Earthquakes in Lassen Volcanic National Park, California

1979 ◽  
Vol 69 (3) ◽  
pp. 867-875
Author(s):  
Fred W. Klein
Keyword(s):  
National Park ◽  
Radial Symmetry ◽  
Seismic Zone ◽  
Focal Mechanism Solutions ◽  
The North ◽  
Lassen Peak ◽  
Lassen Volcanic National Park ◽  
Surface Geology ◽  
Seismograph Network ◽  
Chaos Crags

abstract A small seismograph network of six stations now monitors earthquakes in and near Lassen Volcanic National Park. The first 14 months of recording has revealed a northwest-trending seismic zone passing through the park. This zone is the resolved equivalent of a diffuse zone of historical epicenters passing through Lassen Park and Truckee, California, and is parallel to nearby lineaments in California, Oregon, and Nevada recognized from surface geology. Three dense concentrations of earthquakes correlate very closely with three geothermal areas. One concentration also outlines the north and east sides of the 4-km-diameter Mt. Tehama caldera. The recent dacite plug domes of Lassen Peak and Chaos Crags are nearly aseismic, however. Several approximate focal mechanism solutions indicate primarily normal faulting with east-west extension. This implies the northwest-trending seismic zone is undergoing extension and right-lateral shear. Extension directions near the center of the network display a radial symmetry that could be caused by a broad updoming or magma injection centered near Lassen Peak or Chaos Crags.

Microseismicity and tectonics of the Nevada Seismic Zone

1971 ◽  
Vol 61 (5) ◽  
pp. 1413-1432 ◽  
Author(s):  
Frank J. Gumper ◽  
Christopher Scholz
Keyword(s):  
Sierra Nevada ◽  
Focal Mechanism ◽  
Basin And Range ◽  
Mono Lake ◽  
Tectonic Activity ◽  
Seismic Zone ◽  
Owens Valley ◽  
Western Basin ◽  
Focal Mechanism Solutions ◽  
Composite Focal Mechanism

abstract Microseismicity, composite focal-mechanism solutions, and previously-published focal parameter data are used to determine the current tectonic activity of the prominent zone of seismicity in western Nevada and eastern California, termed the Nevada Seismic Zone. The microseismicity substantially agrees with the historic seismicity and delineates a narrow, major zone of activity that extends from Owens Valley, California, north past Dixie Valley, Nevada. Focal parameters indicate that a regional pattern of NW-SE tension exists for the western Basin and Range and is now producing crustal extension within the Nevada Seismic Zone. An eastward shift of the seismic zone along the Excelsior Mountains and left-lateral strike-slip faulting determined from a composite focal mechanism indicate transform-type faulting between Mono Lake and Pilot Mountain. Based on these results and other data, it is suggested that the Nevada Seismic Zone is caused by the interaction of a westward flow of mantle material beneath the Basin and Range Province with the boundary of the Sierra Nevada batholith.

Earthquake migration in the Fairbanks, Alaska seismic zone

1980 ◽  
Vol 70 (1) ◽  
pp. 223-241
Author(s):  
Larry Gedney ◽  
Steve Estes ◽  
Nirendra Biswas
Keyword(s):  
B Value ◽  
Aftershock Sequence ◽  
Stress Axis ◽  
Seismic Zone ◽  
Epicentral Area ◽  
Focal Mechanism Solutions ◽  
Relative Stress ◽  
Earthquake Migration ◽  
Dislocation Process ◽  
High Level

abstract Since a series of moderate earthquakes near Fairbanks, Alaska in 1967, the “Fairbanks seismic zone” has maintained a consistently high level of seismicity interspersed with sporadic earthquake swarms. Five swarms occurring since 1970 demonstrate that tightly compacted centers of activity have tended to migrate away from the epicentral area of the 1967 earthquakes. Comparative b-coefficients of the first four swarms indicate that they occurred under different relative stress conditions than the last episode, which exhibited a higher b-value and was, in fact, a main shock of magnitude 4.6 with a rapidly decaying aftershock sequence. This last recorded sequence in February 1979 was an extension to greater depths along a lineal seismic zone whose first recorded activation occurred during a swarm two years earlier. Focal mechanism solutions indicate a north-south orientation of the greatest principal stress axis, σ1, in the area. A dislocation process related to crustal spreading between strands of a right-lateral fault, similar to that which has been inferred for southern California, is suggested.

scholarly journals The influence of the 1991/92 drought on the woody vegetation of the Kruger National Park

Koedoe ◽  
1995 ◽  
Vol 38 (2) ◽  
Author(s):  
A.J. Viljoen
Keyword(s):  
National Park ◽  
Woody Species ◽  
Aerial Photographs ◽  
Woody Vegetation ◽  
General Area ◽  
Variable Intensity ◽  
The North ◽  
Olifants River ◽  
Area North ◽  
The Impact

All observations and data related to the impact of the 1991/92 drought on the woody vegetation, excluding the riverine vegetation of major rivers, are summarised. This includes data from a visual estimate of damage from aerial photographs, surveys on selected sites, and general observations. Despite lower rainfall, the area north of the Olifants River (excluding the far-northern part) was less affected than the area south of it, suggesting that the woody vegetation in the north is more adapted to drought. A characteristic of the drought was the localised distribution pattern and variable intensity of damage to the same species in the same general area. Information on 31 species are presented briefly. Although a large number of woody species was to some extent damaged, when the woody vegetation is considered as a whole, the influence of the drought was not very severe.

scholarly journals Double seismic zone in the North Mariana region revealed by long-term ocean bottom array observation

2010 ◽  
Vol 183 (3) ◽  
pp. 1455-1469 ◽  
Author(s):  
Hajime Shiobara ◽  
Hiroko Sugioka ◽  
Kimihiro Mochizuki ◽  
Satoko Oki ◽  
Toshihiko Kanazawa ◽  
...  
Keyword(s):  
Ocean Bottom ◽  
Seismic Zone ◽  
The North ◽  
Double Seismic Zone

Tectonic implications of seismic activity recorded by the northern Ontario seismograph network

1989 ◽  
Vol 26 (2) ◽  
pp. 376-386 ◽  
Author(s):  
R. J. Wetmiller ◽  
M. G. Cajka
Keyword(s):  
Horizontal Stress ◽  
Seismic Profile ◽  
Management Program ◽  
Earthquake Activity ◽  
Seismic Velocities ◽  
Northern Ontario ◽  
Focal Mechanism Solutions ◽  
National Networks ◽  
Nuclear Fuel Waste ◽  
Seismograph Network

The northern Ontario seismograph network, which has operated under the Canadian Nuclear Fuel Waste Management Program since 1982, has provided valuable data to supplement those recorded by the Canadian national networks on earthquake activity, rockburst activity, the distribution of regional seismic velocities, and the contemporary stress field in northern Ontario. The combined networks recorded the largest earthquake known in northwestern Ontario, M 3.9 near Sioux Lookout on February 11, 1984, and many smaller earthquakes in northeastern Ontario. Focal mechanism solutions of these and older events showed high horizontal stress and thrust faulting to be the dominant features of the contemporary tectonics of northern Ontario. The zone of more intense earthquake activity in western Quebec appeared to extend northwestward into the Kapuskasing area of northeastern Ontario, where an area of persistent microearthquake activity had been identified by a seismograph station near Kapuskasing.Controlled explosions of the 1984 Kapuskasing Uplift seismic profile experiment recorded on the northern Ontario seismograph network showed the presence of anomalously high LG velocities in northeastern Ontario (3.65 km/s) that when properly taken into account reduced the mislocation errors of well-recorded seismic events by 50% on average.

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