scholarly journals Earthquake relocation for North-Western Greece using 3D crustal model; method comparison and seismotectonic interpretation.

2016 ◽  
Vol 47 (3) ◽  
pp. 1269 ◽  
Author(s):  
O. Stavroulopoulou ◽  
E. Sokos ◽  
N. Martakis ◽  
G. A. Tselentis
Keyword(s):  
Standard Procedure ◽  
Method Comparison ◽  
Velocity Model ◽  
Focal Mechanisms ◽  
Double Difference ◽  
Location Method ◽  
Hypocenter Distribution ◽  
3D Velocity Model ◽  
1D Model ◽  
Northwestern Greece

A dense microseismic network was installed in Northwestern Greece for a period of eleven months. A total of 1368 events were recorded and located using a 1D model. These events were also used to derive a 3D velocity model for the area. This work presents results from further processing of the data using (a) simple location method of events in a 1D medium through Hypo71 standard procedure; (b) location via the probabilistic, non-linear earthquake location method in 3D medium; (c) relocation of the events using the Double - Difference method in 1D medium; and (d) the same relocation  procedure  invoking  3D  medium.  The  application  of  different  location methodologies results in slightly different locations, which are evaluated using as criterion the compactness of hypocenter distribution. The three point method was used in order to derive linear characteristics from the hypocenter distribution and the final results were compared against the focal mechanisms of the events as computed using the polarity method and the 3D velocity model. The combination of accurately computed hypocenters and focal mechanisms provides important information for the seismotectonics of Epirus

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.

Preliminary result of teleseismic double-difference relocation of earthquakes in the Molucca collision zone with a 3D velocity model

2015 ◽  
Author(s):  
Hasbi Ash Shiddiqi ◽  
Sri Widiyantoro ◽  
Andri Dian Nugraha ◽  
Mohamad Ramdhan ◽  
Wandono ◽  
...  
Keyword(s):  
Velocity Model ◽  
Double Difference ◽  
Collision Zone ◽  
3D Velocity Model

scholarly journals Locating Mine Microseismic Events in a 3D Velocity Model through the Gaussian Beam Reverse-Time Migration Technique

Sensors ◽  
2020 ◽  
Vol 20 (9) ◽  
pp. 2676 ◽  
Author(s):  
Yi Wang ◽  
Xueyi Shang ◽  
Kang Peng
Keyword(s):  
Gaussian Beam ◽  
Back Propagation ◽  
Velocity Model ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Location Method ◽  
Velocity Models ◽  
Time Migration ◽  
3D Velocity Model ◽  
Event Location

Microseismic (MS) source location is a fundamental and critical task in mine MS monitoring. The traditional ray tracing-based location method can be easily affected by many factors, such as multi-ray path effects, waveform focusing and defocusing of wavefield propagation, and low picking precision of seismic phase arrival. By contrast, the Gaussian beam reverse-time migration (GBRTM) location method can effectively and correctly model the influences of multi-path effects and wavefield focusing and defocusing in complex 3D media, and it takes advantages of the maximum energy focusing point as the source location with the autocorrelation imaging condition, which drastically reduces the requirements of signal-to-noise ratio (SNR) and picking accuracy of P-wave arrival. The Gaussian beam technique has been successfully applied in locating natural earthquake events and hydraulic fracturing-induced MS events in one-dimensional (1D) or simple two-dimensional (2D) velocity models. The novelty of this study is that we attempted to introduce the GBRTM technique into a mine MS event location application and considered utilizing a high-resolution tomographic 3D velocity model for wavefield back propagation. Firstly, in the synthetic test, the GBRTM location results using the correct 2D velocity model and different homogeneous velocity models are compared to show the importance of velocity model accuracy. Then, it was applied and verified by eight location premeasured blasting events. The synthetic results show that the spectrum characteristics of the recorded blasting waveforms are more complicated than those generated by the ideal Ricker wavelet, which provides a pragmatic way to evaluate the effectiveness and robustness of the MS event location method. The GBRTM location method does not need a highly accurate picking of phase arrival, just a simple detection criterion that the first arrival waveform can meet the windowing requirements of wavefield back propagation, which is beneficial for highly accurate and automatic MS event location. The GBRTM location accuracy using an appropriate 3D velocity model is much higher than that of using a homogeneous or 1D velocity model, emphasizing that a high-resolution velocity model is very critical to the GBRTM location method. The average location error of the GBRTM location method for the eight blasting events is just 17.0 m, which is better than that of the ray tracing method using the same 3D velocity model (26.2 m).

Seismic activity along a Cretaceous magmatic intrusion in Monchique, SW Iberia

2020 ◽  
Author(s):  
Analdyne Soares ◽  
Susana Custódio ◽  
Marta Neres ◽  
Dina Vales ◽  
Luís Matias
Keyword(s):  
Seismic Activity ◽  
Active Faults ◽  
Plate Boundary ◽  
Velocity Model ◽  
Historical Record ◽  
Focal Mechanisms ◽  
Magmatic Intrusion ◽  
Mainland Portugal ◽  
3D Velocity Model ◽  
Paleozoic Rocks

<p>Iberia, located at the southwestern end of Europe, displays a complex pattern of seismic activity, with most known active faults slipping at low rates (< 1 mm/yr). However, the seismic activity is remarkable, with numerous earthquakes in the historical record proving destructive. The earthquake cluster in mainland Portugal that has a highest rate of seismic activity is very localized (small spatial extent), extends vertically from 5 to 20 km depth and lays on the Monchique late Cretaceous magmatic intrusion, in SW Portugal. This magmatic intrusion forms strong rheological contrast between the intruded magmatic rocks and surrounding Paleozoic rocks. Furthermore, it is the locus of abundant natural water springs. Several pertinent questions remain to be answered concerning earthquakes in Monchique: Are earthquakes in Monchique simply a response to tectonic stresses (given the proximity of Monchique to the EU-AF plate boundary), with the localization of brittle failure in the region facilitated by the rheological contrast between the Cretaceous intrusion and surrounding Paleozoic rocks? Do fluids play a role in facilitating slip in existing fractures? Or, conversely, is the circulation of fluids facilitated by the faulting that results from the rheological contrasts? Are there hazardous faults in Monchique? In this presentation, we re-analyze in detail the seismic data recorded by the regional permanent seismic network, in order to better understand the relationship between seismic activity and igneous intrusion. In particular, we re-locate earthquakes using NonLinLoc and PRISM3D, a 3D velocity model for the region. At a subsequent step, we re-locate earthquakes using HypoDD. We also perform a clustering analysis based on waveform similarity and compute focal mechanisms for the region. The results show that earthquakes align along two main directions, E-W and NNE-SSW, coinciding with surface features of the magmatic intrusion. Focal mechanisms indicate dominantly strike-slip faulting, with the possible fault planes coinciding with the favored directions of earthquake lineations. We investigate the spatio-temporal evolution of seismicity and address possible forcing mechanisms, including tidal forcing.</p><p> </p><p> </p><p><span>The author would like to acknowledge the financial support  FCT through project</span><span> UIDB/50019/2020 </span>– IDL and PTDC/GEO-FIQ/2590/2014 - SPIDER.</p>

scholarly journals Improved earthquake location in the area of North Euboean Gulf after the implementation of a 3D non-linear location method in combination with a 3D velocity model.

2016 ◽  
Vol 47 (3) ◽  
pp. 1185
Author(s):  
E. Mouzakiotis ◽  
K. V. Karastathis
Keyword(s):  
Depth Distribution ◽  
Velocity Model ◽  
Local Area ◽  
Local Models ◽  
Velocity Models ◽  
3D Velocity Model ◽  
Non Linear ◽  
1D Model ◽  
Location Algorithm ◽  
Minimum 1D Model

Considerably improved hypocentral locations of the 274 earthquakes, with magnitudes between 1.5 to 4.1 Ml recorded during the period from 2009 to 2010 by the Hellenic Unified Seismographic Network (HUSN), have been obtained for the area of North Euboean Gulf after the implementation of a 3D non-linear location algorithm and a previously calculated local 3D velocity model for both P and S wavephases. To assess the effectiveness of the 3D locations we compared the results with the solutions obtained with alternative 1D velocity models such as the minimum 1D model calculated with the VELEST algorithm and the 1D model used by the National Observatory of Athens (NOA) for daily earthquake analysis. We were further ableto assess the location accuracy of each model by comparing the location results for a number of quarry blasts that occurred in the area in that period. The use of the local 3D velocity model provides considerably more accurate than the minimum 1D model which in turn provides more constrained locations from the 1D model of NOA. The epicentral locations calculated by each model are almost similar; however the depth distribution of the events varies, with depth differences of up to 12 km for some earthquakes. The results prove that accurate, local models are necessary in order to achieve more accurate locations for the events in a local area. 

Complex magmatic-tectonic interactions during the 2020 Makushin Volcano, Alaska, earthquake swarm

2021 ◽  
Author(s):  
Diana Roman ◽  
Federica Lanza ◽  
John Power ◽  
Cliff Thurber ◽  
Thomas Hudson
Keyword(s):  
Earthquake Swarm ◽  
Velocity Model ◽  
Aftershock Sequence ◽  
Double Difference ◽  
Magma Intrusion ◽  
Fault Plane Solutions ◽  
3D Velocity Model ◽  
Double Couple ◽  
Seismic Swarms ◽  
Lower Magnitude

<p>We investigate the processes driving<strong> </strong>a significant earthquake swarm that occurred between June and December 2020 on Unalaska Island, Alaska, ~12 km southeast of the summit of Makushin Volcano. The swarm was energetic, with two M>4 events that were widely felt by the population in Dutch Harbor, ~ 15 km west of the epicenters. This is the strongest seismic activity ever recorded at Makushin since instrumental monitoring began in 1996. To date, no eruptive activity or other surface changes have been observed at the volcano in satellite views, webcam images, GPS or InSAR. Seismic swarms close to volcanoes are often associated with the onset of unrest that can lead to eruption. However, determining whether they reflect magmatic rather than tectonic stresses is challenging. Here, we integrate information from space-time patterns of the hypocenters of the swarm earthquakes with their double-couple fault-plane solutions (FPS). We relocate swarm events using double-difference relocation techniques and a 3D velocity model. We find that most of the events cluster into two perpendicular lineaments with NW-SE and SW-NE orientations, but no apparent migration in time towards a preferred fault. On the one hand, the lack of temporal migration (with both faults slipping concurrently), and FPS for M3+ events consistent with regional stresses, seem to indicate a tectonic driving process. On the other hand, FPS for the lower-magnitude earthquakes have 90°-rotated P-axes perpendicular to the regional principal stress orientation, providing strong evidence for dike inflation/magma intrusion. Coulomb stress modeling indicates that the rotated FPS are best explained by an inflating dike to the SW of the swarm epicenters, in a zone of long-term elevated seismicity. This complex overlapping of regional and magmatic stresses is also evident in the statistical analysis of the sequence, which started as a main-shock/aftershock sequence with the first event having the largest magnitude, and evolved into a swarm sequence indicative of a more pronounced role of magmatic processes.</p>

scholarly journals Application of Double Difference Tomography Method to Determine The 3D Seismic Wave Velocity Structure of GoLF Geothermal Field

2018 ◽  
Vol 16 (1) ◽  
pp. 27
Author(s):  
Kana N. Naamin ◽  
David P. Sahara ◽  
Andri D. Nugraha ◽  
Irvan Ramadhan
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Correlation Method ◽  
Velocity Model ◽  
Geothermal Field ◽  
Double Difference ◽  
Seismic Wave Velocity ◽  
Recording Time ◽  
3D Velocity Model ◽  
Geophysical Surveys

GoLF geothermal eld is located in South Solok Regency, 150 km SE of Padang city, West Sumatra.Geology, geochemistry and geophysical surveys had been conducted since 2008. Geophysical survey which had been performed including microseismic and magnetotelluric surveys. Seismic velocity structure modelling need to be conducted in order to characterize geothermal reservoir.This study uses microseismic data recorded from 36 seismometers which installed in two time recording time ranges; from September 2010 to April 2011 and from September 2012 to December 2013, with microseismic events recorded respectively 135 and 2692 events. To maximize the result of picking waveform, the data is processed using the Master Event Cross Correlation method to update the catalog data and get more accurate arrival time. Furthermore, the author used TomoDD software to produce hypocenter relocation and the 3D velocity structure under GoLF's geothermal reservoir. The results of the 3D velocity model can be used to determine the structure and phase of the fluid under GoLF geothermal field.

The 25 October, 2018 Zakynthos (Greece) earthquake: seismic activity at the transition between a transform fault and a subduction zone.

2020 ◽  
Author(s):  
P Papadimitriou ◽  
V Kapetanidis ◽  
A Karakonstantis ◽  
I Spingos ◽  
K Pavlou ◽  
...  
Keyword(s):  
Spatial Clustering ◽  
Accretionary Prism ◽  
Velocity Model ◽  
Strike Slip ◽  
Double Difference ◽  
Strain Partitioning ◽  
Transform Fault ◽  
Fault Plane Solutions ◽  
The North ◽  
Waveform Modelling

Summary The properties of the Mw = 6.7 earthquake that took place on 25 October 2018, 22:54:51 UTC, ∼50 km SW of the Zakynthos Island, Greece, are thoroughly examined. The main rupture occurred on a dextral strike-slip, low-angle, east-dipping fault at a depth of 12 km, as determined by teleseismic waveform modelling. Over 4000 aftershocks were manually analysed for a period of 158 days. The events were initially located with an optimal 1D velocity model and then relocated with the double-difference method to reveal details of their spatial distribution. The latter spreads in an area spanning 80 km NNW-SSE and ∼55 km WSW-ENE. Certain parts of the aftershock zone present strong spatial clustering, mainly to the north, close to Zakynthos Island, and at the southernmost edge of the sequence. Focal mechanisms were determined for 61 significant aftershocks using regional waveform modelling. The results revealed characteristics similar to the mainshock, with few aftershocks exhibiting strike-slip faulting at steeper dip angles, possibly related to splay faults on the accretionary prism. The slip vectors that correspond to the east-dipping planes are compatible with the long-term plate convergence and with the direction of coseismic displacement on the Zakynthos Island. Fault-plane solutions in the broader study area were inverted for the determination of the regional stress-field. The results revealed a nearly horizontal, SW-NE to E-W-trending S1 and a more variable S3 axis, favouring transpressional tectonics. Spatial clusters at the northern and southern ends of the aftershock zone coincide with the SW extension of sub-vertical along-dip faults of the segmented subducting slab. The mainshock occurred in an area where strike-slip tectonics, related to the Cephalonia Transform Fault and the NW Peloponnese region, gradually converts into reverse faulting at the western edge of the Hellenic subduction. Plausible scenarios for the 2018 Zakynthos earthquake sequence include a rupture on the subduction interface, provided the slab is tilted eastwards in that area, or the reactivation of an older east-dipping thrust as a low-angle strike-slip fault that contributes to strain partitioning.

scholarly journals Structure-controlled asperities of the 1920 Haiyuan M8.5 and 1927 Gulang M8 earthquakes, NE Tibet, China, revealed by high-resolution seismic tomography

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Quan Sun ◽  
Shunping Pei ◽  
Zhongxiong Cui ◽  
Yongshun John Chen ◽  
Yanbing Liu ◽  
...  
Keyword(s):  
High Resolution ◽  
Seismic Tomography ◽  
High Velocity ◽  
Three Dimensional ◽  
Large Earthquake ◽  
Velocity Model ◽  
Tectonic Stress ◽  
Double Difference ◽  
Source Regions ◽  
Large Earthquakes

AbstractDetailed crustal structure of large earthquake source regions is of great significance for understanding the earthquake generation mechanism. Numerous large earthquakes have occurred in the NE Tibetan Plateau, including the 1920 Haiyuan M8.5 and 1927 Gulang M8 earthquakes. In this paper, we obtained a high-resolution three-dimensional crustal velocity model around the source regions of these two large earthquakes using an improved double-difference seismic tomography method. High-velocity anomalies encompassing the seismogenic faults are observed to extend to depths of 15 km, suggesting the asperity (high-velocity area) plays an important role in the preparation process of large earthquakes. Asperities are strong in mechanical strength and could accumulate tectonic stress more easily in long frictional locking periods, large earthquakes are therefore prone to generate in these areas. If the close relationship between the aperity and high-velocity bodies is valid for most of the large earthquakes, it can be used to predict potential large earthquakes and estimate the seismogenic capability of faults in light of structure studies.

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