The Crustal Seismicity of the Western Andean Thrust (Central Chile, 33°–34° S): Implications for Regional Tectonics and Seismic Hazard in the Santiago Area

2019 ◽  
Vol 109 (5) ◽  
pp. 1985-1999
Author(s):  
Jean-Baptiste Ammirati ◽  
Gabriel Vargas ◽  
Sofía Rebolledo ◽  
Rachel Abrahami ◽  
Bertrand Potin ◽  
...  
Keyword(s):  
Velocity Model ◽  
Fault Scarp ◽  
S Wave ◽  
The West ◽  
Nazca Plate ◽  
Study Region ◽  
Central Chile ◽  
3D Velocity Model ◽  
Wave Travel ◽  
Regional Tectonics

Abstract Most of the recorded seismicity in central Chile can be linked to the subduction of the Nazca plate. To the east, a much smaller fraction is observed at 0–30 km depths beneath the western Andean thrust. Paleoseismic studies evidenced the occurrence of at least two major earthquakes (M>7) over the past 17 ka, associated with the San Ramón fault (SRF): an important tectonic feature characterizing the west Andean thrust, close the Santiago metropolitan area. To better constrain the crustal seismicity in this area, the Chilean Seismological Center (CSN) extended its permanent seismic network with seven new broadband seismometers deployed around the scarp of the SRF and farther east. The improved azimuthal distribution and reduced station spacing allowed to complete the CSN catalog with more than 900 smaller magnitude earthquakes (ML<2.5) detected and located within the study region. The use of a 3D velocity model derived from P- and S-wave travel-time tomography considerably lowered the uncertainties associated with hypocentral locations. Our results show an important seismicity beneath the Principal Cordillera located at a depth of ∼10  km, and a deeper seismicity (~15 km) aligned with the main Andean thrust more to the west, parallel to the scarp of the SRF. Regional stress inversion results suggest that the seismicity of the west Andean thrust is accommodating northeast–southwest compressional stress, consistent with the convergence of the Nazca plate. Based on our improved crustal seismicity, combined with observations from previous studies, we have been able to refine the scenario of an Mw 7.5 earthquake rupturing the SRF. Ground-motion prediction results show peak ground accelerations of ∼0.8g close to the fault scarp.

Passive seismic tomography using recorded microseismicity: Application to mining-induced seismicity

Geophysics ◽  
2019 ◽  
Vol 84 (1) ◽  
pp. B41-B57 ◽  
Author(s):  
Himanshu Barthwal ◽  
Mirko van der Baan
Keyword(s):  
Seismic Tomography ◽  
Velocity Model ◽  
P Wave ◽  
Double Difference ◽  
Lateral Velocity ◽  
Study Region ◽  
Arrival Times ◽  
3D Velocity Model ◽  
Passive Seismic ◽  
Dip Angle

Microseismicity is recorded during an underground mine development by a network of seven boreholes. After an initial preprocessing, 488 events are identified with a minimum of 12 P-wave arrival-time picks per event. We have developed a three-step approach for P-wave passive seismic tomography: (1) a probabilistic grid search algorithm for locating the events, (2) joint inversion for a 1D velocity model and event locations using absolute arrival times, and (3) double-difference tomography using reliable differential arrival times obtained from waveform crosscorrelation. The originally diffusive microseismic-event cloud tightens after tomography between depths of 0.45 and 0.5 km toward the center of the tunnel network. The geometry of the event clusters suggests occurrence on a planar geologic fault. The best-fitting plane has a strike of 164.7° north and dip angle of 55.0° toward the west. The study region has known faults striking in the north-northwest–south-southeast direction with a dip angle of 60°, but the relocated event clusters do not fall along any mapped fault. Based on the cluster geometry and the waveform similarity, we hypothesize that the microseismic events occur due to slips along an unmapped fault facilitated by the mining activity. The 3D velocity model we obtained from double-difference tomography indicates lateral velocity contrasts between depths of 0.4 and 0.5 km. We interpret the lateral velocity contrasts in terms of the altered rock types due to ore deposition. The known geotechnical zones in the mine indicate a good correlation with the inverted velocities. Thus, we conclude that passive seismic tomography using microseismic data could provide information beyond the excavation damaged zones and can act as an effective tool to complement geotechnical evaluations.

Hypocenter Analysis of Aftershocks Data of the Mw 6.3, 27 May 2006 Yogyakarta Earthquake Using Oct-Tree Importance Sampling Method

2018 ◽  
Vol 881 ◽  
pp. 89-97 ◽  
Author(s):  
Asri Wulandari ◽  
Ade Anggraini ◽  
Wiwit Suryanto
Keyword(s):  
Importance Sampling ◽  
Sampling Method ◽  
Velocity Model ◽  
Fault Scarp ◽  
P Wave ◽  
Double Difference ◽  
S Wave ◽  
Maximum Probability ◽  
Importance Sampling Method ◽  
Dip Angle

Yogyakarta earthquake, Mw 6.3, 27 May 2006 had killed 5,571 victims and destroyed more than 1 million buildings. This incident became the most destructive earthquake disaster over the last 11 years in Indonesia. Earthquake mitigation plan in the area has been carried out by understands the location of the fault. The location of the fault is still unclear among geoscientists until now. In this case, analysis of the aftershocks using oct-tree importance sampling method was applied to support the location of the fault that responsible for the 2006 Yogyakarta earthquake. Oct-tree importance sampling is a method that is recursively subdividing the solution domain into exactly eight children for estimating properties of a particular distribution. The final result of the subdividing process is a cell that has a maximum Probability Density Function (PDF) and identified as the location of the hypocenter. Input data consists of the arrival time of the P wave and S wave of the aftershocks catalog from 3-7 June 2006 and the coordinate of the 12 seismometers, and 1D velocity model of the study area. Based on the hypocenter distribution of the aftershocks data with the proposed method show a clearer trend of the fault compared with the aftershocks distribution calculated with theHypo71program. The fault trend has a strike orientation of N 42° E with a dip angle of 80° parallel with the fault scarp along the Opak River at the distance of about 15 km to the east. This fault trend is similar with the fault orientation obtained using the Double Difference Algorithm.

The January 2019 (Mw 6.7) Coquimbo Earthquake: Insights from a Seismic Sequence within the Nazca Plate

2019 ◽  
Author(s):  
Sergio Ruiz ◽  
Jean‐Baptiste Ammirati ◽  
Felipe Leyton ◽  
Leoncio Cabrera ◽  
Bertrand Potin ◽  
...  
Keyword(s):  
Moment Tensor ◽  
High Stress ◽  
Normal Fault ◽  
Seismic Source ◽  
Velocity Model ◽  
Seismic Sequence ◽  
Ground Acceleration ◽  
Nazca Plate ◽  
3D Velocity Model ◽  
Macroseismic Intensities

ABSTRACT On 20 January 2019, the Chilean cities of Coquimbo and La Serena were shaken by an intraplate earthquake of Mw 6.7 located at 70 km depth. High peak ground acceleration values and macroseismic intensities were reported. The mainshock was followed by more than 150 aftershocks higher than ML 2.5, a seismic sequence completely recorded by local stations. Using a 3D velocity model, we precisely located the seismicity. The aftershocks were located some 20 km above and shifted from the mainshock but still inside the Nazca plate. We also performed moment tensor inversion of nine events obtaining mostly normal‐fault focal mechanisms and kinematic inversions using the elliptical‐patch approach. We found that the mainshock broke an approximated zone of 6 km by 8 km, propagated upward in the northwest direction and away from the aftershock area. The rupture inverted from accelerograms containing up to 1 Hz was characterized with a high stress drop of 7.51 MPa and a short seismic source time function of only 3 s duration.

scholarly journals Earthquake location in tectonic structures of the Alpine Chain: the case of the Constance Lake (Central Europe) seismic sequence

2021 ◽  
Author(s):  
Francesca D’Ajello Caracciolo ◽  
Rodolfo Console
Keyword(s):  
Central Europe ◽  
Velocity Model ◽  
Moho Depth ◽  
Seismic Sequence ◽  
Tectonic Structures ◽  
Study Region ◽  
Waveform Data ◽  
Seismic Stations ◽  
Velocity Models ◽  
Master Event

AbstractA set of four magnitude Ml ≥ 3.0 earthquakes including the magnitude Ml = 3.7 mainshock of the seismic sequence hitting the Lake Constance, Southern Germany, area in July–August 2019 was studied by means of bulletin and waveform data collected from 86 seismic stations of the Central Europe-Alpine region. The first single-event locations obtained using a uniform 1-D velocity model, and both fixed and free depths, showed residuals of the order of up ± 2.0 s, systematically affecting stations located in different areas of the study region. Namely, German stations to the northeast of the epicenters and French stations to the west exhibit negative residuals, while Italian stations located to the southeast are characterized by similarly large positive residuals. As a consequence, the epicentral coordinates were affected by a significant bias of the order of 4–5 km to the NNE. The locations were repeated applying a method that uses different velocity models for three groups of stations situated in different geological environments, obtaining more accurate locations. Moreover, the application of two methods of relative locations and joint hypocentral determination, without improving the absolute location of the master event, has shown that the sources of the four considered events are separated by distances of the order of one km both in horizontal coordinates and in depths. A particular attention has been paid to the geographical positions of the seismic stations used in the locations and their relationship with the known crustal features, such as the Moho depth and velocity anomalies in the studied region. Significant correlations between the observed travel time residuals and the crustal structure were obtained.

Rayleigh Wave Dispersion Curve Inversion with the Artificial Bee Colony Algorithm

2021 ◽  
Vol 26 (2) ◽  
pp. 99-110
Author(s):  
Xin Wang ◽  
Hongyan Shen ◽  
Xinxin Li ◽  
Qin Li ◽  
Daoyuan Wang
Keyword(s):  
Rayleigh Wave ◽  
Dispersion Curve ◽  
Artificial Bee Colony Algorithm ◽  
Artificial Bee Colony ◽  
Wave Dispersion ◽  
Velocity Model ◽  
S Wave ◽  
Bee Colony ◽  
Search Optimization ◽  
Rayleigh Wave Dispersion

Rayleigh wave dispersion curve inversion is a non-linear iterative optimization process with multi-parameter and multi-extrema. It is difficult to carry out inversion and reconstruction of stratigraphic parameters quickly and accurately with a single linear or non-linear inversion for the data processing of Rayleigh waves with complex seismic geological conditions. We proposed a new method that combines artificial bee colony algorithm (ABC) and damped least squares algorithm (DLS) to invert Rayleigh wave dispersion curve. First, food sources are initialized in a large scale of the model based on the prior geological information. Then, after three kinds of bee operators (employed bees, onlooker bees and scout bees) transform each other and perform search optimization with several iterations, the targets are converged near the optimal solution to obtain an initial S-wave velocity model. Finally, the final S-wave velocity model is obtained by local optimization of DLS inversion with fast convergence and strong stability. The correctness of the method has been verified by one high-velocity interlayer model, and it was further applied to a real Rayleigh wave dataset. The results show that our method not only absorbs the advantages of ABC global search optimization and strong adaptability, but also makes full use of the advantages of DLS inversion, such as high accuracy and fast convergence speed. The inversion strategy can effectively suppress the inversion falling into local extrema, get rid of the dependence on an initial model, enhance the inversion stability, further improve the convergence speed and inversion accuracy, while has good anti-noise ability.

Three-dimensional lithospheric S wave velocity model of the NE Tibetan Plateau and western North China Craton

2017 ◽  
Vol 122 (8) ◽  
pp. 6703-6720 ◽  
Author(s):  
Xingchen Wang ◽  
Yonghua Li ◽  
Zhifeng Ding ◽  
Lupei Zhu ◽  
Chunyong Wang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Wave Velocity ◽  
North China Craton ◽  
North China ◽  
Three Dimensional ◽  
Velocity Model ◽  
S Wave ◽  
Ne Tibetan Plateau

scholarly journals Antarctic Upper Mantle Rheology

2021 ◽  
pp. M56-2020-19
Author(s):  
E. R. Ivins ◽  
W. van der Wal ◽  
D. A. Wiens ◽  
A. J. Lloyd ◽  
L. Caron
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Effective Viscosity ◽  
Seismic Velocity ◽  
Imaging Techniques ◽  
Three Dimensional ◽  
Velocity Model ◽  
Mantle Flow ◽  
S Wave ◽  
Velocity Changes

AbstractThe Antarctic mantle and lithosphere are known to have large lateral contrasts in seismic velocity and tectonic history. These contrasts suggest differences in the response time scale of mantle flow across the continent, similar to those documented between the northeastern and southwestern upper mantle of North America. Glacial isostatic adjustment and geodynamical modeling rely on independent estimates of lateral variability in effective viscosity. Recent improvements in imaging techniques and the distribution of seismic stations now allow resolution of both lateral and vertical variability of seismic velocity, making detailed inferences about lateral viscosity variations possible. Geodetic and paleo sea-level investigations of Antarctica provide quantitative ways of independently assessing the three-dimensional mantle viscosity structure. While observational and causal connections between inferred lateral viscosity variability and seismic velocity changes are qualitatively reconciled, significant improvements in the quantitative relations between effective viscosity anomalies and those imaged by P- and S-wave tomography have remained elusive. Here we describe several methods for estimating effective viscosity from S-wave velocity. We then present and compare maps of the viscosity variability beneath Antarctica based on the recent S-wave velocity model ANT-20 using three different approaches.

Sign in / Sign up

Export Citation Format

Share Document