scholarly journals SPITAK-V EARTHQUAKE on July 6, 2014 with МL=4.0, I0=5–6 (Armenia)

2020 ◽  
pp. 344-349
Author(s):  
Heghine Sargsyan ◽  
Gohar Abgaryan ◽  
Anjela Makaryan ◽  
Ani Gevorgyan
Keyword(s):  
Focal Mechanism ◽  
Strike Slip ◽  
Isoseismal Map ◽  
Spitak Earthquake ◽  
Focal Zone ◽  
Macroseismic Survey

The work presents the results of macroseismic survey of the Spitak-V earthquake which occurred on July 6, 2014 with МL=4.0, I0=5–6 in the focal zone of the destructive Spitak earthquake 1988 with I0=10. The isoseismal map of the July 6, 2014 earthquake was made and the focal mechanism parameters were determined. According to the focal mechanism decision, the movement in the source was a strike-slip with minor uplift components.

Inversion of regional surface-wave spectra for source parameters of aftershocks from the 1992 Petrolia earthquake sequence

1995 ◽  
Vol 85 (3) ◽  
pp. 705-715
Author(s):  
Mark Andrew Tinker ◽  
Susan L. Beck
Keyword(s):  
Surface Wave ◽  
Focal Mechanism ◽  
Source Parameters ◽  
Strike Slip ◽  
Earthquake Sequence ◽  
Fault System ◽  
Accretionary Wedge ◽  
Wave Spectra ◽  
The North ◽  
Gorda Plate

Abstract Regional distance surface waves are used to study the source parameters for moderate-size aftershocks of the 25 April 1992 Petrolia earthquake sequence. The Cascadia subduction zone had been relatively seismically inactive until the onset of the mainshock (Ms = 7.1). This underthrusting event establishes that the southern end of the North America-Gorda plate boundary is seismogenic. It was followed by two separate and distinct large aftershocks (Ms = 6.6 for both) occurring at 07:41 and 11:41 on 26 April, as well as thousands of other small aftershocks. Many of the aftershocks following the second large aftershock had magnitudes in the range of 4.0 to 5.5. Using intermediate-period surface-wave spectra, we estimate focal mechanisms and depths for one foreshock and six of the larger aftershocks (Md = 4.0 to 5.5). These seven events can be separated into two groups based on temporal, spatial, and principal stress orientation characteristics. Within two days of the mainshock, four aftershocks (Md = 4 to 5) occurred within 4 hr of each other that were located offshore and along the Mendocino fault. These four aftershocks comprise one group. They are shallow, thrust events with northeast-trending P axes. We interpret these aftershocks to represent internal compression within the North American accretionary prism as a result of Gorda plate subduction. The other three events compose the second group. The shallow, strike-slip mechanism determined for the 8 March foreshock (Md = 5.3) may reflect the right-lateral strike-slip motion associated with the interaction between the northern terminus of the San Andreas fault system and the eastern terminus of the Mendocino fault. The 10 May aftershock (Md = 4.1), located on the coast and north of the Mendocino triple junction, has a thrust fault focal mechanism. This event is shallow and probably occurred within the accretionary wedge on an imbricate thrust. A normal fault focal mechanism is obtained for the 5 June aftershock (Md = 4.8), located offshore and just north of the Mendocino fault. This event exhibits a large component of normal motion, representing internal failure within a rebounding accretionary wedge. These two aftershocks and the foreshock have dissimilar locations in space and time, but they do share a north-northwest oriented P axis.

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 KAJI-SAIEARTHQUAKEonNovember 14, 2014 withКР=13.7, Mw=5.4, I0=7 (Kyrgyzstan, SouthernIssyk-Kul’)

2020 ◽  
pp. 364-374
Author(s):  
V. Grebennikova ◽  
A. Frolova ◽  
N. Bagmanova ◽  
A. Berezina ◽  
A. Pershina ◽  
...  
Keyword(s):  
Main Shock ◽  
Weather Conditions ◽  
Reverse Fault ◽  
Depth Range ◽  
Southern Coast ◽  
Epicentral Zone ◽  
Isoseismal Map ◽  
Fault Type ◽  
Macroseismic Survey ◽  
H 20

Information on the earthquake with Mw=5.4 that occurred on the southern coast of the Issyk-Kul lake on the southwestern slope of the Tegerek mountains (Kyrgyzstan) on November 14, 2014 is given. The epicenter is located in the Jumgalo-Terskey zone, identified as the Tonsky block, in which felt earthquakes with intensity up to 7 have occurred repeatedly. 231 aftershocks were recorded in the first day, in the second day – 13 aftershocks, then seismic activity decreased. Most of the aftershocks are localized in the depth range of 17–21 km, close to the depth of the main shock (h=20 km). The earthquake had the reverse fault type. Macroseismic survey was fulfilled only in the epicentral zone due to the complex weather conditions (late autumn, highlands). The theoretical isoseismal map was created for receiving the more complete picture of the earthquake impact outside of its epicentral zone.

scholarly journals Classification of Zagros earthquakes based on focal mechanism

2021 ◽  
Vol 51 (3) ◽  
pp. 265-275
Author(s):  
Mehdi Nouri DELOUEI ◽  
Mohammad-Reza GHEITANCHI
Keyword(s):  
Focal Mechanism ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Nodal Plane ◽  
Iranian Plateau ◽  
Populated Region ◽  
Compression Type ◽  
Selection Of

The Zagros suture zone is seismically active region in Iranian plateau. This region is of high importance in terms of seismicity, since it is a vast and populated region and in recent years the earthquakes with high intensities have frequently occurred and have caused extensive destruction and heavy human loss. The study of the focal mechanism is very important in understanding the seismotectonic characteristics. Focal mechanisms of Zagros were collected over a period of 20 years and they were classified by FMC software. Seven groups were considered for the type of faulting and Zagros was divided into three zones. For each zone, the frequency percentage of each group of faults was determined. The most of faulting are of the reverse and compression type with the strike-slip component. Finally, the role of nodal plane selection in determining the type of faulting was discussed and it was found that the selection of each nodal plane in determining the type of faulting has the same result.

scholarly journals GEODYNAMICS

GEODYNAMICS ◽  
2011 ◽  
Vol 2(11)2011 (2(11)) ◽  
pp. 260-262
Author(s):  
B. H. Pustovitenko ◽  
◽  
R. S . Pronyshyn ◽  
Keyword(s):  
Focal Mechanism ◽  
Strike Slip ◽  
Motion Type ◽  
First Motion ◽  
First Time

For the first time for Transcarpathian region the solution of the focal mechanism of perceptible earthquake was solved. Earthquake occurred under the influence of the horizontal compression, oriented in latitudinal direction and near-horizontal tension of the submeridional orientation. A first-motion type in the source – strike-slip combined with reverse-oblique.

scholarly journals Intensity and isoseismal map of 25th November 2007 Delhi earthquake

MAUSAM ◽  
2021 ◽  
Vol 62 (3) ◽  
pp. 417-424
Author(s):  
RAJESH PRAKASH ◽  
R.K. SINGH ◽  
A.K. SHUKLA ◽  
D. SINGH ◽  
B.S. RANA ◽  
...  
Keyword(s):  
Focal Depth ◽  
Analysis Tool ◽  
Stress Release ◽  
Isoseismal Map ◽  
Intensity Field ◽  
Statistical Analysis Tool ◽  
The Mean ◽  
Local Populace ◽  
Earthquake Effects ◽  
Macroseismic Survey

An earthquake of magnitude ML: 4.3 occurred on 25th November 2007 (2312 UTC) in Delhi with hypocenter at 28.56° N / 77.08° E and focal depth 33.1 km. The epicenter was at about 21 km SW of Delhi University. It was widely felt in and around Delhi and created panic among the local populace. A macroseismic survey was conducted in about ten days starting from 27th November, 2007 at 89 locations covering an area of about 1500 sq. km in Delhi and its neighborhood through a questionnaire. The results of the macroseismic survey allowed establishment of spatial distribution of the earthquake effects in the form of isoseismal map generated using geo-statistical analysis tool of ArcGIS 9.1. The isoseismal map shows that most parts of Delhi region experienced an intensity of V on MMI scale, except on northern most region of Delhi where intensity was found IV. The mean isoseismal radii for the zones V, IV, III and II are 29.13, 57.78, 83.63 and 100.75 km, respectively. The orientation of elongated epicentral track of intensity field shows that the stress release was pronounced along Delhi-Sargodha ridge and earthquake was attributed to activities of this ridge.

The Quebec–Maine Border Earthquake, 15 June 1973

1975 ◽  
Vol 12 (11) ◽  
pp. 1917-1928 ◽  
Author(s):  
R. J. Wetmiller
Keyword(s):  
New England ◽  
Focal Mechanism ◽  
Appalachian Mountains ◽  
Strike Slip ◽  
Maximum Intensity ◽  
Focal Mechanism Solution ◽  
Epicentral Area ◽  
Eastern Ontario ◽  
Shallow Focus ◽  
Strike Slip Movement

On 15 June 1973, a shallow-focus earthquake with magnitude mb 4.8 occurred in southern Quebec, in an area that has a record of only a few minor earthquakes during the previous 200 years. This event was felt throughout southern Quebec, eastern Ontario, and the New England States, to a distance of 300 km from the epicenter. A small amount of minor damage to plaster and chimneys occurred in the immediate epicentral area, indicating a maximum intensity of VI. The focal mechanism solution suggests that the earthquake was the result of primarily strike-slip movement along a plane trending northeast or a plane trending northwest. Arguments are presented that this event is part of the seismicity associated with the northern Appalachian Mountains.

scholarly journals The Waveform Inversion of Mainshock and Aftershock Data of the 2006 M6.3 Yogyakarta Earthquake

2020 ◽  
Author(s):  
Hijrah Saputra ◽  
Wahyudi Wahyudi ◽  
Iman Suardi ◽  
Wiwit Suryanto
Keyword(s):  
Focal Mechanism ◽  
Green’S Functions ◽  
Near Field ◽  
Waveform Inversion ◽  
Strike Slip ◽  
Earthquake Source ◽  
Source Mechanism ◽  
Far Field ◽  
Signal Component ◽  
Reflectivity Method

Abstract This research was examines the focal mechanism associated with the mainshock and three aftershocks of the magnitude 6.3 Yogyakarta earthquake on May 27, 2006. This study, therefore, aims to provide a cleareranswer on the source mechanism of the earthquake, which has been debated. Data were obtained from the mainshock and aftershock sources, on June 8, 9, and 16, 2006. The mainshock and three aftershocks were used to conduct waveform inversion by calculating the Green's functions through the extended reflectivity method of the near-field and the far-field signal component. The mainshock's focal mechanism has a strike, dip, and range angle of 243.40o, 77.50o, and -28.30o, respectively.Furthermore, the mainshock is not a pure strike-slip as previously hypothesized. The focal mechanism for the aftershock earthquake source on Mw 4.4, obtained on June 8, had a strike, dip, rake, and variance of 192.20o, 29.70o, -48.30o and 0.22, respectively. This aftershock had a different segment from the mainshock event and those obtained on the 9 and 16 of June with the same type of faulting as the mainshock with variance values of 0.195 and 0.243. These results showed that the mainshock of May 27, 2006, activated the aftershock on June 8, with a different type of fault.

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