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>

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>

Southern California Earthquake Data Now Available in the AWS Cloud

2021 ◽  
Author(s):  
Ellen Yu ◽  
Aparna Bhaskaran ◽  
Shang-Lin Chen ◽  
Zachary E. Ross ◽  
Egill Hauksson ◽  
...  
Keyword(s):  
Southern California ◽  
Data Availability ◽  
First Year ◽  
Earthquake Catalog ◽  
High Data ◽  
Seismic Waveform ◽  
Challenges And Opportunities ◽  
Amazon Web Services ◽  
Computationally Intensive ◽  
Earthquake Data

Abstract The Southern California Earthquake Data Center is hosting its earthquake catalog and seismic waveform archive in the Amazon Web Services (AWS) Open Dataset Program (s3://scedc-pds; us-west-2 region). The cloud dataset’s high data availability and scalability facilitate research that uses large volumes of data and computationally intensive processing. We describe the data archive and our rationale for the formats and data organization. We provide two simple examples to show how storing the data in AWS Simple Storage Service can benefit the analysis of large datasets. We share usage statistics of our data during the first year in the AWS Open Dataset Program. We also discuss the challenges and opportunities of a cloud-hosted archive.

Evolution of the East Africa-Arabia plume head

2021 ◽  
Author(s):  
Chiara Civiero ◽  
Sergei Lebedev ◽  
Nicolas L. Celli
Keyword(s):  
East Africa ◽  
Basic Mechanism ◽  
Continental Lithosphere ◽  
Gulf Of Aden ◽  
Low Velocity ◽  
Velocity Anomaly ◽  
Seismic Waveform ◽  
Igneous Provinces ◽  
Lithospheric Plates ◽  
Plate Reconstructions

<p>Hot plumes rising from Earth’s deep mantle are thought to form broad plume heads beneath lithospheric plates. In continents, mantle plumes cause uplift, rifting and volcanism, often dispersed over surprisingly broad areas. Using seismic waveform tomography, we image <span>a star-shaped, low-velocity anomaly centered at Afar and composed of three narrow branches: beneath East Africa, beneath the Gulf of Aden, and beneath the Red Sea and West Arabia, extending north to Levant. We interpret this anomaly as the seismic expression of </span>interconnected corridors of hot, partially molten rock beneath the East Africa-Arabia region. The corridors underlie areas of uplift, rifting and volcanism and accommodate an integral, active plume head. Eruption ages and plate reconstructions indicate that it developed south-to-north, and tomography shows it being fed by three deep upwellings beneath Kenya, Afar and Levant. <span>These results demonstrate the complex feedbacks between the continental-lithosphere heterogeneity and plume-head evolution. </span>Star-shaped plume heads sprawling within thin-lithosphere valleys can account for the enigmatic dispersed volcanism in large igneous provinces and are likely to be a basic mechanism of plume-continent interaction.</p>

scholarly journals Crustal velocity structure of the Apennines (Italy) from P-wave travel time tomography

1996 ◽  
Vol 39 (6) ◽  
Author(s):  
C. Chiarabba ◽  
A. Amato
Keyword(s):  
Velocity Structure ◽  
P Wave ◽  
Depth Interval ◽  
Low Velocity ◽  
Data Set ◽  
Arrival Times ◽  
Velocity Anomaly ◽  
Minimum Number ◽  
Velocity Images ◽  
Lower Crustal

In this paper we provide P-wave velocity images of the crust underneath the Apennines (Italy), focusing on the lower crustal structure and the Moho topography. We inverted P-wave arrival times of earthquakes which occurred from 1986 to 1993 within the Apenninic area. To overcome inversion instabilities due to noisy data (we used bulletin data) we decided to resolve a minimum number of velocity parameters, inverting for only two layers in the crust and one in the uppermost mantle underneath the Moho. A partial inversion of only 55% of the overall dataset yields velocity images similar to those obtained with the whole data set, indicating that the depicted tomograms are stable and fairly insensitive to the number of data used. We find a low-velocity anomaly in the lower crust extending underneath the whole Apenninic belt. This feature is segmented by a relative high-velocity zone in correspondence with the Ortona-Roccamonfina line, that separates the northern from the southern Apenninic arcs. The Moho has a variable depth in the study area, and is deeper (more than 37 km) in the Adriatic side of the Northern Apennines with respect to the Tyrrhenian side, where it is found in the depth interval 22-34 km.

Non-linear 3-D Born shear waveform tomography in Southeast Asia

2012 ◽  
Vol 190 (1) ◽  
pp. 463-475 ◽  
Author(s):  
Mark P. Panning ◽  
Aimin Cao ◽  
Ahyi Kim ◽  
Barbara A. Romanowicz
Keyword(s):  
Southeast Asia ◽  
Non Linear ◽  
Waveform Tomography

scholarly journals Upper-plate structure in Ecuador coincident with the subduction of the Carnegie Ridge and the southern extent of large mega-thrust earthquakes

2019 ◽  
Vol 220 (3) ◽  
pp. 1965-1977 ◽  
Author(s):  
Colton Lynner ◽  
Clinton Koch ◽  
Susan L Beck ◽  
Anne Meltzer ◽  
Lillian Soto-Cordero ◽  
...  
Keyword(s):  
Ambient Noise ◽  
Velocity Structure ◽  
Sedimentary Basins ◽  
Past Century ◽  
Ambient Noise Tomography ◽  
Plate Interface ◽  
Crust And Upper Mantle ◽  
Southern Boundary ◽  
Plate Structure ◽  
Velocity Anomaly

SUMMARY The Ecuadorian convergent margin has experienced many large mega-thrust earthquakes in the past century, beginning with a 1906 event that propagated along as much as 500 km of the plate interface. Many subsections of the 1906 rupture area have subsequently produced Mw ≥ 7.7 events, culminating in the 16 April 2016, Mw 7.8 Pedernales earthquake. Interestingly, no large historic events Mw ≥ 7.7 appear to have propagated southward of ∼1°S, which coincides with the subduction of the Carnegie Ridge. We combine data from temporary seismic stations deployed following the Pedernales earthquake with data recorded by the permanent stations of the Ecuadorian national seismic network to discern the velocity structure of the Ecuadorian forearc and Cordillera using ambient noise tomography. Ambient noise tomography extracts Vsv information from the ambient noise wavefield and provides detailed constraints on velocity structures in the crust and upper mantle. In the upper 10 km of the Ecuadorian forearc, we see evidence of the deepest portions of the sedimentary basins in the region, the Progreso and Manabí basins. At depths below 30 km, we observe a sharp delineation between accreted fast forearc terranes and the thick crust of the Ecuadorian Andes. At depths ∼20 km, we see a strong fast velocity anomaly that coincides with the subducting Carnegie Ridge as well as the southern boundary of large mega-thrust earthquakes. Our observations raise the possibility that upper-plate structure, in addition to the subducting Carnegie Ridge, plays a role in the large event segmentation seen along the Ecuadorian margin.

Detecting near-surface objects with seismic waveform tomography

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. WCC119-WCC127 ◽  
Author(s):  
Brendan Smithyman ◽  
R. Gerhard Pratt ◽  
John Hayles ◽  
Ralph Wittebolle
Keyword(s):  
Seismic Attenuation ◽  
Blind Test ◽  
Near Surface ◽  
Traveltime Tomography ◽  
Seismic Waveform ◽  
Long Offset ◽  
Velocity Images ◽  
Weight Drop ◽  
Waveform Tomography ◽  
Geophysical Imaging

Three shallow, high-velocity, rubble-filled targets are imaged using waveform tomography in an engineering-scale clay embankment at Seven Sisters Falls, Manitoba, Canada, to locate targets buried at approximately [Formula: see text] as a blind test of geophysical imaging methods. Previous studies use near-offset reflection methods to image the targets; however, this test uses waveform tomography of the long-offset, refracted arrivals to image P-velocity and seismic attenuation. The targets are invisible to standard traveltime tomography. Using weight-drop data, with frequencies of 20–150 Hz, the subwavelength targets are resolved in the velocity images and complementary images of seismic [Formula: see text] are produced. The interpreted target locations are consistent with limited survey information from the embankment construction. Multiple quality-control efforts, paired with a very good fit between model and observed data, indicate the reliability of the results.

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