Anatomy of a crustal-scale accretionary complex: Insights from deep seismic sounding of the onshore western Makran subduction zone, Iran

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.

Supplemental Material: Anatomy of a crustal-scale accretionary complex: Insights from deep seismic sounding of the onshore western Makran subduction zone, Iran

Description and illustrations of the seismic data set, methods, and resolution estimates.<br>

Supplemental Material: Anatomy of a crustal-scale accretionary complex: Insights from deep seismic sounding of the onshore western Makran subduction zone, Iran

Description and illustrations of the seismic data set, methods, and resolution estimates.<br>

Post-critical SsPmp and its applications to virtual deep seismic sounding (VDSS)—3: back-projection imaging of the crust–mantle boundary in a heterogeneous lithosphere, theory and application

SUMMARY Virtual deep seismic sounding (VDSS) uses the arrival time of post-critical SsPmp relative to the direct S wave to infer Moho depth at the Pmp reflection point. Due to the large offset between the virtual source and the receiver, SsPmp is more sensitive to lateral variations of structures than near-vertical phases such as Ps, which is used to construct conventional P receiver functions. However, the way post-critical SsPmp is affected by lateral variations in lithospheric structure is not well understood, and previous studies largely assumed a 1-D structure when analysing SsPmp waveforms. Here we present synthetic tests with various 2-D models to show that lateral variations in lithospheric structures, from the lithosphere–asthenosphere boundary (LAB) to sedimentary basins, profoundly affect traveltime, phase and amplitude of post-critical SsPmp, and that a 1-D approximation is usually inappropriate when analysing 2-D data. Despite these strong effects we show, with synthetic examples and the ChinArray data from the Ordos Block in northern China, that a simple ray-theory-based back-projection method can retrieve the geometry of the crust–mantle boundary (CMB) given array observations in cases with moderate lateral variations in the CMB and/or the LAB. The success of our back-projection method indicates that ray-theory approximations are sufficient in modelling SsPmp traveltimes in the presence of moderate lateral heterogeneity. In contrast, we show that the ray theory is generally insufficient in modelling SsPmp phase shifts in a strongly heterogeneous lithosphere due to non-planar downgoing P waves incident at the CMB. Nonetheless, our results demonstrate the feasibility of direct imaging of the CMB with post-critical SsPmp even in the presence of 2-D variations of lithospheric structure.

Results of application of adapted finite impulse response filter for deep seismic data quality improvement

Deep seismic sounding data of earth’s crust explorations are complicated by intensive additive noise consist of man–caused multiplex wave compositions. Therefore intense interfering effect embarrass to detect and trace the target waves. Authors made a suggestion of application of adaptive finite impulse response filter in order to enhance wave field resolution. This article describes the results of spectral analysis of seismic data are derived from deep seismic sounding on the geological–geophysical survey 8–DV.

Towards an Open Access European Database for Deep Seismic Sounding data

&lt;p&gt;Controlled source seismic data acquisition experiments have produced a vast amount of Deep Seismic Sounding (DSS) data since its development in the late 50&amp;#8217;s. These datasets provide critical information on the structure and nature of the crust and the lithosphere, which constitutes a fundamental research tool within Solid Earth Sciences. The DSS datasets are unique and constitute the output of an expensive (in time, effort and cost) scientific process, which evidences the need for their preservation, both the recently acquired and the legacy data. Furthermore, the new developments in processing and imaging techniques generate new possibilities for re-use of the vintage datasets. The availability and accessibility of these datasets, therefore, is of foremost importance for scientists, decision-makers and the general public.&lt;/p&gt;&lt;p&gt;The research community, aware of the value of these data, has pushed forward Open Data policies based on the FAIR principles of data management (Findable, Accessible, Interoperable and Reusable). In this respect, a long-term plan has been launched by the European Plate Observation System (EPOS, https://www.epos-ip.org/) e-infrastructure. The focus is to streamline the integrated use of scientific data, data products and services. In close link with EPOS, the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA, http://www.sera-eu.org/home, a Horizon 2020 project) includes a working package to set up a network on DSS data and products management. This initiative ensures the traceability of the data allowing that third parties can freely access, exploit and disseminate the data by means of permanent, international identifiers: a Digital Object Identifier (DOI) and a Uniform Resource Identifier (URI) or handle. Furthermore, the current aim is to go beyond the FAIR principles by linking the data with its related peer-reviewed publications, other scientific contributions and technical reports, facilitating its re-use.&lt;/p&gt;&lt;p&gt;A prototype DSS data exchange system has been developed jointly between the DIGITAL.CSIC (the Spanish National Research Council) services and the Institute of Earth Sciences Jaume Almera-CSIC (https://digital.csic.es/handle/10261/101879, last access January 2020). Within the platform, each dataset includes the acquired raw data and a metadata file. The metadata provides information of the nature of the data itself, list of authors, the context of the data (time and location of the experiments), funding agencies and other relevant legal aspects. The technical information includes the acquisition parameters, data processing and format of the data (SEGY standard in this case - www.seg.org-, broadly used in the geophysics community). In the developed storage protocol, a permanent identifier is assigned once it has been checked that the data meets all the described requirements. This permanent identifier ensures that any visit or download is accounted for. This information is entered into a statistics referencing database and can also be used as a measure of the impact of the data and/or data product.&lt;/p&gt;&lt;p&gt;This work is funded by the European Commission (Grant Agreement no: 676564-EPOS IP, Call H2020-INFRADEV-2014-2015/H2020-INFRADEV-1-2015-1, SERA 730900).&lt;/p&gt;

Toward Simultaneous Determination of Bulk Crustal Properties Using Virtual Deep Seismic Sounding

ABSTRACT We augment the method of virtual deep seismic sounding (VDSS) by adding the phases Sp, the SV-P conversion across the Moho, to determine the average speed of the S wave (VS) in the crust. VDSS uses the strong SV-P conversion below the free surface from teleseismic earthquakes as a virtual source for wide-angle reflections of the P wave. The large signal generated by the virtual source is the strongest aspect of VDSS in which no stacking is necessary to build up the signal. Previous work used the large moveout of the wide-angle reflection, phase SsPmp, relative to the direct S-wave arrival, phase Ss, to minimize the trade-off between bulk P-wave speed (VP) and thickness of the crust (H). It is then straightforward to use the timing of the phase Sp to constrain VS. As examples, we show that this method works for data from both temporary and permanent seismic deployments in contrasting tectonic settings. Specifically, VS under station FORT in western Australia and H1620 in central Tibet are 3.77±0.08 and 3.42±0.11 km/s, respectively. This development complements the undertaking of using information from only the S-wave train to extract all three seismic parameters of the bulk crust, VP, VS, and H. These parameters are important for constraining overall silica content of the crust.