scholarly journals Relocation and Focal Mechanism of Aftershocks Pidie Jaya Earthquake (Mw6.5) Dec 7th, 2016 using BMKG Network

2017 ◽  
Vol 15 (3) ◽  
pp. 17 ◽  
Author(s):  
Pepen Supendi ◽  
Andri D. Nugraha ◽  
Tony Agus Wijaya
Keyword(s):  
Data Processing ◽  
Focal Mechanism ◽  
Difference Method ◽  
Active Fault ◽  
Strike Slip ◽  
Double Difference ◽  
Mechanism Analysis ◽  
Residual Value ◽  
Focal Mechanism Solutions ◽  
Focus Depth

We have successfully relocated 74 out of 89 aftershocks until December 19, 2016, by using hypocenter double-difference method. We also have conducted focal mechanism analysis to estimate the type of fault slip. The results indicate improvement in hypocenter location, where the initial earthquakes focus depth at a fixed depth of 10 km have been updated and have described the patterns of active fault in the area trending Northwest-Southeast. The validity through the histogram of travel-time residual shows fairly good data processing where the residual value is close to zero (t.obs - t.cal ~ 0). Based on focal mechanism solutions of mainshock and two selected aftershocks, the type of fault is right lateral strike-slip.

scholarly journals Analysis of swarm earthquakes around Mt. Agung Bali, Indonesia prior to November 2017 eruption using regional BMKG network

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Mohamad Taufik Gunawan ◽  
Ridwan Kusnandar ◽  
Pepen Supendi ◽  
Andri Dian Nugraha ◽  
Nanang T. Puspito ◽  
...  
Keyword(s):  
Focal Mechanism ◽  
Seismic Data ◽  
Seismic Activity ◽  
Strike Slip ◽  
Double Difference ◽  
S Wave ◽  
Focal Mechanism Solutions ◽  
Time Period ◽  
Swarm Earthquakes ◽  
Recent Eruption

Abstract Mt. Agung, located in Karangasem-Bali, Indonesia, had a significant increase of swarm earthquakes from September 2017 until the recent eruption in November 2017. To analyze the seismic swarm and its correlation with the magmatic movement, we worked on the regional seismic data recorded by Agency for Meteorology, Climatology and Geophysics of Indonesia (BMKG) between September 14 to October 20, 2017. P-and S-wave phases of the swarm events had been manually picked. In total, 804 events in the time period of September 14 to October 20, 2017 were successfully determined. To improve the location precision, the double-difference relocation method was performed. We identified most of the events as Volcano-Tectonic type A (VT-A) earthquakes and located between Mt. Batur and Mt. Agung. Those events form a cluster striking in NE-SW direction at a depth between 2 and 20 km. Focal mechanism solutions for selected events below Mt. Agung show a thrust and strike-slip faulting regime. Interestingly, a trend of event propagation toward the summit of Mt. Agung was observed. The frequency of VT-A event occurrences is significantly increased at the later stage of the swarms. We concluded that the increased seismic activity in Mt. Agung was due to the migration of magma from the deep chamber to the shallow reservoir.

scholarly journals Focal Mechanism Analysis of the September 25th, 2019 Mw 6.5 Ambon Earthquake and Its Implication for Seismotectonics

2021 ◽  
Vol 873 (1) ◽  
pp. 012032
Author(s):  
Gatut Daniarsyad ◽  
Aprilia Nur Vita ◽  
Shengji Wei
Keyword(s):  
Focal Mechanism ◽  
Fault Plane ◽  
Source Parameters ◽  
Focal Depth ◽  
Strike Slip ◽  
Inversion Method ◽  
Mechanism Analysis ◽  
Focal Mechanism Solutions ◽  
Seismic Waveforms ◽  
Tectonically Active

Abstract On September 25th, 2019, an Mw 6.5 earthquake occurred in Ambon, Maluku Province, Indonesia, and caused casualties and infrastructures damages. The epicenter located in a tectonically active region with the potential strike-slip and thrust faulting earthquake sources, yet the responsible fault is still not well understood. Based on focal mechanism solutions from available seismological agencies, i.e. USGS, GFZ, GCMT, and BMKG, the earthquake has a similar strike-slip focal mechanism, although there are discrepancies on detailed source parameters. To provide a better understanding of the earthquake mechanism and seismotectonic, we apply the Cut-and-Paste (CAP) focal mechanism inversion method to broadband seismic waveforms from regional and teleseismic distances. The CAP inversion results on the regional data grouped in different distance ranges show a robust strike-slip solution. We then refine the earthquake focal depth by performing the CAPtele inversion and resulted in a depth of 12 km with similar fault plane solution as the regionals. The ruptured fault plane is resolved by a directivity analysis using azimuthal pattern of the apparent source durations, which indicates an obvious unilateral rupture propagation toward SSE direction. Our result suggests the NNW-SSE orientated fault is the ruptured fault plane, which is also consistent with the near N-S distributed aftershocks. This fault is located in a narrow sea between Seram, Ambon and Haruku island and was not reported yet in previous studies. The Coulomb failure stress (CFS) changes analysis of the mainshock shows that the Ambon earthquake has promoted the off-fault aftershocks which occurred to the west of the ruptured fault.

Secondary faulting near the terminus of a seismogenic strike-slip fault: Aftershocks of the 1976 Guatemala earthquake

1979 ◽  
Vol 69 (2) ◽  
pp. 427-444
Author(s):  
C. J. Langer ◽  
G. A. Bollinger
Keyword(s):  
Focal Mechanism ◽  
Linear Trend ◽  
Strike Slip ◽  
Strike Slip Fault ◽  
Aftershock Activity ◽  
Focal Mechanism Solutions ◽  
The North ◽  
Composite Focal Mechanism ◽  
Theoretical Pattern ◽  
Main Fault

abstract Aftershocks of the February 4, 1976 Guatemalan earthquake (Ms = 7.5) were monitored by a network of portable seismographs from February 9 to February 27. Although seismic data were obtained all along the 230-km surface rupture of the causal Motagua fault, the field program was designed to concentrate on the aftershock activity at the western terminus of the fault. Data from that locale revealed several linear or near-linear trends of aftershock epicenters that splay to the southwest away from the western end of the main fault. These trends correlate spatially with mapped surface lineaments and, to some degree, with ground breakage patterns near Guatemala City. The observed splay pattern of aftershocks and the normal-faulting mode of the splay earthquakes determined from composite focal mechanism solutions, may be explained by a theoretical pattern of stress trajectories at the terminus of a strike-slip fault. Composite focal mechanism solutions for aftershocks located on or near the surface break of the Motagua fault, to the north and east of the linear trend splay area, agree with the mapped surface movements, i.e., left-lateral strike-slip.

Aftershocks and surface faulting associated with the intraplate Guinea, West Africa, earthquake of 22 December 1983

1987 ◽  
Vol 77 (5) ◽  
pp. 1579-1601
Author(s):  
C. J. Langer ◽  
M. G. Bonilla ◽  
G. A. Bollinger
Keyword(s):  
West Africa ◽  
Focal Mechanism ◽  
Main Shock ◽  
Strike Slip ◽  
Fault System ◽  
Epicentral Area ◽  
Lateral Strike Slip ◽  
Focal Mechanism Solutions ◽  
Short Period ◽  
East West

Abstract This study reports on the results of geological and seismological field studies conducted following the rare occurrence of a moderate-sized West African earthquake (mb = 6.4) with associated ground breakage. The epicentral area of the northwestern Guinea earthquake of 22 December 1983 is a coastal margin, intraplate locale with a very low level of historical seismicity. The principal results include the observation that seismic faulting occurred on a preexisting fault system and that there is good agreement among the surface faulting, the spatial distribution of the aftershock hypocenters, and the composite focal mechanism solutions. We are not able, however, to shed any light on the reason(s) for the unexpected occurrence of this intraplate earthquake. Thus, the significance of this study is its contribution to the observational datum for such earthquakes and for the seismicity of West Africa. The main shock was associated with at least 9 km of surface fault-rupture. Trending east-southeast to east-west, measured fault displacements up to ∼13 cm were predominantly right-lateral strike slip and were accompanied by an additional component (5 to 7 cm) of vertical movement, southwest side down. The surface faulting occurred on a preexisting fault whose field characteristics suggest a low slip rate with very infrequent earthquakes. There were extensive rockfalls and minor liquefaction effects at distances less than 10 km from the surface faulting and main shock epicenter. Main shock focal mechanism solutions derived from teleseismic data by other workers show a strong component of normal faulting motion that was not observed in the ground ruptures. A 15-day period of aftershock monitoring, commencing 22 days after the main shock, was conducted. Eleven portable, analog short-period vertical seismographs were deployed in a network with an aperture of 25 km and an average station spacing of 7 km. Ninety-five aftershocks were located from the more than 200 recorded events with duration magnitudes of about 1.5 or greater. Analysis of a selected subset (91) of those events define a tabular aftershock volume (26 km long by 14 km wide by 4 km thick) trending east-southeast and dipping steeply (∼60°) to the south-southwest. Composite focal mechanisms for groups of events, distributed throughout the aftershock volume, exhibit right-lateral, strike-slip motion on subvertical planes that strike almost due east. Although the general agreement between the field geologic and seismologic results is good, our preferred interpretation is for three en-echelon faults striking almost due east-west.

PRESENT-DAY STATE-OF-STRESS OF SOUTHEAST AUSTRALIA

2006 ◽  
Vol 46 (1) ◽  
pp. 283 ◽  
Author(s):  
E. Nelson ◽  
R. Hillis ◽  
M. Sandiford ◽  
S. Reynolds ◽  
S. Mildren
Keyword(s):  
Focal Mechanism ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Focal Mechanism Solutions ◽  
Southeast Australia ◽  
State Of Stress ◽  
Earthquake Focal Mechanism ◽  
Minimum Horizontal Stress ◽  
Maximum Horizontal Stress ◽  
Gippsland Basin

There have been several studies, both published and unpublished, of the present-day state-of-stress of southeast Australia that address a variety of geomechanical issues related to the petroleum industry. This paper combines present-day stress data from those studies with new data to provide an overview of the present-day state-of-stress from the Otway Basin to the Gippsland Basin. This overview provides valuable baseline data for further geomechanical studies in southeast Australia and helps explain the regional controls on the state-of-stress in the area.Analysis of existing and new data from petroleum wells reveals broadly northwest–southeast oriented, maximum horizontal stress with an anticlockwise rotation of about 15° from the Otway Basin to the Gippsland Basin. A general increase in minimum horizontal stress magnitude from the Otway Basin towards the Gippsland Basin is also observed. The present-day state-of-stress has been interpreted as strike-slip in the South Australian (SA) Otway Basin, strike-slip trending towards reverse in the Victorian Otway Basin and borderline strike-slip/reverse in the Gippsland Basin. The present-day stress states and the orientation of the maximum horizontal stress are consistent with previously published earthquake focal mechanism solutions and the neotectonic record for the region. The consistency between measured present-day stress in the basement (from focal mechanism solutions) and the sedimentary basin cover (from petroleum well data) suggests a dominantly tectonic far-field control on the present-day stress distribution of southeast Australia. The rotation of the maximum horizontal stress and the increase in magnitude of the minimum horizontal stress from west to east across southeast Australia may be due to the relative proximity of the New Zealand segment of the plate boundary.

scholarly journals Hypocenter relocation of the aftershocks of the Mw 7.5 Palu earthquake (September 28, 2018) and swarm earthquakes of Mamasa, Sulawesi, Indonesia, using the BMKG network data

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Pepen Supendi ◽  
Andri Dian Nugraha ◽  
Sri Widiyantoro ◽  
Chalid Idham Abdullah ◽  
Nanang T. Puspito ◽  
...  
Keyword(s):  
Focal Mechanism ◽  
Normal Fault ◽  
Local Area ◽  
Double Difference ◽  
Mechanism Analysis ◽  
Seismicity Pattern ◽  
Fault Type ◽  
Strong Tremors ◽  
The City ◽  
Swarm Earthquakes

AbstractOn September 28, 2018, the Mw 7.5 earthquake occurred in Palu, Central Sulawesi, Indonesia. This earthquake produced strong tremors, landslides, liquefaction and a tsunami and caused thousands of fatalities and damaged houses and infrastructure. We have relocated 386 of the 554 Palu aftershocks by using the double-difference relocation method (hypoDD) from September 28 to November 22, 2018. The aftershock pattern is consistent with the crustal deformation in the area and generally shows that the events have a NW–SE trending of ~ 200 km in length and ~ 50 km in width. Most of the aftershocks are located to the east of the Palu-Koro Fault Line. Since November 2, 2018, there have been hundreds of swarm earthquakes in the area of Mamasa, West Sulawesi, which is about 230 km south of the city of Palu. Some of these earthquakes were felt, and houses were even damaged. We have relocated 535 of the 556 swarm earthquakes having a magnitude of M 2 to M 5.4. Our results show that the seismicity pattern has a dip that becomes shallower to the west (dipping at a ~ 45° angle) and extends from north to south for a length of ~ 50 km. We also conducted a focal mechanism analysis to estimate the type of fault slip for selected events of an M > 4.5 magnitude. Most of the solutions of the focal mechanism analysis show a normal fault type. This swarm earthquake probably corresponds to the activity of the fault in the local area.

scholarly journals Analysis of M 5.3 Sumbawa, Indonesia earthquake 2020 and its aftershocks based on hypocenter relocation from BMKG seismic stations

2021 ◽  
Vol 873 (1) ◽  
pp. 012070
Author(s):  
M Ramdhan ◽  
Priyobudi ◽  
A Mursityanto ◽  
K H Palgunadi ◽  
Daryono
Keyword(s):  
Focal Mechanism ◽  
Difference Method ◽  
Fault Plane ◽  
Active Faults ◽  
Disaster Mitigation ◽  
Double Difference ◽  
Seismic Stations ◽  
Hypocenter Relocation ◽  
Splay Faults ◽  
Moderate Magnitude

Abstract The 2020 Sumbawa earthquake of moderate magnitude (M 5.3) produced very significant aftershocks. Based on the computation of Utsu’s method, those aftershocks would be ended after the 20th day. Those earthquakes along 20 days were relocated using double-difference method. The relocation results show the southwest-northeast orientation and getting deeper into the northwest direction. Those two directions show the strike and the dip from the fault plane of the earthquake which was consistent with the focal mechanism released by the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG). Those results showed the majority of earthquakes occurred at a depth of shallower than 20 km. Those earthquake depths were fit with the previous study showing the crustal thickness beneath Sumbawa Island that was about 28 km. We also found that those earthquakes occurred at splay faults propagating to decollement structure. This study is beneficial for earthquake disaster mitigation especially in updating active faults on Sumbawa Island.

Focal mechanisms of Indian earthquakes

1972 ◽  
Vol 62 (2) ◽  
pp. 603-608 ◽  
Author(s):  
A. R. Banghar
Keyword(s):  
Focal Mechanism ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Peninsular India ◽  
S Waves ◽  
Focal Mechanism Solutions

abstract Focal mechanism solutions are presented for two earthquakes that occurred in peninsular India. The first motions of P, PKP and the polarization (or first motions) of S waves were used for this investigation. Both of these mechanisms are found to be associated with strike-slip faulting.

scholarly journals Microseismicity and stress in the vicinity of the Alpine Fault, central Southern Alps, New Zealand

2021 ◽  
Author(s):  
C Boese ◽  
John Townend ◽  
Euan Smith ◽  
Timothy Stern
Keyword(s):  
Focal Mechanism ◽  
Attenuation Factor ◽  
Strike Slip ◽  
Southern Alps ◽  
Active Deformation ◽  
Focal Mechanism Solutions ◽  
Alpine Fault ◽  
Horizontal Compressive Stress ◽  
American Geophysical ◽  
American Geophysical Union

We investigate present-day microseismicity associated with the central Alpine Fault and the zone of active deformation and uplift in the central Southern Alps. Using 14 months of data, robust hypocenter locations have been obtained for ∼1800 earthquakes of magnitudes between -0.3 and 4.2. We derived a magnitude scale with a frequency-dependent attenuation factor, γ(f) = γ0f, where γ0 = 1.89 ± 0.02 × 10-3 s/km, that enables magnitudes to be calculated consistently for earthquakes of different sizes and frequency contents. The maximum depth of the seismicity varies systematically with distance from the Alpine Fault, from 10 ± 2 km near the fault to 8 ± 2 km within 20 km and 15 ± 2 km further southeast. This distribution correlates with lateral variations in crustal resistivity: earthquake hypocenters are concentrated in areas of strong resistivity gradients and restricted to depths of resistivities >100 Ωm. Rocks at greater depth are too hot, too fluid-saturated, or too weak to produce detectable earthquakes. Focal mechanism solutions computed for 211 earthquakes (ML > 0.44) exhibit predominantly strike-slip mechanisms. We obtain a maximum horizontal compressive stress direction of 115 ± 10° from focal mechanism inversion. This azimuth is consistent with findings from elsewhere in the central and northern South Island, and indicates a uniform crustal stress field despite pronounced variations in crustal structure and topographic relief. Our stress estimates suggest that the Alpine Fault (with a mean strike of 055°) is poorly oriented in an Andersonian sense but that individual thrust and strike-slip segments of the fault's surface trace have close to optimal orientations. Copyright 2012 by the American Geophysical Union.

scholarly journals First-Motion Focal Mechanism Solutions for 2015–2019 M ≥ 4.0 Italian Earthquakes

2021 ◽  
Vol 9 ◽  
Author(s):  
Maria G. Ciaccio ◽  
Raffaele Di Stefano ◽  
Luigi Improta ◽  
Maria T. Mariucci ◽  
Keyword(s):  
Focal Mechanism ◽  
Carbonate Platform ◽  
Central Italy ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Seismic Sequence ◽  
Earthquake Parameters ◽  
Focal Mechanism Solutions ◽  
Initial Rupture ◽  
First Motion

A list of 100 focal mechanism solutions that occurred in Italy between 2015 and 2019 has been compiled for earthquakes with magnitude M ≥ 4.0. We define earthquake parameters for additional 22 seismic events with 3.0 ≤ M < 4.0 for two specific key zones: Muccia, at the northern termination of the Amatrice–Visso–Norcia 2016–2018 central Italy seismic sequence, and Montecilfone (southern Italy) struck in 2018 by a deep, strike-slip Mw 5.1 earthquake apparently anomalous for the southern Apennines extensional belt. First-motion focal mechanism solutions are a good proxy for the initial rupture and they provide important additional information on the source mechanism. The catalog compiled in the present paper provides earthquake parameters for individual events of interest to contribute, as a valuable source of information, for further studies as seismotectonic investigations and stress distribution maps. We calculated the focal mechanisms using as a reference the phase pickings reported in the Italian Seismic Bulletin (BSI). We visually checked the reference picks to accurately revise manual first-motion polarities, or include new onsets when they are not present in the BSI dataset, for the selected earthquakes within the whole Italian region, with a separate focus on the Amatrice–Visso–Norcia seismic sequence area from August 24, 2016 to August 24, 2018. For the Montecilfone area, we combined the information on the geometry and kinematics of the source of the 2018 Mw 5.1 event obtained in this study with available subsurface and structural data on the Outer Apulia Carbonate Platform to improve understanding of this intriguing strike-slip sequence. Our analysis suggests that the Montecilfone earthquake ruptured a W–E trending strike-slip dextral fault. This structure is confined within the Apulia crystalline crust and it might represent the western prolongation of the Mattinata Fault–Apricena Fault active and seismogenic structures. The calculated focal mechanisms of the entire catalog are of good quality complementing important details on source mechanics from moment tensors and confirming the relevance of systematically including manually revised and more accurate polarity data within the BSI database.

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