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| USGS earthquake location. |
February 4, 2016 - MONTANA, UNITED STATES - A 3.7 magnitude earthquake was recorded near Helena early Thursday morning, according to an initial report from the U.S. Geological Survey.
The quake was centered six miles south of Helena at 12:47 a.m.
An earthquake of that size could be felt quite noticeably by people indoors, according to the USGS.
Clancy, mt - Shook the knobs on dresser Helena - Windows were rattling, woke me up. Clancy - happened about 1am local time, thought it was the wind or somebody in the house jumping, enough to wake up the wife Clancy - Violent rattling of windows that woke us up at 12:46 AM, house shaking and creaking. Clancy - About 12:35am and woke up from sleep due to shaking and our huskies howling, felt several aftershocks too. We live at the end of Halford Rd up Lump Gulch in Clancy, Mt Clancy - It woke me just around 1:00 am. Felt very similar to the last one. I had to get out of bed to see if something fell over or a person was in my house.
Thursday's quake came on the heels of a 4.3 magnitude earthquake centered 12 miles east of Lincoln at 12:31 p.m. Saturday, according to an updated USGS report.
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| USGS shakemap intensity. |
An online search of USGS archives did not show any earthquakes with a magnitude of greater than 3.4 within 40 miles of Helena in all of 2015. - IR.
Seismicity of Yellowstone
Earthquake epicenters in Yellowstone reveal a pattern of intense seismicity related to faults and volcanic features. Plotted here are Yellowstone's 1973-1996 earthquakes on digital topography showing their relation of epicenters to faults and post-caldera (post 631,000 year old) volcanic vents.Intense swarms of shallow earthquakes and occasional moderate-sized earthquakes as large as the MS = 6.1 earthquake in 1975 near Norris Junction, characterize the seismicity of Yellowstone. Norris also has the highest temperature hydrothemal system in the park. The geophysical evidence suggests that earthquakes of Yellowstone are influenced by the presence of magmas, partial melts, and hydrothermal activity at crustal depths from near surface to depths of ~5 km. Earthquakes occur on faults that form boundaries of small upper-crustal blocks and reflect a combination of deformation caused by local transport of magma and hydrothermal fluids as well as by the regional northeast extension superimposed from the Basin-Range tectonic stress field.
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| USGS earthquake historic seismicity. |
Earthquakes reveal a pattern of seismicity over the Yellowstone-Hebgen Lake region that extends into the Yellowstone caldera along northwesting trending clusters of epicenters. Earthquakes extend ~25 km from Hebgen Lake, Montana, along an east-west trend into Yellowstone National Park where they take on a northwest trend along distinct seismic zones about 25 km long that cross the caldera boundary. Within the caldera, earthquakes have not exceeded magnitude MS = 5.0 and generally have scattered epicenters; in the western part of the caldera, northwest-trending clusters of epicenters, together with aligned volcanic vents, may be related to buried, but still active, Quaternary faults. In several cases, there are good correlations between earthquake swarms and major changes in hydrothermal activity. Local faulting along the west side of Yellowstone Lake has Holocene displacements and appears to be seismically active.
Parts of the Gallatin and Teton normal fault systems, which generally have a northerly trends outside the Yellowstone region, presumably lie beneath the area now covered by the Quaternary volcanics of the Yellowstone Plateau. A broader view of Yellowstone seismicity and that of Teton region is shown here.
Focal depths of earthquakes in Yellowstone reveal notable variations across the caldera that are related to variations in heat flux and rock composition.
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| Earthquake historic seismicity. University of Utah. |
Maximum focal depths outside the caldera are generally less than 15 to 20 km, and mostly less than 5 km beneath the inner caldera. This pattern of earthquake- shallowing suggests a thin seismogenic brittle upper crust beneath the thermally active inner caldera. Rheologic models imply that below about 5 km, the crust is in a quasi-plastic, ductile state at temperatures in excess of 350°C - incapable of supporting large stresses. Note that the MS = 6.1 earthquake in 1975 occurred along the caldera's northwest boundary. On a regional scale, earthquakes are most intense on the west side of Yellowstone National Park. The most seismically active area is associated with the 1959, MS = 7.5, Hebgen Lake main shock that occurred within about 30 km of the northwestern side of the Yellowstone caldera. This large earthquake may have resulted from unusual lithospheric uplift and viscoelastic relaxation associated with the Yellowstone hotspot.
Along the northwest side of the eastern Snake River Plain, earthquakes have a notable northwest alignment of epicenters in central Idaho, which is aftershock activity of the 1983, MS = 7.3, Borah Peak earthquake on the Lost River fault. This pattern contrasts with the scatter of what we have called background seismicity elsewhere in the central ISB. The "turning on" of earthquakes on the Lost River fault emphasizes the relative seismic quiescence of the neighboring Lemhi and Beaverhead faults to the northeast. All three faults are part of a domain of active, latest Quaternary basin-range normal faulting northwest of the SRP. Hence, the paucity of earthquakes between the Lost River fault and the Idaho-Montana border marks an important seismic gap in the central ISB. Seismic surveillance by the Idaho National Engineering Laboratory reveals few earthquakes within the Snake River Plain itself. The lack of earthquakes is thought to be related to increased crustal strength resisting earthquakes, to high temperatures that inhibit earthquakes, or to complex stresses related to the Yellowstone hotspot. - The Yellowstone-Teton Epicenter.
Seismicity of Yellowstone.
Earthquake epicenters in Yellowstone reveal a pattern of intense seismicity related to faults and volcanic features. Plotted here
are Yellowstone's 1973-1996 earthquakes on digital topography showing
their relation of epicenters to faults and post-caldera (post 631,000
year old) volcanic vents. Intense swarms of shallow earthquakes and occasional moderate-sized earthquakes as large as the MS = 6.1 earthquake in 1975 near Norris Junction, characterize the seismicity of Yellowstone. Norris also has the highest temperature hydrothemal system in the park. The geophysical evidence suggests that earthquakes of Yellowstone are influenced by the presence of magmas, partial melts, and hydrothermal activity at crustal depths from near surface to depths of ~5 km. Earthquakes occur on faults that form boundaries of small upper-crustal blocks and reflect a combination of deformation caused by local transport of magma and hydrothermal fluids as well as by the regional northeast extension superimposed from the Basin-Range tectonic stress field.
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| USGS earthquake historic seismicity. |
Earthquakes reveal a pattern of seismicity over the Yellowstone-Hebgen Lake region that extends into the Yellowstone caldera along northwesting trending clusters of epicenters. Earthquakes extend ~25 km from Hebgen Lake, Montana, along an east-west trend into Yellowstone National Park where they take on a northwest trend along distinct seismic zones about 25 km long that cross the caldera boundary. Within the caldera, earthquakes have not exceeded magnitude MS = 5.0 and generally have scattered epicenters; in the western part of the caldera, northwest-trending clusters of epicenters, together with aligned volcanic vents, may be related to buried, but still active, Quaternary faults. In several cases, there are good correlations between earthquake swarms and major changes in hydrothermal activity. Local faulting along the west side of Yellowstone Lake has Holocene displacements and appears to be seismically active.
Parts of the Gallatin and Teton normal fault systems, which generally have a northerly trends outside the Yellowstone region, presumably lie beneath the area now covered by the Quaternary volcanics of the Yellowstone Plateau. A broader view of Yellowstone seismicity and that of Teton region is shown here.
Focal depths of earthquakes in Yellowstone reveal notable variations across the caldera that are related to variations in heat flux and rock composition.
|
| Earthquake historic seismicity. University of Utah. |
Maximum focal depths outside the caldera are generally less than 15 to 20 km, and mostly less than 5 km beneath the inner caldera. This pattern of earthquake- shallowing suggests a thin seismogenic brittle upper crust beneath the thermally active inner caldera. Rheologic models imply that below about 5 km, the crust is in a quasi-plastic, ductile state at temperatures in excess of 350°C - incapable of supporting large stresses. Note that the MS = 6.1 earthquake in 1975 occurred along the caldera's northwest boundary. On a regional scale, earthquakes are most intense on the west side of Yellowstone National Park. The most seismically active area is associated with the 1959, MS = 7.5, Hebgen Lake main shock that occurred within about 30 km of the northwestern side of the Yellowstone caldera. This large earthquake may have resulted from unusual lithospheric uplift and viscoelastic relaxation associated with the Yellowstone hotspot.
Along the northwest side of the eastern Snake River Plain, earthquakes have a notable northwest alignment of epicenters in central Idaho, which is aftershock activity of the 1983, MS = 7.3, Borah Peak earthquake on the Lost River fault. This pattern contrasts with the scatter of what we have called background seismicity elsewhere in the central ISB. The "turning on" of earthquakes on the Lost River fault emphasizes the relative seismic quiescence of the neighboring Lemhi and Beaverhead faults to the northeast. All three faults are part of a domain of active, latest Quaternary basin-range normal faulting northwest of the SRP. Hence, the paucity of earthquakes between the Lost River fault and the Idaho-Montana border marks an important seismic gap in the central ISB. Seismic surveillance by the Idaho National Engineering Laboratory reveals few earthquakes within the Snake River Plain itself. The lack of earthquakes is thought to be related to increased crustal strength resisting earthquakes, to high temperatures that inhibit earthquakes, or to complex stresses related to the Yellowstone hotspot. - The Yellowstone-Teton Epicenter. - See more at: http://thecelestialconvergence.blogspot.com/2013/03/planetary-tremors-32-magnitude.html#sthash.5tKgK5Mw.dpuf
