The Livermore Valley, California, sequence of January 1980

1981 ◽  
Vol 71 (2) ◽  
pp. 451-463
Author(s):  
B. A. Bolt ◽  
T. V. McEvilly ◽  
R. A. Uhrhammer
Keyword(s):  
Fault Plane ◽  
B Value ◽  
Strike Slip ◽  
Causal Connection ◽  
Fault Plane Solutions ◽  
Lateral Strike Slip ◽  
Marsh Creek ◽  
Long Duration ◽  
The University ◽  
Rapid Deployment

abstract At 19h00m09.46s UTC, on 24 January 1980, a strong earthquake (ML = 5.5) that caused a surprising amount of damage occurred north of Livermore Valley about 12 km to the southeast of Mt. Diablo, and was associated with surface rupture along the Greenville Fault. There was a foreshock (ML = 2.7) a minute and a half earlier and a sequence of 59 events (ML ≧ 2.5) in the ensuing 6 days. On 27 January at 02h33m35.96s, a larger magnitude earthquake occurred in the sequence (ML = 5.6). This second principal shock was located 14 km to the south of the first principal earthquake toward the southern end of the Greenville Fault. Preliminary estimates of the seismic moments of the two principal shocks are 5.3 × 1024 and 1.3 × 1024 dyne-cm, respectively. In addition to the lower seismic moment, the ML = 5.6 shock on 27 January exhibits a clearly focused radiation pattern, with large amplitudes toward the northeast. Field investigations after the first principal shock indicated surfaced rupture along the Greenville fault zone for at least 6 km, with both right-lateral strike-slip and some dip-slip motion with the northeast side up. Variable offsets on surface cracks suggested displacements of a few centimeters (with evidence of increases in some places after the second 27 January earthquake). There were eight earthquakes with ML ≧ 4.0 in the sequence up to 5 February 1980. No foreshocks near the Greenville Fault (ML ≧ 1.5) were observed by the University of California Seismographic Stations in the prior 3 months. Rapid deployment of field seismographs by a number of seismological organizations permitted precise locations and fault-plane solutions. Some results on seismicity are as follows. The rupture propagated over 15 km to the southeast along the Marsh Creek-Greenville faults on 24 January and stopped in the vicinity of Highway 580. This southern progression may have had some causal connection with the relatively high intensities reported near the southwest end of the Greenville Fault. The two principal shocks of the sequence have slight but significant differences in the fault-plane solutions; both are predominantly right-lateral strike-slip, but the strike of the northern one is N13°W, whereas the strike of the southern one is N39°W. This change in strike is not evident in the mapped strikes of the Marsh Creek and the Greenville faults. In contrast to the second principal earthquake, the first principal shock was followed by two others (ML > 4.0) in rapid succession, one 53 sec and the other 97 sec after. This repetition gave a relatively long duration to the shaking on 24 January, and was commented on in felt reports. It may explain the greater intensity reported in many localities on 24 January compared to 27 January. The b value (0.64 ± 0.13) for the sequence is somewhat lower than the b = 0.70 ± 0.17 for the recent Coyote Lake earthquake sequence on the Calaveras Fault on 5 August 1979. There are fewer earthquakes than normal in the range 3.0 < ML < 4.0 in the Greenville sequence.

Rampart seismic zone of central Alaska

1983 ◽  
Vol 73 (3) ◽  
pp. 813-829
Author(s):  
P. Yi-Fa Huang ◽  
N. N. Biswas
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
B Value ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Lithospheric Plate ◽  
Normal Faults ◽  
Seismic Zone ◽  
The West ◽  
Fault Plane Solutions

abstract This paper describes the characteristics of the Rampart seismic zone by means of the aftershock sequence of the Rampart earthquake (ML = 6.8) which occurred in central Alaska on 29 October 1968. The magnitudes of the aftershocks ranged from about 1.6 to 4.4 which yielded a b value of 0.96 ± 0.09. The locations of the aftershocks outline a NNE-SSW trending aftershock zone about 50 km long which coincides with the offset of the Kaltag fault from the Victoria Creek fault. The rupture zone dips steeply (≈80°) to the west and extends from the surface to a depth of about 10 km. Fault plane solutions for a group of selected aftershocks, which occurred over a period of 22 days after the main shock, show simultaneous occurrences of strike-slip and normal faults. A comparison of the trends in seismicity between the neighboring areas shows that the Rampart seismic zone lies outside the area of underthrusting of the lithospheric plate in southcentral and central Alaska. The seismic zone outlined by the aftershock sequence appears to represent the formation of an intraplate fracture caused by regional northwest compression.

Aftershocks of the Managua, Nicaragua, earthquake of December 23, 1972

1974 ◽  
Vol 64 (4) ◽  
pp. 1005-1016
Author(s):  
C. J. Langer ◽  
M. G. Hopper ◽  
S. T. Algermissen ◽  
J. W. Dewey
Keyword(s):  
Fault Plane ◽  
Strike Slip ◽  
Fault System ◽  
Fault Plane Solutions ◽  
Lateral Strike Slip ◽  
Seismic Zones ◽  
The North ◽  
Primary Zone ◽  
Slip Displacement ◽  
Strain Release

abstract Epicenters determined from 164 of the Managua aftershocks define two seismic zones. The primary zone, which is 15 to 20 km in length and strikes northeast along the Tiscapa-Ciudad Jardin fault system, contains 80 per cent of the aftershock locations. A subsidiary zone, northwest of Managua, suggests strain release possibly related to the north-south striking San Judas fault. Depth of foci are principally in the upper 7 km for both zones. Composite fault-plane solutions indicate a predominate left-lateral strike-slip displacement; the preferred planes for each zone agree with the strike of surface fractures or previously mapped faults.

Relocation of Koyna earthquakes

1980 ◽  
Vol 70 (5) ◽  
pp. 1849-1868
Author(s):  
B. K. Rastogi ◽  
P. Talwani
Keyword(s):  
Fault Plane ◽  
Seismic Velocity ◽  
Landsat Imagery ◽  
Velocity Model ◽  
Strike Slip ◽  
Normal Faulting ◽  
Large Area ◽  
Fault Plane Solutions ◽  
Lateral Strike Slip ◽  
Induced Earthquake

abstract The Koyna earthquake of December 10, 1967 was the most damaging reservoir-induced earthquake. It was followed by a long sequence of earthquakes which is still continuing. Precise locations of the Koyna earthquakes have been very much disputed as different locations of the main earthquake and stronger aftershocks were obtained by various workers. Over 1,500 epicenters of Koyna earthquakes through 1973 were obtained by Guha et al. (1974). They cover a large area in a diffused pattern. In view of the continuing seismicity and a recently obtained seismic velocity model, the larger events (ML ≧ 4.0) and about 300 selected smaller events (ML < 4.0) were relocated. The relocated epicenters show some concentration and suggest the possibility of two trends in the NNE and NW directions. There is a NNE trend of epicenters near the dam and another about 20 km west of the reservoir. The NW trend cuts through these NNE trends. The events were grouped to obtain their composite fault-plane solutions which indicate left-lateral strike-slip faulting along the NNE faults and normal faulting in the NW direction. Faults observed in the LANDSAT imagery match with these trends.

The Oroville earthquake sequence of August 1975

1976 ◽  
Vol 66 (4) ◽  
pp. 1065-1084 ◽  
Author(s):  
Paul W. Morrison ◽  
Brian W. Stump ◽  
Robert Uhrhammer
Keyword(s):  
Sierra Nevada ◽  
Fault Plane ◽  
B Value ◽  
Earthquake Sequence ◽  
Occurrence Rate ◽  
California Department ◽  
Fault Plane Solutions ◽  
Aftershock Sequences ◽  
The University ◽  
The City

abstract The characteristics of the Oroville, California earthquake sequence of 1975 are presented. Historically, the Oroville area is one of low seismicity; the largest earthquake in the region occurred with a magnitude (ML) 5.7 in 1940 some 50 km north of Oroville. The first foreshock of the sequence occurred on June 28, 1975. Twnety-one foreshocks (ML ≧ 1.6), the largest of magnitude 4.7, preceded the magnitude 5.7 main shock of August 1. All foreshocks and aftershocks of ML ≧ 3.0 were located using seismographs operated by the University of California at Berkeley, USGS, and the California Department of Water Resources. The aftershock region covers an area approximately 14 by 10 km southeast of the city of Oroville. The depth distribution of the earthquakes indicates a west dipping fault plane. The b value of 0.61 shows the sequence to be rich in larger magnitude aftershocks. Similar b values have been determined for other aftershock sequences in California, such as a sequence near Coalinga in August 1975. The aftershock occurrence rate follows an Omori relation with n(t∞t−0.70. Apparent variability in the earthquake mechanisms of the series makes interpretation of composite fault-plane solutions difficult, but the data indicate normal faulting striking NNW and a west dip of about 30°–40°, the Sierra Nevada moving up with respect to the Great Valley.

Microearthquake seismicity and tectonics of Coastal Northern California

1970 ◽  
Vol 60 (5) ◽  
pp. 1669-1699 ◽  
Author(s):  
Leonardo Seeber ◽  
Muawia Barazangi ◽  
Ali Nowroozi
Keyword(s):  
High Frequency ◽  
Fault Plane ◽  
San Andreas Fault ◽  
High Gain ◽  
Strike Slip ◽  
Fault System ◽  
Northern California ◽  
Fault Plane Solutions ◽  
Sharp Bend ◽  
San Andreas

Abstract This paper demonstrates that high-gain, high-frequency portable seismographs operated for short intervals can provide unique data on the details of the current tectonic activity in a very small area. Five high-frequency, high-gain seismographs were operated at 25 sites along the coast of northern California during the summer of 1968. Eighty per cent of 160 microearthquakes located in the Cape Mendocino area occurred at depths between 15 and 35 km in a well-defined, horizontal seismic layer. These depths are significantly greater than those reported for other areas along the San Andreas fault system in California. Many of the earthquakes of the Cape Mendocino area occurred in sequences that have approximately the same magnitude versus length of faulting characteristics as other California earthquakes. Consistent first-motion directions are recorded from microearthquakes located within suitably chosen subdivisions of the active area. Composite fault plane solutions indicate that right-lateral movement prevails on strike-slip faults that radiate from Cape Mendocino northwest toward the Gorda basin. This is evidence that the Gorda basin is undergoing internal deformation. Inland, east of Cape Mendocino, a significant component of thrust faulting prevails for all the composite fault plane solutions. Thrusting is predominant in the fault plane solution of the June 26 1968 earthquake located along the Gorda escarpement. In general, the pattern of slip is consistent with a north-south crustal shortening. The Gorda escarpment, the Mattole River Valley, and the 1906 fault break northwest of Shelter Cove define a sharp bend that forms a possible connection between the Mendocino escarpment and the San Andreas fault. The distribution of hypocenters, relative travel times of P waves, and focal mechanisms strongly indicate that the above three features are surface expressions of an important structural boundary. The sharp bend in this boundary, which is concave toward the southwest, would tend to lock the dextral slip along the San Andreas fault and thus cause the regional north-south compression observed at Cape Mendocino. The above conclusions support the hypothesis that dextral strike-slip motion along the San Andreas fault is currently being taken up by slip along the Mendocino escarpment as well as by slip along northwest trending faults in the Gorda basin.

Aftershocks of the Benham nuclear explosion

1969 ◽  
Vol 59 (6) ◽  
pp. 2271-2281
Author(s):  
R. M. Hamilton ◽  
J. H. Healy
Keyword(s):  
Fault Plane ◽  
Nuclear Explosion ◽  
Test Site ◽  
Strike Slip ◽  
Nevada Test Site ◽  
Ground Zero ◽  
Fault Plane Solutions ◽  
Fault Movement ◽  
Near Surface ◽  
Earthquake Distribution

abstract The Benham nuclear explosion, a 1.1 megaton test 1.4 km beneath Pahute Mesa at the Nevada Test Site, initiated a sequence of earthquakes lasting several months. The epicenters of these shocks were located within 13 km of ground zero in several linear zones that parallel the regional fault trends. Focal depths range from near surface to 6 km. The earthquakes are not located in the zone of the major ground breakage. The earthquake distribution and fault plane solutions together indicate that both right-lateral strike-slip fault movement and dip-slip fault movement occurred. The explosion apparently caused the release of natural tectonic strain.

scholarly journals The 1991 Sierra Madre earthquake sequence in southern California: Seismological and tectonic analysis

1994 ◽  
Vol 84 (4) ◽  
pp. 1058-1074 ◽  
Author(s):  
Egill Hauksson
Keyword(s):  
Los Angeles ◽  
Fault Plane ◽  
B Value ◽  
Tectonic Stress ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Stress Axis ◽  
The North ◽  
Sierra Madre

Abstract The (ML 5.8) Sierra Madre earthquake of 28 June 1991 occurred at a depth of 12 km under the San Gabriel Mountains of the central Transverse Ranges. Since at least 1932 this region had been quiescent for M ≧ 3. The mainshock focal mechanism derived from first-motion polarities exhibited almost pure thrust faulting, with a rake of 82° on a plane striking N62°E and dipping 50° to the north. The event appears to have occurred on the Clamshell-Sawpit fault, a splay of the Sierra Madre fault zone. The aftershock sequence following the mainshock occurred at a depth of 9 to 14 km and was deficient in small earthquakes, having a b value of 0.6. Twenty nine single-event focal mechanisms were determined for aftershocks of M > 1.5. The 4-km-long segment of the Clamshell-Sawpit fault that may have ruptured in the mainshock is outlined by several thrust focal mechanisms with an east-northeast-striking fault plane dipping to the north. To the west, several thrust aftershocks with east-striking nodal planes suggest some complexity in the aftershock faulting, such as a curved rupture surface. In addition, several strike-slip and normal faulting events occurred along the edges of the mainshock fault plane, indicating secondary tear faulting. The tectonic stress field driving the coexisting left-lateral strike-slip and thrust faults in the northern Los Angeles basin is north-south horizontal compression with vertical intermediate or minimum principal stress axis.

Seismicity in South Carolina

1988 ◽  
Vol 59 (4) ◽  
pp. 165-171
Author(s):  
Kaye M. Shedlock
Keyword(s):  
South Carolina ◽  
Compressive Stress ◽  
Coastal Plain ◽  
Fault Plane ◽  
Strike Slip ◽  
Fault Plane Solutions ◽  
Reservoir Induced Seismicity ◽  
Southeastern Us ◽  
Horizontal Compressive Stress ◽  
Shallow Crust

Abstract The largest historical earthquake in South Carolina, and in the southeastern US, occurred in the Coastal Plain province, probably northwest of Charleston, in 1886. Locations for aftershocks associated with this earthquake, estimated using intensities based on newspaper accounts, defined a northwest trending zone about 250 km long that was at least 100 km wide in the Coastal Plain but widened to a northeast trending zone in the Piedmont. The subsequent historical and instrumentally recorded seismicity in South Carolina images the 1886 aftershock zone. Except for a few scattered earthquakes and a swarm of shallow (≤ 4 km deep), small (ML ≤ 2.5), primarily reverse faulting earthquakes that occurred along the flanks of a granite pluton about 60 km northwest of Columbia, the seismicity in the Piedmont province has been associated with water level changes in reservoirs. Reservoir induced seismicity (RIS) is shallow (≤ 6 km deep), primarily strike-slip or thrust faulting corresponding to an inferred maximum horizontal compressive stress oriented approximately N 60° E. Instrumentally recorded seismicity in the Coastal Plain province occurs in 3 seismic zones or clusters: Middleton Place-Summerville (MPSSZ), Adams Run (ARC), and Bowman (BSZ). Approximately 68% of the Coastal Plain earthquakes occur in the MPSSZ, a north trending zone about 22 km long and 12 km wide, lying about 20 km northwest of Charleston. The hypocenters of MPSSZ earthquakes range in depth from near the surface to almost 12 km. Thrust, strike-slip, and some normal faulting are indicated by the fault plane solutions for Coastal Plain earthquakes. The maximum horizontal compressive stress, inferred from the P-axes of the fault plane solutions, is oriented NE-SW in the shallow crust (< 9 km deep) but appears to be diffusely E-W between 9 to 12 km deep. Although there is localized variability, the current seismicity and associated faulting in South Carolina probably represent a regional response to the NE-SW maximum horizontal compressive stress prevalent throughout eastern North America.

scholarly journals The Gagatli swarm of weak earthquakes - seismo activity manifestation of the Andean fault

2019 ◽  
Vol 1 (1) ◽  
pp. 46-56
Author(s):  
Irina Gabsatarova ◽  
Natalia Ponomareva ◽  
Ludmila Koroletski ◽  
Madina Akhmedova
Keyword(s):  
Normal Component ◽  
Normal Fault ◽  
Wave Pattern ◽  
Strike Slip ◽  
Fault Plane Solutions ◽  
Lateral Strike Slip ◽  
Double Differences ◽  
Fault Kinematics ◽  
Similar Distance ◽  
Weak Earthquakes

The swarm of more than a hundred weak earthquakes, the bulk of which occurred in the second decade of January 2019, was recorded at the end of 2018 and at the beginning of 2019 in the area of the western borders of the Dagestan salient. Refinement of the position of the epicenters of the swarm events by the method of double differences showed their compact location to the northeast of the village Gagatli on the eastern latitudinal branch of the Andean fault, known for left-lateral strike-slip and normal fault kinematics. According to the results of the study of the fault plane solutions of the five most strong earthquakes in the swarm, the type of movement was established - a left-lateral strike-slip and normal component, which allowed the investigated activation to be attributed to the discharge of accumulated stresses in the eastern part of the Andean fault. A characteristic feature of the recordings of these events by the nearest stations located in the territory of Dagestan and Chechnya was the similarity of the wave pattern, established when they correlated in different frequency bands (1-2 Hz, 1-3 Hz, 1-5 Hz). The correlation matrix of the records of 19 events filtered in the 1-3 Hz band was used to construct cluster analysis dendrograms showing different correlation of the events of the swarm and other earthquakes of Dagestan at a similar distance.

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.

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