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

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.

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

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.10901 ◽

2016 ◽

Vol 47 (3) ◽

pp. 1269 ◽

Cited By ~ 1

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

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

10.5194/egusphere-egu21-16252 ◽

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&#176;-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>

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

Jurnal Geofisika ◽

10.36435/jgf.v16i1.62 ◽

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.

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Development of a 3D Velocity Model of the Canterbury, New Zealand, Region for Broadband Ground‐Motion Simulation

Bulletin of the Seismological Society of America ◽

10.1785/0120160326 ◽

2017 ◽

Vol 107 (5) ◽

pp. 2131-2150 ◽

Cited By ~ 15

Author(s):

Robin L. Lee ◽

Brendon A. Bradley ◽

Francesca C. Ghisetti ◽

Ethan M. Thomson

Keyword(s):

New Zealand ◽

Ground Motion ◽

Velocity Model ◽

Motion Simulation ◽

Ground Motion Simulation ◽

3D Velocity Model ◽

Broadband Ground Motion Simulation ◽

Broadband Ground Motion

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Characteristics of relocated hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its aftershocks with a three-dimensional seismic velocity structure

Earth Planets and Space ◽

10.1186/s40623-019-1100-0 ◽

2019 ◽

Vol 71 (1) ◽

Cited By ~ 1

Author(s):

Saeko Kita

Keyword(s):

Seismic Velocity ◽

Three Dimensional ◽

Double Difference ◽

Earthquake Catalog ◽

Seismic Structure ◽

Depth Limit ◽

High Attenuation ◽

South Central ◽

Collision Zone ◽

Hidaka Collision Zone

AbstractI relocated the hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its surrounding area, using a three-dimensional seismic structure, the double-difference relocation method, and the JMA earthquake catalog. After relocation, the focal depth of the mainshock became 35.4 km. As previous studies show, in south-central Hokkaido, the Hidaka collision zone is formed, and anomalous deep and thickened forearc crust material is subducting at depths of less than 70 km. The mainshock and its aftershocks are located at depths of approximately 10 to 40 km within the lower crust of the anomalous deep and thickened curst near the uppermost mantle material intrusions in the northwestern edge of this Hidaka collision zone. Like the two previous large events, the aftershocks of this event incline steeply eastward and appear to be distributed in the deeper extension of the Ishikari-teichi-toen fault zone. The highly inclined fault in the present study is consistent with a fault model by a geodetic analysis with InSAR. The aftershocks at depths of 10 to 20 km are located at the western edge of the high-attenuation (low-Qp) zone. These kinds of relationships between hypocenters and materials are the same as the 1970 and 1982 events in the Hidaka collision zone. The anomalous large focal depths of these large events compared with the average depth limit of inland earthquakes in Japan could be caused by the locally lower temperature in south-central Hokkaido. This event is one of the approximately M7 large inland earthquakes that occurred repeatedly at a recurrence interval of approximately 40 years and is important in the collision process in the Hidaka collision zone.

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

Geophysical Journal International ◽

10.1093/gji/ggaa575 ◽

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.

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

Scientific Reports ◽

10.1038/s41598-021-84642-7 ◽

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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