Seismic velocity structure of the Queen Charlotte terrace off western Canada in the region of the 2012 Haida Gwaii Mw 7.8 thrust earthquake

A well-recorded Mw 7.8 megathrust earthquake occurred on 27 October 2012 under the Queen Charlotte terrace off the west coast of Haida Gwaii, western Canada. In this study, we supplement limited earlier seismic refraction work on the offshore velocity structure off Haida Gwaii with data from ocean bottom seismometers (OBS) operating between 6 December 2012 and 5 January 2013. The OBS recorded a portion of the aftershock sequence, and an active-source seismic survey was conducted in January 2013 to acquire seismic refraction data in the region of the Haida Gwaii earthquake across the Queen Charlotte terrace. P-wave velocity analyses using first-arrival tomography showed relatively shallow (2.0–3.0 km below seafloor) high-velocity material with values up to 4.0 km/s beneath the terrace. At the one OBS station seaward of the deformation front on the abyssal plain, refraction velocities of ~4.5 km/s indicated the top of the oceanic plate at ~1–2 km below the seafloor. At several OBS stations, converted shear-wave velocities were determined within the sediment cover using reflected arrivals. The S-wave velocities ranged from 0.5 to 1.5 km/s, and the corresponding P/S velocity ratio was between 3.0 and 4.2. The new refraction data confirm earlier interpretations of high-velocity material in the shallow terrace that may indicate fractured oceanic crustal material lies significantly above the location where a subducted slab is thought to occur under the terrace. Transpressive deformation of the Pacific plate may explain these observations.

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Crustal velocity structure in the southern Coast Belt, British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e93-207 ◽

1993 ◽

Vol 30 (12) ◽

pp. 2389-2403 ◽

Cited By ~ 15

Author(s):

D. M. O'Leary ◽

R. M. Clowes ◽

R. M. Ellis

Keyword(s):

Upper Mantle ◽

Velocity Structure ◽

Seismic Refraction ◽

Velocity Model ◽

Structural Features ◽

P Wave ◽

Crust And Upper Mantle ◽

Near Surface ◽

Collision Zone ◽

Refraction Data

We applied an iterative combination of two-dimensional traveltime inversion and amplitude forward modelling to seismic refraction data along a 350 km along-strike profile in the Coast Belt of the southern Canadian Cordillera to determine crust and upper mantle P-wave velocity structure. The crustal model features a thin (0.5–3.0 km) near-surface layer with an average velocity of 4.4 km/s, and upper-, middle-, and lower-crustal strata which are each approximately 10 km thick and have velocities ranging from 6.2 to 6.7 km/s. The Moho appears as a 2 km thick transitional layer with an average depth of 35 km and overlies an upper mantle with a poorly constrained velocity of over 8 km/s. Other interpretations indicate that this profile lies within a collision zone between the Insular superterrane and the ancient North American margin and propose two collision-zone models: (i) crustal delamination, whereby the Insular superterrane was displaced along east-vergent faults over the terranes below; and (ii) crustal wedging, in which interfingering of Insular rocks occurs throughout the crust. The latter model involves thick layers of Insular material beneath the Coast Belt profile, but crustal velocities indicate predominantly non-Insular material, thereby favoring the crustal delamination model. Comparisons of the velocity model with data from the proximate reflection lines show that the top of the Moho transition zone corresponds with the reflection Moho. Comparisons with other studies suggest that likely sources for intracrustal wide-angle reflections observed in the refraction data are structural features, lithological contrasts, and transition zones surrounding a region of layered porosity in the crust.

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GEOTECHNICAL PARAMETERS STUDY USING SEISMIC REFRACTION TOMOGRAPHY

Jurnal Teknologi ◽

10.11113/jt.v78.9645 ◽

2016 ◽

Vol 78 (8-6) ◽

Cited By ~ 1

Author(s):

Rose Nadia ◽

Rosli Saad ◽

Nordiana Muztaza ◽

Nur Azwin Ismail ◽

Mohd Mokhtar Saidin

Keyword(s):

Parameter Estimation ◽

Seismic Refraction ◽

Standard Penetration Test ◽

P Wave ◽

Cohesive Soils ◽

Penetration Test ◽

Geotechnical Parameters ◽

Wave Velocities ◽

Refraction Tomography ◽

Loose Medium

In this study, correlation is made between seismic P-wave velocities (Vp) with standard penetration test (SPT-N) values to produce soil parameter estimation for engineering site applications. A seismic refraction tomography (SRT) line of 69 m length was spread across two boreholes with 3 m geophones spacing. The acquired data were processed using Firstpix, SeisOpt2D and surfer8 software. The Vp at particular depths were pinpointed and correlated with geotechnical parameters (SPT-N values) from the borehole records. The correlation between Vp and SPT-N values has been established. For cohesive soils, it is grouped into three categories according to consistencies; stiff, very stiff and hard, having velocity rangesof 575-314 m/s, 808-1483 m/s and 1735-2974 m/s, respectively. For non-cohesive soils, it is also divided into three categories based on the denseness as loose, medium dense and dense with Vp ranges of 528-622 m/s, 900-2846 m/s and 2876-2951 m/s, respectively

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Shallow velocity structure and poisson's ratio at the Tarzana, California, strong-motion accelerometer site

Bulletin of the Seismological Society of America ◽

10.1785/bssa0860061704 ◽

1996 ◽

Vol 86 (6) ◽

pp. 1704-1713 ◽

Cited By ~ 2

Author(s):

R. D. Catchings ◽

W. H. K. Lee

Keyword(s):

Urban Areas ◽

Velocity Structure ◽

Strong Motion ◽

P Wave ◽

S Wave ◽

Near Surface ◽

Velocity Models ◽

Wave Velocities ◽

Poisson's Ratios ◽

Poisson’S Ratios

Abstract The 17 January 1994, Northridge, California, earthquake produced strong ground shaking at the Cedar Hills Nursery (referred to here as the Tarzana site) within the city of Tarzana, California, approximately 6 km from the epicenter of the mainshock. Although the Tarzana site is on a hill and is a rock site, accelerations of approximately 1.78 g horizontally and 1.2 g vertically at the Tarzana site are among the highest ever instrumentally recorded for an earthquake. To investigate possible site effects at the Tarzana site, we used explosive-source seismic refraction data to determine the shallow (<70 m) P-and S-wave velocity structure. Our seismic velocity models for the Tarzana site indicate that the local velocity structure may have contributed significantly to the observed shaking. P-wave velocities range from 0.9 to 1.65 km/sec, and S-wave velocities range from 0.20 and 0.6 km/sec for the upper 70 m. We also found evidence for a local S-wave low-velocity zone (LVZ) beneath the top of the hill. The LVZ underlies a CDMG strong-motion recording site at depths between 25 and 60 m below ground surface (BGS). Our velocity model is consistent with the near-surface (<30 m) P- and S-wave velocities and Poisson's ratios measured in a nearby (<30 m) borehole. High Poisson's ratios (0.477 to 0.494) and S-wave attenuation within the LVZ suggest that the LVZ may be composed of highly saturated shales of the Modelo Formation. Because the lateral dimensions of the LVZ approximately correspond to the areas of strongest shaking, we suggest that the highly saturated zone may have contributed to localized strong shaking. Rock sites are generally considered to be ideal locations for site response in urban areas; however, localized, highly saturated rock sites may be a hazard in urban areas that requires further investigation.

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Gas hydrate occurrences along the Haida Gwaii margin—Constraints on the geothermal regime and implications for fluid flow

Geosphere ◽

10.1130/ges02103.1 ◽

2019 ◽

Vol 16 (1) ◽

pp. 1-12 ◽

Cited By ~ 1

Author(s):

Michael Riedel ◽

Kristin M.M. Rohr ◽

Michelle M. Côté ◽

Ulrike Schmidt ◽

Terryl Richardson

Keyword(s):

Gas Hydrate ◽

Velocity Structure ◽

North American Plate ◽

P Wave ◽

Topographic Effects ◽

Thermal Gradients ◽

Haida Gwaii ◽

Seismic Reflection Data ◽

Geothermal Gradients ◽

Oblique Convergence

Abstract Seismic-reflection data along the Haida Gwaii margin collected from 1967 to 2013 were used to identify gas hydrate–related bottom-simulating reflectors (BSRs). The BSRs occur along the Queen Charlotte Terrace only, within more strongly folded and tectonically deformed sedimentary ridges. The BSRs are absent within well-bedded and sediment-filled minibasins. The BSR is modeled as the base of the phase boundary of the methane hydrate (structure I) stability zone and is used to estimate geothermal gradients. The P-wave velocity structure required to convert observed depths of the BSR in two-way time to meters below seafloor was constrained from ocean-bottom seismometers. The BSR-derived gradients are lower than data from heat-probe deployments in the region, as well as predicted values from previous modeling of the large-scale tectonic thermal regime. Lower values of the BSR-derived thermal gradients may be due to topographic effects across the ridges where BSRs were observed. The previously identified landward decrease in thermal gradients across the terrace was also identified to a lesser extent from the BSRs, in accordance with the effects of oblique convergence of the Pacific plate with the North American plate. Geothermal gradients decreased from south to north by a factor of two, which is likely an effect of plate cooling due to an increase in age of the underlying plate (ca. 8 Ma off southern Haida Gwaii to ca. 12 Ma at Dixon Entrance) as well as the fact that sediments triple in thickness over the same distance. This may be due to downward flexure of the underlying crust during transpression and/or a high flux of sediments through Dixon Entrance.

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Interpretation of three-dimensional seismic refraction data from western Hecate Strait, British Columbia: structure of the crust

Canadian Journal of Earth Sciences ◽

10.1139/e93-124 ◽

1993 ◽

Vol 30 (7) ◽

pp. 1440-1452 ◽

Cited By ~ 6

Author(s):

J. A. Hole ◽

R. M. Clowes ◽

R. M. Ellis

Keyword(s):

Velocity Structure ◽

Seismic Refraction ◽

Three Dimensional ◽

Surface Expression ◽

Wide Angle ◽

Lateral Velocity ◽

Near Surface ◽

Velocity Anomaly ◽

Air Gun ◽

Refraction Data

As part of a multidisciplinary investigation of the structure and tectonics of the Queen Charlotte Basin and underlying crust, deep multichannel seismic reflection and coincident crustal refraction data were collected in 1988. Energy from the reflection air-gun array source was recorded at land sites at offsets appropriate to record crustal refraction and wide-angle reflection data. Refraction data recorded in a broadside geometry provide good three-dimensional coverage of western Hecate Strait. These data are modelled using tomographic inversion techniques to determine the three-dimensional velocity structure of the crust in this region. The one-dimensional average velocity increases rapidly with depth to 6.5 km/s at 7 km depth. Velocities from 7 to at least 12 km depth remain approximately constant and are associated with rocks of the Wrangellia terrane. Significant lateral velocity variations, including large differences in near-surface velocities attributable to surface features, relatively low velocities representing interbedded Tertiary sediments and volcanics, and a deep high-velocity anomaly that may represent the root of an igneous intrusion, are mapped. Wide-angle reflections from the Moho are used to determine the thickness of the crust. The Moho is at 29 km depth beneath the east coast of the Queen Charlotte Islands. This is deeper than the Moho observed below Queen Charlotte Sound and as deep as, or deeper than, that below Hecate Strait. Crustal thinning during Tertiary extension was thus greatest beneath the surface expression of the Queen Charlotte Basin, leaving the crust under the islands considerably thicker than under the basin. In an alternate or additional explanation, compression at the continental margin during the last 4 Ma may have been taken up by thickening or underplating of the continental crust beneath the islands. If the Pacific plate is subducting beneath the islands, the Moho observations constrain the slab to dip greater than 20–26°.

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A Seismic Reconnaissance in the Mcmurdo Sound Region, Antarctica

Journal of Glaciology ◽

10.1017/s0022143000019225 ◽

1966 ◽

Vol 6 (44) ◽

pp. 209-221 ◽

Cited By ~ 7

Author(s):

Robin A. I. Bell

Keyword(s):

Seismic Velocity ◽

Seismic Refraction ◽

P Wave ◽

Velocity Measurements ◽

Frozen Ground ◽

Mcmurdo Sound ◽

Wave Velocities ◽

Taylor Valley ◽

Minimum Age ◽

First Arrival

AbstractA portable first-arrival seismic refraction instrument was used to measure seismic P-wave velocities in ice, frozen ground, till and shattered rock at various places in the McMurdo Sound region, Antarctica. It was found that some frozen ground exhibits the same seismic velocity as ice, so that buried ice cannot be idengified by seismic velocity measurements.The depth of exfoliation of a granite outcrop in Taylor Valley was successfully measured, as was the depth of an ice-free moraine in Wright Valley. From this latter depth, and from reasonable assumptions about the diffusion of water vapour through till, a minimum age of 75,000 yr. has been deduced for the moraine. This age implies that no through-glacier occupied Wright Valley during the last Northern Hemisphere glaciation.

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P-wave velocity structure under the Changbaishan volcanic region, NE China, from wide-angle reflection and refraction data

Tectonophysics ◽

10.1016/j.tecto.2006.09.012 ◽

2007 ◽

Vol 433 (1-4) ◽

pp. 127-139 ◽

Cited By ~ 16

Author(s):

Jianli Song ◽

Eric A. Hetland ◽

Francis T. Wu ◽

Xiankang Zhang ◽

Guodong Liu ◽

...

Keyword(s):

Wave Velocity ◽

Velocity Structure ◽

P Wave ◽

Wide Angle ◽

Ne China ◽

Volcanic Region ◽

Reflection And Refraction ◽

P Wave Velocity ◽

Refraction Data ◽

P Wave Velocity Structure

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2-D tomographic imaging of velocities in the Wichita uplift-Anadarko basin region of southwestern Oklahoma

Bulletin of the Seismological Society of America ◽

10.1785/bssa0790030873 ◽

1989 ◽

Vol 79 (3) ◽

pp. 873-887 ◽

Cited By ~ 1

Author(s):

Xianhuai Zhu ◽

George A. McMechan

Keyword(s):

High Velocity ◽

El Paso ◽

Tomographic Imaging ◽

P Wave ◽

Crustal Material ◽

Low Velocity ◽

Anadarko Basin ◽

University Of Texas ◽

Seismic Experiment ◽

The University

Abstract In January of 1985, a densely-recorded, wide-aperture seismic experiment was performed by the University of Texas at El Paso and at Dallas, across the southwestern Oklahoma aulacogen. A two-dimensional P-wave velocity distribution is estimated for the Wichita uplift, the Anadarko basin, and the interface between them, by iterative tomographic imaging of travel-time picks from seven shots located near the 100-km-long recording line. The region that is imaged is roughly triangular in shape, with depth = 0 km at the ends of line and ≈ 15 km near its center. The main features that are revealed are a high-velocity (>6.8 km/sec) central core in the Wichita uplift and an asymmetrical Anadarko basin with decreasing velocities toward the basin axis. There are indications, within the uplift, of local high-velocity sills and a local low-velocity region that may be a remnant of normal crustal material.

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The structure of Archean–Ketilidian crust along the continental shelf of southwestern Greenland from a seismic refraction profile

Canadian Journal of Earth Sciences ◽

10.1139/e92-027 ◽

1992 ◽

Vol 29 (2) ◽

pp. 301-313 ◽

Cited By ~ 38

Author(s):

Deping Chian ◽

Keith Louden

Keyword(s):

Lower Crust ◽

Velocity Structure ◽

Seismic Refraction ◽

Mobile Belt ◽

Ocean Bottom ◽

Upper Crust ◽

S Wave ◽

Seismic Line ◽

Wave Velocities ◽

Air Gun

The velocity structure of the continental crust on the outer shelf of southwestern Greenland is determined from dense wide-angle reflection–refraction data obtained with large air-gun sources and ocean bottom seismometers along a 230 km seismic line. This line crosses the geological boundary between the Archean block and the Ketilidian mobile belt. Although the data have high noise levels, P- and S-wave arrivals from within the upper, intermediate, and lower crust, and at the Moho boundary, can be consistently identified and correlated with one-dimensional WKBJ synthetic seismograms. In the Archean, P- and S-wave velocities in the upper crust are 6.0 and 3.4 km/s, while in the intermediate crust they are 6.4 and 3.6 km/s. These velocities match for the upper crust a quartz–feldspar gneiss composition and for the intermediate crust an amphibolitized pyroxene granulite. In the Ketilidian mobile belt, P- and S-wave velocities are 5.6 and 3.3 km/s for the upper crust and 6.3 and 3.6 km/s for the intermediate crust. These velocities may represent quartz granite in the upper crust and granite and granitic gneiss in the intermediate crust. The upper crust is ~5 km thick in the Archean block and the Ketilidian mobile belt, and thickens to ~9 km in the southern part of the Archean. This velocity structure supports a Precambrian collisional mechanism between the Archean block and Ketilidian mobile belt. The lower crust has a small vertical velocity gradient from 6.6 km/s at 15 km depth to 6.9 km/s at 30 km depth (Moho) along the refraction line, with a nearly constant S-wave velocity around 3.8 km/s. These velocities likely represent a gabbroic and hornblende granulite composition for the lower crust. This typical (but somewhat thin) Precambrian crustal velocity structure in southwestern Greenland shows no evidence for a high-velocity, lower crustal, underplated layer caused by the Mesozoic opening of the Labrador Sea.

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Heterogeneous modification and reactivation of craton margin in northeast Asia: insight from teleseismic traveltime tomography of the Korean Peninsula

10.5194/egusphere-egu2020-12562 ◽

2020 ◽

Author(s):

Jung-Hun Song ◽

Seongryong Kim ◽

Junkee Rhie

Keyword(s):

Upper Mantle ◽

High Velocity ◽

Korean Peninsula ◽

Velocity Structure ◽

Northeast Asia ◽

Continental Collision ◽

P Wave ◽

Mantle Dynamics ◽

Traveltime Tomography ◽

Yeongnam Massif

Margins of craton lithosphere are prone to ongoing modification process. Marginal tectonism such as slab subduction, continental collision, and mantle dynamics significantly influence properties of lithosphere in various scales. Thus, constraints on the detailed properties of craton margin are essential to understand the evolution of continental lithosphere. The eastern margin of the Eurasian plate is a natural laboratory that allows us to study the strong effects from multiple episodes of continental collision and subduction of different oceanic plates since their formation. Extensive reworking and destruction of the cratonic lithosphere mainly occurred in eastern China during the Mesozoic to Cenozoic, which leaves distinct geochemical and geophysical signatures. Specifically, the Korean Peninsula (KP) is known to consist of Archean&#8211;Proterozoic massifs (e.g., Gyeonggi, Yeongnam Massif) located in the forefront in northeast Asia, where current dynamics in the upper mantle and effects due to nearby subducting slabs are the most significant.Here we present, for the first time in detail, 3-D velocity structure of KP by teleseismic body wave traveltime tomography. Detailed P-wave and S-wave images of the crust and upper mantle were constructed by approximately 5 years of data from dense arrays of seismometers. We newly found a thick high-velocity body beneath the southwestern KP with a thickness of ~150 km, which is thought as a fragment of lithospheric root beneath the Proterozoic Yeongnam Massif. Also, we found low velocities beneath the Gyeonggi Massif, eastern KP margin, and Gyeongsang continental arc-back-arc system, showing significant velocity contrasts (dlnVp of ~4.0% and dlnVs of ~6.0%) to the high-velocity structure. These features indicate significantly modified regions. In addition, there was a clear correlation of the upper mantle low-velocity anomalies and areas characterized by Cenozoic basaltic eruptions, high heat flow, and high tomography, suggesting that there are close associations between mantle dynamics and recent tectonic reactivation.The presence of a remnant cratonic root beneath the KP and contrasting lithospheric structures across the different Precambrian massifs suggests highly heterogeneous modification along the Sino-Korean craton margin, which includes the KP and North China Craton. A striking localization of lithosphere modification among the different Precambrian massifs within the KP suggests that the structural heterogeneity of the craton margin is likely sharp in scale and thickness within a confined area. We suggest that intense interaction of upper mantle dynamics and inherent structural heterogeneities of a craton margin played an important role in shaping the current marginal lithosphere structure in northeast Asia.

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