Early Results of Eastern Indonesia P-wave Tomography Study Using Regional Events

Abstract The tectonic system of Eastern Indonesia is controlled by several major and minor plates, such as Indo-Australian, Australian plate, and Pacific plates. This area is known for its complexity, and high seismic activity. This study tries to image the complex structures beneath this region by employing regional events data and seismic tomography methods. We used five years of regional events catalog provided by the Indonesian Agency of Meteorology, Climatology, and Geophysics. We have sorted 7336 events recorded between 120° – 136° longitude and 0° – 13°(-) latitude consisting of 46446 P and 15467 S wave arrival data. Relocated hypocenter map shows a better constrain location on seismicity along outer Bandar Arc. A dipping pattern of seismicity is seen that is going deeper to the Banda Sea. The seismicity map also images a steep angle pattern of seismicity that could be related to the subduction slab roll-back model at North of Wetar island. Interestingly, we spotted a seismicity gap in West Seram that could be linked with slab tear zone. The checker-board test suggests a proper resolution is still reliable to a depth of 200 km with a less interpretable model at a depth of 300 km. P-wave tomographic models image the high velocity dipping down going slab. The Banda slab is seen to subduct from south Timor Island to the north, from east Tanimbar and Aru Island to west part, and from north Seram Island to south. We observed the down-going slab meet from all directions at about 300 km beneath the Banda sea. P wave tomogram also shows the Timor Island slab has a steeper dip that agrees with the seismicity pattern. Near the Seram island, we identify a low-velocity anomaly zone infiltrate the Banda slab beneath the shallow part of West Seram, which was previously interpreted as slab tear zone. This study also noticed a higher velocity tomogram model at North of Wetar island that might indicate a back-arc thrust. Lastly, a low-velocity band is also exposed at a shallow depth close to the volcano chain along that Banda volcanic arc.

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Preliminary Results of Double Difference Tomography at Sunda-Banda Arc

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/873/1/012067 ◽

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.

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Adjoint traveltime tomography unravels a scenario of horizontal mantle flow beneath the North China craton

Scientific Reports ◽

10.1038/s41598-021-92048-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Xingpeng Dong ◽

Dinghui Yang ◽

Fenglin Niu ◽

Shaolin Liu ◽

Ping Tong

Keyword(s):

North China Craton ◽

Lithospheric Mantle ◽

North China ◽

Three Dimensional ◽

Mantle Flow ◽

S Wave ◽

Low Velocity ◽

Traveltime Tomography ◽

Velocity Anomaly ◽

The North

AbstractThe North China craton (NCC) was dominated by tectonic extension from late Cretaceous to Cenozoic, yet seismic studies on the relationship between crust extension and lithospheric mantle deformation are scarce. Here we present a three dimensional radially anisotropic model of NCC derived from adjoint traveltime tomography to address this issue. We find a prominent low S-wave velocity anomaly at lithospheric mantle depths beneath the Taihang Mountains, which extends eastward with a gradually decreasing amplitude. The horizontally elongated low-velocity anomaly is also featured by a distinctive positive radial anisotropy (VSH > VSV). Combining geodetic and other seismic measurements, we speculate the presence of a horizontal mantle flow beneath central and eastern NCC, which led to the extension of the overlying crust. We suggest that the rollback of Western Pacific slab likely played a pivotal role in generating the horizontal mantle flow at lithospheric depth beneath the central and eastern NCC.

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Wave-equation Traveltime Tomography Unravels a Scenario of Horizontal Mantle Flow Beneath the North China Craton

10.21203/rs.3.rs-250919/v1 ◽

2021 ◽

Author(s):

Xingpeng Dong ◽

Dinghui Yang ◽

Fenglin Niu ◽

Shaolin Liu ◽

Ping Tong

Keyword(s):

Wave Equation ◽

North China Craton ◽

Lithospheric Mantle ◽

North China ◽

Mantle Flow ◽

S Wave ◽

Low Velocity ◽

Traveltime Tomography ◽

Velocity Anomaly ◽

The North

Abstract The North China craton (NCC) was dominated by tectonic extension from late Cretaceous to Cenozoic, yet seismic studies on the relationship between crust extension and lithospheric mantle deformation are scarce. Here we present a three dimensional radially anisotropic model of NCC derived from wave-equation traveltime tomography to address this issue. We find a prominent low S-wave velocity anomaly at lithospheric mantle depths beneath the Taihang Mountains, which extends eastward with a gradually decreasing amplitude. The horizontally elongated low-velocity anomaly is also featured by a distinctive positive radial anisotropy (VSH>VSV). Combining geodetic and other seismic measurements, we speculate the presence of a horizontal mantle flow beneath central and eastern NCC, which led to the extension of the overlying crust. We suggest that the rollback of Western Pacific slab likely played a pivotal role in generating the horizontal mantle flow at lithospheric depth beneath the central and eastern NCC.

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Three-dimensional seismic structure of the lithosphere under Montana Lasa

Bulletin of the Seismological Society of America ◽

10.1785/bssa0660020501 ◽

1976 ◽

Vol 66 (2) ◽

pp. 501-524

Author(s):

Keiiti Aki ◽

Anders Christoffersson ◽

Eystein S. Husebye

Keyword(s):

Generalized Inverse ◽

Random Medium ◽

Three Dimensional ◽

P Wave ◽

Seismic Structure ◽

Low Velocity ◽

Medium Theory ◽

Velocity Anomaly ◽

Inversion Techniques ◽

Teleseismic Events

abstract Using P-wave residuals for teleseismic events observed at the Montana Large Aperture Seismic Array (LASA), we have determined the three-dimensional seismic structure of the lithosphere under the array to a depth of 140 km. The root-mean-square velocity fluctuation was found to be at least 3.2 per cent which may be compared to estimate of ca. 2 per cent based on the Chernov random medium theory. The solutions are given by both the generalized inverse and stochastic inverse methods in order to demonstrate the relative merit of different inversion techniques. The most conspicuous feature of the lithosphere under LASA is a low-velocity anomaly in the central and northeast part of the array siting area with the N60°E trend and persisting from the upper crust to depths greater than 100 km. We interpret this low-velocity anomaly as a zone of weakness caused by faulting and shearing associated with the building of the Rocky Mountains.

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Shear‐wave velocity and density estimation from PS-wave AVO analysis: Application to an OBS dataset from the North Sea

Geophysics ◽

10.1190/1.1444833 ◽

2000 ◽

Vol 65 (5) ◽

pp. 1446-1454 ◽

Cited By ~ 33

Author(s):

Side Jin ◽

G. Cambois ◽

C. Vuillermoz

Keyword(s):

Wave Velocity ◽

North Sea ◽

Random Noise ◽

P Wave ◽

S Wave ◽

Data Set ◽

Avo Analysis ◽

The North ◽

Avo Inversion ◽

The North Sea

S-wave velocity and density information is crucial for hydrocarbon detection, because they help in the discrimination of pore filling fluids. Unfortunately, these two parameters cannot be accurately resolved from conventional P-wave marine data. Recent developments in ocean‐bottom seismic (OBS) technology make it possible to acquire high quality S-wave data in marine environments. The use of (S)-waves for amplitude variation with offset (AVO) analysis can give better estimates of S-wave velocity and density contrasts. Like P-wave AVO, S-wave AVO is sensitive to various types of noise. We investigate numerically and analytically the sensitivity of AVO inversion to random noise and errors in angles of incidence. Synthetic examples show that random noise and angle errors can strongly bias the parameter estimation. The use of singular value decomposition offers a simple stabilization scheme to solve for the elastic parameters. The AVO inversion is applied to an OBS data set from the North Sea. Special prestack processing techniques are required for the success of S-wave AVO inversion. The derived S-wave velocity and density contrasts help in detecting the fluid contacts and delineating the extent of the reservoir sand.

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

Annals of Geophysics ◽

10.4401/ag-4042 ◽

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.

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The Australian Plate and underlying mantle from waveform tomography with massive datasets

10.5194/egusphere-egu21-5272 ◽

2021 ◽

Author(s):

Janneke de Laat ◽

Sergei Lebedev ◽

Bruna Chagas de Melo ◽

Nicolas Celli ◽

Raffaele Bonadio

Keyword(s):

Structural Information ◽

Azimuthal Anisotropy ◽

P Wave ◽

Depth Range ◽

S Wave ◽

Crust And Upper Mantle ◽

Southern Boundary ◽

Velocity Anomaly ◽

Australian Plate ◽

Australian Continent

We present a new S-wave velocity tomographic model of the Australian Plate, Aus21.&#160; It is constrained by waveforms of 0.9 million seismograms with both the corresponding sources and stations located within the half-hemisphere centred at the Australian continent. Waveform inversion extracts structural information from surface, S- and multiple S-waves on the seismograms in the form of a set of linear equations. These equations are then combined in a large linear system and inverted jointly to obtain a tomographic model of S- and P-wave speeds and S-wave azimuthal anisotropy of the crust and upper mantle. The model has been validated by resolution tests and, for particular locations in Australia with notable differences with previous models, by independent inter-station measurements of surface-wave phase velocities, which we performed using available array data.&#160;&#160;Aus21 offers new insights into the structure and evolution of the Australian Plate and its boundaries. The Australian cratonic lithosphere occupies nearly all of the western and central Australia but shows substantial lateral heterogeneity. It extends up to the northern edge of the plate, where it is colliding with island arcs, without subducting. The rugged eastern boundary of the cratonic lithosphere provides a lithospheric definition of the Tasman Line. The thin, warm lithosphere below the eastern part of the continent, east of the Tasman Line, underlies the Cenozoic volcanism locations in the area. The lithosphere is also thin and warm below much of the Tasman Sea, underlying the Lord Howe hotspot and the submerged part of western Zealandia. A low velocity anomaly that may indicate the single source of the Lord Howe and Tasmanid hotspots is observed in the transition zone offshore the Australian continent, possibly also sourcing the East Australia hotspot. Another potential hotspot source is identified below the Kermadec Trench, causing an apparent slab gap in the overlying slab and possibly related to the Samoa Hotspot to the north. Below a portion of the South East Indian Ridge (the southern boundary of the Australian Plate) a pronounced high velocity anomaly is present in the 200-400 km depth range just east of the Australian-Antarctic Discordance (AAD), probably linked to the evolution of this chaotic ridge system.

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Bayesian closed-skew Gaussian inversion of seismic AVO data for elastic material properties

Geophysics ◽

10.1190/1.3299291 ◽

2010 ◽

Vol 75 (1) ◽

pp. R1-R11 ◽

Cited By ~ 26

Author(s):

Omid Karimi ◽

Henning Omre ◽

Mohsen Mohammadzadeh

Keyword(s):

Elastic Material ◽

Material Properties ◽

P Wave ◽

S Wave ◽

High Dimensions ◽

Seismic Amplitude ◽

The North ◽

Avo Inversion ◽

Amplitude Versus Offset ◽

The North Sea

Bayesian closed-skew Gaussian inversion is defined as a generalization of traditional Bayesian Gaussian inversion, which is used frequently in seismic amplitude-versus-offset (AVO) inversion. The new model captures skewness in the variables of interest; hence, the posterior model for log-transformed elastic material properties given seismic AVO data might be a skew probability density function. The model is analytically tractable, and this makes it applicable in high-dimensional 3D inversion problems. Assessment of the posterior models in high dimensions requires numerical approximations, however. The Bayesian closed-skew Gaussian inversion approach has been applied on real elastic material properties from a well in the Sleipner field in the North Sea. A comparison with results from traditional Bayesian Gaussian inversion shows that the mean square error of predictions of P-wave and S-wave velocities are reduced by a factor of two, although somewhat less for density predictions.

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The impact of common‐offset migration on porosity estimation by AVO inversion

Geophysics ◽

10.1190/1.1444965 ◽

2001 ◽

Vol 66 (3) ◽

pp. 755-762 ◽

Cited By ~ 9

Author(s):

Arild Buland ◽

Martin Landrø

Keyword(s):

P Wave ◽

High Porosity ◽

S Wave ◽

Seismic Line ◽

Data Set ◽

The North ◽

Avo Inversion ◽

Time Migration ◽

The Impact ◽

Porosity Estimation

The impact of prestack time migration on porosity estimation has been tested on a 2-D seismic line from the Valhall/Hod area in the North Sea. Porosity is estimated in the Cretaceous chalk section in a two‐step procedure. First, P-wave and S-wave velocity and density are estimated by amplitude variation with offset (AVO) inversion. These parameters are then linked to porosity through a petrophysical rock data base based on core plug analysis. The porosity is estimated both from unmigrated and prestack migrated seismic data. For the migrated data set, a standard prestack Kirchhoff time migration is used, followed by simple angle and amplitude corrections. Compared to modern high‐cost, true amplitude migration methods, this approach is faster and more practical. The test line is structurally fairly simple, with a maximum dip of 5°; but the results differ significantly, depending on whether migration is applied prior to the inversion. The maximum difference in estimated porosity is of the order of 10% (about 50% relative change). High‐porosity zones estimated from the unmigrated data were not present on the porosity section estimated from the migrated data.

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An Awakening Magmatic System beneath the Udina Volcanic Complex (Kamchatka): Evidence from Seismic Unrest of 2017–2019

Russian Geology and Geophysics ◽

10.2113/rgg20194098 ◽

2021 ◽

Vol 62 (2) ◽

pp. 223-238

Author(s):

Yu.A. Kugaenko ◽

V.A. Saltykov ◽

I.Yu. Koulakov ◽

V.M. Pavlov ◽

P.V. Voropaev ◽

...

Keyword(s):

P Wave ◽

Volcanic Complex ◽

Earthquake Catalog ◽

Magmatic System ◽

S Wave ◽

Southeastern Part ◽

Velocity Anomaly ◽

Wave Velocities ◽

Magma Sources ◽

Kamchatka Earthquake

Abstract —The Udina volcanic complex located in the southeastern part of the Klyuchevskoy group of volcanoes in Kamchatka remained dormant for several thousand years, but the magmatic system beneath the area may be awakening judging by seismic unrest. Seismicity in the area is characterized by data from permanent regional seismic stations and campaign local stations, as well as by data of the Kamchatka earthquake catalog. Seismic activity having nucleated at shallow depths in the vicinities of the Udina volcanoes since October 2017 may reflect a beginning cycle of volcanism. The earthquakes are mainly long-period (LP) 0.5–5 Hz events, which are commonly attributed to the movement of viscous magma and resonance phenomena in magma conduits. Such earthquakes may be a response to inputs of new magma batches to the plumbing system that feeds the volcanoes and thus may be precursors of volcanic unrest. Seismic campaigns of May–July 2018 near the Udina complex provided more rigorous constraints on earthquake coordinates and origin depths and showed that most of the earthquakes originated within 5 km beneath the Bolshaya Udina Volcano. Seismic tomographic inversion using the LOTOS code revealed a zone of high P-wave velocities, low S-wave velocities, and a high vP/vS ratio directly beneath the volcano. Such a combination of parameters typically occurs in active volcanic areas and marks intrusion of partially molten magma and/or liquid fluids. The velocity anomaly detected in 2018 is shallower than that recovered in 2014–2015. The seismic evidence, along with the available geological and geophysical data, record the movement of viscous magma related to the Udina feeding system in the middle crust, which is implicit proof for connection between the intermediate crustal and deep mantle magma sources renewed after a long lull.

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