scholarly journals Modelling the seismic potential of the Indo-Burman megathrust

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Inessa Vorobieva ◽  
Alexander Gorshkov ◽  
Prantik Mandal
Keyword(s):  
Subduction Zones ◽  
Northeast India ◽  
Indian Plate ◽  
Strain Partitioning ◽  
Plate Convergence ◽  
Average Return ◽  
Great Earthquakes ◽  
Short Period ◽  
Integral Characteristics ◽  
Earthquake Size

AbstractThe Indo-Burman arc is the boundary between the India and Burma plates, north of the Sumatra–Andaman subduction zone. The existence of active subduction in the Indo-Burman arc is a debatable issue because the Indian plate converges very obliquely beneath the Burma plate. Recent GPS measurements in Bangladesh, Myanmar, and northeast India indicate 13–17 mm/y of plate convergence along a shallow dipping megathrust while most of the strike-slip motion occurs on several steep faults, consistent with patterns of strain partitioning at subduction zones. A short period of instrumentally recorded seismicity and sparse historical records are insufficient to assess the possibility of great earthquakes at the Indo-Burman megathrust. Using the advantage of the Block-and-Fault Dynamics model allowing simultaneous simulation of slow tectonic motions and earthquakes, we test the hypothesis whether the India-Burma detachment is locked and able to produce great earthquakes, or it slips aseismically? We have shown that the model of locked detachment is preferred because it more adequately reproduces observed tectonic velocities. The integral characteristics of synthetic seismicity, the earthquake size distribution, and the rate of seismic activity are consistent with those derived from observations. Our results suggest that the megathrust is locked and can generate great M8+ earthquakes. The estimated average return period of great events exceeds one thousand years. Earthquakes of this size pose a great threat to NE India, Bangladesh and Myanmar, the most densely populated areas of the world.

Geological signatures of slab shear-off during ongoing India-Asia convergence

2021 ◽  
Author(s):  
Abdul Qayyum ◽  
Nalan Lom ◽  
Eldert L Advokaat ◽  
Wim Spakman ◽  
Douwe J.J van Hinsbergen
Keyword(s):  
Numerical Models ◽  
Leading Edge ◽  
Plate Motion ◽  
Indian Plate ◽  
Mantle Structure ◽  
Continental Lithosphere ◽  
Common View ◽  
Plate Convergence ◽  
Collision Zone ◽  
The Himalaya

<p>Much of our understanding of the dynamics of slab break-off and its geological signatures rely on numerical models with a simplified set-up, in which slab break-off follows arrival of a continent in a mantle-stationary trench, the subsequent arrest of plate convergence, and after a delay time of 10 Ma or more, slab break off under the influence of slab pull. However, geological reconstructions show that plate tectonic reality deviates from this setup: post-collisional convergence is common, trenches are generally not stationary relative to mantle, neither before nor after collision, and there are many examples in which the mantle structure below collision zones is characterized by more, or fewer slabs than collisions.</p><p>A key example of the former is the India-Asia collision zone, where the mantle below India hosts two major, despite the common view of a single collision. Kinematic reconstructions reveal that post-collisional convergence amounted 1000s of kms, and was associated with ~1000 km of trench/collision zone advance. Collision between India-Asia collision zone may provide a good case study to determine the result of post-collisional convergence and absolute lower and upper plate motion on mantle structure, and to evaluate to what extent commonly assumed diagnostic geological phenomena of slab break-off apply.</p><p>In addition to the previously identified major India, Himalaya, and Burma slabs, we here map smaller slabs below Afghanistan and the Himalaya that reveal the latest phases of break-off. We show that west-dipping and east-dipping slabs west and east of India, respectively, are dragged northward parallel to the slab, slabs subducting north of India are overturned, and that the shallowest slab fragments are found in the location where the horizontally underthrust Indian lithosphere below Tibet is narrowest. Our results confirm that northward Indian absolute plate motion continued during two episodes of break-off of large (>1000 km wide) slabs, and decoupling of several smaller fragments. These slabs are currently found south of the present day trench locations. The slabs are located even farther south (>1000 km) of the leading edge of the Indian continental lithosphere, currently underthrust below Tibet, from which the slabs detached, signalling ongoing absolute Indian plate motion. We conclude that the multiple slab break-off events in this setting of ongoing plate convergence and trench advance is better explained by shearing off of slabs from the downgoing plate, possibly at a depth corresponding to the base of the Indian continental lithosphere, are not (necessarily) related to the timing of collision. A recently proposed, detailed diachronous record of deformation, uplift, and oroclinal bending in the Himalaya that was liked to slab break-off fits well with our kinematically reconstructed timing of the last slab shear-off, and may provide an important reference geological record for this process. We find that the commonly applied conceptual geological signatures of slab break-off do not apply to the India-Asia collision zone, or to similar settings and histories such as the Arabia-Eurasia collision zone. Our study provides more realistic boundary conditions for future numerical models that aim to assess the dynamics of subduction termination and its geological signatures.</p>

scholarly journals Illuminating subduction zone rheological properties in the wake of a giant earthquake

2019 ◽  
Vol 5 (12) ◽  
pp. eaax6720 ◽  
Author(s):  
Jonathan R. Weiss ◽  
Qiang Qiu ◽  
Sylvain Barbot ◽  
Tim J. Wright ◽  
James H. Foster ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Three Dimensional ◽  
Surface Strain ◽  
Postseismic Deformation ◽  
Crust And Upper Mantle ◽  
Plate Convergence ◽  
Maule Earthquake ◽  
History Of ◽  
Dependent Viscosity

Deformation associated with plate convergence at subduction zones is accommodated by a complex system involving fault slip and viscoelastic flow. These processes have proven difficult to disentangle. The 2010 Mw 8.8 Maule earthquake occurred close to the Chilean coast within a dense network of continuously recording Global Positioning System stations, which provide a comprehensive history of surface strain. We use these data to assemble a detailed picture of a structurally controlled megathrust fault frictional patchwork and the three-dimensional rheological and time-dependent viscosity structure of the lower crust and upper mantle, all of which control the relative importance of afterslip and viscoelastic relaxation during postseismic deformation. These results enhance our understanding of subduction dynamics including the interplay of localized and distributed deformation during the subduction zone earthquake cycle.

scholarly journals Seismic scatterers in the lower mantle near subduction zones

2019 ◽  
Vol 219 (Supplement_1) ◽  
pp. S2-S20 ◽  
Author(s):  
Satoshi Kaneshima
Keyword(s):  
Oceanic Crust ◽  
Lower Mantle ◽  
Subduction Zones ◽  
P Waves ◽  
Waveform Data ◽  
Basaltic Rocks ◽  
Short Period ◽  
Subducted Oceanic Crust ◽  
Conversion Depth ◽  
Seismic Networks

SUMMARY We investigate the global distribution of S-to-P scatterers in the shallow to mid-lower mantle beneath subduction zones, where deep seismicity extends down to the bottom of the upper mantle. By array processing broadband and short period waveform data obtained at seismic networks, we seek anomalous later phases in the P coda within about 15–150 s after direct P waves. The later phases usually arrive along off-great circle paths and significantly later than S-to-P conversion from the ‘660 km’ discontinuity, often show positive slowness anomalies relative to direct P, and do not show a conversion depth that is consistent among nearby events. They are thus adequately regarded as scattered waves, rather than conversion at a global horizontal discontinuity. The S-to-P scattered waves often show amplitudes comparable to ‘S660P’ waves, which indicates that a spatial change in elastic properties by several percent occurs at the scatterers as abruptly as the post-spinel transformation and should arise from compositional heterogeneity. We locate prominent S-to-P scatterers beneath Pacific subduction zones and beneath southern Spain. Nearly half of 137 S-to-P scatterers located in this study and previous studies by the authors are shallower than 1000 km, and the number of scatterers decreases with depth. Scatterers deeper than 1800 km are rare and mostly weak. We examine relations between the locations of the scatterers and recently subducted slabs inferred from seismic tomography. The scatterers of mid-mantle depths, deeper than about 1000 km, are located distant from tomographic slabs. On the other hand, the majority of shallower scatterers are located beneath the slabs rather than near their fastest portions, which would indicate that chemically heterogeneous materials are not extensively entrained within thickened and folded slabs when the slabs impinge on the lower mantle. We also find scatterers near the locations where basaltic rocks of recently subducted oceanic crust are expected to exist, which suggests that oceanic crust is not delaminating when slabs impinge on the lower mantle.

scholarly journals New constraints on the 1922 Atacama, Chile, earthquake from Historical seismograms

2019 ◽  
Vol 219 (1) ◽  
pp. 645-661 ◽  
Author(s):  
Hiroo Kanamori ◽  
Luis Rivera ◽  
Lingling Ye ◽  
Thorne Lay ◽  
Satoko Murotani ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Source Region ◽  
Plate Boundary ◽  
Spatial Proximity ◽  
Motion Data ◽  
Megathrust Earthquakes ◽  
Great Earthquakes ◽  
Chile Earthquake ◽  
Earthquake Research ◽  
Earthquake Research Institute

SUMMARY We recently found the original Omori seismograms recorded at Hongo, Tokyo, of the 1922 Atacama, Chile, earthquake (MS = 8.3) in the historical seismogram archive of the Earthquake Research Institute (ERI) of the University of Tokyo. These recordings enable a quantitative investigation of long-period seismic radiation from the 1922 earthquake. We document and provide interpretation of these seismograms together with a few other seismograms from Mizusawa, Japan, Uppsala, Sweden, Strasbourg, France, Zi-ka-wei, China and De Bilt, Netherlands. The 1922 event is of significant historical interest concerning the cause of tsunami, discovery of G wave, and study of various seismic phase and first-motion data. Also, because of its spatial proximity to the 1943, 1995 and 2015 great earthquakes in Chile, the 1922 event provides useful information on similarity and variability of great earthquakes on a subduction-zone boundary. The 1922 source region, having previously ruptured in 1796 and 1819, is considered to have significant seismic hazard. The focus of this paper is to document the 1922 seismograms so that they can be used for further seismological studies on global subduction zones. Since the instrument constants of the Omori seismographs were only incompletely documented, we estimate them using the waveforms of the observed records, a calibration pulse recorded on the seismogram and the waveforms of better calibrated Uppsala Wiechert seismograms. Comparison of the Hongo Omori seismograms with those of the 1995 Antofagasta, Chile, earthquake (Mw = 8.0) and the 2015 Illapel, Chile, earthquake (Mw = 8.3) suggests that the 1922 event is similar to the 1995 and 2015 events in mechanism (i.e. on the plate boundary megathrust) and rupture characteristics (i.e. not a tsunami earthquake) with Mw = 8.6 ± 0.25. However, the initial fine scale rupture process varies significantly from event to event. The G1 and G2, and R1 and R2 of the 1922 event are comparable in amplitude, suggesting a bilateral rupture, which is uncommon for large megathrust earthquakes.

The great Lisbon earthquake and tsunami of 1755: lessons from the recent Sumatra earthquakes and possible link to Plato's Atlantis

2006 ◽  
Vol 14 (2) ◽  
pp. 181-191 ◽  
Author(s):  
M.-A. GUTSCHER
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Coarse Grained ◽  
Great Earthquake ◽  
Seismic Profiles ◽  
Great Earthquakes ◽  
Lisbon Earthquake ◽  
Southern Iberia ◽  
High Resolution Bathymetry ◽  
Sumatra Earthquakes

Great earthquakes and tsunami can have a tremendous societal impact. The Lisbon earthquake and tsunami of 1755 caused tens of thousands of deaths in Portugal, Spain and NW Morocco. Felt as far as Hamburg and the Azores islands, its magnitude is estimated to be 8.5–9. However, because of the complex tectonics in Southern Iberia, the fault that produced the earthquake has not yet been clearly identified. Recently acquired data from the Gulf of Cadiz area (tomography, seismic profiles, high-resolution bathymetry, sampled active mud volcanoes) provide strong evidence for an active east dipping subduction zone beneath Gibraltar. Eleven out of 12 of the strongest earthquakes (M>8.5) of the past 100 years occurred along subduction zone megathrusts (including the December 2004 and March 2005 Sumatra earthquakes). Thus, it appears likely that the 1755 earthquake and tsunami were generated in a similar fashion, along the shallow east-dipping subduction fault plane. This implies that the Cadiz subduction zone is locked (like the Cascadia and Nankai/Japan subduction zones), with great earthquakes occurring over long return periods. Indeed, the regional paleoseismic record (contained in deep-water turbidites and shallow lagoon deposits) suggests great earthquakes off South West Iberia every 1500–2000 years. Tsunami deposits indicate an earlier great earthquake struck SW Iberia around 200 BC, as noted by Roman records from Cadiz. A written record of even older events may also exist. According to Plato's dialogues The Critias and The Timaeus, Atlantis was destroyed by ‘strong earthquakes and floods … in a single day and night’ at a date given as 11,600 BP. A 1 m thick turbidite deposit, containing coarse grained sediments from underwater avalanches, has been dated at 12,000 BP and may correspond to the destructive earthquake and tsunami described by Plato. The effects on a paleo-island (Spartel) in the straits of Gibraltar would have been devastating, if inhabited, and may have formed the basis for the Atlantis legend.

Structural framework and regional significance of the Northandean Cretaceous subduction cycle

2020 ◽  
Author(s):  
Andreas Kammer ◽  
Michael Avila
Keyword(s):  
Subduction Zones ◽  
Normal Fault ◽  
Large Igneous Province ◽  
Mantle Flow ◽  
Spreading Ridge ◽  
Forearc Basin ◽  
Plate Convergence ◽  
Continental Plate ◽  
Igneous Province ◽  
Cretaceous Subduction

<p>The Northandean plate margin underwent a fundamental change in its structural configuration during a Cretaceous subduction cycle, as evidenced by the formation and accretion of a province of basic igneous arc rocks that gave rise to the basement of an Northandean Western Cordillera. Further north, this igneous terrane links to the Caribbean Large Igneous Province and has been associated, with respect to its origin, to an actively spreading ridge of the Farallon plate, implying a far-travelled origin with respect to Southamerica and calling for the existence of giant strike-slip faults. We challenge this allochthonous scenario by an alternative option of a forearc origin, invoking the possibility of a forearc opening by the forcing of a toroidal mantle flow at the northern end of the Andean trench, which would have introduced mantle material from the Pacific into the Andean realm through a Central American gap. Support for such an opening mode of a forearc basin comes from extensional tectonics, that accompanied the emplacement of the basic arc units and a concomitant subduction of the extrusive basic units at the inner border of this postulated forearc basin. This intraplate subduction comprises a distinct three-partite evolution: (I) Convergence first became manifest by the reactivation of a normal fault located within the supposed forearc basin and inboard of an inherited Triassic-Jurassic suture, but still failed at a crustal level. (II) A succeeding contractional stage involved the reactivation of the inherited Triassic-Jurassic suture and the tectonic erosion of a frontal compartment of the continental margin. After an incipient underplating, slivers of this continental compartment returned within a time span of about 20 Ma. (III) A final Late Cretaceous subduction stage evolved under the conditions of an oblique SW-NE oriented plate convergence and is characterized by extensional pulses, as may be concluded from the structural setting of the giant Antioquia batholith. In the Campanian subduction definitely locked, as evidenced by the regional buckling of the forearc realm and a rebound of the upper continental plate. Both onset and shutoff of this subduction cycle may be linked to deformation phases and are dated by syntectonic, fault-guided intrusions. This scenario of a forearc origin of the basic igneous province calls for the existence of two paired subduction zones: on its outer margin the subducting Farallon slab imposed a trench-parallel mantle flow and constrained an expansion of the forarc basin by slab rollback. On its inner margin, a secondary subduction compensated a surplus expansion of the actively forming forearc basin.</p>

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