scholarly journals Travel Time Tomography to Delineate 3-D Regional Seismic Velocity Structure in the Banyumas Basin, Central Java, Indonesia, Using Dense Borehole Seismographic Stations

2021 ◽  
Vol 9 ◽  
Author(s):  
Hidayat Hidayat ◽  
Andri Dian Nugraha ◽  
Awali Priyono ◽  
Marjiyono Marjiyono ◽  
Januar H. Setiawan ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Crustal Layer ◽  
Central Java ◽  
Resolution Element ◽  
Passive Seismic ◽  
Dextral Strike Slip Fault ◽  
Southern Central ◽  
Well Data

The Banyumas Basin is a tertiary sedimentary basin located in southern Central Java, Indonesia. Due to the presence of volcanic deposits, 2-D seismic reflection methods cannot provide a good estimation of the sediment thickness and the subsurface geology structure in this area. In this study, the passive seismic tomography (PST) method was applied to image the 3-D subsurface Vp, Vs, and Vp/Vs ratio. We used 70 seismograph borehole stations with a recording duration of 177 days. A total of 354 events with 9, 370 P and 9, 368 S phases were used as input for tomographic inversion. The checkshot data of a 4, 400-meter deep exploration well (Jati-1) located within the seismic network were used to constrain the shallow crustal layer of the initial 1-D velocity model. The model resolution of the tomographic inversions was assessed using the checkerboard resolution test (CRT), the diagonal resolution element (DRE), and the derivative weight sum (DWS). Using the obtained Vp, Vs, and Vp/Vs ratio, we were able to sharpen details of the geological structures within the basin from previous geological studies, and a fault could be well-imaged at a depth of 4 km. We interpreted this as the main dextral strike-slip fault that controls the pull apart process of the Banyumas Basin. The thickness of the sediment layers, as well as its layering, were also could be well determined. We found prominent features of the velocity contrast that aligned very well with the boundary between the Halang and Rambatan formations as observed in the Jati-1 well data. Furthermore, an anticline structure, which is a potential structural trap for the petroleum system in the Banyumas Basin, was also well imaged. This was made possible due to the dense borehole seismographic stations which were deployed in the study area.

scholarly journals Seismic velocity model of the crust in the northern Canadian Cordillera from Rayleigh wave dispersion data

2017 ◽  
Vol 54 (2) ◽  
pp. 163-172 ◽  
Author(s):  
Shutian Ma ◽  
Pascal Audet
Keyword(s):  
Rayleigh Wave ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Group Velocity Dispersion ◽  
Velocity Model ◽  
Canadian Cordillera ◽  
Seismic Velocities ◽  
Crustal Layer ◽  
Velocity Models ◽  
Moderate Earthquake

Models of the seismic velocity structure of the crust in the seismically active northern Canadian Cordillera remain poorly constrained, despite their importance in the accurate location and characterization of regional earthquakes. On 29 August 2014, a moderate earthquake with magnitude 5.0, which generated high-quality Rayleigh wave data, occurred in the Northwest Territories, Canada, ∼100 km to the east of the Cordilleran Deformation Front. We carefully selected 23 seismic stations that recorded the Rayleigh waves and divided them into 13 groups according to the azimuth angle between the earthquake and the stations; these groups mostly sample the Cordillera. In each group, we measured Rayleigh wave group velocity dispersion, which we inverted for one-dimensional shear-wave velocity models of the crust. We thus obtained 13 models that consistently show low seismic velocities with respect to reference models, with a slow upper and lower crust surrounding a relatively fast mid crustal layer. The average of the 13 models is consistent with receiver function data in the central portion of the Cordillera. Finally, we compared earthquake locations determined by the Geological Survey of Canada using a simple homogenous crust over a mantle half space with those estimated using the new crustal velocity model, and show that estimates can differ by as much as 10 km.

scholarly journals Seismic Velocity Structure in the Area of the 2007, Mw 8.0, Pisco-Peru Earthquake: Implications for the Mechanics of Subduction in the Vicinity of the Nazca Ridge

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
I. Bernal ◽  
H. Tavera
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Double Difference ◽  
Seismic Velocity Structure ◽  
Uplift Rates ◽  
Northern Edge ◽  
Nazca Ridge ◽  
Geomorphological Features ◽  
Postseismic Slip

In this study, we present a velocity model for the area of the 2007 Pisco-Peru earthquake ( Mw = 8.0 ) obtained using a double-difference tomography algorithm that considers aftershocks acquired for 6 months. The studied area is particularly interesting because it lies on the northern edge of the Nazca Ridge, in which the subduction of a large bathymetric structure is the origin of geomorphological features of the central coast of Peru. Relocated seismicity is used to infer the geometry of the subduction slab on the northern flank of the Nazca Ridge. The results prove that the geometry is continuous but convex because of the subduction of the ridge, thereby explaining the high uplift rates observed in this area. Our inferred distribution of seismicity agrees with both the coseismic and postseismic slip distributions.

Shallow crustal structure of the continental margin off Nova Scotia

1983 ◽  
Vol 20 (11) ◽  
pp. 1657-1672 ◽  
Author(s):  
Thomas M. Brocher
Keyword(s):  
Nova Scotia ◽  
Velocity Structure ◽  
Velocity Model ◽  
Passive Margin ◽  
Ocean Bottom ◽  
Stoneley Waves ◽  
Unconsolidated Sand ◽  
Ocean Bottom Seismometers ◽  
Well Data ◽  
Sand And Gravel

The nature of the upper sediments of the shelf and slope on a passive margin was investigated by using high-quality refraction profiles recorded by ocean-bottom seismometers off Nova Scotia. In agreement with previously published reflection profiles, well data, and lithospheric models for the evolution of passive margins, we found little thickening of the post-Early Cretaceous section, implying an even sedimentation rate over the outer shelf for this time period. The velocity model determined from slant stacks agreed reasonably well with well-log data, but had velocities slightly lower than those found from a nearby refraction line using first-arrival travel-time methods. Starting at the sea floor the compressional velocity–depth model consists of a gradient of roughly 0.4 s−1 to a depth of about 1.25 km, followed by another gradient of roughly 1 s−1 to a depth of about 3.5 km. Beneath this depth the velocity gradient approaches zero and can be modelled as a constant velocity layer. Stoneley waves were used to investigate the velocity structure of the upper 260 m of the sediment column. These velocities cannot be measured in the oil wells located on the shelf by conventional 3.5 kHz echo sounders or by measuring the sonic velocities of sediments collected in piston cores. A thinning of the Pleistocene–Holocene Sable Island Sand and Gravel layer was documented by pronounced differences in the propagation of Stoneley waves across the shelf. Although the origin of the thinning is uncertain, the shear-wave velocity determined for this unit, 260 m/s, is appropriate for an unconsolidated sand.

scholarly journals An Investigation of Seismic Velocity Variation through a Tectonic Boundaries-Case Study in Central Iraq

2021 ◽  
pp. 2614-2626
Author(s):  
Ahmed S. AL-Banna ◽  
Hassan E. Al-Assady
Keyword(s):  
High Velocity ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Seismic Inversion ◽  
Velocity Variation ◽  
Time Model ◽  
3D Velocity Model ◽  
Western Side ◽  
Well Data ◽  
Seismic Lines

      A 3D velocity model was created by using stacking velocity of 9 seismic lines and average velocity of 6 wells drilled in Iraq. The model was achieved by creating a time model to 25 surfaces with an interval time between each two successive surfaces of about 100 msec.  The summation time of all surfaces reached about 2400 msec, that was adopted according to West Kifl-1 well, which penetrated to a depth of 6000 m, representing the deepest well in the study area. The seismic lines and well data were converted to build a 3D cube time model and the velocity was spread on the model. The seismic inversion modeling of the elastic properties of the horizon and well data was applied to achieve a corrected velocity cube. Then, the velocity cube was converted to a time model and, finally, a corrected 3D depth model was obtained. This model shows that the western side of the study area, which is a part of the stable shelf, is characterized by relatively low thickness and high velocity layers. While the eastern side of the study area, which is a part of the Mesopotamian, is characterized by high thickness and low velocity of the Cretaceous succession. The Abu Jir fault is considered as a boundary between the stable and unstable shelves in Iraq, situated at the extreme west part of the study area. The area of relatively high velocity gradient is considered as the limit of the western side of the Mesopotamian basin. This area extends from Najaf-Karbala axis in the west to the Euphrates River in the east. It is found that the 3D stacking velocity model can be used to obtain good results concerning the tectonic boundary.  

scholarly journals One dimensional seismic velocity structure beneath Western Nepal

2002 ◽  
Vol 27 ◽  
Author(s):  
S. Rajaure
Keyword(s):  
Arrival Time ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Compressional Wave ◽  
S Wave ◽  
Time Data ◽  
Seismic Velocity Structure ◽  
One Dimensional ◽  
Wave Velocities

An attempt has been made to study the velocity structure of western Nepal. Arrival time data of local earthquakes occurring in that region were used to derive the model. A three layered velocity model both for the P- as well as S-wave velocity has been estimated. The compressional wave velocities in the first, second and the third layers have been estimated to be 5.53 km/sec. 6.29 km/sec and 8.13 km/sec respectively. Similarly the corresponding S-wave velocities are 3.18, 3.62, 4.66 km/sec respectively. The model for the Western Nepal and that for the Centre-East Nepal are almost same. The crust and the mantle beneath west and center-east are homogeneous.

Seismic tomography at a fire‐flood site

Geophysics ◽  
1989 ◽  
Vol 54 (9) ◽  
pp. 1082-1090 ◽  
Author(s):  
N. D. Bregman ◽  
P. A. Hurley ◽  
G. F. West
Keyword(s):  
Oil Recovery ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Pilot Project ◽  
Velocity Model ◽  
High Amplitude ◽  
Oil Sand ◽  
Low Velocity ◽  
Study Region ◽  
Velocity Channel

A crosshole seismic experiment was conducted to locate and characterize a firefront at an enhanced oil recovery (EOR) pilot project. The reservoir engineers involved in the project were interested in finding out why the burnfront apparently had stalled between two wells 51 m apart. In a noisy producing environment, good quality seismic data were recorded at depths ranging from 710 to 770 m. The frequency range of the data, 500 to 1500 Hz, allows resolution of the velocity structure on a scale of several meters. The moveout of first arrivals indicates that there are large velocity variations in the study region; a high‐amplitude, late arriving channel wave points to the existence of a low‐velocity channel connecting the boreholes. Using an iterative, nonlinear scheme which incorporates curved ray tracing and least‐squares inversion in each iteration, the first‐arrival times were inverted to obtain a two‐dimensional model of the compressional seismic velocity between the boreholes. The velocities range from 1.5 km/s to 3.2 km/s, with a low‐velocity channel at the depth of the producing oil sand. Sonic, core, and temperature logs lead us to conclude that the extremely low velocities in the model are probably due to gases produced by the burn. Increased velocities in an adjacent shale may be a secondary effect of the burn. The velocity model also indicates an irregularity in the topography at the bottom of the reservoir, an irregularity which may be responsible for blocking the progress of the burnfront.

Seismic velocity structure and event relocation in Kazakhstan from secondary P phases

1992 ◽  
Vol 82 (6) ◽  
pp. 2494-2510
Author(s):  
H. R. Quin ◽  
C. H. Thurber
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Epicentral Distance ◽  
Focal Depth ◽  
Velocity Model ◽  
P Wave ◽  
Secondary Phases ◽  
Arrival Times ◽  
Event Location ◽  
Reflectivity Method

Abstract Three-component seismic data from a set of presumed explosions recorded by stations at Bayanaul and Karkaralinsk in Kazakhstan were analyzed in order to model the crustal structure of the region and to examine the use of the arrival times of secondary P phases, primarily PmP, in regional event location. Polarization analysis aided in the identification of the secondary phases. Low-pass filtered data (4-Hz corner) from the first 5 to 10 sec of 13 presumed explosions were modeled with the reflectivity method. The two chemical explosions in 1987 provided a check on accuracy, as their locations and origin times are accurately known. A good fit to the arrival times and amplitudes in the first 5 sec of the P wave (Pn, Pg, and PmP) was obtained in the epicentral distance range of 100 to 300 km. Beyond 300 km, the simple layered model was not adequate to model the PmP arrival. The crustal P-wave velocity model we derived has an upper crustal velocity increasing fairly rapidly from 4.5 km/sec near the surface to 6.5 km/sec at 15-km depth, then increasing more slowly to 7.05 km/sec at 50-km depth. The observed difference in the arrival times of the phases Pg, PmP, and Pn in the range between 100- and 250-km distance required a relatively sharp transition at the crust mantle boundary. The model is generally similar to previous estimates of P velocity structure in the region, though with a gentler gradient in the upper crust and a steeper gradient in the lower crust. We used the derived crustal model and the primary and secondary P-wave arrival times to relocate events in the Kazakhstan region. Inclusion of the phase PmP substantially decreases the focal depth uncertainty for many of the events. All but one of the events analyzed are concluded to be surface explosions; the identity of the remaining event is uncertain.

Crustal velocity structure across the Orphan Basin and Orphan Knoll to the continent–ocean transition, offshore Newfoundland, Canada

2019 ◽  
Vol 221 (1) ◽  
pp. 37-59 ◽  
Author(s):  
J Kim Welford ◽  
Sonya A Dehler ◽  
Thomas Funck
Keyword(s):  
Continental Crust ◽  
Transition Zone ◽  
Oceanic Crust ◽  
Newfoundland And Labrador ◽  
Velocity Structure ◽  
Velocity Model ◽  
Crustal Layer ◽  
Thickness Variations ◽  
Thinned Continental Crust ◽  
Sedimentary Layer

SUMMARY Orphan Basin, a massive deepwater rifted basin off the northeastern coast of Newfoundland, was one of the targets of the 2009 SIGNAL (Seismic Investigations off Greenland, Newfoundland and Labrador) experiment to collect refraction/wide-angle reflection (RWAR) data from the Bonavista Platform, through the Orphan Basin, to the Orphan Knoll, and beyond into oceanic crust. Both the data from an earlier RWAR acquisition and the new data were jointly analysed in order to improve on the earlier velocity model and extend its coverage landward and seaward. The resulting velocity model is characterized by an 8–9-km-thick sedimentary package immediately outboard of the Bonavista Platform, which thins toward the Orphan Knoll and beyond. The shallowest modelled sedimentary layer, interpreted as Paleocene and younger post-rift sediments, does not show significant thickness variations and velocities do not exceed 3.3 km s–1. The second modelled sedimentary layer with laterally variable velocities ranging from 2.3 to 5.3 km s–1, interpreted as Late Cretaceous post-rift sediments, is thickest over an interpreted failed rift. The deepest modelled sedimentary layer consists of laterally variable velocities that do not exceed 5.9 km s–1 and is interpreted as possibly Jurassic to Early Cretaceous syn-rift sediments. The crust beneath the Bonavista Platform is subdivided into an upper (5.4–5.9 km s–1), middle (5.9–6.4 km s–1) and lower crust (6.4–6.9 km s–1). The middle crust is modelled as disappearing beneath the seaward limit of the Bonavista Platform at an interpreted failed rift, only to re-appear 100 km further seaward beneath the central Orphan Basin and extend to the seaward limit of the Orphan Knoll, beyond which the crust can be modelled by just an upper (5.0–6.7 km s–1) and a lower (6.7–7.0 km s–1) crustal layer. Towards land, for the first 450 km of the model, velocities generally follow the globally averaged velocity trend for rifted continental crust, albeit with slightly elevated velocities suggestive of magmatic contributions. At the failed rift, within the continental domain, hyperextended crust is modelled, overlying a limited zone of serpentinized mantle. Seaward of Orphan Knoll, the interpretation for the velocity structure is less definitive but an 80-km-wide continent–ocean transition zone consisting of either transitional embryonic oceanic crust or thinned continental crust overlying serpentinized mantle is proposed. Upper mantle velocities as low as 7.7 km s–1 are modelled beneath the interpreted failed continental rift as well as beneath the continent–ocean transition zone, while the rest of the crustal model is underlain by typical mantle velocities of 8 km s–1. Analysis of extension and thinning factors based on the velocity model reveal that the failed rift experienced hyperextension and should have achieved full crustal embrittlement, consistent with localized mantle serpentinization.

Crustal structure beneath the southern Grand Banks: seismic-refraction results and their implications

1988 ◽  
Vol 25 (5) ◽  
pp. 760-772 ◽  
Author(s):  
I. Reid
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Ocean Bottom ◽  
Crustal Layer ◽  
Ocean Bottom Seismograph ◽  
Grand Banks ◽  
Reflection Data ◽  
Air Gun ◽  
Lower Crustal

A seismic-refraction profile was shot on the southern Grand Banks using large air-gun sources and an array of ocean-bottom seismograph receivers. A sediment column 1–2 km thick directly overlies Paleozoic basement with velocity structure similar to that of the Meguma Zone of Nova Scotia. The main crustal layer is 27 km thick, with seismic velocity of 6.3 km/s increasing to about 6.5 km/s in the lowest few kilometres. Complexity is apparent in the crust–mantle transition around 32 km depth. Comparison with deep multichannel reflection data suggests that the increased velocity in the lower part of the crust may be associated with a reflective zone and shows the Mohorovičić discontinuity to be delineated by a well-defined reflection. The absence of a major lower crustal layer of intermediate velocity (> 7 km/s) is consistent with observations elsewhere in the region.

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