Basin architecture and density structure beneath the Strait of Georgia, British Columbia

2003 ◽  
Vol 40 (7) ◽  
pp. 965-981 ◽  
Author(s):  
C Lowe ◽  
S A Dehler ◽  
B C Zelt
Keyword(s):  
Seismic Velocity ◽  
Gravity Data ◽  
Velocity Model ◽  
Seismic Structure ◽  
Strait Of Georgia ◽  
3 Dimensional ◽  
The North ◽  
Georgia Basin ◽  
Geologic Interpretation ◽  
Velocity Information

Georgia Basin is located within one of the most seismically active and populated areas on Canada's west coast. Over the last decade, geological investigations have resolved important details concerning the basin's shallow structure and composition. Yet, until recently, relatively little was known about deeper portions of the basin. In this study, new seismic velocity information is employed to develop a 3-dimensional density model of the basin. Comparison of the calculated gravity response of this model with the observed gravity field validates the velocity model at large scales. At smaller scales, several differences between model and observed gravity fields are recognized. Analysis of these differences and correlation with independent geoscience data provide new insights into the structure and composition of the basin-fill and underlying basement. Specifically, four regions with thick accumulations of unconsolidated Pleistocene and younger sediments, which were not resolved in the velocity model, are identified. Their delineation is particularly important for studies of seismic ground-motion amplification and offshore aggregate assessment. An inconsistency between the published geology and the seismic structure beneath Texada and Lasqueti Islands in the central Strait of Georgia is investigated; however, the available gravity data cannot preferentially validate either the geologic interpretation or the seismic model in this region. We interpret a northwest-trending and relatively linear gradient extending from Savory Island in the north to Boundary Bay in the south as the eastern margin of Wrangellia beneath the basin. Finally, we compare Georgia Basin with the Everett and Seattle basins in the southern Cascadia fore arc. This comparison indicates that while a single mechanism may be controlling present-day basin tectonics and deformation within the fore arc this was not the case for most of the Mesozoic and Tertiary time periods.

From Corinth gulf extension to Ionian subduction/collision (W. Greece): micro-seismicity survey to constrain local tectonics and regional geodynamics

2020 ◽  
Author(s):  
Valentine Lefils ◽  
Alexis Rigo ◽  
Efthimios Sokos
Keyword(s):  
Seismic Velocity ◽  
Deformation Mode ◽  
Velocity Model ◽  
Fault System ◽  
Normal Faults ◽  
Corinth Gulf ◽  
National Network ◽  
The North ◽  
Gulf Of Corinth ◽  
Seismological Network

<p>The North-Eastern zone of the Gulf of Corinth in Greece is characterized by the rotation of a micro-plate in formation. The Island Akarnanian Block (IAB) have been progressively individualized since the Pleistocene (less than ~ 1.5 My ago). This micro-plate is the result of a larger-scale tectonic context with, on one side the N-S extension of the Gulf of Corinth to the East, and on the other side the Hellenic subduction to the South and the Apulian collision to the West. To the Northeast, the IAB micro-plate is bounded by a large North-South sinistral strike-slip fault system, the Katouna-Stamna Fault (KSF) and by several normal faults. To the North, normal faults reach the limit between Apulian and Eurasian plates and to the East, they form the East-West graben of Trichonis lake.</p><p>Although the structures and dynamics behind the Gulf of Corinth extension are today relatively known, nevertheless, the set of faults linking the Gulf of Corinth to the Western subduction structures remain poorly studied. The seismicity recorded by the Greek national network shows discrepancies regarding to the faults mapped on the surface.</p><p>At the end of 2015, a new micro-seismicity campaign started with the deployment of a temporary seismological network in an area ranging from the Gulf of Patras to the Amvrakikos Gulf toward the North. This network includes 17 seismic stations, recording continuously, added to the permanent stations of the Corinth Rift Laboratory (CRL) and of the Hellenic Unified Seismic Network (HUSN).</p><p>The analysis of the seismological records is still in process for the 2016 and 2017 years. Our study consists first in picking the <em>P</em>- and <em>S</em>- waves, and then to precisely localize the seismic events recorded by our temporary seismological network combined with the permanent ones. We will present here the event location map obtained for the 2016-2017 period, a new seismic velocity model, and focal mechanisms. The seismic activity including thousands of events, is characterized by the presence of numerous clusters of few days to few weeks duration. The clusters are analysed in detail by relative relocations in order to appraise their physical processes and their implications in the fault activity. We will discuss the deformation mode of the region and build a seismotectonic model consistent with the regional geodynamics and observations.</p>

Improved seismic interpretation of a salt diapir by utilization of diffractions, exemplified by 2D reflection seismics, Danish sector of the North Sea

2020 ◽  
Vol 8 (1) ◽  
pp. T77-T88 ◽  
Author(s):  
Mahboubeh Montazeri ◽  
Lars Ole Boldreel ◽  
Anette Uldall ◽  
Lars Nielsen
Keyword(s):  
North Sea ◽  
Seismic Imaging ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Salt Diapir ◽  
The North ◽  
Reflection Seismics ◽  
The North Sea ◽  
Sediment Layers

Development of salt diapirs affects the hydrocarbon trapping systems in the Danish sector of the North Sea, where the reservoirs mainly consist of chalk. Seismic imaging and interpretation of the salt structures are challenging, primarily due to the complex geometry of the salt bodies and typically strong velocity contrast with the neighboring sediment layers. The quality of seismic imaging in the North Sea is highly dependent on the quality of the estimated velocity model. We have studied diffracted arrivals originating from the salt flanks and adjacent sedimentary structures using a diffraction imaging technique. The diffracted waves carry valuable information regarding seismic velocity and the location of geologic discontinuities, such as faults, fractures, and salt delimitations. We apply a plane-wave destruction method to separate diffractions from our stacked data. We optimize imaging based on diffraction analysis by using a velocity continuation migration technique, which leads to an estimation of the optimum focusing velocity model. We determine that the diffraction-based approach significantly improves the seismic imaging adjacent to the salt diapirs and the neighboring layers when compared with a standard approach in which we mostly ignore the diffractions. The new poststack time-migrated results provide detailed information that optimizes our interpretation of the salt diapir itself (e.g., the width of the salt neck) as well as the sediment layers related to the rim synclines. Processing schemes such as prestack depth migration and full-waveform inversion may potentially provide high-resolution images of the salt structures. We only account for diffractions in nonmigrated stacked data to better constrain seismic velocity and improve imaging around the salt diapir. The obtained results are critical for reservoir characterization.

scholarly journals 3D Subsurface Modeling of Multi-Scenario Rock Property and AVO Feasibility Cubes—An Integrated Workflow

2021 ◽  
Vol 9 ◽  
Author(s):  
Per Avseth ◽  
Ivan Lehocki
Keyword(s):  
Barents Sea ◽  
Seismic Velocity ◽  
Rock Physics ◽  
Training Data ◽  
Well Control ◽  
Rock Property ◽  
The North ◽  
The North Sea ◽  
Velocity Information ◽  
2D And 3D

A novel inter-disciplinary methodology for the generation of rock property and AVO feasibility maps or cubes to be used in subsurface characterization and prospect de-risking is presented. We demonstrate the workflow for 1D, 2D and 3D cases on data from the North Sea and the Barents Sea, offshore Norway. The methodology enables rapid extrapolation of expected rock physics properties away from well control along selected horizons, constrained by seismic velocity information, geological inputs (basin modeling, seismic stratigraphy and facies maps) and rock physics depth trend analysis. In this way, the expected rock physics properties of a reservoir sandstone (saturated with any pore fluid) can be predicted at any given location between or away from existing wells while honoring rock’s burial and thermal history at this same location. The workflow should allow for more rapid, seamless and geologically consistent subsurface mapping and de-risking of prospects in areas with complex geology and tectonic influence. The AVO feasibility results can furthermore be utilized to generate non-stationary training data for AVO classification.

A robust seismic structure along the North Anatolian Fault beneath the Central Marmara Sea, and its implication for seismogenesis

2021 ◽  
Author(s):  
Yojiro Yamamoto ◽  
Dogan Kalafat ◽  
Ali Pinar ◽  
Narumi Takahashi ◽  
Remzi Polat ◽  
...  
Keyword(s):  
High Velocity ◽  
Seismic Velocity ◽  
Large Earthquake ◽  
North Anatolian Fault ◽  
Seismic Gap ◽  
Observation Data ◽  
Marmara Region ◽  
Marmara Sea ◽  
Seismic Structure ◽  
The North

<p>The offshore part of the North Anatolian Fault (NAF) beneath the Marmara Sea is a well-known seismic gap for future M > 7 earthquakes in the sense that more than 250 years have passed since the last major earthquake in the Central Marmara region. Here, an assessment on the location of possible asperities to host the expected next large earthquake is done based on the heterogeneities on the seismic velocity structure. Using long-term ocean bottom seismograph (OBS) observation data, seismic tomography and precise hypocenter estimations have been conducted. As a result, about five times more microearthquakes than the events in a land-based catalog has been detected. A comparison with previously published results suggests that the seismicity pattern has not changed during the three years period between Sep. 2014 and Jun. 2017. The obtained velocity model shows strong lateral contrast whose changing points locate at 28.10°E and 28.50°E. The western corner of the area (28.10°E) corresponds to a segmentation boundary where the dip angle of the NAF segments changed. The high velocity zones in the tomographic images are characterized by low seismicity eastward from the segment boundary at 28.10°E. Eastern 28.50°E, the high velocity zone becomes thicker in the depth direction. These zones are interpreted as asperities to be ruptured by the next large earthquake which are possibly accumulating strain since the mainshock rupture associated with the May 1766 Ms7.3 earthquake.</p>

Crustal structure across the northern Cordillera, Yukon Territory, from seismic wide-angle studies: Omineca Belt to Intermontane Belt

2005 ◽  
Vol 42 (6) ◽  
pp. 1187-1203 ◽  
Author(s):  
Brian Creaser ◽  
George Spence
Keyword(s):  
Upper Mantle ◽  
Gravity Data ◽  
Seismic Refraction ◽  
Velocity Model ◽  
High Heat ◽  
Yukon Territory ◽  
Wide Angle ◽  
The North ◽  
Structural Differences ◽  
Lower Crustal

A seismic refraction – wide-angle reflection experiment shot in 1997 in the southern Yukon Territory crosses the Omineca Belt, which includes the strike-slip Tintina Fault, and terminates within the Intermontane Belt of the northern Canadian Cordillera. Lithospheric structure is interpreted from two-dimensional forward and inverse modelling of traveltimes, combined with forward-amplitude modelling, and from 2.5-dimensional modelling of gravity data. Beneath the Cassiar terrane and the North America miogeocline, average velocities in the upper 20 km of crust are < 6.1 km/s. In the west beneath the accreted Cache Creek, Slide Mountain, and Yukon–Tanana terranes, average velocities increase to ∼6.3 km/s. In the upper crust, the velocity model beneath these terranes thus correlates with more mafic accreted material and not with a subsurface extension of the Cassiar terrane. The Tintina Fault is a crustal-scale structure across which significant structural differences occur. A mid-crustal reflector terminates to the east of the Tintina Fault. The crust immediately west of the fault is thicker (∼37 km) than the crust to the east (∼34 km); the thick crust may suggest movement along the fault from a region of thicker crust to the south. Lower crustal velocities range from 6.4 to 6.7 km/s, with the lowest velocities located 25–50 km west of the Tintina Fault, coincident with the location of the thickest crust. A reflector at 28 km depth may correspond to the top of Proterozoic cratonic basement in the lowermost crust. Upper mantle velocities just below the Moho range from 7.8 to 7.9 km/s, consistent with the high heat flow in the region.

Coupling USArray and satellite gravity data – an integrated conductivity, density and seismic velocity model of the western USA

2020 ◽  
Author(s):  
Bernhard Weise ◽  
Max Moorkamp ◽  
Stewart Fishwick
Keyword(s):  
Seismic Velocity ◽  
Joint Inversion ◽  
Gravity Data ◽  
Velocity Model ◽  
Data Sets ◽  
Satellite Gravity ◽  
Consistent Model ◽  
The Usa ◽  
The Individual ◽  
Tectonic Boundaries

&lt;p&gt;The EarthScope USArray project provides high quality magnetotelluric and seismic observations, which have been used to identify tectonic boundaries of the USA. Combining these data sets together with satellite gravity observations, we investigate how the different data sets can complement each other in order to find a consistent model of the subsurface. Using a cross-gradient constraint, we first invert the magnetotelluric and gravity data sets in order to demonstrate the feasibility of our approach and to identify any difficulties. Once a joint conductivity and density model is found, we perform a full joint inversion of all three data sets. By comparison with models derived from separate inversions of the individual observables we can show how the different data sets interact. Examining the magnitude of the cross-gradient lets us distinguish parts of the model where a good agreement of the recovered structures has been achieved from those where differing patterns are necessary in order to achieve an acceptable data fit. In this presentation we will give an overview of our approach, highlight our strategy and show results from individual and joint inversions.&lt;/p&gt;

scholarly journals Three-dimensional gravity anomaly inversion in the Pyrenees using compressional seismic velocity model as structural similarity constraints

2020 ◽  
Author(s):  
Roland Martin ◽  
Jérémie Giraud ◽  
Vitaliy Ogarko ◽  
Sébastien Chevrot ◽  
Stephen Beller ◽  
...  
Keyword(s):  
Seismic Tomography ◽  
Seismic Velocity ◽  
Thermal State ◽  
Gravity Data ◽  
Waveform Inversion ◽  
Gravity Anomalies ◽  
Velocity Model ◽  
Density Model ◽  
Real Field ◽  
Structural Constraints

Summary We explore here the benefits of using constraints from seismic tomography in gravity data inversion and how inverted density distributions can be improved by doing so. The methodology is applied to a real field case in which we reconstruct the density structure of the Pyrenees along a southwest-northeast transect going from the Ebro basin in Spain to the Arzacq basin in France. We recover the distribution of densities by inverting gravity anomalies under constraints coming from seismic tomography. We initiate the inversion from a prior density model obtained by scaling a pre-existing compressional seismic velocity Vp model using a Nafe-Drake relationship : the Vp model resulting from a full-waveform inversion of teleseismic data. Gravity data inversions enforce structural similarities between Vp and density by minimizing the norm of the cross-gradient between the density and Vp models. We also compare models obtained from 2.5D and 3D inversions. Our results demonstrate that structural constraints allow us to better recover the density contrasts close to the surface and at depth, without degrading the gravity data misfit. The final density model provides valuable information on the geological structures and on the thermal state and composition of the western region of the Pyrenean lithosphere.

scholarly journals 2D density model of the Chinese continental lithosphere along a NW-SE transect

2015 ◽  
Vol 45 (2) ◽  
pp. 135-148
Author(s):  
Barbora Šimonová ◽  
Miroslav Bielik ◽  
Jana Dérerová
Keyword(s):  
Seismic Velocity ◽  
Qaidam Basin ◽  
Gravity Data ◽  
Junggar Basin ◽  
Density Model ◽  
Low Velocity ◽  
The North ◽  
Deep Seismic Soundings ◽  
Qilian Orogen ◽  
North Western

Abstract This paper presents a 2D density model along a transect from NW to SE China. The model was first constructed by the transformation of seismic velocity to density, revealed by previous deep seismic soundings (DSS) investigations in China. Then, the 2D density model was updated using the GM-SYS software by fitting the computed to the observed gravity data. Based on the density distribution of anomalous layers we divided the Chinese continental crust along the transect into three regions: north-western, central and south-eastern. The first one includes the Junggar Basin, Tianshan and Tarim Basin. The second part consists of the Qilian Orogen, the Qaidam Basin and the Songpan Ganzi Basin. The third region is represented by the Yangtze and the Cathaysia blocks. The low velocity body (vp =5.2 – 6.2 km/s) at the junction of the North-western and Central parts at a depth between 21 – 31 km, which was discovered out by DSS, was also confirmed by our 2D density modelling.

scholarly journals Characteristics of relocated hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its aftershocks with a three-dimensional seismic velocity structure

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Saeko Kita
Keyword(s):  
Seismic Velocity ◽  
Three Dimensional ◽  
Double Difference ◽  
Earthquake Catalog ◽  
Seismic Structure ◽  
Depth Limit ◽  
High Attenuation ◽  
South Central ◽  
Collision Zone ◽  
Hidaka Collision Zone

AbstractI relocated the hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its surrounding area, using a three-dimensional seismic structure, the double-difference relocation method, and the JMA earthquake catalog. After relocation, the focal depth of the mainshock became 35.4 km. As previous studies show, in south-central Hokkaido, the Hidaka collision zone is formed, and anomalous deep and thickened forearc crust material is subducting at depths of less than 70 km. The mainshock and its aftershocks are located at depths of approximately 10 to 40 km within the lower crust of the anomalous deep and thickened curst near the uppermost mantle material intrusions in the northwestern edge of this Hidaka collision zone. Like the two previous large events, the aftershocks of this event incline steeply eastward and appear to be distributed in the deeper extension of the Ishikari-teichi-toen fault zone. The highly inclined fault in the present study is consistent with a fault model by a geodetic analysis with InSAR. The aftershocks at depths of 10 to 20 km are located at the western edge of the high-attenuation (low-Qp) zone. These kinds of relationships between hypocenters and materials are the same as the 1970 and 1982 events in the Hidaka collision zone. The anomalous large focal depths of these large events compared with the average depth limit of inland earthquakes in Japan could be caused by the locally lower temperature in south-central Hokkaido. This event is one of the approximately M7 large inland earthquakes that occurred repeatedly at a recurrence interval of approximately 40 years and is important in the collision process in the Hidaka collision zone.

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