismicity is distributed unevenly and a dramatic increase correlates with the onset of a change in subduction obliqueness. Earthquakes in the South American crust show a remarkably homogenous trench-parallel, compressional stress field. Earthquake fault mechanisms are dominated by trench-perpendicular thrusts. Further inland, where the lower plate becomes uncoupled, the stress field is more varied with a compression direction approx. convergence parallel. The stress regime above the plate-coupling-zone, almost perpendicular to the plate convergence direction, may be explained by a change in subduction obliqueness due to the concave shape of the plate margin, which we demonstrate by investigating inter-plate earthquake slip vectors. From these, we derive a strain rate and compare it to one derived from upper plate earthquakes and geological time-scale shortening. Based on the distribution of the type of faulting we investigate the trench-perpendicular stress field with a force balance model taking into account gravitational stresses and the traction along the megathrust. The observed deep strike-slip earthquakes, expression of trench-perpendicular tension, require the deepest extent of the megathrust to be very weak.

Description: The Burmese arc consists of the Indo-Burman Ranges (IBR), an accretionary wedge in the west and the Central Myanmar Basin (CMB) in the east. It is bounded in the east by the seismically active Sagaing Fault to the Shan Plateau. Intermediate-depth seismicity below Myanmar occurs at depths up to ~150 km, generally understood to be related to the subducting Burma slab. We use ambient noise tomography to construct a regional three-dimension (3-D) shear wave velocity model, aiming at figuring out the transition from oceanic subduction to continental subduction/collision along the Burmese arc and how it affects the upper plate crustal deformation. Our dataset includes 30 seismic stations from a recently deployed temporary seismic array and ~50 permanent stations in and around Myanmar. Ambient noise corss-correlations are calculated at periods of 5-60 s and are inverted for a 3-D velocity model from the crust to the uppermost mantle. Our model shows a low-velocity anomaly extending to 〉20 km depths beneath the northern part of the CMB that accurately defines the Chindwin Subbasin. The crust beneath the IBM is characterized by low velocity, which probably reflects the fluid-rich accreted sediments that has experienced metamorphism in the mid-lower crust. Underneath the Sagaing Fault an N-S trending high-velocity anomaly is clearly visible at depths of 40-70 km in the uppermost mantle extending from 20°N to 24°N. The anomaly could represent a remnant slab of the Incertus Arc collision/subduction and mark the eastern boundary of the Burma plate.