scholarly journals Three dimensional velocity structure and relocated aftershocks for the 1985 Constantine, Algeria (MS = 5.9) earthquake

1998 ◽  
Vol 41 (1) ◽  
Author(s):  
M. ou A. Bounif ◽  
C. Dorbath
Keyword(s):  
Velocity Structure ◽  
Three Dimensional ◽  
Velocity Model ◽  
P Wave ◽  
Time Data ◽  
Data Set ◽  
S Waves ◽  
Travel Time Data ◽  
Velocity Image ◽  
Local Earthquake

Local earthquake travel-time data were inverted to obtain a three dimensional tomographic image of the region centered on the 1985 Constantine earthquake. The resulting velocity model was then used to relocate the events. The tomographic data set consisted of P and S waves travel-times from 653 carefully selected aftershocks of this moderate size earthquake, recorded at 10 temporary stations. A three-dimensional P-wave velocity image to a depth of 12 km was obtained by Thurber's method. At shallower depth, the velocity contrasts reflected the differences in tectonic units. Velocities lower than 4 km/s corresponded to recent deposits, velocities higher than 5 km/s to the Constantine Neritic and the Tellian nappes. The relocation of the aftershocks indicates that most of the seismicity occured where the velocity exceeded 5.5 km/s. The aftershock distribution accurately defined the three segments involved in the main shock and led to a better understanding of the rupture process.

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 Shear waves through the Earth's core

1935 ◽  
Vol 149 (866) ◽  
pp. 88-103 ◽  
Keyword(s):  
Magnetic Properties ◽  
P Wave ◽  
Time Data ◽  
P Waves ◽  
Nickel Iron ◽  
S Waves ◽  
The Core ◽  
The Earth ◽  
Travel Time Data ◽  
Core Depth

Seismological evidence of a central core to the earth was first pointed out by Oldham in 1906. From his analysis of travel-time data regarding longitudinal (P) and transverse (S) waves observed at great distances from earthquake epicentres, he concluded that at a depth equal to about three-fifths of the radius there occurs a transition to material possessing radically different physical properties from that external to this boundary. With the aid of more extensive data assembled by Turner and others, the problem was later re-examined independently by Knott and by Gutenberg. The latte concluded that at a depth of 2900 km the velocity of P waves suddenly decreases from over 13 km per sec to about 8 1/2. The theory involves the appearance of a delayed P wave at epicentral distances beyond 143º, and the chief characteristics predicted for this wave have been amply verified by Gutenberg, by Macelwane and by Lehmann. Also Wadati has lately confirmed the earlier estimates of the core depth from observation on S c S. Mean density considerations suggest that this core is metallic; and the magnetic properties of the earth are consistent with a nickel-iron composition resembling that found in many meteors.

scholarly journals VELOCITY MODEL OF CRUST OF AZERBAIDJAN ON DATA OF DIGITAL SEISMIC STATIONS

2012 ◽  
Author(s):  
Г.Д. Етирмишли ◽  
С.Э. Казымова
Keyword(s):  
Velocity Structure ◽  
Three Dimensional ◽  
Velocity Model ◽  
Design Calculation ◽  
Travel Times ◽  
Seismic Stations ◽  
One Dimensional ◽  
S Waves ◽  
Velocity Models ◽  
Seismological Data

При изучении скоростной структуры земной коры Азербайджана по сейсмологическим данным ис- пользовались в основном два подхода. Первый состоит в уточнении модели среды на основании наблюда- емых отклонений времен пробега волн от землетрясений относительно стандартного годографа. Второй основан на использовании разности времен пробега от источников до станции для групп близко располо- женных событий. Одномерные скоростные модели Р и S-волн были построены на основе одномерных моделей, пред- ложенных в работе Гасанова А.Г. Построение модели, расчет станционных поправок и перелокация со- бытий производились в программе Velest. Исследуемый объем до глубины 60 км был разбит на мелкие слои толщиной 2 км в интервале глубин 010 км и толщиной 510 км в интервале глубин 1060 км. В ходе исследования рассматривались сейсмологические данные о параметрах локальных землетрясений и вре- менах прихода P и S-волн зарегистрированных сетью телеметрических станций за период 20042011 гг. Анализировались данные 28-ми сейсмических станций Азербайджана, охватывающие всю исследуемую территорию. Для расчета трехмерного скоростного поля использовалась программа TomotetraFD. В этой програм- ме реализован классический сейсмотомографический метод для случая, когда источники и приемники находятся внутри исследуемого региона. Two approaches were used for investigation of crust velocity structure of Azerbaijan on the basis of seismological data. The first one consists in medium model adjustment on the basis of observed deviation of travel times of waves from earthquakes relative to standard hodograph. The second is based on difference in travel times from source to station for a group of close located stations. One dimensional velocity models of P- and S-waves were constructed on the basis of one dimensional models proposed by A.G.Gasanov. Model design, calculation of stations corrections and relocationing of events 74 Геология и геофизика Юга России, 1, 2012 were performed in Velest program. Investigating volume to depth of 60 km was divided in small layers of 2 km thickness in 0-10 km interval and 5-10 km in 10-60 km interval. Seismological data about parameters of local earthquakes registered by network of telemetric stations in 2004-2011 and arrival times of P- and S-waves were used. Data of 28 seismic stations of Azerbaijan covering all the investigating territory were analyzed. Three dimensional velocity field was calculated by means of TomotetraFD program. Classical seismotomographical method for the case when sources and receivers are located within investigating region is realized in the program.

scholarly journals 3D Seismic Waves Velocity Structure of West Sumatera Seismic Waves Using Earthquake Data from January 2010-December 2017

2021 ◽  
Vol 873 (1) ◽  
pp. 012003
Author(s):  
Rizki Wulandari ◽  
Tedi Yudistira ◽  
Erlangga Ibrahim Fattah ◽  
Atin Nur Aulia ◽  
Adhi Wibowo
Keyword(s):  
Fault Zone ◽  
Seismic Tomography ◽  
Seismic Waves ◽  
Velocity Structure ◽  
Secondary Data ◽  
Velocity Model ◽  
P Wave ◽  
3D Seismic ◽  
Time Data ◽  
West Sumatra

Abstract This study analyses the P wave velocity (Vp) and Vp/Vs based on 3D seismic tomography in West Sumatra. Seismic tomography is a method of reconstructing the image of the subsurface structure of the earth using travel time data. This research uses secondary data obtained from the Incorporated Research Institutions for Seismology (IRIS) from January 2010 to December 2017. The data obtained were 472 earthquake events and 21 seismic stations that recorded the earthquake events. This research consists of are the hypocenter relocation, which will simultaneously renew the 1D velocity model using VELEST software, and tomographic inversion using SIMULPS12 software. The minimum anomaly of Vp/Vs value is around 1.39, while the maximum anomaly Vp/Vs value is around 2.05. The Vp distribution results have low and high Vp/Vs values around Sumatra Fault Zone and Mentawai Fault Zone. Anomaly results from the tomogram of these areas have an association with saturated pressure sedimentary areas and the presence of fractures which will further contribute to earthquake events.

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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