Sunday, September 4, 2011

Unusual Earthquake Swarms. New Dangerous Fault In Oregon. New Zealand Christchurch Earthquake Anniversary.

Earthquake Swarm Continues In German-Czech Border Region

By MARK DUNPHY - Sun Sep 04, 1:08 pm

Towns and villages across the western Czech Republic were shaken Sunday afternoon by a magnitude 4.0 earthquake, the latest in a series of tremors to hit the region.
The Geophysical Institute, Academy of Sciences of the Czech Republic says it has recorded 10,000 earthquakes during the last 10 days in Nový Kostel area of the Cheb District, a region located close to the Czech Republic’s western border with Germany.....

Location and magnitude of earthquakes. Image Geophysical Institute, Academy of Sciences...In recent years, scientists have noted an increase in the movement of magma towards the earth’s surface in the Cheb Basin, western Czech Republic.  They say rising magma could be one of the causes of the earthquake swarms, which regularly occur in the Vogtland, North-West Bohemia, the Fichtelgebirge and the Upper Palatinate.  The last earthquake swarm to occur before this week’s activity was in 2008.

Laser flashes expose Oregon earthquake faults

Scientists using lidar, a system that bounces laser flashes off the ground, have found hidden seismic faults in Oregon, including one on the northern flank of Mount Hood that appears to be active — and dangerous.
PORTLAND — On the northern flank of Mount Hood, a scar in the earth's crust stretches for several miles beneath the fir trees that hide it from airborne observers.
It is the mark of a previously undetected seismic fault that appears to be active — and dangerous. The last time the fault ruptured, opposing sections of the earth's crust jolted 6 feet apart horizontally, leaving a miles-long raised edge, or scarp.
This image shows the region on Mount Hood about 10 miles west of Parkdale, Ore., where geologists have discovered a hidden seismic fault.
Disaster preparedness in Oregon has largely focused on massive earthquakes on the Cascadia Subduction Zone, where an ocean-spanning slab called the Juan de Fuca Plate is plunging beneath the North American plate along the coast. A subduction-zone earthquake could cause magnitude-9 ground-shaking that persists for several minutes across Oregon and Washington.
At shallow crustal faults, earthquakes last for seconds rather than minutes and the ground-shaking is more limited in reach than from a subduction quake. But shallow faults can be deadly and massively destructive to nearby cities. The magnitude 6.3 earthquake in February on a shallow fault beneath Christchurch, New Zealand, killed more than 180 people and collapsed modern, seismically reinforced buildings.
Connections between the faults and volcanic activity at Mount Hood are uncertain. At Mount St. Helens, a shallow crustal fault played a major role in the 1980 eruption. A magnitude 5.1 earthquake on the fault triggered a landslide that collapsed the north side of the mountain.
Nearly all of the recently disclosed faults in Oregon remain a complete mystery. Progress on defining the risks has been slow because the state has invested little in the field work required.
"It was probably a magnitude 6 or 7 earthquake," says Ian Madin, chief scientist with the Oregon Department of Geology and Mineral Industries. "That would be felt in Hood River. It might be damaging in Hood River valley communities."

N.Z. Ministers Mark Quake Anniversary With Christchurch Meeting

By Tracy Withers - Sep 4, 2011 6:01 AM MT

New Zealand’s Cabinet meets in Christchurch today, marking the one-year anniversary of the first of a series of earthquakes that hit the southern city and cost the nation more than NZ$15 billion ($13 billion).
The magnitude-7 quake on Sept. 4, 2010, began a year of seismic upheaval that included 29 temblors of magnitude 5 or more, according to the government. A quake measuring 6.3 on Feb. 22 was the deadliest in 80 years, killing more than 180 people and closing the heart of the nation’s second-largest city, home to a population of 350,000.
The September earthquake “kicked off a series of seismic events the likes of which hasn’t been seen anywhere else in the world,” Earthquake Recovery Minister Gerry Brownlee said yesterday. “We’ve come a long way since that day, through some dark and very trying times.”

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