Modelling the Moho depth and Flexure parameters across the Indo-Burma subduction zone.

2021 ◽  
Author(s):  
Anirban Biswas ◽  
Srinivasa Rao Gangumalla
Keyword(s):  
Subduction Zone ◽  
Ocean Circulation ◽  
Active Regions ◽  
Indian Plate ◽  
Moho Depth ◽  
Gravity Inversion ◽  
Stress Regime ◽  
Moho Interface ◽  
Moho Depths ◽  
Vertical Gravity

<p>Indo-Burma subduction zone is one of the seismically active regions in India where the Indian plate is underthrusting the Burmese arc. However, the nature of the slab subduction in this region and its associated stress-regime are less understood due to the lack of deep crustal information. In the present study, we analyze the vertical gravity component of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) and topography data to model the Moho depth interface and flexure parameters of the Indo-Burmese subduction region. Here, Moho depths are obtained by performing the non-linear gravity inversion using tesseroids in spherical coordinates. It is observed that the Moho interface in the Bay of Bengal (Indian plate) lies at a depth of 20-30 km and then deepens to a depth of 50-60 km towards the Burmese region. Beneath the Shan Plateau, Moho depth varies gently from 35 to 40 km and shows an eastward dip at Sagaing fault.  We also constructed eight profiles across the subduction zone to model the flexure parameters such as effective elastic thickness (Te), forebulge, and bending moments (Mo). The modelling results indicate that both Te (15-55 km) and Mo (1.12×10-19 to 2.84×10-19 N.m) values vary significantly along the subduction zone and show correlation with slab depth. Larger values of Te (55 km) and Mo (2.84×10-19 N.m) are noticed in the central Indo-Burmese subduction zone, where the slab depth is around 110-120 km. Whereas the lowest values of Te (15 km) and Mo (1.12×10-19 N.m) are inferred for the profiles lying in the southern Indo-Burmese subduction.</p>

scholarly journals Moho beneath Tibet based on a joint analysis of gravity and seismic data

2020 ◽  
Author(s):  
Guangdong Zhao ◽  
Jianxin Liu ◽  
Bo Chen ◽  
Mikhail K. Kaban
Keyword(s):  
Tibetan Plateau ◽  
Gravity Field ◽  
Tarim Basin ◽  
Plate Tectonics ◽  
Moho Depth ◽  
Joint Analysis ◽  
Gravity Inversion ◽  
The Tibetan Plateau ◽  
Gravity Effects ◽  
Moho Depths

<p>The Tibetan Plateau, known as the roof of the Earth, is considered as the “Golden Key” for understanding plate tectonics, continental collisions and continental orogenic formation. A reliable Moho structure is also vital for understanding the deformation mechanism of the Tibetan Plateau.</p><p>In this study, we use improved Parker−Oldenburg’s formulas that include a reference depth into the exponential term and employ a Gauss-FFT method to determine Moho depths beneath the Tibetan Plateau. The synthetic models demonstrate that the improved Parker’s formula has higher accuracy with the maximum absolute error less than 0.25 mGal.</p><p>Two inversion parameters, namely the reference depth and the density contrast are essential for the Moho estimation based on the gravity field, and they need to be determined in advance to obtain correct results. Therefore, the Moho estimates derived from existing seismic studies (Stolk et al., 2013) are used to reduce the non-uniqueness of the gravity inversion and to determine these parameters by searching for the maximum correlation between the gravity-inverted and seismic-derived Moho depths.</p><p>Another critical issue is to remove beforehand the gravity effects of other factors, which affect the observed gravity field. In addition to the topography, the gravity effects of the sedimentary layer and crystalline crust are removed based on existing crustal models, while the upper mantle impact is determined based on the seismic tomography model.</p><p>The inversion results show that the Moho structure under the Tibetan plateau is very complex with the depths varying from about 30 ~ 40 km in the surrounding basins (e.g., the Ganges basin, the Sichuan basin, and the Tarim basin) to 60 ~ 80 km within the plateau. This considerable difference up to 40 km on the Moho depth reveals the substantial uplift and thickening of the crust in the Tibetan Plateau.</p><p>Furthermore, two visible “Moho depression belts” are observed within the plateau with the maximum Moho deepening along the Indus-Tsangpo Suture and along the northern margin of Tibet bounding the Tarim basin with the relatively shallow Moho in central Tibet between them. The southern “belt” is likely formed in compressional environment, where the Indian plate underthrusts northwards beneath the Tibetan Plateau, while the northern one could be formed by the southward underthrust of the Asian lithosphere beneath Tibet.</p><p>Stolk, W., Kaban, M., Beekman, F., Tesauro, M., Mooney, W. D., & Cloetingh, S. (2013). High resolution regional crustal models from irregularly distributed data: Application to Asia and adjacent areas. Tectonophysics, 602, 55-68. https://doi.org/10.1016/j.tecto.2013.01.022</p>

Sensitivity analysis of gravity gradient inversion of the Moho depth—a case example for the Amazonian Craton

2020 ◽  
Vol 221 (3) ◽  
pp. 1896-1912
Author(s):  
Peter Haas ◽  
Jörg Ebbing ◽  
Wolfgang Szwillus
Keyword(s):  
Variable Density ◽  
Density Contrast ◽  
Moho Depth ◽  
Gravity Gradient ◽  
Gravity Inversion ◽  
Vertical Gravity Gradient ◽  
Novel Approach ◽  
Amazonian Craton ◽  
Fold Belts ◽  
Vertical Gravity

SUMMARY We present a novel approach for linearized gravity inversion to estimate the Moho depth, which allows the use of any gravitational component instead of the vertical gravity component only. The inverse problem is solved with the Gauss–Newton algorithm and the gravitational field of the undulating Moho depth is calculated with tesseroids. Hereby, the density contrast can be laterally variable by using information from seismological regionalization. Our approach is illustrated with a synthetic example, which we use to explore different regularization parameters. The vertical gravity gradient gzz provides the most reasonable results with appropriate parameters. As a case example, we invert for the Moho depth of the Amazonian Craton and its surroundings. The results are constrained by estimates from active seismic measurements. Our new Moho depth model correlates to tectonic domains and is in agreement with previous models. The estimated density contrasts of the tectonic domains agree well with the lithospheric architecture and show with 300–450 kg m–3 lower density contrasts for continental domains, whereas the oceans reveal a density contrast of 450–500 kg m–3. The wider range of estimated density contrast for the continent reflects uncertainties in Precambrian Fold Belts that arise from its small gravity signal. Our results demonstrate that a variable density contrast at the Moho depth is a valuable enhancement for gravity inversion.

Contributions from the detrital approach to unravelling the timing of India-Asia collision and Himalayan evolution

2021 ◽  
Author(s):  
Yani Najman ◽  
Shihu Li
Keyword(s):  
Subduction Zone ◽  
Crustal Deformation ◽  
Earth Science ◽  
Island Arc ◽  
Current Understanding ◽  
Indian Plate ◽  
Geophysical Research

<p>Knowledge of the timing of India-Asia collision and associated Tethyan closure in the region is critical to advancement of models of crustal deformation.   One of a number of methods traditionally used to constrain the time of India-Asia collision is the detrital approach. This involves determination of when Asian material first arrived on the Indian plate, with most recent estimates documenting collision at ca 60 Ma (e.g. Hu et al, Earth Science Reviews 2016). However, more recently, such data and a number of other approaches providing data previously used to determine the timing of India-Asia collision, have been controversially re-interpreted to represent collision of India with an Island arc, with terminal India-Asia collision occurring significantly later, ca 34 Ma (e.g. Aitchison et al, J. Geophysical Research 2007). Clearly, for the detrital approach to advance the debate, discrimination between Asian detritus and arc detritus is required. Such a discrimination was proposed in Najman et al (EPSL 2017), dating the timing of terminal India-Asia collision at 54 Ma. However, this evidence is far from universally accepted.  For example, such data are at variance with various palaeomagnetic studies which suggest that an oceanic Transtethyan subduction zone existed 600-2300 kms south of the Eurasian margin in the Paleocene  (e.g. Martin et al, PNAS 2020) and therefore these authors propose different explanations to explain the detrital data.  This presentation will discuss the uncertainties associated with our current understanding of the timing of India-Asia collision.</p>

Moho Variations across the Northern Canadian Cordillera

2020 ◽  
Vol 91 (6) ◽  
pp. 3076-3085 ◽  
Author(s):  
Pascal Audet ◽  
Derek L. Schutt ◽  
Andrew J. Schaeffer ◽  
Clément Estève ◽  
Richard C. Aster ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
High Elevation ◽  
Receiver Functions ◽  
Moho Depth ◽  
Canadian Cordillera ◽  
Regional Seismicity ◽  
Thermal Buoyancy ◽  
Mackenzie Mountains ◽  
Moho Depths ◽  
Array Density

Abstract Moho morphology in orogens provides important constraints on the rheology and density structure of the crust and underlying mantle. Previous studies of Moho geometry in the northern Canadian Cordillera (NCC) using very sparse seismic data have indicated a flat and shallow (∼30–35  km) Moho, despite an average elevation of >1000  m above sea level attributable to increased thermal buoyancy and lower crustal flow due to elevated temperatures. We estimate Moho depth using receiver functions from an expanded dataset incorporating 173 past and recently deployed broadband seismic stations, including the EarthScope Transportable Array, Mackenzie Mountains transect, and other recent deployments. We determine Moho depths in the range 27–43 km, with mean and standard deviations of 33.0 and 3.0 km, respectively, and note thickened crust beneath high-elevation seismogenic regions. In the Mackenzie Mountains, thicker crust is interpreted as due to crustal stacking from thrust sheet emplacement. The edge of this region of thickened crust is interpreted to delineate the extent of the former Laurentian margin beneath the NCC and is associated with a transition from thrust to strike-slip faulting observed in regional seismicity. More geographically extensive seismograph deployments at EarthScope Transportable Array density and scale will be required to further extend crustal-scale and lithosphere-scale imaging in western Canada.

Trench-parallel compressive upper plate stress field in the northern Chile forearc from earthquake source mechanisms

2020 ◽  
Author(s):  
Bernd Schurr ◽  
Lukas Lehmann ◽  
Christian Sippl ◽  
Wasja Bloch
Keyword(s):  
Stress Field ◽  
Subduction Zone ◽  
Elastic Response ◽  
Lower Plate ◽  
Northern Chile ◽  
Stress Regime ◽  
Plate Convergence ◽  
Source Mechanisms ◽  
Plate Coupling ◽  
East West

<p>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 spatio-temporally variable plate coupling through the seismic cycle. Long-term deformation depends e.g., on the plate convergence geometry, where obliqueness or change in obliqueness play important roles. Here we use the Integrated Plate Boundary Observatory Chile (IPOC) and additional temporal networks to determine source mechanisms for upper plate earthquakes in the northern Chile subduction zone. We find that earthquakes in the South American crust under the sea and under the Coastal Cordillera show a remarkably homogenous north-south, i.e. trench-parallel, compressional stress field. Earthquake fault mechanisms are dominated by east-west striking thrusts. Further inland, where the lower plate becomes uncoupled, the stress field is more varied with direction east-west to southeast-northwest (approx. convergence parallel) dominating. The peculiar stress-regime above the plate-coupling-zone almost perpendicular to plate convergence direction may be explained by a change in subduction obliqueness due to the concave shape of the plate margin.</p>

Improving Focal Mechanisms for Earthquakes in Taiwan Strait and Ryukyu Subduction Zone with Broadband Waveforms of Combined Networks

2020 ◽  
Author(s):  
Chieh-Chen Lee ◽  
Tai-Lin Tseng ◽  
Pei-Ru Jian
Keyword(s):  
Subduction Zone ◽  
Taiwan Strait ◽  
Focal Mechanisms ◽  
Passive Margin ◽  
Moho Depth ◽  
Offshore Area ◽  
Intermediate Depth ◽  
Velocity Models ◽  
Taiwan Shoal ◽  
Oblique Convergence

<p>  Taiwan region is a seismically active region formed by the oblique convergence between Philippine Sea Plate and Eurasia Plate. Focal mechanisms of most small-moderate sized earthquakes can be well constrained by the local seismic array, except for those occurred offshore Taiwan where azimuthal coverage is limited. To better understand the tectonic structures, it is desirable to improve the focal mechanisms using better located hypocenters, reasonable velocity models, and the best available stations. In this study we focus on the shallow earthquakes in Taiwan Strait and the intermediate-depth earthquakes in southernmost Ryukyu. Both regions are less explored but large historic events had been reported.</p><p>  For earthquakes in Taiwan Strait, we systematically studied earthquakes from 1996 to 2019, including the M<sub>w</sub>5.7 Taiwan Shoal sequence happened on 2018/11/25. A total of 22 new moment tensors (MTs) were resolved in the passive margin by combining Fujian and Taiwan seismic networks from either side of the strait. For events closer to Fujian, China, the velocity model with Moho depth of 35 km yields overall lower compensated linear vector dipole (CLVD) and acceptable misfit values; while as a 40 km thick crust is better for events closer to or on the shore of Taiwan. This Moho variation under the Taiwan Strait, although subtle, agrees well with the velocity structure constrained independently by previous studies. Earthquakes in the middle of the strait are dominant in strike-slip and normal slip within 30 km depth. Shallow thrusting events are found only in the Miaoli offshore area of Taiwan. As for the 2018 Taiwan Shoal earthquake sequence, it is located right on the region absence of known fault-plane solutions, therefore offers important new constraints. All events of the sequence show high angle strike-slips and shallow centroid depth of 11-21 km, more consistent with seismicity determined by Fujian seismic center. This event is far away from the M8 1604 Quanzhou earthquake, and is also clearly unrelated to the structure of 1994 M<sub>w </sub>6.7 normal-faulting event in Tainan Basin. The 2018 sequence is probably the reactivation of a pre-existing normal fault that was created by rifting during the Cenozoic.</p><p>  For future work, we will re-evaluate the MTs of M>5.5 intermediate-depth earthquakes of the Ryukyu subduction zone by including waveforms of stations YNG and IGK from Japan network in the inversion. We will also test different upper mantle velocities in the model for the computation of Green’s functions. We anticipate that our work can provide a set of parameters more suitable for the MT inversion, and the MT results can delineate the Ryukyu subduction zone properties better.</p><p> </p><p>keywords : Taiwan Strait, focal mechanisms, moment tensor inversion</p>

scholarly journals Moho Geometry of the Okinawa Trough Based on Gravity Inversion and Its Implications on the Crustal Nature and Tectonic Evolution

2021 ◽  
Vol 9 ◽  
Author(s):  
Liang Zhang ◽  
Xiwu Luan
Keyword(s):  
Early Stage ◽  
Okinawa Trough ◽  
High Heat ◽  
Crustal Thickness ◽  
Moho Depth ◽  
Gravity Inversion ◽  
The Okinawa Trough ◽  
Oceanic Spreading ◽  
Thickness Variations ◽  
Back Arc

The Okinawa Trough (OT) is an incipient back-arc basin, but its crustal nature is still controversial. Gravity inversion along with sediment and lithospheric mantle density modeling are used to map the regional Moho depth and crustal thickness variations of the OT and its adjacent areas. The gravity inversion result shows that the crustal thicknesses are 17–22 km at the northern OT, 11–19 km at the central OT, and 7–19 km at the southern OT. Because of the crust with a thickness larger than 17 km, the slow southward arc movement, and scarce contemporaneous volcanisms, the northern OT should be in the stage of early back-arc extension. All of the moderate crustal thickness, high heat flow, and intense volcanism at the central OT indicate that this region is probably in the transitional stage from the back-arc rifting to the oceanic spreading. A crust that is only 7 km thick, lithosphere strength as low as the mid-ocean ridge, and MORB-similar basalts at the southern OT demonstrate that the southern OT is at the early stage of seafloor spreading.

scholarly journals On Moho Determination by the Vening Meinesz-Moritz Technique

2021 ◽  
Author(s):  
Lars Erik Sjöberg ◽  
Majid Abrehdary
Keyword(s):  
Least Squares ◽  
Moho Depth ◽  
Glacial Isostatic Adjustment ◽  
Altimetry Data ◽  
Satellite Gravity ◽  
Isostatic Adjustment ◽  
Uncertainty Estimates ◽  
Least Squares Adjustment ◽  
Moho Depths ◽  
Vening Meinesz

This chapter describes a theory and application of satellite gravity and altimetry data for determining Moho constituents (i.e. Moho depth and density contrast) with support from a seismic Moho model in a least-squares adjustment. It presents and applies the Vening Meinesz-Moritz gravimetric-isostatic model in recovering the global Moho features. Internal and external uncertainty estimates are also determined. Special emphasis is devoted to presenting methods for eliminating the so-called non-isostatic effects, i.e. the gravimetric signals from the Earth both below the crust and from partly unknown density variations in the crust and effects due to delayed Glacial Isostatic Adjustment as well as for capturing Moho features not related with isostatic balance. The global means of the computed Moho depths and density contrasts are 23.8±0.05 km and 340.5 ± 0.37 kg/m3, respectively. The two Moho features vary between 7.6 and 70.3 km as well as between 21.0 and 650.0 kg/m3. Validation checks were performed for our modeled crustal depths using a recently published seismic model, yielding an RMS difference of 4 km.

scholarly journals Evaluation of the Influence of In Situ Stress on the Stability of Mine Pit Walls: A Case Study of Songwe Mine

2021 ◽  
Vol 4 (2) ◽  
pp. p1
Author(s):  
Dyson Moses ◽  
Hideki Shimada ◽  
Takashi Sasaoka ◽  
Akihiro Hamanaka ◽  
Tumelo K. M Dintwe ◽  
...  
Keyword(s):  
Active Regions ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
Slope Instability ◽  
Open Pit ◽  
Stress Regime ◽  
Tectonically Active ◽  
The Stability ◽  
The Impact

The investigation of the influence of in situ stress in Open Pit Mine (OPM) projects has not been accorded a deserved attention despite being a fundamental concern in the design of underground excavations. Hence, its long-term potential adverse impacts on pit slope performance are overly undermined. Nevertheless, in mines located in tectonically active settings with a potential high horizontal stress regime like the Songwe mine, the impact could be considerable. Thus, Using FLAC3D 5.0 software, based on Finite Difference Method (FDM) code, we assessed the role of stress regimes as a potential triggering factor for slope instability in Songwe mine. The results of the evaluated shearing contours and quantified strain rate and displacement values reveal that high horizontal stress can reduce the stability performance of the pit-wall in spite of the minimal change in Factor of Safety (FoS). Since mining projects have a long life span, it would be recommendable to consider “in situ stress-stability analyses” for OPM operations that would be planned to extend to greater depths and those located in tectonically active regions.

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