scholarly journals Preliminary Model of P-Wave Tomography Beneath Central Java using FMTOMO

2021 ◽  
Vol 873 (1) ◽  
pp. 012064
Author(s):  
M Yasir ◽  
P T Brilianti ◽  
S S Angkasa ◽  
S Widyanti ◽  
I Herawati ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
P Wave ◽  
Benioff Zone ◽  
Good Resolution ◽  
Ocean Bottom Seismometer ◽  
Low Velocity ◽  
Fast Marching ◽  
Megathrust Earthquakes ◽  
Central Java ◽  
Wave Tomography

Abstract The tectonic setting of Java Island is mainly controlled by the collision of Indo-Australian plate subducting the Eurasian plate. The high collision activity of Eurasian and Indo-Australian plates often causes megathrust earthquakes and the rise of arc magmatism that includes volcanic eruption. This study aims to determine the tectonic pattern beneath Central Java based on P-wave tomography inversion. We used the fast-marching method as ray tracing and subspace inversion to image subsurface velocity model to a depth of 150 km. The data used in this study are catalogue events data derived from a temporary seismometer network MERAMEX installed around central Java and DOMERAPI installed surround Mt. Merapi and Mt. Merbabu. We also include events collected from the International Seismological Centre. In total, we processed 563 earthquake events to illustrate velocity structures under central Java. The checker-board model shows that good resolutions can be identified at shallow depth, including offshore south Java contributed from Ocean Bottom Seismometer data. In vertical axis, good resolution models can be expected down to a depth 150 km following rich events from the Benioff zone. Current P wave model show a distinct low velocity zone under Mt Merapi that can be seen down to a depth of 40 km, suggesting a possible separated deep magma reservoir. To the south of Mt Merapi area also shows a low-velocity band that may be related with the southern mountain arc. Additionally, the northern part of Mt. Merapi displays a band of strong low-velocity anomaly to the East and West with the anomaly in the Eastern Part seems to have a deeper extension to a depth of ~50 km. We related this anomaly with Merapi Lawu Anomaly and Kendeng basin. Our results show a similar result with the previous tomography models in this region.

scholarly journals Preliminary Results of Double Difference Tomography at Sunda-Banda Arc

2021 ◽  
Vol 873 (1) ◽  
pp. 012067
Author(s):  
Haolia ◽  
M. I. Sulaiman ◽  
P. T. Brilianti ◽  
R. P. Nugroho ◽  
I. Madrinovella ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Active Volcano ◽  
P Wave ◽  
Double Difference ◽  
Benioff Zone ◽  
Good Resolution ◽  
S Wave ◽  
Low Velocity ◽  
The North ◽  
Banda Arc

Abstract The Sunda-Arc transition to the Banda Arc is located on the south of the Flores Island, Indonesia, where the Australian lithosphere is moving to the north direction. On-going subduction process dictates the tectonic setting though some studies also suggest a collision and obduction may occur in the past due to of plate buoyancy. This area has active seismicity with frequent large magnitude events. To better understand the tectonic system in this region, we performed double-difference tomography inversion using regional events. We obtained the data catalog from the Indonesian Agency of Meteorology, Climatology, and Geophysics ranging from 116° to 125° east longitude and -6.5° to 12.5° latitude. We collected 4312 events data, detected from 15 stations from January 2015 to December 2019. Final relocated hypocenters showed a reduced fixed-depth problem and a more clustered event, although some deep events disappear. Most events are related to the subducting Benioff zone with some clustered events in the northern area may be related to back-arc thrust. We also observed clustered events near active volcano region and reduced shallow seismicity region to the west of the Timor Island. Resolution test using the checkerboard and Derivative weigh Sum (DWS) shows that fair P wave resolution can be achieved until 300 km, although a smearing start to show at a deeper depth. However, due to lack of arrival S wave data, the resolution test suggest good resolution can only be seen until a depth of 100 km. Tomogram P and S wave models show a clear dipping subducting slab from south to North down to a 250 km. We also spot a fast velocity band near the Timor Island area that similar to the previous tomography study, interpreted as sliver forearm. We spotted a band of lower Vp, lower Vs and higher Vp/Vs at shallow depth close to the volcanic line and we interpreted this as a zone of higher temperature, that may relate to magmatic activity in this region. We also noticed a zone of low velocity and higher Vp/Vs that may relate with dehydration and partial melting. However, we feel this still uncertain due to low Vs resolution.

scholarly journals Initial Result of P Wave Tomography Model in Sunda-Banda Arc Transition using FMTOMO

2021 ◽  
Vol 873 (1) ◽  
pp. 012057
Author(s):  
P T Brilianti ◽  
Haolia ◽  
M I Sulaiman ◽  
S S Angkasa ◽  
S Widyanti ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Tectonic Setting ◽  
Shallow Depth ◽  
P Wave ◽  
Benioff Zone ◽  
Target Area ◽  
Fast Marching Method ◽  
Eurasian Plate ◽  
Fast Marching ◽  
Banda Arc

Abstract Our study area is located near island Sumbawa, Sumba, Flores, West Timor, Indonesia and East Timor, popularly known as Sunda-Banda arc transition zone. The tectonic setting is mainly controlled by the movement of the oceanic lithosphere Indo-Australian plate subducting the Eurasian plate and Northward migration of Australian continental lithosphere into western Banda-arc in the region of Flores, Sumba and Timor island. We tried to image velocity structure beneath these regions using regional events and tomography inversion model. We collected 5 years of regional events from the Indonesian Agency of Meteorology, Climatology and Geophysics. In total, we reserved 3186 events recorded on 29 stations. For data processing, we used fast marching method as ray tracing between sources and receiver. We then employed subspace inversion as the tomography procedure to estimate the best velocity model representing the tectonic model in the region. Hypocenter data distribution is concentrated on shallow parts of the region and along the Benioff zone down to a maximum depth of 400 km. One of challenge of this study is that although events are abundance, the stations used are mostly located onshore and does not extend in the south-north direction that leads us to under determined problem in the inversion process. However, checker-board models show most our target area can be retrieved to its initial model with sign of smearing effects shown start from a depth of 50 km. After six iteration and optimized selection of damping and smoothing parameters, we observed low velocity anomaly under Bali, Lombok, Sumba, East Nusa Tenggara at shallow depth that may be related with volcanic activity. Deeper low anomaly can also be seen that may be related with partial melting process. A band of fast velocity is clearly seen that goes deepen to the north depicting subducting slabs own to a depth of 300 km. We also observed a possible of fast velocity in the northern part of our stations at shallow depth that we believe may represent the back arc thrust.

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 POLENET/LAPNET teleseismic <i>P</i> wave travel time tomography model of the upper mantle beneath northern Fennoscandia

Solid Earth ◽  
2016 ◽  
Vol 7 (2) ◽  
pp. 425-439 ◽  
Author(s):  
Hanna Silvennoinen ◽  
Elena Kozlovskaya ◽  
Eduard Kissling
Keyword(s):  
Upper Mantle ◽  
Fennoscandian Shield ◽  
P Wave ◽  
Significant Feature ◽  
Depth Range ◽  
Low Velocity ◽  
Lateral Velocity ◽  
International Polar Year ◽  
Northern Fennoscandia ◽  
Wave Tomography

Abstract. The POLENET/LAPNET (Polar Earth Observing Network) broadband seismic network was deployed in northern Fennoscandia (Finland, Sweden, Norway, and Russia) during the third International Polar Year 2007–2009. The array consisted of roughly 60 seismic stations. In our study, we estimate the 3-D architecture of the upper mantle beneath the northern Fennoscandian Shield using high-resolution teleseismic P wave tomography. The P wave tomography method can complement previous studies in the area by efficiently mapping lateral velocity variations in the mantle. For this purpose 111 clearly recorded teleseismic events were selected and the data from the stations hand-picked and analysed. Our study reveals a highly heterogeneous lithospheric mantle beneath the northern Fennoscandian Shield though without any large high P wave velocity area that may indicate the presence of thick depleted lithospheric “keel”. The most significant feature seen in the velocity model is a large elongated negative velocity anomaly (up to −3.5 %) in depth range 100–150 km in the central part of our study area that can be followed down to a depth of 200 km in some local areas. This low-velocity area separates three high-velocity regions corresponding to the cratonic units forming the area.

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

3D shear velocity structure of the northwestern South America-Caribbean Subduction Zone from ambient noise and ballistic Rayleigh wave tomography

2021 ◽  
Author(s):  
Wenpei Miao ◽  
John Cornthwaite ◽  
Alan Levander ◽  
Fenglin Niu ◽  
Michael Schmitz ◽  
...  
Keyword(s):  
South America ◽  
Rayleigh Wave ◽  
Ambient Noise ◽  
Crustal Thickness ◽  
P Wave ◽  
Moho Depth ◽  
Good Resolution ◽  
Phase Velocities ◽  
Maracaibo Basin ◽  
Wave Tomography

&lt;p&gt;The Caribbean plate (CAR) collided with and initiated subduction beneath northwestern South America (SA) at about 60-55 Ma. Since the onset of subduction, it has formed the Lara nappes and subsequently the Laramide-style uplifts of the Merida Andes, Sierra de la Perija and Santa Marta ranges, with maximum elevations &gt; 5km. The triangular Maracaibo block, bounded by the Santa Marta-Bucaramanga, Bocono and Oca-Ancon Faults, is currently escaping to the north relative to SA over both the subducting and nonsubducting elements of the CAR plate.&lt;/p&gt;&lt;p&gt;Although many petroleum related seismic studies have been done in this area, the details of the subduction geometry of the CAR plate beneath the Maracaibo block remain unclear. The few deeper seismic investigations are either very large scale, very local, or only peripheral to this area. Previous geodetic studies have suggested that this region has potential for a great (M~8+) earthquake (Bilham and Mencin, 2013). To investigate this complex region we fielded a 65 element broadband seismic array to complement the 48 existing stations of the Colombian and Venezuelan national seismic networks. The array is collectively referred to as the CARMArray.&lt;/p&gt;&lt;p&gt;In this study, we jointly inverted ambient noise Rayleigh wave Z/H ratios, phase velocities in the 8-30s band and ballistic Rayleigh wave phase velocities in 30-80s band to construct a 3D S-wave velocity model in the area from 75&lt;sup&gt;o&lt;/sup&gt;-65&lt;sup&gt;o&lt;/sup&gt; west and 5&lt;sup&gt;o&lt;/sup&gt;-12&lt;sup&gt;o&lt;/sup&gt; north. Rayleigh wave Z/H ratios are sensitive to the shallow sedimentary structure, while the phase velocity data have good resolution of the crust and upper mantle. The Vs model shows strong low-velocity anomalies beneath the Barinas-Apure and Maracaibo Basins, and the Paraguana Peninsula that are well correlated with surface geology. Sediment thickness beneath the Maracaibo basin reaches up to ~9 km depth, consistent with previous studies (Kellogg &amp; Bonini, 1982). Crustal thickness beneath the Santa Marta uplift is 27-30 km, shallow for its nearly 4km elevation. From the trench to the southeast, Moho depth increases from 25-30 km near the coast to 40-45 km beneath the Maracaibo Basin, with the thickest crust, ~50 km, lying under the Merida Andes beneath the Bocono Fault. Crustal thickness decreases under the Venezeulan interior to ~45 km. From 50km to 150km depth, the CAR plate shows ~2% high Vs anomalies beneath the Santa Marta uplift and the Serrania de Perija range. Our slab image matches local slab seismicity very well (Cornthwaite et al., EGU 2021 GD7.1), and is consistent with and complements images from teleseismic P-wave tomography (Cornthwaite et al, 2021, submitted).&lt;/p&gt;

scholarly journals Evidence of stretching of the lithosphere under Denmark

2008 ◽  
Vol 15 ◽  
pp. 53-56
Author(s):  
Søren Gregersen ◽  
Lene Vandur Nielsen ◽  
Peter Voss
Keyword(s):  
Field Work ◽  
P Wave ◽  
Depth Interval ◽  
Low Velocity ◽  
Teleseismic Tomography ◽  
The North ◽  
Crystalline Crust ◽  
Wave Tomography ◽  
National Boundaries ◽  
The Many

The structure of the lithosphere under Denmark has been investigated in relation to adjacent regions of Sweden and Germany. The most interesting result of the study is that the 120 km thick lithosphere under Denmark appears to be a stretched version of the Swedish lithosphere, which is more than twice as thick. During the international project Tele seismic Tomography across the Tornquist Zone (Tor), field work and international interpretation were carried out between 1996 and 2002. Following the field work period, modelvelocity computations were undertaken based on ob ser vations of distant earthquakes (e.g. Arlitt 1999; Shomali et al. 2002; Voss et al. 2006), and recently an evaluation of the Tor results was completed (Nielsen 2007). The Tor project investigates deeper parts of the Earth than previous projects, and in particular the depth interval 50–300 km, which is below the crystalline crust. The investigations have included many geophysical features such as teleseismic P-wave tomography, Rayleigh wave velocities, shear wave splitting and wave scattering. We have distinguished between relatively high- and low-velocity zones, which also show variations in anisotropy and scatter characteristics. Generalised high-velocity zones correspond to the lithosphere, while generalised relatively low-velocity zones are equivalent to the asthenosphere. The main outcome of the combined studies is that the deep lithosphere can be divided into three blocks separated approximately along the national boundaries between Sweden and Denmark and between Denmark and Germany. The boundaries between the blocks are steep, almost vertical. The Denmark block has lithosphere properties between those to the north and south. Based on previous crustal studies and the Tor results, we suggest that the Denmark block has evolved by stretching. The details in the new evaluation are derived from teleseismic tomography. Here we present a synthesis of the many derived models in the light of the new evaluation.

scholarly journals No mafic layer in 80 km thick Tibetan crust

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Gaochun Wang ◽  
Hans Thybo ◽  
Irina M. Artemieva
Keyword(s):  
Seismic Data ◽  
P Wave ◽  
Indian Plate ◽  
Low Velocity ◽  
Crustal Earthquakes ◽  
Tectonic Processes ◽  
P Wave Velocity ◽  
Juvenile Crust ◽  
Mafic Lower Crust ◽  
Thick Crust

AbstractAll models of the magmatic and plate tectonic processes that create continental crust predict the presence of a mafic lower crust. Earlier proposed crustal doubling in Tibet and the Himalayas by underthrusting of the Indian plate requires the presence of a mafic layer with high seismic P-wave velocity (Vp > 7.0 km/s) above the Moho. Our new seismic data demonstrates that some of the thickest crust on Earth in the middle Lhasa Terrane has exceptionally low velocity (Vp < 6.7 km/s) throughout the whole 80 km thick crust. Observed deep crustal earthquakes throughout the crustal column and thick lithosphere from seismic tomography imply low temperature crust. Therefore, the whole crust must consist of felsic rocks as any mafic layer would have high velocity unless the temperature of the crust were high. Our results form basis for alternative models for the formation of extremely thick juvenile crust with predominantly felsic composition in continental collision zones.

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