scholarly journals A three-dimensional crustal velocity model of the southwestern Alps from local earthquake tomography

2001 ◽  
Vol 106 (B9) ◽  
pp. 19367-19389 ◽  
Author(s):  
Anne Paul ◽  
Marco Cattaneo ◽  
François Thouvenot ◽  
Daniele Spallarossa ◽  
Nicole Béthoux ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Velocity Model ◽  
Local Earthquake Tomography ◽  
Crustal Velocity ◽  
Crustal Velocity Model ◽  
Local Earthquake ◽  
Southwestern Alps

scholarly journals Three-dimensional shear velocity structure of the Mauleon and Arzacq basins (Western Pyrenees)

2021 ◽  
Author(s):  
Maximilien Lehujeur ◽  
Sébastien Chevrot ◽  
Antonio Villaseñor ◽  
Emmanuel Masini ◽  
Nicolas Saspiturry ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Hanging Wall ◽  
Three Dimensional ◽  
Sedimentary Basins ◽  
Shear Velocity ◽  
Velocity Model ◽  
Tomographic Images ◽  
Reflection Seismic ◽  
Local Earthquake Tomography ◽  
Local Earthquake

We present a 3-D shear wave velocity model of the Mauleon and Arzacq basins from the surface down to 10~km depth. This model is obtained by inverting phase velocity maps for periods from 2 to 9~s measured on coherent surface wavefronts extracted from ambient seismic noise by matched filtering. This new model, which is found in good agreement with local earthquake tomography, reveals the architecture of the Mauleon and Arzacq basins which were poorly imaged by conventional reflection seismic data. Combining these new tomographic images with surface and subsurface geological information allows us to trace major orogenic structures from the basement to the surface. In the basin, the models are successfully imaging first-order folds and thrusts at kilometric scale. The velocity structure within the basement and its geometrical relationship with the base of inverted rift basins supports a progressive northward exhumation of deep crustal and mantle rocks in the hanging wall of north-vergent Pyrenean thrusts. Our tomographic models image in 3-D orogen-perpendicular structures responsible for crustal segmentation as the Saison and Barlanes transfer zones. We propose that these steep structures consist in tear faults that accommodate the deepening of the Mauleon basin basement from west to east. To the west, this basement made of former hyper-extended rift domains (including mantle rocks) is anomalously sampled within the hanging-wall of north-directed orogenic thrusts, explaining its shallow attitude and its best preservation in comparison to the eastern segment of the study area. Eastward, the vertical shift of the basement makes that the former Mauleon basin hyper-extended rift basement remained in a footwall situation in respect of orogenic thrust and was underthrust. The comparison of the tomographic models obtained with surface wave tomography and local earthquake tomography shows that each approach has its own advantages and shortcomings but also that they are very complementary in nature, which would suggest to combine them in joint inversions to further improve passive imaging of the shallow crust and sedimentary basins.

scholarly journals Characteristics of local earthquake seismograms of varying dislocation sources in a stratified upper crust and modeling for P and S velocity structure: comparison with observations in the Koyna-Warna region, India

2016 ◽  
Vol 58 (6) ◽  
Author(s):  
V. G. Krishna
Keyword(s):  
Velocity Structure ◽  
Source Parameters ◽  
Velocity Model ◽  
Strike Slip ◽  
Synthetic Seismograms ◽  
Structure Comparison ◽  
Earthquake Sources ◽  
Crustal Velocity ◽  
Source Mechanisms ◽  
Local Earthquake

<p>Vertical component record sections of local earthquake seismograms from a state-of-the-art Koyna-Warna digital seismograph network are assembled in the reduced time versus epicentral distance frame, similar to those obtained in seismic refraction profiling. The record sections obtained for an average source depth display the processed seismograms from nearly equal source depths with similar source mechanisms and recorded in a narrow azimuth range, illuminating the upper crustal P and S velocity structure in the region. Further, the seismogram characteristics of the local earthquake sources are found to vary significantly for different source mechanisms and the amplitude variations exceed those due to velocity model stratification. In the present study a large number of reflectivity synthetic seismograms are obtained in near offset ranges for a stratified upper crustal model having sharp discontinuities with 7%-10% velocity contrasts. The synthetics are obtained for different source regimes (e.g., strike-slip, normal, reverse) and different sets of source parameters (strike, dip, and rake) within each regime. Seismogram sections with dominantly strike-slip mechanism are found to be clearly favorable in revealing the velocity stratification for both P and S waves. In contrast the seismogram sections for earthquakes of other source mechanisms seem to display the upper crustal P phases poorly with low amplitudes even in presence of sharp discontinuities of high velocity contrasts. The observed seismogram sections illustrated here for the earthquake sources with strike-slip and normal mechanisms from the Koyna-Warna seismic region substantiate these findings. Travel times and reflectivity synthetic seismograms are used for 1-D modeling of the observed virtual source local earthquake seismogram sections and inferring the upper crustal velocity structure in the Koyna-Warna region. Significantly, the inferred upper crustal velocity model in the region reproduces the synthetic seismograms comparable to the observed sections for earthquake sources with differing mechanisms in the Koyna and Warna regions.</p>

scholarly journals NAD83v70VG: a new national crustal velocity model for Canada

2020 ◽  
Author(s):  
C M I Robin ◽  
M Craymer ◽  
R Ferland ◽  
T S James ◽  
E Lapelle ◽  
...  
Keyword(s):  
Velocity Model ◽  
Crustal Velocity ◽  
Crustal Velocity Model

scholarly journals The Local Earthquake Tomography of Erzurum (Turkey) Geothermal Area

2019 ◽  
Vol 23 (3) ◽  
pp. 209-223 ◽  
Author(s):  
Caglar Ozer ◽  
Mehmet Ozyazicioglu
Keyword(s):  
Wave Velocity ◽  
Seismic Velocity ◽  
Three Dimensional ◽  
P Wave ◽  
Geothermal Area ◽  
S Wave ◽  
Velocity Models ◽  
Local Earthquake Tomography ◽  
P Wave Velocity ◽  
Local Earthquake

Erzurum and its surroundings are one of the seismically active and hydrothermal areas in the Eastern part of Turkey. This study is the first approach to characterize the crust by seismic features by using the local earthquake tomography method. The earthquake source location and the three dimensional seismic velocity structures are solved simultaneously by an iterative tomographic algorithm, LOTOS-12. Data from a combined permanent network comprising comprises of 59 seismometers which was installed by Ataturk University-Earthquake Research Center and Earthquake Department of the Disaster and Emergency Management Authority  to monitor the seismic activity in the Eastern Anatolia, In this paper, three-dimensional Vp and Vp/Vs characteristics of Erzurum geothermal area were investigated down to 30 km by using 1685 well-located earthquakes with 29.894 arrival times, consisting of 17.298 P- wave and 12.596 S- wave arrivals. We develop new high-resolution depth-cross sections through Erzurum and its surroundings to provide the subsurface geological structure of seismogenic layers and geothermal areas. We applied various size horizontal and vertical checkerboard resolution tests to determine the quality of our inversion process. The basin models are traceable down to 3 km depth, in terms of P-wave velocity models. The higher P-wave velocity areas in surface layers are related to the metamorphic and magmatic compact materials. We report that the low Vp and high Vp/Vs values are observed in Yedisu, Kaynarpinar, Askale, Cimenozu, Kaplica, Ovacik, Yigitler, E part of Icmeler, Koprukoy, Uzunahmet, Budakli, Soylemez, Koprukoy, Gunduzu, Karayazi, Icmesu, E part of Horasan and Kaynak regions indicated geothermal reservoir.

scholarly journals A tomographic crustal velocity model of the central Fennoscandian Shield

2007 ◽  
Vol 168 (3) ◽  
pp. 1210-1226 ◽  
Author(s):  
Tellervo Hyvönen ◽  
Timo Tiira ◽  
Annakaisa Korja ◽  
Pekka Heikkinen ◽  
Elisa Rautioaho ◽  
...  
Keyword(s):  
Velocity Model ◽  
Fennoscandian Shield ◽  
Crustal Velocity ◽  
Crustal Velocity Model
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