scholarly journals Preliminary Results of Receiver Function Forward Velocity Modelling at Merapi Volcano

2021 ◽  
Vol 873 (1) ◽  
pp. 012056
Author(s):  
M F R Auly ◽  
A K Ilahi ◽  
I Madrinovella ◽  
S Widyanti ◽  
S K Suhardja ◽  
...  
Keyword(s):  
Receiver Function ◽  
Tectonic Setting ◽  
Vertical Component ◽  
P Wave ◽  
Function Technique ◽  
Boundary Current ◽  
Low Velocity ◽  
Mantle Boundary ◽  
Velocity Models ◽  
Synthetic Model

Abstract The tectonic setting of Java island, located at southwestern edge of the Eurasia continent, is dominated by the subduction of Indo-Australia plate. One of the characteristics of active subduction is active seismicity, the generation of arc magmatism and volcanic activity. Mt. Merapi is one example of active volcano related with the subduction process. It is one of the most active volcanoes with location close to high population area. To better understand this area, we employed the Receiver Function technique, a method to image sub surface structure by removing the vertical component from horizontal component. First, we collected high magnitude events and processed RF with water level deconvolution method. Then, we constructed synthetic model with initial velocity input from previous tomography model. Note that we used reflectivity method in generating synthetic model with input parameters matched with parameters from real data processing. Next, we adjusted velocity inputs mainly on tops sediments (1-3 km) to include sediment layers and volcanic rocks, mid-depth low velocity zone that may be related with magma chamber and depth of crust-mantle boundary. Current forward velocity models show a relatively good agreement from 3 stations (ME25, ME32 and ME36). We estimate a thin layer of sediments followed a zone of velocity layer at a depth of 10-15 km and crust-mantle boundary ranging from 26-29 km. In this study, simulated that the signal of sediments layer and low velocity layers interfere main crust mantle boundary that supposed to be highest signal after the P wave in the typical receiver function study.

scholarly journals Seismic Structure of Local Crustal Earthquakes beneath the Zipingpu Reservoir of Longmenshan Fault Zone

2011 ◽  
Vol 2011 ◽  
pp. 1-6 ◽  
Author(s):  
Haiou Li ◽  
Xiwei Xu ◽  
Wentao Ma ◽  
Ronghua Xie ◽  
Jingli Yuan ◽  
...  
Keyword(s):  
Fault Zone ◽  
Three Dimensional ◽  
P Wave ◽  
The Tibetan Plateau ◽  
Seismic Structure ◽  
Infiltration Depth ◽  
Low Velocity ◽  
Longmenshan Fault Zone ◽  
Velocity Models ◽  
Longmenshan Fault

Three-dimensional P wave velocity models under the Zipingpu reservoir in Longmenshan fault zone are obtained with a resolution of 2 km in the horizontal direction and 1 km in depth. We used a total of 8589 P wave arrival times from 1014 local earthquakes recorded by both the Zipingpu reservoir network and temporary stations deployed in the area. The 3-D velocity images at shallow depth show the low-velocity regions have strong correlation with the surface trace of the Zipingpu reservoir. According to the extension of those low-velocity regions, the infiltration depth directly from the Zipingpu reservoir itself is limited to 3.5 km depth, while the infiltration depth downwards along the Beichuan-Yingxiu fault in the study area is about 5.5 km depth. Results show the low-velocity region in the east part of the study area is related to the Proterozoic sedimentary rocks. The Guanxian-Anxian fault is well delineated by obvious velocity contrast and may mark the border between the Tibetan Plateau in the west and the Sichuan basin in the east.

Common-Reflection-Point-Based Prestack Depth Migration for Imaging Lithosphere in Python: Application to the Dense Warramunga Array in Northern Australia

2020 ◽  
Vol 91 (5) ◽  
pp. 2890-2899 ◽  
Author(s):  
Weijia Sun ◽  
Brian L. N. Kennett
Keyword(s):  
Open Source ◽  
Receiver Function ◽  
Function Analysis ◽  
Vertical Component ◽  
P Wave ◽  
Northern Australia ◽  
Reflection Point ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
Conversion Point

Abstract We exploit estimates of P-wave reflectivity from autocorrelation of transmitted teleseismic P arrivals and their coda in a common reflection point (CRP) migration technique. The approach employs the same portion of the vertical-component seismogram, as in standard Ps receiver function analysis. This CRP prestack depth migration approach has the potential to image lithospheric structures on scales as fine as 4 km or less. The P-wave autocorrelation process and migration are implemented in open-source software—the autocorrelogram calculation (ACC) package, which builds on the widely used the seismological Obspy toolbox. The ACC package is written in the open-source and free Python programming language (3.0 or newer) and has been extensively tested in an Anaconda Python environment. The package is simple and friendly to use and runs on all major operating systems (e.g., Windows, macOS, and Linux). We utilize Python multiprocessing parallelism to speed up the ACC on a personal computer system, or servers, with multiple cores and threads. The application of the ACC package is illustrated with application to the closely spaced Warramunga array in northern Australia. The results show how fine-scale structures in the lithospheric can be effectively imaged at relatively high frequencies. The Moho ties well with conventional H−κ receiver analysis and deeper structure inferred from stacked autocorrelograms for continuous data. CRP prestack depth migration provides an important complement to common conversion point receiver function stacks, since it is less affected by surface multiples at lithospheric depths.

Indication of active Faults in the New Madrid Seismic Zone from Precise Location of Hypocenters

1988 ◽  
Vol 59 (4) ◽  
pp. 123-131 ◽  
Author(s):  
L. Himes ◽  
W. Stauder ◽  
R. B. Herrmann
Keyword(s):  
Active Faults ◽  
P Wave ◽  
New Madrid Seismic Zone ◽  
Supporting Evidence ◽  
Seismic Zone ◽  
Low Velocity ◽  
Focal Mechanism Solutions ◽  
Velocity Models ◽  
Planar Surfaces ◽  
New Madrid

Abstract The hypocenter locations of the larger and better recorded earthquakes of the New Madrid seismic zone are examined in order to determine how closely the hypocenters lie along planar surfaces, thus relating the foci to active fault surfaces. For this purpose more than 500 earthquakes of the region have been selected for study, based on the number (7 or more) of observing stations used in the initial hypocenter location and on the quality of the P-wave onset. These events are relocated using a joint hypocenter-velocity-depth (JHVD) algorithm. The relocated earthquakes are separated geographically into three trends: ARK, the southwest trending zone from Caruthersville, Missouri, to Marked Tree, Arkansas; DWM, the northeast trending zone from New Madrid to Charleston, Missouri; and CEN, the central, left-stepping offset zone from Ridgely, Tennessee, to New Madrid, Missouri. Vertical profiles taken along and across the ARK and DWM trends verify the strike and dip of dominantly strike slip motion on near vertical active faults along these trends. These results agree with previously determined composite focal mechanism solutions for these trends. No coherent picture has been obtained for the CEN trend. As a by-product of the study, velocity models from the JHVD inversion are found to be reasonably uniform throughout the New Madrid seismic zone, and to offer supporting evidence for the presence of a shallow low velocity zone in the central portion of the Mississippi embayment.

Mapping crustal structure of the Nechako–Chilcotin plateau using teleseismic receiver function analysis,

2014 ◽  
Vol 51 (4) ◽  
pp. 407-417 ◽  
Author(s):  
H.S. Kim ◽  
J.F. Cassidy ◽  
S.E. Dosso ◽  
H. Kao
Keyword(s):  
Wave Velocity ◽  
Crustal Structure ◽  
Velocity Structure ◽  
Receiver Function ◽  
Function Analysis ◽  
Crustal Thickness ◽  
Receiver Functions ◽  
S Wave ◽  
Low Velocity ◽  
Velocity Models

This paper presents results of a passive-source seismic mapping study in the Nechako–Chilcotin plateau of central British Columbia, with the ultimate goal of contributing to assessments of hydrocarbon and mineral potential of the region. For the present study, an array of nine seismic stations was deployed in 2006–2007 to sample a wide area of the Nechako–Chilcotin plateau. The specific goal was to map the thickness of the sediments and volcanic cover, and the overall crustal thickness and structural geometry beneath the study area. This study utilizes recordings of about 40 distant earthquakes from 2006 to 2008 to calculate receiver functions, and constructs S-wave velocity models for each station using the Neighbourhood Algorithm inversion. The surface sediments are found to range in thickness from about 0.8 to 2.7 km, and the underlying volcanic layer from 1.8 to 4.7 km. Both sediments and volcanic cover are thickest in the central portion of the study area. The crustal thickness ranges from 22 to 36 km, with an average crustal thickness of about 30–34 km. A consistent feature observed in this study is a low-velocity zone at the base of the crust. This study complements other recent studies in this area, including active-source seismic studies and magnetotelluric measurements, by providing site-specific images of the crustal structure down to the Moho and detailed constraints on the S-wave velocity structure.

P-wave velocity structure of the Earth's crust beneath Vancouver Island

1983 ◽  
Vol 20 (5) ◽  
pp. 742-752 ◽  
Author(s):  
George A. McMechan ◽  
George D. Spence
Keyword(s):  
Velocity Structure ◽  
General Structure ◽  
Vertical Component ◽  
Vancouver Island ◽  
P Wave ◽  
Low Velocity ◽  
Velocity Anomaly ◽  
P Wave Velocity ◽  
Refraction Data ◽  
Velocity Zone

Refraction data were recorded from three shot points out to a maximum distance of ~330 km as part of the 1980 Vancouver Island Seismic Project (VISP80). These vertical component data are partially reversed and so can be interpreted in terms of two-dimensional structures by iterative modeling of P-wave travel times and amplitudes. The structure of the upper crust is the best constrained part of the model. It consists, generally, of a gradually increasing velocity from ~5.3 km/s at the surface to ~6.4 km/s at 2 km depth to ~6.75 km/s at 15.5 km depth, where the velocity increases sharply to ~7 km/s. Below ~20 km depth, the model becomes speculative because the data provide only indirect constraints on velocities at these depths. An interpretation that fits the observed times and amplitudes has a low velocity zone in the lower crust and a Moho at 37 km depth. The only significant departure from this general structure is beneath the central part of Vancouver Island where the 15.5 km boundary in the model attains a depth of ~23 km, below which there appears to be a local high velocity anomaly.

scholarly journals Preliminary Results of Regional P and S Wave Tomography at Seram, Indonesia

2021 ◽  
Vol 873 (1) ◽  
pp. 012066
Author(s):  
P A Subakti ◽  
M I Sulaiman ◽  
D Y Faimah ◽  
I Madrinovella ◽  
I Herawati ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Shallow Depth ◽  
Double Difference ◽  
S Wave ◽  
Low Velocity ◽  
Seismicity Pattern ◽  
Velocity Models ◽  
Event Distribution ◽  
Wave Tomography ◽  
Subduction System

Abstract The Seram Trough is located in the northern part of Indonesia and has a complex tectonic setting. The uniqueness of these regions lies in the U-shape subduction system. Several models have been proposed in this region, such as one subduction system that has been rotated 90° or 180°, two subduction systems, and one subduction that having a slab roll-back that causes extension systems. In this study, we try to invert velocity and seismicity using double-difference tomography with the target of better imaging the sub-surface structure in the region. We use data catalogue collection from the Indonesian Agency of Meteorology, Climatology, and Geophysics. The length of data is 4 years from January 2015 to December 2019 from 16 permanent stations. Earthquake relocations show a focused hypocenter distribution at shallow depth, and we interpreted some of these shallow depth events are related to the magmatic activity. Event distribution also displays a steep angle of seismicity pattern that represents the dipping subduction slab. Inverted Tomography models show a band of faster velocity models that dip from North to South, suggesting a subductions slab. We also observe a possibility of a tear in the slab from the seismicity pattern and tomogram model. The slower velocity perturbation is seen at shallow depth that may associate with magmatic and frequent shallow seismicity. A possibility of partial melting is also seen with low-velocity zone at a depth of 70 km next to the fast dipping velocity.

scholarly journals Comparison of P-Wave Tomography Model in Sunda-Banda Arc by Using Data from BMKG and ISC

2021 ◽  
Vol 873 (1) ◽  
pp. 012058
Author(s):  
P T Brilianti ◽  
M S Haq ◽  
Haolia ◽  
M I Sulaiman ◽  
R P Nugroho ◽  
...  
Keyword(s):  
Delay Time ◽  
Tectonic Setting ◽  
Depth Estimation ◽  
P Wave ◽  
Eurasian Plate ◽  
Low Velocity ◽  
Data Set ◽  
Local Agency ◽  
Eastern Area ◽  
Shallow Part

Abstract The tectonic setting of our study area is located between the Island of Java and Timor Leste. The complexity of this region is started with two different plates, The Indo-Australian plate and the Eurasian plate that move with different orientations and convergence rate. This area also shows active seismic activity and has a series of active volcanoes as a product of subduction and collision. To deepen understand this area, we perform delay time tomography using FMTOMO package that includes 3-D finite-difference based ray tracing and sub-space inversion procedure. We used two different sets of data, the first one is 4 years data catalog from the Indonesian Agency of Meteorology, Climatology and Geophysics, and the second one is 47 years of data from the International Seismological Centre. Data from the local Indonesian show agency shows a fewer number of events but more focus clusters. Meanwhile, the data from ISC catalog has more events and evenly distributed data. However, we also noticed that data from ISC has cluster events located at the same depth that can be improved with events relocation for better depth estimation. The Checkerboard models from both data set show a comparable result, though data from ISC show a better recovered model at a deeper depth and shallow part in the eastern area. The checkerboard from the local Agency shows slightly better results in the shallow part. Next, we invert delay time for each data set using we optimized damping and smoothing parameters. Final tomogram models show that data from the local Agency show a more continuous fast velocity band representing a downgoing subducting slab and possible back-arc thrust while results from the ISC data show a more detached fast velocity band that could be contributed from fixed depth problem in the data set. However, we noticed that data from ISC show a higher amplitude low-velocity anomaly especially in the shallow depth

Crustal Structure and Earthquakes beneath the Jammu and Kashmir Himalaya

2020 ◽  
Author(s):  
Supriyo Mitra ◽  
Swati Sharma ◽  
Debarchan Powali ◽  
Keith Priestley ◽  
Sunil Wanchoo
Keyword(s):  
Seismic Velocity ◽  
Receiver Function ◽  
Joint Inversion ◽  
P Wave ◽  
Kashmir Valley ◽  
Low Velocity ◽  
Surface Wave Dispersion ◽  
Jammu And Kashmir ◽  
Moderate Earthquake ◽  
Tethyan Himalaya

<p align="justify"><span>We use P-wave receiver function (P-RF) analysis of broadband teleseismic data recorded at twenty two stations spanning the Jammu-Kishtwar Himalaya, Pir Panjal Ranges, Kashmir Valley, and Zanskar Ranges in Northwest Himalaya to model the seismic velocity structures of the crust and the uppermost mantle. Our network extends from the Shiwalik Himalaya (S) to the Tethyan Himalaya (N), across the major Himalayan thrust systems and litho-tectonic units. We perform Vp/Vs-Depth stacking of P-RF and joint inversion with surface wave dispersion data. Our analysis show that the underthrust Indian crust, beneath the Jammu-Kishtwar Himalaya, has an average thickness of ~40 km and dips northward at ~7-9º. The overlying Himalayan wedge increases in thickness northward from the Shiwalik Himalaya (~8–10 km) to the Tethyan Himalaya (~25–30 km). The underthrust Indian crust Moho is marked by a large positive impedance contrast and lies at a depth of ~45 km beneath the Shiwalik Himalaya and ~65 km beneath the Higher Himalaya, deepening northward beneath the Tethyan Himalaya. We observe Moho flexure across the Mandli-Kishanpur Thrust (MKT), in the Shiwalik Himalaya, and beneath the Kishtwar window. Each time to Moho deepens by ~10 km, from ~45 km to ~55 km, and from ~55 km to ~65 km, respectively. The Moho is remarkably flat at ~56 km beneath the Pir Panjal Ranges, from its southern foothills to the northern flank in the Kashmir Valley. North of the Kashmir Valley the Moho dips steeply underneath the Zanskar Ranges from ~56 km to ~62 km. Along the Jammu-Kishtwar common conversion point (CCP) profile the Main Himalayan Thrust (MHT) is highlighted by the low velocity layer (LVL) at a depth of ~8 km beneath the Shiwalik Himalaya to ~25 km beneath the Higher Himalaya. The average dip on the MHT is ~9º and has a frontal ramp beneath the Kishtwar window. The MKT, MBT and MCT are marked by LVLs which splays updip from the MHT. Average crustal Vp/Vs shows that beneath the Shiwalik Himalaya, west of the MFT anticline the crust is mafic in nature while towards the east the crust is felsic in nature. Beneath the Lesser Himalaya the crust is largely felsic, while beneath the Pir Panjal range the crust is intermediate to mafic. North of the Kashmir Valley, beneath the Zanskar range the crust is felsic to intermediate in nature. We compare the source mechanism of the 2013 Kishtwar earthquake (Mw 5.7) and hypocentral location of small-to-moderate earthquake beneath Kishtwar region with the CCP profile. Our results show that these earthquakes occurred on or above the MHT in the unlocking zone, between the frictionally locked shallow segment and deeper creeping segment of the MHT. This marks the zone of stress build-up on the MHT in the interseismic period and is possibly the zone of megathrust initiation.</span></p>

Magma accumulation beneath Santorini volcano, Greece, from P-wave tomography

Geology ◽  
2019 ◽  
Vol 48 (3) ◽  
pp. 231-235 ◽  
Author(s):  
B.G. McVey ◽  
E.E.E. Hooft ◽  
B.A. Heath ◽  
D.R. Toomey ◽  
M. Paulatto ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Seismic Attenuation ◽  
P Wave ◽  
Structural Constraints ◽  
Low Velocity ◽  
Magma Body ◽  
Velocity Anomaly ◽  
Velocity Models ◽  
Santorini Volcano ◽  
Ray Bending

Abstract Despite multidisciplinary evidence for crustal magma accumulation below Santorini volcano, Greece, the structure and melt content of the shallow magmatic system remain poorly constrained. We use three-dimensional (3-D) velocity models from tomographic inversions of active-source seismic P-wave travel times to identify a pronounced low-velocity anomaly (–21%) from 2.8 km to 5 km depth localized below the northern caldera basin. This anomaly is consistent with depth estimates of pre-eruptive storage and a recent inflation episode, supporting the interpretation of a shallow magma body that causes seismic attenuation and ray bending. A suite of synthetic tests shows that the geometry is well recovered while a range of melt contents (4%–13% to fully molten) are allowable. A thin mush region (2%–7% to 3%–10% melt) extends from the main magma body toward the northeast, observed as low velocities confined by tectono-magmatic lineaments. This anomaly terminates northwest of Kolumbo; little to no melt underlies the seamount from 3 to 5 km depth. These structural constraints suggest that crustal extension and edifice loads control the geometry of magma accumulation and emphasize that the shallow crust remains conducive to melt storage shortly after a caldera-forming eruption.

Seismic velocity models for heat zones in Athabasca tar sands

Geophysics ◽  
1990 ◽  
Vol 55 (8) ◽  
pp. 1108-1112 ◽  
Author(s):  
Larry R. Lines ◽  
Ronald Jackson ◽  
James D. Covey
Keyword(s):  
Seismic Velocity ◽  
Three Dimensional ◽  
Velocity Model ◽  
Steam Injection ◽  
P Wave ◽  
Injection Velocity ◽  
Low Velocity ◽  
Borehole Data ◽  
Tar Sands ◽  
Velocity Models

Recent laboratory and field studies indicate that the P-wave velocity in Athabasca tar sands decreases when temperature increases during steam injection. In this paper we derive time variant velocity models from seismic traveltime inversions of both reflection and borehole data. Prior to steam injection, three‐dimensional (3-D) reflector velocity‐depth models are established using image‐ray conversions of traveltimes to depth. The changes in velocity due to steam injection are modeled by inverting traveltime data from seismic monitor surveys after steam injection and comparing these results to velocities computed prior to steam injection. Velocity models are essentially determined by traveltimes from the 3-D seismic reflection survey. The surface‐to‐wellbore data traveltimes show the expected delay caused by steam injection but do not significantly alter the velocity model produced by reflection traveltimes. For seismic monitor surveys, low‐velocity zones show a very good correlation with zones of temperature increase at injector well positions. The results indicate that velocity models obtained from seismic traveltimes may prove useful in detecting steam fronts in tar sands.

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