scholarly journals Influence of incoming plate relief on overriding plate deformation and earthquake nucleation: Cocos Ridge subduction (Costa Rica)

2020 ◽  
Author(s):  
Sara Martínez-Loriente ◽  
Valentí Sallarès ◽  
César R. Ranero ◽  
Jonas B. Ruh ◽  
Udo Barckhausen ◽  
...  
Keyword(s):  
Costa Rica ◽  
Continental Shelf ◽  
Velocity Structure ◽  
Numerical Models ◽  
P Wave ◽  
Seismic Reflection Profile ◽  
Rock Fracturing ◽  
Ridge Subduction ◽  
Shelf Sediment ◽  
Earthquake Nucleation

<p>We present a 2D p-wave velocity (Vp) model and a coincident multichannel seismic reflection profile mapping the structure of the southern Costa Rica margin and incoming Cocos Ridge. The seismic profiles image the ocean and overriding plates from the trench across the entire offshore margin, including the structures involved in the 2002 Mw6.4 Osa earthquake. The overriding plate consists of three domains: Domain I at the margin front displays thin-skinned deformation of an imbricated-thrust system composed of fractured rocks with relatively low Vp. Domain II under the middle continental shelf is comparatively less fractured, showing ~15 km long landward-dipping reflection packages and discrete active deformation of the shelf sediment and seafloor. Domain III in the inner shelf is little fractured and appears to be dominated by elastic deformation, with inactive structures of an extensional basin consisting of tilted blocks overlain by ~2 km-thick gently landward-dipping strata. The velocity structure supports the argument that the bulk of the margin is highly consolidated rock possibly similar to outcrops in the Osa Peninsula. Thick-skinned tectonics probably causes the uplift of Domains II and III. The incoming oceanic plate shows crustal thickness variations from ~14 km at the trench (Cocos Ridge) to 6-7 km beneath the continental shelf. We combine (1) inter-plate geometry and velocity-derived fracturing degree at the base of the overriding plate, (2) tectonic stresses and brittle strain above the inter-plate boundary extracted from 3D numerical models, and (3) earthquake locations, to investigate potential relationships between structure and earthquake generation. The 2002 Osa earthquake and its aftershocks appear to have nucleated at the leading flank of two subducting seamounts, coinciding with the area of highest tectonic overpressure in numerical models. Both estimated rock fracturing and modelled brittle strain, steadily increase from the leading flank of the subducting seamounts to their top, which we interpret to reflect the progressive damage caused by the incoming plate relief. Therefore, the analysis supports a spatial and temporal relationship between subducting seamount location, upper plate fracturing, brittle strain, tectonic overpressure, and earthquake nucleation.</p>

Crust and upper mantle velocity structure of the Intermontane belt, southern Canadian Cordillera

1992 ◽  
Vol 29 (7) ◽  
pp. 1530-1548 ◽  
Author(s):  
B. C. Zelt ◽  
R. M. Ellis ◽  
R. M. Clowes ◽  
E. R. Kanasewich ◽  
I. Asudeh ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Velocity Structure ◽  
P Wave ◽  
Seismic Reflection Profile ◽  
Wide Angle ◽  
Low Velocity ◽  
Crust And Upper Mantle ◽  
Middle Crust ◽  
Refraction Data

As part of the Lithoprobe Southern Cordillera transect, seismic refraction data were recorded along a 330 km long strike profile in the Intermontane belt. An iterative combination of two-dimensional traveltime inversion and amplitude forward modelling was used to interpret crust and upper mantle P-wave velocity structure. This region is characterized by (i) a thin near-surface layer with large variations in velocity between 2.8 and 5.4 km/s, and low-velocity regions that correlate well with surface expressions of Tertiary sedimentary and volcanic rocks; (ii) an upper and middle crust with low average velocity gradient, possibly a weak low-velocity zone, and lateral velocity variations between 6.0 and 6.4 km/s; (iii) a distinctive lower crust characterized by significantly higher average velocities relative to midcrustal values beginning at 23 km depth, approximately 8 km thick with average velocities of 6.5 and 6.7 km/s at top and base; (iv) a depth to Moho, as defined by wide-angle reflections, that averages 33 km with variations up to 2 km; and (v) a Moho transition zone of depth extent 1–3 km, below which lies the upper mantle with velocities decreasing from 7.9 km/s in the south to 7.7 km/s in the north. Where the refraction line obliquely crosses a Lithoprobe deep seismic-reflection profile, good agreement is obtained between the interpreted reflection section and the derived velocity structure model. In particular, depths to wide-angle reflectors in the upper crust agree with depths to prominent reflection events, and Moho depths agree within 1 km. From this comparison, the upper and middle crust probably comprise the upper part of the Quesnellia terrane. The lower crust from the refraction interpretation does not show the division into two components, parautochthonous and cratonic North America, that is inferred from the reflection data, indicating that their physical properties are not significantly different within the resolution of the refraction data. Based on these interpretations, the lower lithosphere of Quesnellia is absent and presumably was recycled in the mantle. At a depth of ~ 16 km below the Moho, an upper mantle reflector may represent the base of the present lithosphere.

Crustal structure across the Nain – Makkovik boundary on the continental shelf off Labrador from seismic refraction data

1996 ◽  
Vol 33 (3) ◽  
pp. 460-471 ◽  
Author(s):  
Ian Reid
Keyword(s):  
Continental Shelf ◽  
Wave Velocity ◽  
Crustal Structure ◽  
Lower Crust ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
P Wave ◽  
Air Gun ◽  
P Wave Velocity

A detailed seismic refraction profile was shot along the continental shelf off Labrador, across the boundary between the Archean Nain Province to the north and the Proterozoic Makkovik orogenic zone to the south. A large air-gun source was used, with five ocean-bottom seismometers as receivers. The data were analysed by forward modelling of traveltimes and amplitudes and provided a well-determined seismic velocity structure of the crust along the profile. Within the Nain province, thin postrift sediments are underlain by crust with a P-wave velocity of 6.1 km/s, which increases with depth and reaches 6.6 km/s at about 8 km. Moho is at around 28 km, and there is no evidence for a high-velocity (>7 km/s) lower crust. The P- and S-wave velocity structure is consistent with a gneissic composition for the Archean upper crust, and with granulites becoming gradually more mafic with depth for the intermediate and lower crust. In the Makkovik zone, the sediments are thicker, and a basement layer of P-wave velocity 5.5–5.7 km/s is present, probably due to reworking of the crust and the presence of Early Proterozoic volcanics and metasediments. Upper crustal velocities are lower than in the Nain Province. The crustal thickness, at 23 km, is less, possibly due in part to greater crustal stretching during the Mesozoic rifting of the Labrador Sea. The crustal structure across the Nain–Makkovik boundary is similar to that across the corresponding Archean–Ketilidian boundary off southwest Greenland.

Simultaneous inversion for earthquake location and velocity structure beneath central Costa Rica

1996 ◽  
Vol 86 (1A) ◽  
pp. 19-31 ◽  
Author(s):  
Marino Protti ◽  
Susan Y. Schwartz ◽  
George Zandt
Keyword(s):  
Costa Rica ◽  
Velocity Structure ◽  
P Wave ◽  
Inversion Method ◽  
Cocos Plate ◽  
Low Velocity ◽  
Arrival Times ◽  
Simultaneous Inversion ◽  
Late Tertiary ◽  
Shallow Crust

Abstract We have imaged the complex crustal and upper mantle structure beneath central Costa Rica using P-wave arrival times from locally recorded earthquakes. Thurber's (1983) iterative inversion method is used to simultaneously estimate velocities along a three-dimensional grid and hypocentral parameters of local earthquakes. Our data consist of over 12,000 arrival times from more than 1300 earthquakes recorded by stations of a permanent seismographic network in Costa Rica. Our resulting velocity model correlates well with mapped geologic units at very shallow depth and with tectonic features at greater depth. We find low velocities (4.0 to 4.8 km/sec) in the shallow crust (above 10 km) near the active volcanoes and associated with a NW-SE trending late Cretaceous to late Tertiary sedimentary basin southeast of Herradura peninsula. High velocities (5.4 to 5.7 km/sec) in the shallow crust correlate with outcrops of late Jurassic to early Tertiary ultramafic ophiolitic units and with basic Tertiary volcanic units. At depths between 20 and 30 km, high velocities (6.8 to 7.2 km/sec) are associated with the subducting Cocos plate under Costa Rica and two prominent low-velocity bodies (6.3 to 6.5 km/sec) are present about 30 km trenchward of the volcanic arc and along the projection of the aseismic Cocos Ridge as it subducts beneath Costa Rica. The thickened oceanic crust of the Cocos Ridge is most likely responsible for its low velocities. The deep low-velocity anomaly located trenchward of the axis of the volcanoes may indicate the presence of a low-density intrusive resulting from an earlier phase of magmatism, possibly the late Miocene episode that produced the Talamanca intrusive complex.

scholarly journals Influence of Incoming Plate Relief on Overriding Plate Deformation and Earthquake Nucleation: Cocos Ridge Subduction (Costa Rica)

Tectonics ◽  
2019 ◽  
Vol 38 (12) ◽  
pp. 4360-4377 ◽  
Author(s):  
Sara Martínez‐Loriente ◽  
Valentí Sallarès ◽  
César R. Ranero ◽  
Jonas B. Ruh ◽  
Udo Barckhausen ◽  
...  
Keyword(s):  
Costa Rica ◽  
Plate Deformation ◽  
Ridge Subduction ◽  
Earthquake Nucleation

Crustal P-wave velocity structure and earthquake distribution in the Jiaodong Peninsula, China

2021 ◽  
pp. 228973
Author(s):  
Junhao Qu ◽  
Stephen S. Gao ◽  
Changzai Wang ◽  
Kelly H. Liu ◽  
Shaohui Zhou ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Velocity Structure ◽  
P Wave ◽  
Jiaodong Peninsula ◽  
P Wave Velocity ◽  
Earthquake Distribution ◽  
P Wave Velocity Structure

Estimates of velocity structure and source depth using multiple P waves from aftershocks of the 1987 Elmore Ranch and Superstition Hills, California, earthquakes

1991 ◽  
Vol 81 (2) ◽  
pp. 508-523
Author(s):  
Jim Mori
Keyword(s):  
Velocity Structure ◽  
Velocity Model ◽  
P Wave ◽  
Sediment Layer ◽  
Source Depth ◽  
Imperial Valley ◽  
P Waves ◽  
Main Shocks ◽  
Aftershock Sequences ◽  
Event Record

Abstract Event record sections, which are constructed by plotting seismograms from many closely spaced earthquakes recorded on a few stations, show multiple free-surface reflections (PP, PPP, PPPP) of the P wave in the Imperial Valley, California. The relative timing of these arrivals is used to estimate the strength of the P-wave velocity gradient within the upper 5 km of the sediment layer. Consistent with previous studies, a velocity model with a value of 1.8 km/sec at the surface increasing linearly to 5.8 km/sec at a depth of 5.5 km fits the data well. The relative amplitudes of the P and PP arrivals are used to estimate the source depth for the aftershock distributions of the Elmore Ranch and Superstition Hills main shocks. Although the depth determination has large uncertainties, both the Elmore Ranch and Superstition Hills aftershock sequences appear to have similar depth distribution in the range of 4 to 10 km.

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