The relationship between Vs, Vp, density and depth based on PS-logging data at K-NET and KiK-net sites

2021 ◽  
Author(s):  
Fumiaki Nagashima ◽  
Hiroshi Kawase
Keyword(s):  
Standard Deviation ◽  
Seismic Velocity ◽  
Saturated Soil ◽  
P Wave ◽  
Soil Types ◽  
Depth Range ◽  
Velocity Inversion ◽  
Velocity Models ◽  
Regression Curves ◽  
Ps Logging

Summary P-wave velocity (Vp) is an important parameter for constructing seismic velocity models of the subsurface structures by using microtremors and earthquake ground motions or any other geophysical exploration data. In order to reflect the ground survey information in Japan to the Vp structure, we investigated the relationships among Vs, Vp, and depth by using PS-logging data at all K-NET and KiK-net sites. Vp values are concentrated at around 500 m/s and 1,500 m/s when Vs is lower than 1,000 m/s, where these concentrated areas show two distinctive characteristics of unsaturated and saturated soil, respectively. Many Vp values in the layer shallower than 4 m are around 500 m/s, which suggests the dominance of unsaturated soil, while many Vp values in the layer deeper than 4 m are larger than 1,500 m/s, which suggests the dominance of saturated soil there. We also investigated those relationships for different soil types at K-NET sites. Although each soil type has its own depth range, all soil types show similar relationships among Vs, Vp, and depth. Then, considering the depth profile of Vp, we divided the dataset into two by the depth, which is shallower or deeper than 4 m, and calculated the geometrical mean of Vp and the geometrical standard deviation in every Vs bins of 200 m/s. Finally, we obtained the regression curves for the average and standard deviation of Vp estimated from Vs to get the Vp conversion functions from Vs, which can be applied to a wide Vs range. We also obtained the regression curves for two datasets with Vp lower and higher than 1,200 m/s. These regression curves can be applied when the groundwater level is known. In addition, we obtained the regression curves for density from Vs or Vp. An example of the application for those relationships in the velocity inversion is shown.

Crustal velocity structure beneath the NW Dinarides from 1-D hypocenter-velocity inversion

2021 ◽  
Author(s):  
Gregor Rajh ◽  
Josip Stipčević ◽  
Mladen Živčić ◽  
Marijan Herak ◽  
Andrej Gosar
Keyword(s):  
Velocity Structure ◽  
Velocity Model ◽  
P Wave ◽  
Depth Range ◽  
Velocity Inversion ◽  
Arrival Times ◽  
Simultaneous Inversion ◽  
Velocity Modeling ◽  
Velocity Models ◽  
Station Corrections

<p>The investigated area of the NW Dinarides is bordered by the Adriatic foreland, the Southern Alps, and the Pannonian basin at the NE corner of the Adriatic Sea. Its complex crustal structure is the result of interactions among different tectonic units. Despite numerous seismic studies taking place in this region, there still exists a need for a detailed, smaller scale study focusing mainly on the brittle part of the Earth's crust. Therefore, we decided to investigate the velocity structure of the crust using concepts of local earthquake tomography (LET) and minimum 1-D velocity model. Here, we present the results of the 1-D velocity modeling and the catalogue of the relocated seismicity. A minimum 1-D velocity model is computed by simultaneous inversion for hypocentral and velocity parameters together with seismic station corrections and represents the best fit to the observed arrival times.</p><p>We used 15,579 routinely picked P wave arrival times from 631 well-located earthquakes that occurred in Slovenia and in its immediate surroundings (mainly NW Croatia). Various initial 1-D velocity models, differing in velocity and layering, were used as input for velocity inversion in the VELEST program. We also varied several inversion parameters during the inversion runs. Most of the computed 1-D velocity models converged to a stable solution in the depth range between 0 and 25 km. We evaluated the inversion results using rigorous testing procedures and selected two best performing velocity models. Each of these models will be used independently as the initial model in the simultaneous hypocenter-velocity inversion for a 3-D velocity structure in LET. Based on the results of the 1-D velocity modeling, seismicity distribution, and tectonics, we divided the study area into three parts, redefined the earthquake-station geometry, and performed the inversion for each part separately. This way, we gained a better insight into the shallow velocity structure of each subregion and were able to demonstrate the differences among them.</p><p>Besides general structural implications and a potential to improve the results of LET, the new 1-D velocity models along with station corrections can also be used in fast routine earthquake location and to detect systematic travel time errors in seismological bulletins, as already shown by some studies using similar methods.</p>

New insights into structure and seismicity of the Central Alps from 3D Pg and Sg tomography and improved hypocenter relocations

2021 ◽  
Author(s):  
Tobias Diehl ◽  
Edi Kissling ◽  
Marco Herwegh ◽  
Stefan Schmid
Keyword(s):  
Velocity Structure ◽  
Focal Depth ◽  
Small Scale ◽  
Earthquake Catalog ◽  
Depth Range ◽  
Central Alps ◽  
Quartz Content ◽  
Phase Selection ◽  
Velocity Inversion ◽  
Velocity Models

<p>Accuracy of hypocenter location, in particular focal depth, is a precondition for high-resolution seismotectonic analysis of natural and induced seismicity. For instance, linking seismicity with mapped fault segments requires hypocenter accuracy at the sub-kilometer scale. In this study, we demonstrate that inaccurate velocity models and improper phase selection can bias absolute hypocenter locations and location uncertainties, resulting in errors larger than the targeted accuracy. To avoid such bias in densely instrumented seismic networks, we propose a coupled hypocenter-velocity inversion restricted to direct, upper-crustal Pg and Sg phases. The derived three-dimensional velocity models, combined with dynamic phase selection and non-linear location algorithms result in a highly accurate earthquake catalog, including consistent hypocenter uncertainties. We apply this procedure to about 60’000 Pg and 30’000 Sg quality-checked phases of local earthquakes in the Central Alps region. The derived tomographic models image the Vp and Vs velocity structure of the Central Alps’ upper crust at unprecedented resolution, including small-scale anomalies such as those caused by a Permo-Carboniferous trough in the northern foreland, Subalpine Molasse below the Alpine front or crystalline basement units within the Penninic nappes. The external Aar Massif is characterized by low Vp/Vs ratios of about 1.625-1.675 in the depth range of 2-6.5 km, which we relate to a felsic composition of the uplifted crustal block, possibly with increased quartz content. Finally, we discuss along-strike variations imaged by relocated seismicity in the Central Alps and demonstrate how joint interpretation of velocity structure and hypocenters provides additional constraints on lithologies of upper-crustal seismicity.</p>

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.

Focal mechanism of intermediate depth earthquakes in the Alboran Sea (Western Mediterranean)

2021 ◽  
Author(s):  
Carolina López-Sánchez ◽  
Elisa Buforn ◽  
Maurizio Mattesini ◽  
Simone Cesca ◽  
Juan Vicente Cantavella ◽  
...  
Keyword(s):  
Moment Tensor ◽  
Probabilistic Approach ◽  
Focal Mechanisms ◽  
P Wave ◽  
Earth Model ◽  
Depth Range ◽  
Alboran Sea ◽  
Intermediate Depth ◽  
Velocity Models ◽  
Alborán Sea

<p>One of the characteristics of the seismicity in the Ibero-Maghrebian region is the occurrence of intermediate depth earthquakes (50<h<100 km), their largest concentration located at the western part of the Alboran Sea, with epicenters following an NNE-SSW alignment. In this study, we have relocated over 200 intermediate depth earthquakes (M≥3) occurred in this region in the period 2000-2020, using a non-linear probabilistic approach (NonLinLoc algorithm) together with a recent regional 3D tomography lithospheric velocity model for the Alboran-Betic Rif Zone. Maximum likelihood hypocenters confirm the NNE-SSW distribution in a depth range between 50 and 100 km. We have determined the focal mechanisms of 26 of these earthquakes with magnitudes (mb) greater than 3.9. We first derived focal mechanisms using the P-wave first motion polarity method and then performed a moment tensor inversion, using a probabilistic inversion approach based on the simultaneous fit of waveforms and amplitude spectra of P and S phases. We performed an accurate resolution study, by repeating the inversion using different 1-D velocity models and testing different moment tensor (MT) constraints: a full moment tensor, a deviatoric moment tensor and a pure double couple (DC). Misfit values are similar for different MT constraints. Most solutions have a non-DC component larger than 30%. This may be due to the tectonic complexity of the region and the use on the inversion of 1-D Earth model. The DC components obtained from the inversion show different orientations of the nodal planes. A first group of events to the northern part with epicenters inland on south Spain have horizontal tension axes in NE-SW direction. A second group of earthquakes with epicenters off-shore, but close to the Spanish coast, presents near-vertical pressure axes. The third group, formed by deeper earthquakes, with epicenters on the center of the Alboran sea have dip slip focal mechanisms of either normal or reverse motion with planes either vertical or dipping 45º plane oriented in NNE-SSW direction, approximately the same orientation as the alignment of their epicenters. The distribution of these intermediate depth earthquakes and their focal mechanisms evidence the seismotectonic complexity of the region related with a possible subduction.</p>

CSEM-regularized seismic velocity inversion: A multiscale, hierarchical workflow for subsalt imaging

Geophysics ◽  
2018 ◽  
Vol 83 (5) ◽  
pp. B241-B252 ◽  
Author(s):  
Daniele Colombo ◽  
Diego Rovetta ◽  
Ersan Turkoglu
Keyword(s):  
Seismic Velocity ◽  
Fundamental Problem ◽  
Velocity Model ◽  
Seismic Inversion ◽  
Velocity Fields ◽  
Coupling Mechanism ◽  
Correct Result ◽  
Velocity Analysis ◽  
Velocity Inversion ◽  
Velocity Models

Seismic imaging in salt geology is complicated by highly contrasted velocity fields and irregular salt geometries, which cause complex seismic wavefield scattering. Although the imaging challenges can be addressed by advanced imaging algorithms, a fundamental problem remains in the determination of robust velocity fields in high-noise conditions. Conventional migration velocity analysis is often ineffective, and even the most advanced methods for depth-domain velocity analysis, such as full-waveform inversion, require starting from a good initial estimate of the velocity model to converge to a correct result. Nonseismic methods, such as electromagnetics, can help guide the generation of robust velocity models to be used for further processing. Using the multiphysics data acquired in the deepwater section of the Red Sea, we apply a controlled-source electromagnetic (CSEM) resistivity-regularized seismic velocity inversion for enhancing the velocity model in a complex area dominated by nappe-style salt tectonics. The integration is achieved by a rigorous approach of multiscaled inversions looping over model dimensions (1D first, followed by 3D), variable offsets and increasing frequencies, data-driven and interpretation-supported approaches, leading to a hierarchical inversion guided by a parameter sensitivity analysis. The final step of the integration consists of the inversion of seismic traveltimes subject to CSEM model constraints in which a common-structure coupling mechanism is used. Minimization is performed over the seismic data residuals and cross-gradient objective functions without inverting for the resistivity model, which is used as a reference for the seismic inversion (hierarchical approach). Results are demonstrated through depth imaging in which the velocity model derived through CSEM-regularized hierarchical inversion outperforms the results of a seismic-only derived velocity model.

scholarly journals New insights into Mt. Vesuvius hydrothermal system and its dynamic based on a critical review of seismic tomography and geochemical features

2013 ◽  
Vol 56 (4) ◽  
Author(s):  
Edoardo Del Pezzo ◽  
Giovanni Chiodini ◽  
Stefano Caliro ◽  
Francesca Bianco ◽  
Rosario Avino
Keyword(s):  
Hydrothermal System ◽  
Seismic Velocity ◽  
Seismic Energy ◽  
P Wave ◽  
Depth Range ◽  
Low Velocity ◽  
High Attenuation ◽  
Amplitude Spectra ◽  
Wave Travel ◽  
Attenuation Values

<p>The seismic velocity and attenuation tomography images, calculated inverting respectively P-wave travel times and amplitude spectra of local VT quakes at Mt. Vesuvius have been reviewed and graphically represented using a new software recently developed using Mathematica<span><sup>8TM</sup></span>. The 3-D plots of the interpolated velocity and attenuation fields obtained through this software evidence low-velocity volumes associated with high attenuation anomalies in the depth range from about 1 km to 3 km below the sea level. The heterogeneity in the distribution of the velocity and attenuation values increases in the volume centred around the crater axis and laterally extended about 4 km, where the geochemical interpretation of the data from fumarole emissions reveals the presence of a hydrothermal system with temperatures as high as 400-450°C roughly in the same depth range (1.5 km to 4 km). The zone where the hydrothermal system is space-confined possibly hosted the residual magma erupted by Mt. Vesuvius during the recent eruptions, and is the site where most of the seismic energy release has occurred since the last 1944 eruption.</p>

3-D microearthquake attenuation tomography at the Northwest Geysers geothermal region, California

Geophysics ◽  
1997 ◽  
Vol 62 (1) ◽  
pp. 149-167 ◽  
Author(s):  
Arturo E. Romero ◽  
Thomas V. McEvilly ◽  
Ernest L. Majer
Keyword(s):  
Geothermal Field ◽  
Text Structure ◽  
P Wave ◽  
Inversion Method ◽  
Reference Spectrum ◽  
Spectral Ratios ◽  
Velocity Inversion ◽  
Velocity Models ◽  
Average Spectrum ◽  
Attenuation Structure

We present the results of the modeling of a 3-D differential attenuation structure [Formula: see text] beneath the Northwest Geysers geothermal field. A set of 480 high‐quality microearthquakes distributed evenly throughout the field and with a minimum of 10 P‐wave arrivals was selected for the study. We constructed spectral ratios by dividing each spectrum with a reference spectrum from each observing station. The reference spectrum was derived from the average spectrum of all events that were recorded at that station to correct for the strong site dependence of the observed spectra. We then estimated the differential attenuation operator from the slopes of the spectral ratios. The velocity models and the raypaths for all events are known from a previous velocity inversion study. The inversion for the differential attenuation structure was carried out using a modified progressive inversion method. The observed [Formula: see text] structure correlates well with mapped geologic units. High [Formula: see text] and lower velocities correlate with Franciscan melange, while lower attenuation and higher velocities correspond to metagraywacke units. High P‐wave [Formula: see text] also underlies the southern region between 2 and 3 km depth where low [Formula: see text] values suggest undersaturation of the reservoir rocks. Most of the steam entries also occur within this region and probably delineate the steam reservoir. These anomalies may be explained by high rock temperatures and the presence of steam and other gases.

Seismic velocity models for heat zones in Athabasca tar sands

Geophysics ◽  
1990 ◽  
Vol 55 (8) ◽  
pp. 1108-1112 ◽  
Author(s):  
Larry R. Lines ◽  
Ronald Jackson ◽  
James D. Covey
Keyword(s):  
Seismic Velocity ◽  
Three Dimensional ◽  
Velocity Model ◽  
Steam Injection ◽  
P Wave ◽  
Injection Velocity ◽  
Low Velocity ◽  
Borehole Data ◽  
Tar Sands ◽  
Velocity Models

Recent laboratory and field studies indicate that the P-wave velocity in Athabasca tar sands decreases when temperature increases during steam injection. In this paper we derive time variant velocity models from seismic traveltime inversions of both reflection and borehole data. Prior to steam injection, three‐dimensional (3-D) reflector velocity‐depth models are established using image‐ray conversions of traveltimes to depth. The changes in velocity due to steam injection are modeled by inverting traveltime data from seismic monitor surveys after steam injection and comparing these results to velocities computed prior to steam injection. Velocity models are essentially determined by traveltimes from the 3-D seismic reflection survey. The surface‐to‐wellbore data traveltimes show the expected delay caused by steam injection but do not significantly alter the velocity model produced by reflection traveltimes. For seismic monitor surveys, low‐velocity zones show a very good correlation with zones of temperature increase at injector well positions. The results indicate that velocity models obtained from seismic traveltimes may prove useful in detecting steam fronts in tar sands.

scholarly journals Extensional tectonics during the Tyrrhenian back-arc basin formation synthetized in a new morpho-tectonic map

2020 ◽  
Author(s):  
Maria Filomena Loreto ◽  
Nevio Zitellini ◽  
César Rodriguez Ranero ◽  
Camilla Palmiotto ◽  
Manel Prada
Keyword(s):  
Seismic Velocity ◽  
Single Channel ◽  
Regional Scale ◽  
P Wave ◽  
Tyrrhenian Sea ◽  
Seismic Structure ◽  
Velocity Models ◽  
Mantle Exhumation ◽  
Back Arc ◽  
Tyrrhenian Basin

&lt;p&gt;A new tectonic map is presented focused upon the extensional style accompanying the formation of the Tyrrhenian back-arc basin. Our basin-wide analysis synthetizes the interpretation of vintage multichannel and single channel seismic profiles integrated with modern seismic images and P-wave velocity models, and with a new morpho-tectonic map of the Tyrrhenian (Palmiotto &amp; Loreto, 2019). Four distinct evolutionary opening stages have been constrained: 1) the initial Langhian(?)/Serravallian opening phase actives offshore central/southern Sardinia and offshore western Calabria; 2) the Tortonian/Messinian phase dominated by extension offshore North Sardinia-Corsica, and by oceanic accretion in the Cornaglia and Campania Terraces; 3) the Pliocene phase, dominated by mantle exhumation which was active mainly in the central Tyrrhenian and led to the full opening of Vavilov Basin; and 4) the Quaternary phase characterized by the opening of the Marsili back-arc basin. Listric and planar normal faults and their conjugates bound a series of horst and graben, half-graben and triangular basins. Distribution of extensional faults, active since Middle Miocene, throughout the basin allowed us to define a faults arrangement in the northern / central Tyrrhenian mainly related to in a pure shear which evolved a simple shear opening of continental margins. At depth, faults accommodate over a Ductile-Brittle Transitional zone cut by a low-angle detachment fault possibly responsible for mantle exhumation in the Vavilov and Magnaghi abyssal plains. In the southern Tyrrhenian, normal, inverse and transcurrent faults appear to be related to a large shear zone located along the continental margin of the northern Sicily. Extensional style variationthroughout the back-arc basin combined with wide-angle seismic velocity models, from Prada et al. (2014; 2015), allow to explore the relationship between shallow deformation, represented by faults distribution throughout the basin, and crustal-scale processes, subduction of Ionian slab and exhumation.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;REFERENCES&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Palmiotto, C., &amp; Loreto, M. F., (2019). Regional scale morphological pattern of the Tyrrhenian Sea: New insights from EMODnet bathymetry. Geomorphology, 332, 88-99.&lt;/p&gt;&lt;p&gt;Prada, M., Sallar&amp;#232;s, V., Ranero, C.R., Vendrell, M.G., Grevemeyer, I., Zitellini, N. &amp; De Franco, R., 2014. Seismic structure of the Central Tyrrhenian basin: Geophysical constraints on the nature of the main crustal domains. J. Geophys. Res.: Solid Earth, 119(1), 52-70.&lt;/p&gt;&lt;p&gt;Prada, M., Sallar&amp;#232;s, V., Ranero, C.R., Vendrell, M.G., Grevemeyer, I., Zitellini, N. &amp; De Franco, R., 2015. The complex 3-D transition from continental crust to backarc magmatism and exhumed mantle in the Central Tyrrhenian basin. Geophys. J. Int., 203(1), 63-78.&lt;/p&gt;

Distribution of Paleogene and Cretaceous rocks around the Nazko River belt of central British Columbia from 3-D long-offset first-arrival seismic tomography

2014 ◽  
Vol 51 (4) ◽  
pp. 358-372 ◽  
Author(s):  
Draga Talinga ◽  
Andrew J. Calvert
Keyword(s):  
British Columbia ◽  
Seismic Velocity ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Three Dimensional ◽  
Gravity Anomalies ◽  
Hydrocarbon Exploration ◽  
P Wave ◽  
Velocity Models ◽  
First Arrival

Across the Nechako–Chilcotin plateau of British Columbia, the distribution of Cretaceous sedimentary rocks, which are considered prospective for hydrocarbon exploration, is poorly known due to the surface cover of glacial deposits and Tertiary volcanic rocks. To constrain the subsurface distribution of these Cretaceous rocks, in 2008 Geoscience BC acquired seven long, up to 14.4 km, offset vibroseis seismic reflection lines across a north-northwest-trending belt of exhumed sedimentary rocks inferred to be part of the Taylor Creek Group. P-wave velocity models, which are consistent with sonic logs from nearby wells, have been estimated using three-dimensional first-arrival tomography to depths ranging from 1 to 4 km. Igneous basement can be identified on most lines using the 5.5 km/s isovelocity contour, which locates the top of the basement to an accuracy of ∼400 m where its depth is known in exploration wells. There is no general distinction on the basis of seismic velocity between Cretaceous sedimentary and Paleocene–Eocene volcanic–volcaniclastic rocks, both of which appear to be characterized in the tomographic models by velocities of 3.0–5.0 km/s. The geometry of the igneous basement inferred from the velocity models identifies north-trending basins and ridges, which correlate with exposed rocks of the Jurassic Hazelton Group. Identified Cretaceous sedimentary rocks occur beneath less negative Bouguer gravity anomalies, but the original distribution of these rocks has been disrupted by later Tertiary extension that created north-trending basins associated with the most negative gravity anomalies. We suggest that Cretaceous sedimentary rocks, if deposited, could be preserved within these basins if the rocks had not been eroded prior to Tertiary extension.

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