We use teleseismic data from the Jammu and Kashmir Seismological NETwork, to perform P-wave receiver function spatial and common-conversion-point (CCP) stacks, and joint inversion with Rayleigh-wave group-velocity dispersion, to construct 3D Vs model of the Jammu and Kashmir (J&K) Himalaya. 2D-CCP and Vs profiles reveal increasing crustal thickness from the foreland-to-hinterland, and an under-thrust Indian crust beneath J&K. The Moho positive impedance-contrast boundary is at ∼45 km depth beneath Sub-Himalaya and deepens to ∼70 km beneath Higher-to-Tethyan Himalaya, with an overall gentle NE dip. The Main Himalayan Thurst (MHT) forms a low velocity layer (LVL) with negative impedance contrast, and has a flat–ramp geometry. The flat segment is beneath Sub-to-Lesser Himalaya at 6–10 km depth, and dips ∼4◦. The mid-crustal (frontal) ramp is beneath Kishtwar Higher-Himalaya and Zanskar Ranges at 10–16 km depth, and dips ∼13–17◦. Significant along-arc variation in crustal structure is observed between east (Kishtwar) and west (Kashmir Valley) segments. Beneath the Kishtwar Window we image a Lesser Himalayan duplex (LHD) bound between MHT sole-thrust and MCT roof-thrust. LHD horses dip at high angle to the bounding structures and are illuminated by moderate seismicity. Beneath the Pir-Panjal Ranges and Kashmir Valley, the underthrust crust is ∼10 km thicker, has higher crustal Vs , and a shallower flat MHT at ∼10 km depth. The westward shallowing of the MHT occurs through a lateral ramp beneath Kishtwar Himalaya. Aftershocks of the 2013 Kishtwar earthquake concentrate on the MHT frontal and lateral ramp intersection, and possibly marks the down-dip locked-to-creep transition.

Earthquake moment tensors and centroid locations in the catalogue of the Global CMT (gCMT) project, formerly the Harvard CMT project, have become an essential and extraordinarily valuable resource for studying active global tectonics, used by many solid-Earth researchers. The catalogue’s quality, long duration (1976–present), ease of access and global coverage of earthquakes larger than about Mw~5.5 has transformed our ability to study regional patterns of earthquake locations and focal mechanisms. It also allows researchers to easily identify earthquakes with anomalous mechanisms and depths that stand out from the global or regional patterns, some of which require us to look more closely at accepted interpretations of geodynamics, tectonics or rheology. But, as in all catalogues that are, to some extent and necessarily, produced in a semi-routine fashion, the catalogue may contain anomalies that are in fact errors. Thus, before re-assessing geodynamic, tectonic or rheological understanding on the basis of anomalous earthquake locations or mechanisms in the gCMT catalogue, it is first prudent to check those anomalies are real. The purpose of this paper is to illustrate that necessity in the eastern Himalayas and SE Tibet, where two earthquakes that would otherwise require a radical revision of current geodynamic understanding are shown, in fact, to have gCMT depths (and, in one case, also focal mechanism) that are incorrect — in spite of the overwhelming majority of gCMT solutions in that region being unremarkable and likely to be approximately correct.

Nepal is an actively deforming region due to its tectonic setting that hosts many destructive earthquakes including the recent 2015 Mw 7.8 Gorkha earthquake. To better understand the physics of earthquakes and their precise location as well as monitoring of seismicity and real-time seismic hazard in the region, a highly resolved 3-D structure of the crust is essential. This study presents a new 3-D S-wave velocity structure of the crust using ambient noise tomography (ANT). This study further constrains the discontinuities beneath Himalaya Nepal using teleseismic P-wave coda autocorrelation. The results from the P-wave coda autocorrelation identify major seismic discontinuities in the crust including the Main Himalayan Thrust (MHT). The MHT with two ramps correlates well with a low S-wave velocity layer obtained from the ANT. The first ramp agrees with the duplex structure in the MHT beneath Lesser Himalaya while the second connects flat low velocity beneath High Himalaya to a broad low-velocity zone beneath South Tibet. The geometry and extent of the High Himalaya low-velocity layer mimics the decollement coupling zone inferred from GPS data with widths of 50-70 km north of the nucleation of the 2015 Mw 7.8 Gorkha earthquake and 90-100 km north of the source of the Mw 8.4 1934 earthquake. The occurrence of millenary Mw>9.0 earthquakes in Central and Eastern Nepal would require either a wider coupling low velocity zone compared to the ones identified in this work or the involvement of southernmost Tibet low velocity decoupling zone so to store enough elastic energy.

From a joint analysis of fundamental mode Rayleigh wave group velocities and P-wave receiver functions, we derive a new, high-resolution 3D shear-wave velocity (Vs) model for the crust and uppermost mantle of the Iranian Plateau. The thickest crust (>55km) is located beneath the deforming belts of the Plateau (e.g., the Sanandaj-Sirjan Zone (SSZ) and Talesh-Alborz-Binalud Mountains), whereas regions of lower topography/deformation (e.g., central Iran and the Lut Block), and the regions of very younger deformation such as the Makran Accretionary Wedge and the Zagros Simply Folded Belt (SFB) have a thinner (<45km) crust. Our model reveals a low-Vs tongue-shaped feature, indicating the underthrusting of the Arabian crust beneath central Iran. In the central Zagros, underthrusting of the Arabian crust is steeper, resulting in a narrower (~150km) deforming zone with thicker (~60-65km) crust compared to the crust beneath the broader (~250km) deforming zone and somewhat thinner (~55-60km) crust below the Lorestan Arc. Regions of low-Vs in the upper crust correspond to regions of thick sediments (e.g., the South Caspian Basin, the SFB and foreland basin of the Zagros, and the Makran Subduction Wedge). The subcrustal Rayleigh wave azimuthal anisotropy of the Plateau shows a rather uniform and smoothly-varying pattern. In the NW Zagros the crustal and subcrustal pattern of anisotropy agrees with that previously estimated from the shear-wave core phases, implying that the whole lithosphere deforms coherently, but for other regions (e.g., the western Alborz and Kopet Dag), the anisotropic pattern does not support a coherent deformational fabric throughout the lithosphere.