The Vancouver Island earthquake of 5 July 1972

1976 ◽  
Vol 13 (1) ◽  
pp. 92-101 ◽  
Author(s):  
Garry C. Rogers
Keyword(s):  
Vancouver Island ◽  
Strike Slip ◽  
Nodal Plane ◽  
Lateral Strike Slip ◽  
Pressure Axis ◽  
Tension Axis ◽  
Close Proximity ◽  
Vertical Fault ◽  
Largest Aftershock ◽  
Distance Relation

An earthquake occurred at 10 h 16 m 39 s GMT on 5 July 1972 in close proximity to the west coast of Vancouver Island, near 49.5 °N and 127.2 °W. Its magnitude (mb) was 5.7 and the hypocenter was near the middle of the crust. A well defined P nodal solution has a pressure axis with a north-south orientation and a tension axis with an east-west orientation. The preferred nodal plane suggests right lateral strike-slip faulting on a near vertical fault, striking in a north-northwest direction. The other nodal plane suggests that left lateral strike-slip faulting on a near vertical fault striking in an east-northeast direction is also a plausible solution. A field study with portable seismographs revealed that very few aftershocks were associated with this earthquake. The largest aftershock had a magnitude (ML) of 3.4. The distribution of intensity of the mainshock observed on Vancouver Island differs from that predicted by the intensity versus distance relation presently used for western Canada.

scholarly journals MODERN MOVEMENTS OF THE CRUST SURFACE IN GORNY ALTAI FROM GPS DATA

2019 ◽  
Vol 10 (1) ◽  
pp. 123-146
Author(s):  
V. Yu. Timofeev ◽  
D. G. Ardyukov ◽  
A. V. Timofeev ◽  
E. V. Boiko
Keyword(s):  
Anomalous Behavior ◽  
Strike Slip ◽  
Elastic Model ◽  
Displacement Fields ◽  
Epicentral Zone ◽  
Lateral Strike Slip ◽  
Altai Region ◽  
Gorny Altai ◽  
Vertical Fault ◽  
The Right

In 2000–2017, the GPS technology was first applied to study inter-seismic, co-seismic and post-seismic processes in the crust of the Altai Mountains (Gorny Altai). Our study aims at investigating the fields of displacement and deformation in the Gorny Altai region as a part of Asia.The 3D displacement fields are reconstructed for the period before the M 7.3 Chuya earthquake that occurred in the southern sector of the Altai GPS network (49° to 55°N, and 81° to 89°E)on 27 September 2003.Anomalous behavior features are discovered in the displacement orientations, as well as in the distribution of velocities and deformation in the zone of the future earthquake.The spatial displacement pattern defined for the period of co-seismic displacements corresponds to the right-lateral strike-slip along the vertical fault. The fault depth is estimated using the elastic model and the experimental data (change in displacement from 0.30 m to 0.02 m at the distances of 14 km and 84 km from the fault, respectively); it amounts to 8–10 km.The co-seismic deformation field is investigated.In the post-seismic stage (2004–2017), displacements revealedin the epicentral zone show the right-lateral strike-slip along the fault at the rate of 2 mm/yr. Therefore, two-layer viscoelastic models can be considered. The estimated viscosity of the lower crust ranges from 6×1019to 3×1020Pa×s, and the elastic upper crust thickness is 25 km. Analyzed are modern movements in the Gorny Altai region outside the Chuya earthquake area.The results of our study show that modern horizontal displacements occur in the NNW direction at the rate of 1.1 mm/yr, which is twice lower than the displacement rate before the earthquake.

scholarly journals Fault plane solutions of the 1993 and 1995 Gulf of Aqaba earthquakes and their tectonic implications

1997 ◽  
Vol 40 (6) ◽  
Author(s):  
A. K. Abdel-Fattah ◽  
H. M. Hussein ◽  
E. M. Ibrahim ◽  
A. S. Abu El Atta
Keyword(s):  
Fault Plane ◽  
Strike Slip ◽  
P Wave ◽  
Gulf Of Aqaba ◽  
Main Trend ◽  
Gulf Of Suez ◽  
Normal Faulting ◽  
Aftershock Distribution ◽  
Lateral Strike Slip ◽  
Largest Aftershock

The stereographic projection of P-wave first motions for the 3 August 1993 Gulf of Aqaba earthquake, its largest aftershock (16 h 33 min), and for the 22 November 1995 earthquake were constructed using the polarity readings of regional and teleseismic stations. The focal mechanism solutions of the 3 August 1993 mainshock and its largest aftershock represent a normal faulting mechanism with some left lateral strike slip component. The nodal planes selected as the fault imply high similarity in strike and dip. They are related to a local fault striking NW-SE and dipping to the SW. The selected fault planes are in good agreement with the aftershock distribution. For the main shock of the 22 November 1995, the fault plane solution displays the same mechanism (normal faulting with left lateral strike slip component) with a plane striking N-S and dipping to the west. The fault plane is greatly conformable with the direction of the regional tectonics and also with the aftershock distribution. The main trend of the extension stress pattern is in a NE-SW direction, corresponding to the rifting direction of the Gulf of Suez and may be related to the paleostress along the Gulf of Suez and Aqaba during the Middle to Late Miocene.

Microearthquakes in the Mono Lake-Northern Owens Valley, California, region from September 28 to October 18, 1970

1975 ◽  
Vol 65 (4) ◽  
pp. 835-844
Author(s):  
A. M. Pitt ◽  
Don W. Steeples
Keyword(s):  
Strike Slip ◽  
Focal Mechanisms ◽  
Mono Lake ◽  
Owens Valley ◽  
Lateral Strike Slip ◽  
Tension Axis ◽  
Seismograph Network ◽  
Historic Seismicity ◽  
East West ◽  
The U.S

Abstract A portable seismograph network was operated by the U.S. Geological Survey in the Mono Lake-northern Owens Valley, California, region in the autumn of 1970. From 20 days of recording, 74 microearthquakes were located. The geographic extent of the microearthquakes is similar to the historic seismicity from 1934 to 1970. Focal mechanisms are mostly right-lateral strike slip; one very good dip-slip solution was obtained. The relative tension axis was found to be very nearly east-west.

scholarly journals Source processes of large earthquakes along the Xianshuihe fault in southwestern China

1983 ◽  
Vol 73 (2) ◽  
pp. 537-551
Author(s):  
Huilan Zhou ◽  
Hsui-Lin Liu ◽  
Hiroo Kanamori
Keyword(s):  
Fault Zone ◽  
Body Wave ◽  
Active Faults ◽  
Strike Slip ◽  
The Body ◽  
Southwestern China ◽  
Total Moment ◽  
Lateral Strike Slip ◽  
Largest Aftershock ◽  
Large Earthquakes

abstract The Xianshuihe fault is one of the most active faults in southwestern China. Recently, three large earthquakes occurred along it in 1967 (Ms = 6.1), 1973 (Ms = 7.5), and 1981 (Ms = 6.8). The 1981 event occurred near the central portion of the fault zone. Modeling of the body and surface waves indicates pure left-lateral strike-slip motion on a vertical fault striking N40°W consistent with the surface trend of the Xianshuihe fault. Two major ruptures are suggested for this source, with a total moment of 1.3 ×1026 dyne-cm. The 1973 event occurred about 65 km northwest of the 1981 event and ruptured about 90 km bilaterally along the fault. The body-wave synthetics indicate three main ruptures during faulting within 43 sec, with a total moment of 1.8 ×1027 dyne-cm. The mechanisms are similar to the 1981 event, and the average slip is determined to be 3.8 m. The largest aftershock (Ms = 5.9) occurred 1 day after the main event with a normal-fault mechanism striking almost perpendicular to the surface breakage. The 1967 event occurred at the northwestern end of the fault zone, with a strike of N65°E. It had a nearly normalfault mechanism with a seismic moment of 4.5 ×1025 dyne-cm. The largest aftershock (Ms = 5.1) occurred 7 hr later with a similar focal mechanism. The primary faulting along the Xianshuihe fault is left-lateral strike-slip, but the normal faulting with strike direction about perpendicular to the Xianshuihe fault trace is common, especially in the northwestern segment. The faulting pattern in this region is consistent with the regional stress field caused by the India-Tibet collision. The normal event which is not on the major fault seems to have more frequent foreshocks and aftershocks than those on the main fault.

The Meade County, Kentucky, Earthquakes of January and March 1990

1991 ◽  
Vol 62 (2) ◽  
pp. 105-111
Author(s):  
R. Street ◽  
A. Zekulin ◽  
J. Harris
Keyword(s):  
Strike Slip ◽  
Deviatoric Stress ◽  
North Central ◽  
Slip Mechanism ◽  
Pressure Axis ◽  
Tension Axis

Abstract The series of earthquakes that occurred in Meade County, Kentucky, in January and March of 1990, are the first events in an otherwise aseismic area. First motions recorded for the three largest events in January suggest a predominantly strike-slip mechanism with a pressure axis of trend = 275° and plunge = 14° , and a tension axis of trend = 178° and plunge = 31°. A comparison between the mechanisms for the Meade county events and those shown in Taylor et al. (1989) for the southeastern Illinois area, indicates a continuity in the regional deviatoric stress from southeastern Illinois into north-central Kentucky. This finding conflicts with that previously suggested by Ault et al. (1985) who proposed that the two areas were in regions of differing stress regimes.

scholarly journals Geodetic model of the 2015 April 25 Mw 7.8 Gorkha Nepal Earthquake and Mw 7.3 aftershock estimated from InSAR and GPS data

2015 ◽  
Vol 203 (2) ◽  
pp. 896-900 ◽  
Author(s):  
Guangcai Feng ◽  
Zhiwei Li ◽  
Xinjian Shan ◽  
Lei Zhang ◽  
Guohong Zhang ◽  
...  
Keyword(s):  
Surface Deformation ◽  
Strike Slip ◽  
Gps Data ◽  
Reverse Fault ◽  
Lateral Strike Slip ◽  
Nepal Earthquake ◽  
Largest Aftershock ◽  
Total Seismic Moment ◽  
Maximum Thrust ◽  
Seismic Disaster

Abstract We map the complete surface deformation of 2015 Mw 7.8 Gorkha Nepal earthquake and its Mw 7.3 aftershock with two parallel ALOS2 descending ScanSAR paths’ and two ascending Stripmap paths’ images. The coseismic fault-slip model from a combined inversion of InSAR and GPS data reveals that this event is a reverse fault motion, with a slight right-lateral strike-slip component. The maximum thrust-slip and right-lateral strike-slip values are 5.7 and 1.2 m, respectively, located at a depth of 7–15 km, southeast to the epicentre. The total seismic moment 7.55 × 1020 Nm, corresponding to a moment magnitude Mw 7.89, is similar to the seismological estimates. Fault slips of both the main shock and the largest aftershock are absent from the upper thrust shallower than 7 km, indicating that there is a locking lower edge of Himalayan Main Frontal Thrust and future seismic disaster is not unexpected in this area. We also find that the energy released in this earthquake is much less than the accumulated moment deficit over the past seven centuries estimated in previous studies, so the region surrounding Kathmandu is still under the threaten of seismic hazards.

Queen Charlotte fault zone: microearthquakes from a temporary array of land stations and ocean bottom seismographs

1981 ◽  
Vol 18 (4) ◽  
pp. 776-788 ◽  
Author(s):  
R. D. Hyndman ◽  
R. M. Ellis
Keyword(s):  
Fault Zone ◽  
Strike Slip ◽  
Ocean Bottom ◽  
Small Component ◽  
Queen Charlotte Islands ◽  
The North ◽  
Vertical Fault ◽  
Linear Sections ◽  
Ocean Bottom Seismographs ◽  
Steep Slopes

A temporary array of land and ocean bottom seismograph stations was used to accurately locate microearthquakes on the Queen Charlotte fault zone, which occurs along the continental margin of western Canada. The continental slope has two steep linear sections separated by a 25 km wide irregular terrace at a depth of 2 km. Eleven events were located with magnitudes from 0.5 to 2.0, 10 of them beneath the landward one of the two steep slopes, some 5 km off the coast of the southern Queen Charlotte Islands. No events were located beneath the seaward and deeper steep slope. The depths of seven of these events were constrained by the data to between 9 and 21 km with most near 20 km. The earthquake and other geophysical data are consistent with a near vertical fault zone having mainly strike-slip motion. A model including a small component of underthrusting in addition to strike-slip faulting is suggested to account for the some 15° difference between the relative motion of the North America and Pacific plates from plate tectonic models and the strike of the margin. One event was located about 50 km inland of the main active zone and probably occurred on the Sandspit fault. The rate of seismicity on the Queen Charlotte fault zone during the period of the survey was similar to that predicted by the recurrence relation for the region from the long-term earthquake record.

Strong Ground-Motion Measurements during the 2003 Bam, Iran, Earthquake

2005 ◽  
Vol 21 (1_suppl) ◽  
pp. 165-179 ◽  
Author(s):  
Mehdi Zaré ◽  
Hossein Hamzehloo
Keyword(s):  
Ground Motion ◽  
Local Time ◽  
Strong Ground Motion ◽  
Strike Slip ◽  
Bam Earthquake ◽  
Lateral Strike Slip ◽  
Slip Mechanism ◽  
Motion Measurements ◽  
The City ◽  
Strong Ground

The Bam earthquake of 26 December 2003 ( Mw 6.5) occurred at 01:56:56 (GMT, 05:26:56 local time) near the city of Bam in the southeast of Iran. Two strong phases of energy are seen on the accelerograms. The first comprises a starting subevent with right-lateral strike-slip mechanism located south of Bam. The mechanism of the second subevent was a reverse mechanism.

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