scholarly journals Lithoprobe-Phase 1: southern Vancouver Island: preliminary analyses of reflection seismic profiles and surface geological studies

1985 ◽  
Author(s):  
C J Yorath ◽  
R M Clowes ◽  
A G Green ◽  
A Sutherland-Brown ◽  
M T Brandon ◽  
...  
Keyword(s):  
Phase 1 ◽  
Vancouver Island ◽  
Seismic Profiles ◽  
Reflection Seismic

Integrated geophysical modelling of terranes and other structural features along the western Canadian margin

1992 ◽  
Vol 29 (7) ◽  
pp. 1492-1508 ◽  
Author(s):  
S. A. Dehler ◽  
R. M. Clowes
Keyword(s):  
Seismic Refraction ◽  
Vancouver Island ◽  
Structural Features ◽  
Pacific Rim ◽  
Data Set ◽  
Reflection Seismic ◽  
Barkley Sound ◽  
The Pacific ◽  
Wrangellia Terrane ◽  
Lower Crustal

An integrated geophysical data set has been used to develop structural models across the continental margin west of Vancouver Island, Canada. A modern accretionary complex underlies the continental slope and shelf and rests against and below the allochthonous Crescent and Pacific Rim terranes. These terranes in turn abut against the pre-Tertiary Wrangellia terrane that constitutes most of the island. Gravity and magnetic anomaly data, constrained by seismic reflection, seismic refraction, and other data, were interpreted to determine the offshore positions of these terranes and related features. Iterative 2.5-dimensional forward models of anomaly profiles were stepped laterally along the margin to extend areal coverage over a 70 km wide swath oriented normal to the tectonic features. An average model was then developed to represent this part of the margin. The Pacific Rim terrane appears to be continuous and close to the coastline along the length of Vancouver Island, consistent with emplacement by strike-slip motion along the margin. The Westcoast fault, the boundary between the Pacific Rim and Wrangellia terranes, is interpreted to be 15 km farther seaward than in previous interpretations in the region of Barkley Sound. The Crescent terrane forms a thin landward-dipping slab along the southern half of the Vancouver Island margin, and cannot be confirmed along the northern part. Model results suggest the slab has buckled into an anticline beneath southern Vancouver Island and Juan de Fuca Strait, uplifting high-density lower crustal or upper mantle material close to the surface to produce the observed intense positive gravity anomaly. This geometry is consistent with emplacement of the Crescent terrane by oblique subduction.

scholarly journals Geophysical imaging of permafrost in the SW Svalbard – the result of two high arctic expeditions to Spitsbergen

2020 ◽  
Author(s):  
Mariusz Majdanski ◽  
Artur Marciniak ◽  
Bartosz Owoc ◽  
Wojciech Dobiński ◽  
Tomasz Wawrzyniak ◽  
...  
Keyword(s):  
Surface Waves ◽  
Active Layer ◽  
High Arctic ◽  
The Arctic ◽  
Seismic Profiles ◽  
Frozen Ground ◽  
Near Surface ◽  
Seismic Processing ◽  
Reflection Seismic ◽  
Sea Coast

<p>The Arctic regions are the place of the fastest observed climate change. One of the indicators of such evolution are changes occurring in the glaciers and the subsurface in the permafrost. The active layer of the permafrost as the shallowest one is well measured by multiple geophysical techniques and in-situ measurements.</p><p>Two high arctic expeditions have been organized to use seismic methods to recognize the shape of the permafrost in two seasons: with the unfrozen ground (October 2017) and frozen ground (April 2018). Two seismic profiles have been designed to visualize the shape of permafrost between the sea coast and the slope of the mountain, and at the front of a retreating glacier. For measurements, a stand-alone seismic stations has been used with accelerated weight drop with in-house modifications and timing system. Seismic profiles were acquired in a time-lapse manner and were supported with GPR and ERT measurements, and continuous temperature monitoring in shallow boreholes.</p><p>Joint interpretation of seismic and auxiliary data using Multichannel analysis of surface waves, First arrival travel-time tomography and Reflection imaging show clear seasonal changes affecting the active layer where P-wave velocities are changing from 3500 to 5200 m/s. This confirms the laboratory measurements showing doubling the seismic velocity of water-filled high-porosity rocks when frozen. The same laboratory study shows significant (>10%) increase of velocity in frozen low porosity rocks, that should be easily visible in seismic.</p><p>In the reflection seismic processing, the most critical part was a detailed front mute to eliminate refracted arrivals spoiling wide-angle near-surface reflections. Those long offset refractions were however used to estimate near-surface velocities further used in reflection processing. In the reflection seismic image, a horizontal reflection was traced at the depth of 120 m at the sea coast deepening to the depth of 300 m near the mountain.</p><p>Additionally, an optimal set of seismic parameters has been established, clearly showing a significantly higher signal to noise ratio in case of frozen ground conditions even with the snow cover. Moreover, logistics in the frozen conditions are much easier and a lack of surface waves recorded in the snow buried geophones makes the seismic processing simpler.</p><p>Acknowledgements               </p><p>This research was funded by the National Science Centre, Poland (NCN) Grant UMO-2015/21/B/ST10/02509.</p>

scholarly journals Structural analysis of S-wave seismics around an urban sinkhole; evidence of enhanced subrosion in a strike-slip fault zone

2017 ◽  
Author(s):  
Sonja H. Wadas ◽  
David C. Tanner ◽  
Ulrich Polom ◽  
Charlotte M. Krawczyk
Keyword(s):  
Strike Slip ◽  
Strike Slip Fault ◽  
Key Factors ◽  
S Wave ◽  
Seismic Profiles ◽  
Reflection Seismic ◽  
Dextral Strike Slip Fault ◽  
Seismic Sections ◽  
The Town ◽  
Dextral Strike Slip

Abstract. In November 2010, a large sinkhole opened up in the urban area of Schmalkalden, Germany. To determine the key factors which benefited the development of this collapse structure and therefore the subrosion, we carried out several shear wave reflection seismic profiles around the sinkhole. In the seismic sections we see evidence of the Mesozoic tectonic movement, in the form of a NW–SE striking, dextral strike-slip fault, known as the Heßleser Fault, which faulted and fractured the subsurface below the town. The strike-slip faulting created a zone of small blocks (

Twelve years of vertical birefringence in nine‐component VSP data

Geophysics ◽  
2001 ◽  
Vol 66 (2) ◽  
pp. 582-597 ◽  
Author(s):  
Donald F. Winterstein ◽  
Gopa S. De ◽  
Mark A. Meadows
Keyword(s):  
Seismic Data ◽  
Azimuthal Anisotropy ◽  
Vertical Shear ◽  
S Wave ◽  
Seismic Profiles ◽  
Surface Reflection ◽  
Vertical Seismic Profiles ◽  
Reflection Seismic ◽  
San Andreas ◽  
Vsp Data

Since 1986, when industry scientists first publicly showed data supporting the presence of azimuthal anisotropy in sedimentary rock, we have studied vertical shear‐wave (S-wave) birefringence in 23 different wells in western North America. The data were from nine‐component vertical seismic profiles (VSPs) supplemented in recent years with data from wireline crossed‐dipole logs. This paper summarizes our results, including birefringence results in tabular form for 54 depth intervals in 19 of those 23 wells. In the Appendix we present our conclusions about how to record VSP data optimally for study of vertical birefringence. We arrived at four principal conclusions about vertical S-wave birefringence. First, birefringence was common but not universal. Second, birefringence ranged from 0–21%, but values larger than 4% occurred only in shallow formations (<1200 m) within 40 km of California’s San Andreas fault. Third, at large scales birefringence tended to be blocky. That is, both the birefringence magnitude and the S-wave polarization azimuth were often consistent over depth intervals of several tens to hundreds of meters but then changed abruptly, sometimes by large amounts. Birefringence in some instances diminished with depth and in others increased with depth, but in almost every case a layer near the surface was more birefringent than the layer immediately below it. Fourth, observed birefringence patterns generally do not encourage use of multicomponent surface reflection seismic data for finding fractured hydrocarbon reservoirs, but they do encourage use of crossed‐dipole logs to examine them. That is, most reservoirs were birefringent, but none we studied showed increased birefringence confined to the reservoir.

Seismic tomography studies of cover thickness and near-surface bedrock velocities

Geophysics ◽  
2006 ◽  
Vol 71 (6) ◽  
pp. U77-U84 ◽  
Author(s):  
B. Bergman ◽  
A. Tryggvason ◽  
C. Juhlin
Keyword(s):  
Nuclear Waste ◽  
Velocity Structure ◽  
Synthetic Data ◽  
General Situation ◽  
Seismic Profiles ◽  
Low Velocity ◽  
Near Surface ◽  
Reflection Seismic ◽  
Crystalline Bedrock ◽  
Cover Thickness

Reflection seismic imaging of the uppermost kilometer of crystalline bedrock is an important component in site surveys for locating potential storage sites for nuclear waste in Sweden. To obtain high-quality images, refraction statics are calculated using first-break traveltimes. These first-break picks may also be used to produce tomographic velocity images of the uppermost bedrock. In an earlier study, we presented a method applicable to data sets where the vast majority of shots are located in the bedrock below the glacial deposits, or cover, typical for northern latitudes. A by-product of this method was an estimate of the cover thickness from the receiver static that was introduced to sharpen the image. We now present a modified version of this method that is applicable for sources located in or on the cover, the general situation for nuclear waste site surveys. This modified methodalso solves for 3D velocity structure and static correctionssimultaneously in the inversion process. The static corrections can then be used to estimate the cover thickness. First, we test our tomography method on synthetic data withthe shot points in the bedrock below the cover. Next, we developa strategy for the case when the sources are within the cover. Themethod is then applied to field data from five crooked-line,high-resolution reflection seismic profiles ranging in lengthfrom 2 to [Formula: see text]. The crooked-line profiles make the study 2.5dimensional regarding bedrock velocities. The cover thicknessalong the profiles varies from 0 to [Formula: see text]. Estimated thickness ofthe cover agrees well with data from boreholes drilled near theprofiles. Low-velocity zones in the uppermost bedrock generallycorrelate with locations where reflections from the stackedsections project to the surface. Thus, the method is functional,both for imaging the uppermost bedrock velocities as well as for estimating the cover thickness.

scholarly journals Reflexně seismický výzkum pozdně kenozoické zlomové tektoniky na vybraných lokalitách hornomoravského úvalu

2020 ◽  
Vol 27 (1-2) ◽  
Author(s):  
Ondřej Bábek ◽  
Zuzana Lenďáková ◽  
Tamás Tóth ◽  
Daniel Šimíček ◽  
Ondřej Koukal
Keyword(s):  
Low Cost ◽  
Seismic Facies ◽  
Gravity Gradients ◽  
Seismic Profiles ◽  
Low Velocity ◽  
Shallow Subsurface ◽  
Static Correction ◽  
Reflection Seismic ◽  
Weight Drop ◽  
Siliciclastic Sediments

We measured shallow reflection seismic profiles across the assumed faults in the Late Cenozoic (Pliocene – Holocene) Upper Morava Basin (UMB). The faults in the UMB are indicated by horst-and-graben morphology, differential thickness of Pliocene and Quaternary siliciclastic sediments, considerable gravity gradients a present-day seismicity. Four seismic lines, 380 to 860 m long (fixed geophone spread) were designed to cross the assumed faults at three sites, Mezice, Drahlov and Výšovice. The data were acquired by 24-channel ABEM Terraloc Mk-8 seismic system with PEG-40 accelerated weight drop source and processed by Sandmaier ReflexW and Halliburton Landmark ProMax® seismic processing software. The processing included application of filters (DC shift, scaled windowgain, bandpass frequency and muting), stacking using normal moveout constant velocity stack, additional application of subtrack-mean (dewow) filter, topographic correction and low velocity layer static correction. Distinct reflectors were detected up to 400 ms TWT, which corresponds to maximum depth of 280 and 350 m at 1400 and 1750 km.s-1 velocities, respectively. The observed reflection patterns were classified into three seismic facies, which were interpreted as crystalline rocks (Brunovistulicum) and/or well consolidated Paleozoic sedimentary rocks (SF1), unconsolidated Quaternary siliciclastic sediments (SF2) and semi-consolidated Neogene clays (SF3) based on the cores drilled in their close vicinity. Distinct faults were observed at the Drahlov and Výšovice 2 profile, which coincided with the observed topographic steps between the horsts and grabens. Presence of the fault at the Drahlov profile separating the Hněvotín Horst from the Lutín Graben was demonstrated by independent electrical resistivity tomography profile. On the other hand, another topographic step at the Mezice profile, between the Hněvotín Horst and Olomouc Graben, does not correspond to any seismic indication of a fault. The reflection seismic proved to be useful and relatively low-cost method to visualize the shallow subsurface geology in the Upper Morava Basin.

scholarly journals Imaging East European Craton margin in Northern Poland using extended-correlation processing applied to regional reflection seismic profiles

2019 ◽  
Author(s):  
Miłosz Mężyk ◽  
Michał Malinowski ◽  
Stanisław Mazur
Keyword(s):  
Shear Zones ◽  
Seismic Profiles ◽  
East European ◽  
Reflection Seismic ◽  
Ne Poland ◽  
Marginal Part ◽  
Correlation Processing ◽  
New Processing ◽  
The Baltic ◽  
Lower Crustal

Abstract. In NE Poland, the Eastern European Craton (EEC) crust of the Fennoscandian affinity is concealed under a Phanerozoic platform cover and penetrated by the sparse deep research wells. Most of the inferences regarding its structure rely on geophysical data. Until recently, this area was covered only by the refraction/wide-angle reflection (WARR) profiles, which show a relatively simple crustal structure with a typical cratonic 3-layer crust. ION Geophysical PolandSPAN™ regional seismic program, acquired over the marginal part of the EEC in Poland, offered a unique opportunity to derive a detailed image of the deeper crust. Here, we apply extended correlation processing to a subset (~950 km) of the PolandSPAN™ dataset located in NE Poland, which enabled us to extend the nominal record length of the acquired data from 12 to 22 s (~60 km depth). Our new processing revealed reflectivity patterns, that we primarily associate with the Paleoproterozoic crust formation during the Svekofennian (Svekobaltic) orogeny and which are similar to what was observed along the BABEL and FIRE profiles in the Baltic Sea and Finland, respectively. We propose a mid- to lower-crustal lateral flow model to explain the occurrence of two sets of structures that can be collectively interpreted as kilometre-scale S-C' shear zones. The structures define a penetrative deformation fabric invoking ductile extension of hot orogenic crust. Localized reactivation of these structures provided conduits for subsequent emplacement of gabbroic magma that produced a Mesoproterozoic anorthosite-mangerite-charnockite-granite (AMCG) suite in NE Poland. Delamination of overthickened orogenic lithosphere may have accounted for magmatic underplating and fractionation into the AMCG plutons. We also found sub-Moho dipping mantle reflectivity, which we tentatively explain as a signature of the crustal accretion during the Svekofennian orogeny. Later tectonic phases (e.g. Ediacaran rifting, Caledonian orogeny) did not leave a clear signature in the deeper crust, however, some of the subhorizontal reflectors below the basement, observed in the vicinity of the AMCG Mazury complex, can be alternatively linked with lower Carboniferous magmatism.

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