Towards 3D multiscale adjoint waveform tomography of the crust and upper mantle beneath Southeast Asia

2020 ◽  
Author(s):  
Deborah Wehner ◽  
Nienke Blom ◽  
Nick Rawlinson
Keyword(s):  
Southeast Asia ◽  
Upper Mantle ◽  
Signal To Noise Ratio ◽  
Data Availability ◽  
Tectonic Activity ◽  
Initial Model ◽  
Crust And Upper Mantle ◽  
Banda Arc ◽  
Waveform Tomography ◽  
Krakatoa Eruption

<p>Southeast Asia is one of the most complex tectonic regions on Earth. This is mainly a result of its location within the triple junction of the Australian, Eurasian and Philippine Sea plates which has created a complicated configuration of active plate tectonic boundaries. High plate velocities have generated thousands of kilometers of subducted material and ongoing subduction along the Sunda Arc represents a significant natural hazard (such as the 2004 Sumatra-Andaman earthquake, 2012 Indian Ocean earthquakes and 2018 Anak Krakatoa eruption). However, recent tectonic activity around Borneo may be related to postsubduction processes which could be the key to understanding how the tectonic subduction cycle terminates. Further east, the region is dominated by several minor tectonic plates and the spectacular 180-degree curvature of the Banda Arc. Our work aims to further improve the understanding of this area by providing detailed images of the upper mantle.</p><p>Adjoint waveform tomography is especially suitable for imaging such complex regions. By simulating the 3D wavefield, it is possible to directly compare observed and simulated seismograms, thereby taking into account both body and surface waves. The method can account for the effects of anisotropy, anelasticity, wavefront healing, interference and (de)focusing that can hamper other seismological methods, and is thus especially suitable for strongly heterogenous areas such as Southeast Asia.</p><p>To date, sparse instrument coverage in the region has contributed to a heterogeneous path coverage. In this project, we make use of publicly available data as well as our recently deployed networks of broadband seismometers on Borneo and Sulawesi. This, in addition to access to national permanent networks promises a significant improvement in data coverage around the Banda Arc, Borneo and Sulawesi, thereby providing new opportunities to untangle the region’s complexity.</p><p>We compiled a catalogue of well-constrained earthquakes, optimising for coverage, signal-to-noise ratio and data availability across a wide frequency band, and compared our observed data to synthetics generated from an initial model. In the first part of the inversion, we use long periods of 100 - 150 s to update our initial model using a gradient-based optimisation scheme. We use adjoint methods to obtain sensitivity kernels as the corresponding gradients and initial results will be documented in this presentation. In subsequent iterations, we permit increasingly shorter periods in order to progressively recover finer scales structure and avoid cycle skipping issues.</p>

Towards 3D Multiscale Adjoint Waveform Tomography of the Lithosphere and Underlying Mantle beneath Southeast Asia

2021 ◽  
Author(s):  
Deborah Wehner ◽  
Nienke Blom ◽  
Nicholas Rawlinson ◽  
Meghan Miller ◽  
Sri Widiyantoro ◽  
...  
Keyword(s):  
Southeast Asia ◽  
Velocity Structure ◽  
Signal To Noise Ratio ◽  
Data Availability ◽  
Velocity Anomaly ◽  
Seismic Waveform ◽  
Path Coverage ◽  
Gradient Based ◽  
Waveform Tomography ◽  
Window Selection

<p>Southeast Asia is one of the most complex tectonic regions on Earth. This is mainly a result of its location within the triple junction of the Australian, Eurasian and Philippine Sea plates which has created a complicated configuration of active plate tectonic boundaries. Adjoint waveform tomography is especially suitable for imaging such complex regions. By simulating the 3D wavefield, it is possible to directly compare observed and simulated seismograms, thereby taking into account both body and surface waves. The method can account for the effects of anisotropy, anelasticity, wavefront healing, interference and (de)focusing that can hamper other seismological methods.</p><p>To date, sparse instrument coverage in the region has contributed to a heterogeneous path coverage. In this project, we make use of publicly available data as well as our recently deployed networks of broadband seismometers on Borneo and Sulawesi. This, in addition to access to national permanent networks, provides data from over 300 stations which promises a significant improvement in data coverage around the Banda Arc, Borneo and Sulawesi. We employ a geographical weighting scheme to minimise the effect of dense regional arrays and compile a catalogue of 118 well-constrained earthquakes, optimising for coverage, signal-to-noise ratio and data availability. An optimised window selection algorithm allows us to balance amplitude differences and include as much signal as possible while avoiding noisy data.</p><p>Here, we present a seismic waveform tomography for upper mantle structure in Southeast Asia, imaging radially anisotropic S velocity, P velocity and density. We use a gradient-based optimisation scheme (L-BFGS) and adjoint methods to obtain sensitivity kernels as the corresponding gradients. In the first part of the inversion, periods down to 50 s are used to update a 1D initial model, adapting a multi-scale approach in which long periods are inverted for first to avoid cycle skipping. In our long-period results, we observe a strong regional low S-velocity structure with an underlying high-velocity anomaly. The results are consistent with the global <em>S40RTS</em> model. </p>

The consequences of Canadian Cordillera thermal regime in recent tectonics and elevation: a reviewThis article is one of a series of papers published in this Special Issue on the theme Lithoprobe — parameters, processes, and the evolution of a continent.Geological Survey of Canada Contribution 20090195.

2010 ◽  
Vol 47 (5) ◽  
pp. 621-632 ◽  
Author(s):  
R. D. Hyndman
Keyword(s):  
Thermal Regime ◽  
Upper Mantle ◽  
High Surface ◽  
Plate Boundary ◽  
High Elevation ◽  
Mantle Xenoliths ◽  
Tectonic Activity ◽  
Small Scale ◽  
Canadian Cordillera ◽  
Crust And Upper Mantle

The crust and upper mantle thermal regime of the Canadian Cordillera and its tectonic consequences were an important part of the Cordillera Lithoprobe program and related studies. This article provides a review, first of the thermal constraints, and then of consequences in high surface elevation and current tectonics. Cordillera and adjacent craton temperatures are well constrained by geothermal heat flow, mantle tomography velocities, upper mantle xenoliths, and the effective elastic thickness, Te. Cordillera temperatures are very high and laterally uniform, explained by small scale convection beneath a thin lithosphere, 800–900 °C at the Moho, contrasted to 400–500 °C for the craton. The high temperatures provide an explanation for why the Cordillera has high elevation in spite of a generally thin crust, ∼33 km, in contrast to low elevation and thicker crust, 40–45 km, for the craton. The Cordillera is supported ∼1600 m by lithosphere thermal expansion. In the Cordillera only the upper crust has significant strength; Te ∼ 15 km, in contrast to over 60 km for the craton. The Cordillera is tectonically active because the lithosphere is sufficiently weak to be deformed by plate boundary and gravitational forces; the craton is too strong. The Canadian Cordillera results have led to new understandings of processes in backarcs globally. High backarc temperatures and weak lithospheres explain the tectonic activity over long geological times of mobile belts that make up about 20% of continents. They also have led to a new understanding of collision orogenic heat in terms of incorporation of already hot backarcs.

scholarly journals Seismic waveform tomography of the central and eastern Mediterranean upper mantle

Solid Earth ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 669-690 ◽  
Author(s):  
Nienke Blom ◽  
Alexey Gokhberg ◽  
Andreas Fichtner
Keyword(s):  
Subduction Zone ◽  
Transition Zone ◽  
Upper Mantle ◽  
High Velocity ◽  
Eastern Mediterranean ◽  
Crust And Upper Mantle ◽  
Mantle Transition Zone ◽  
Seismic Waveform ◽  
Waveform Tomography ◽  
Seismic Waveform Tomography

Abstract. We present a seismic waveform tomography of the upper mantle beneath the central and eastern Mediterranean down to the mantle transition zone. Our methodology incorporates in a consistent manner the information from body and multimode surface waves, source effects, frequency dependence, wavefront healing, anisotropy and attenuation. This allows us to jointly image multiple parameters of the crust and upper mantle. Based on the data from ∼ 17 000 unique source–receiver pairs, gathered from 80 earthquakes, we image radially anisotropic S velocity, P velocity and density. We use a multi-scale approach in which the longest periods (100–150 s) are inverted first, broadening to a period band of 28–150 s. Thanks to a strategy that combines long-period signals and a separation of body and surface wave signals, we are able to image down to the mantle transition zone in most of the model domain. Our model shows considerable detail in especially the northern part of the domain, where data coverage is very dense, and displays a number of clear and coherent high-velocity structures across the domain that can be linked to episodes of current and past subduction. These include the Hellenic subduction zone, the Cyprus subduction zone and high-velocity anomalies beneath the Italian peninsula and the Dinarides. This model is able to explain data from new events that were not included in the inversion.

Assessment of seismic tomographic models of the contiguous United States using intermediate-period 3D wavefield simulation

2021 ◽  
Author(s):  
Tong Zhou ◽  
Ziyi Xi ◽  
Min Chen ◽  
Jiaqi Li
Keyword(s):  
United States ◽  
North America ◽  
Upper Mantle ◽  
Waveform Inversion ◽  
Selection Procedure ◽  
3D Models ◽  
Initial Model ◽  
Crust And Upper Mantle ◽  
Data Set ◽  
Wavefield Simulation

Summary The contiguous United States has been well instrumented with broadband seismic stations due to the development of the EarthScope Transportable Array. Previous studies have provided various 3D seismic wave speed models for the crust and upper mantle with improved resolution. However, discrepancies exist among these models due to differences in both data sets and tomographic methods, which introduce uncertainties on the imaged lithospheic structure beneath North America. A further model refinement using the best data coverage and advanced tomographic methods such as full-waveform inversion (FWI) is expected to provide better seismological constraints. Initial models have significant impacts on the convergence of FWIs. However, how to select an optimal initial model is not well investigated. Here, we present a data-driven initial model selection procedure for the contiguous US and surrounding regions by assessing waveform fitting and misfit functions between the observations and synthetics from candidate models. We use a data set of waveforms from 30 earthquakes recorded by 5,820 stations across North America. The results suggest that the tested 3D models capture well long-period waveforms while showing discrepancies in short-periods especially on tangential components. This observation indicates that the smaller-scale heterogeneities and radial anisotropy in the crust and upper mantle are not well constrained. Based on our test results, a hybrid initial model combining S40RTS or S362ANI in the mantle and US.2016 for Vsv and CRUST1.0 for Vsh in the crust is compatible for future FWIs to refine the lithospheric structure of North America.

Transcontinental crustal sections of the U.S.S.R. and adjacent areas

1968 ◽  
Vol 5 (4) ◽  
pp. 1067-1078 ◽  
Author(s):  
N. A. Beliayevsky ◽  
A. A. Borisov ◽  
I. S. Volvovsky ◽  
Yu. K. Schukin
Keyword(s):  
Pacific Ocean ◽  
Upper Mantle ◽  
Far East ◽  
Crustal Thickness ◽  
Tien Shan ◽  
Tectonic Activity ◽  
Crust And Upper Mantle ◽  
The Pacific ◽  
Crustal Structures ◽  
The Pacific Ocean

Transcontinental sections of the earth's crust and Upper Mantle from the Kuril Islands to the Carpathians, and along other principal directions, in all about 15 000 km long, show the following features:(1) The depth of an asthenosphere horizon agrees well with the position of a high-conductivity layer in the Upper Mantle.(2) Hypocenters of earthquakes are located in fault zones. In the zone of the Kuril Island arc, they plunge into the Upper Mantle to depths of hundreds of kilometers, dipping towards the continent.(3) Boundary velocities along the Mohorovičić discontinuity are not dependent on its depth, for they are always in the range 8.0–8.2 km/s; velocities within the crust are correlated with the depths of layers; in the roots of high mountains a layer of 7.5–7.8 km/s has been distinguished near the base of the crust.(3) The crustal thickness in folded areas is in a certain accordance with the altitude of the surface of the earth's solid cover, with Bouguer anomalies and amplitudes of neotectonic movements. It varies from 8 km in margin areas of the Pacific Ocean basin to 60 km in the Tien Shan. Average crustal thicknesses within the platforms are in the region of 40 km, increasing to 50 km in the southern outlying areas of the East-European platform and to 46 km in areas of recent tectonic activity within the Turanian and Siberian Platforms.(4) In deep depressions, internal and outlying seas, the crustal thickness is reduced, and 'granite' layer (6.0–6.5 km/s) is absent. Mesozoic formations of the Far East and adjacent zones of transition from the Pacific Ocean to the continent are distinguished by reduced thicknesses. In Alpine formations the 'basalt' layer dominates over the 'granite' layer.(5) Subhorizontal crustal stratification complicated by deep faults has been found everywhere. Plicate geosynclinal folding is not reflected in deep crustal structures.(6) Temperature of the platform folded basement is mainly related to thickness and composition of the sediments.The transcontinental sections provide a clearer idea of the relationship between anomalous geophysical fields and deep and shallow crustal structures than is given in corresponding maps.

scholarly journals Seismic waveform tomography of the Central and Eastern Mediterranean upper mantle

2019 ◽  
Author(s):  
Nienke Blom ◽  
Alexey Gokhberg ◽  
Andreas Fichtner
Keyword(s):  
Subduction Zone ◽  
Transition Zone ◽  
Upper Mantle ◽  
High Velocity ◽  
Eastern Mediterranean ◽  
Crust And Upper Mantle ◽  
Multiple Parameters ◽  
Seismic Waveform ◽  
Waveform Tomography ◽  
Seismic Waveform Tomography

Abstract. We present a seismic waveform tomography of the upper mantle beneath the Central and Eastern Mediterranean down to the mantle transition zone. Our methodology incorporates in a consistent manner the information from body and multimode surface waves, source effects, frequency dependence, wavefront healing, anisotropy and attenuation. This allows us to jointly image multiple parameters of the crust and upper mantle. Based on the data from ~ 17 000 unique source-receiver pairs, gathered from 80 earthquakes, we image radially anisotropic S velocity, P velocity and density. We use a multi-scale approach in which the longest periods (100–150 s) are inverted first, broadening to a period band of 28–150 s. Thanks to a strategy that combines long-period signals and a separation of body and surface wave signals, we are able to image down to the transition zone in most of the model domain. Our model shows considerable detail in especially the northern part of the domain, where data coverage is very dense, and displays a number of clear and coherent high-velocity structures across the domain that can be linked to episodes of current and past subduction. These include the Hellenic subduction zone, the Cyprus subduction zone and high-velocity anomalies beneath the Italian peninsula and the Dinarides. This model is able to explain data from new events that were not included in the inversion.

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