ALBERT

Description: We use traveltime data of local earthquakes and controlled sources observed by a large, temporary, amphibious seismic network to reveal the anatomy of the southcentral Chilean subduction zone (37–39°S) between the trench and the magmatic arc. At this location the giant 1960 earthquake (M = 9.5) nucleated and ruptured almost 1000 km of the subduction megathrust. For the three-dimensional tomographic inversion we used 17,148 P wave and 10,049 S wave arrival time readings from 439 local earthquakes and 94 shots. The resolution of the tomographic images was explored by analyzing the model resolution matrix and conducting extensive numerical tests. The downgoing lithosphere is delineated by high seismic P wave velocities. High v p/v s ratio in the subducting slab reflects hydrated oceanic crust and serpentinized uppermost oceanic mantle. The subducting oceanic crust can be traced down to a depth of 80 km, as indicated by a low velocity channel. The continental crust extends to approximately a 50-km depth near the intersection with the subducting plate. This suggests a wide contact zone between continental and oceanic crust of about 150 km, potentially supporting the development of large asperities. Eastward the crustal thickness decreases again to a minimum of about a 30-km depth. Relatively low v p/v s at the base of the forearc does not support a large-scale serpentinization of the mantle wedge. Offshore, low v p and high v p/v s reflect young, fluid-saturated sediments of forearc basins and the accretionary prism.

Description: We present new seismicity and focal-mechanism data for the Fergana basin and surrounding mountain belts in western Kyrgyzstan from a temporary local seismic network. A total of 210 crustal earthquakes with hypocentral depths shallower than 25 km were observed during a 12-month period in 2009/2010. The hypocenter distribution indicates a complex net of seismically active structures. The seismicity derived in this study is mainly concentrated at the edges of the Fergana basin, whereas the observed rate of seismicity within the basin is low. The seismicity at the dominant tectonic feature of the region, the Talas-Fergana fault, is likewise low, so the fault seems to be inactive or locked. To estimate the uncertainties of earthquake locations derived in this study, a strong explosion with known origin time and location is used as a ground truth calibration event which suggests a horizontal and vertical accuracy of about 1 km for our relocations. We derived 35 focal mechanisms using first motion polarities and retrieved a set of nine moment tensor solutions for earthquakes with moment magnitude (Mw) ranging from 3.3 to 4.9 by waveform inversion. The solutions reveal both thrust and strike-slip mechanisms compatible with a NW-SE direction of compression for the Fergana region. Two previously unknown tectonic structures in the Fergana region could be identified, both featuring strike-slip kinematics. The combined analysis of the results derived in this study allowed a detailed insight into the currently active tectonic structures and their kinematics where little information had previously been available.

Description: We propose to investigate the structure and evolution of the Main Pamir Thrust (MPT) with a high-density seismological array. The MPT, with its surface expression along the east-west trending Alai Valley, marks the northern boundary of the Pamir. The Alai Valley, separating the Pamir and the Tien Shan, constitutes the last vestige of a formerly continuous basin that linked the Tarim and the Tajik Basins. The MPT manifests itself as a place of high seismic activity with frequently occurred disastrous earthquakes. The array is about 50 km long, consisted of 90 three-component geophones (stations G?? and C??) and 10 Trillium-Compact seismometers (stations T??), and equipped with 100 CUBE dataloggers. We will construct a high-resolution receiver function profile to image the MPT and accurately locate the local earthquakes associated with the MPT. Funded by BMBF, within the framework of CaTeNA project – Climatic and Tectonic Natural Hazards in Central Asia. Waveform data are available from the GEOFON data centre, under network code 7A and are embargoed until Jan 2024.

Description: We study the crustal structure of Sri Lanka by analyzing data from a temporary seismic network deployed in 2016-2017 (Seneviratne et al., 2016) to shed light on the amalgamation process from the geophysical perspective. Rayleigh wave phase dispersion from ambient noise cross-correlation and receiver functions were jointly inverted using a transdimensional Bayesian approach (Bodin et al., 2012, Dreiling et al., 2019).

Description: The GeoDataNode project, funded by the Federal Ministry for Research and Education (BMBF) conducted a survey of data management practices at GFZ. The aim was to assess the state of current practices and needs, and their alignment to institutional and national guidelines for data management. The target audience included scientific and technical employees at all levels. A response rate of 24% of the target demographic was achieved. The survey revealed a general need for improvement and structuring of research data handling. This includes provision of adequate storage space, back-up schedules, and the familiarization of young researchers with good scientific practice.

Description: We use local earthquake data observed by the amphibious, temporary seismic MERAMEX array to derive spatial variations of seismic attenuation (Qp) in the crust and upper mantle beneath Central Java. The path-averaged attenuation values (t∗) of a high quality subset of 84 local earthquakes were calculated by a spectral inversion technique. These 1929 t∗-values inverted by a least-squares tomographic inversion yield the 3D distribution of the specific attenuation (Qp). Analysis of the model resolution matrix and synthetic recovery tests were used to investigate the confidence of the Qp-model. We notice a prominent zone of increased attenuation beneath and north of the modern volcanic arc at depths down to 15 km. Most of this anomaly seems to be related to the Eocene–Miocene Kendeng Basin (mainly in the eastern part of the study area). Enhanced attenuation is also found in the upper crust in the direct vicinity of recent volcanoes pointing towards zones of partial melts, presence of fluids and increased temperatures in the middle to upper crust. The middle and lower crust seems not to be associated with strong heating and the presence of melts throughout the arc. Enhanced attenuation above the subducting slab beneath the marine forearc seems to be due to the presence of fluids.

Description: The Makran subduction zone has produced M 8+ earthquakes and subsequent tsunamis in historic times, hence indicating high risk for the coastal regions of southern Iran, Pakistan, and neighboring countries. Besides this, the Makran subduction zone is an end-member subduction zone featuring extreme properties, with one of the largest sediment inputs and the widest accretionary wedge on Earth. While surface geology and shallow structure of the offshore wedge have been relatively well studied, primary information on the deeper structure of the onshore part is largely absent. We present three crustal-scale, trench-perpendicular, deep seismic sounding profiles crossing the subaerial part of the accretionary wedge of the western Makran subduction zone in Iran. P-wave travel-time tomography based on a Monte Carlo Markov chain algorithm as well as the migration of automatic line drawings of wide-angle reflections reveal the crustal structure of the wedge and geometry of the subducting oceanic plate at high resolution. The images shed light on the accretionary processes, in particular the generation of continental crust by basal accretion, and provide vital basic information for hazard assessment and tsunami modeling

Description: The Alps as the result of the convergence of the African and European plates represent extremely complex struc-tures and kinematics. The Southern and Eastern Alps as part of this continental collision are the target area of thecurrent study. In this region, the Priadriatic Fault is sinistrally offset by the Guidicarie Fault and a switch in the sub-duction polarity had been proposed. In order to better understand the crustal and upper-mantle structure and how itis related to faults seen at the surface, we aim to assess the precise distribution of local earthquakes (potentially in-dicating active faults) and the seismic velocity structure in the subsurface. In our investigation, we use the data of avery dense seismic network deployed in the Southern and Eastern Alps (SWATH-D network - DFG funded priorityProgramme 4D-MB) to provide seismicity pattern and velocity structure of the crust and possibly the upper mantle.This temporary network consists of 150 stations with an average inter-station spacing of 15 km complementingthe larger scale AlpArray Seismic Network (AASN). The objectives are, accordingly, to implement a reliable andfully automated algorithm to detect the events and pick the phase onset times of local earthquakes, provide precisehypocentral locations and calculate a velocity model for the target area. Here we focus on the first results of theearthquake analysis procedure and present a 1-D velocity model for the Southern and Eastern Alps. Later, this datawill be used for a 3-D tomographic inversion. So far, we used 10 months of data from September 2017 to Jun 2018and implemented an automated multi-stage processing chain to provide the first catalog. The catalog comprises123 local earthquakes with 5261 P and 2651 S picks. The hypocentral locations were then calculated and a 1-Dvelocity model was also obtained using simultaneous inversion of hypocenters, velocity, and station corrections.The seismicity pattern is characterized by rather diffuse clusters in the Friuli, Lake Garda, Brenner and Trentinoregions with low to medium magnitude (ML 0-4) events within the upper 25 km of the crust. The central part ofthe region, where the Preadriatice fault sinistrally offset by the Guidicarie Fault and its related fold-and-thrust belt,has obviously less activity. Our 1-D velocity model indicates upper crustal velocities that are higher than averagefor the whole Alpine region.

Description: Neogene indentation of the Adriatic plate into Europe led to major modifications of the Alpine orogenic structures and style of deformation in the Eastern and Southern Alps. The Giudicarie Belt is a prime example of this, as it offsets the entire Alpine orogenic edifice; its activity has been kinematically linked to strike-slip faulting and lateral extrusion of the Eastern Alps. Remaining questions on the exact role of this fold-and-thrust belt in the structure of the Alpine orogen at depth necessitate a quantitative analysis of the shortening, kinematics, and depth of decoupling beneath the Giudicarie Belt and adjacent parts of the Southern Alps. Tectonic balancing of a network of seven cross sections through the Giudicarie Belt parallel to the local NNW–SSE shortening direction reveals that this belt comprises two kinematic domains that accommodated different amounts of shortening during overlapping times. These two domains are separated by the NW–SE-oriented strike-slip Trento-Cles–Schio-Vicenza fault system, which offsets the Southern Alpine orogenic front in the south and merges with the Northern Giudicarie Fault in the north. The SW kinematic domain (Val Trompia sector) accommodated at least ∼ 18 km of Late Oligocene to Early Miocene shortening. Since the Middle Miocene, this domain experienced at least ∼ 12–22 km shortening, whereas the NE kinematic domain accommodated at least ∼ 25–35 km shortening. Together, these domains contributed an estimated minimum of ∼ 40–47 km of sinistral strike-slip motion along the Northern Giudicarie Fault, implying that most offset of the Periadriatic Fault is due to Late Oligocene to Neogene indentation of the Adriatic plate into the Eastern Alps. Moreover, the faults linking the Giudicarie Belt with the Northern Giudicarie Fault reach ∼ 15–20 km depth, indicating a thick-skinned tectonic style of deformation. These fault detachments may also connect at depth with a lower crustal Adriatic wedge that protruded north of the Periadriatic Fault and are responsible for N–S shortening and eastward, orogen-parallel escape of deeply exhumed units in the Tauern Window. Finally, the E–W lateral variation of shortening across the Giudicarie Belt indicates internal deformation and lateral variation in strength of the Adriatic indenter related to Permian–Mesozoic tectonic structures and paleogeographic zones.