Magnitude 5.8 - VIRGINIA 2011 August 23 17:51:03 UTC Department
of Geology and Planetary Science, University of Pittsburgh Seismic
records from the University of Pittsburgh Seismograph included
Slide 2
3 component
Slide 3
Slide 4
Magnitude 5.8 Magnitude5.9 Date-Time Tuesday, August 23, 2011
at 17:51:03 UTC Tuesday, August 23, 2011 at 01:51:03 PM at
epicenter Location37.975N, 77.969W Depth1 km (~0.6 mile) (poorly
constrained) RegionVIRGINIA Distances 45 km (27 miles) E of
Charlottesville, Virginia 55 km (34 miles) SW of Fredericksburg,
Virginia 64 km (39 miles) NW of RICHMOND, Virginia 82 km (50 miles)
NNE of Farmville, Virginia Location Uncertainty horizontal +/- 10.9
km (6.8 miles); depth +/- 7.4 km (4.6 miles) Parameters NST=390,
Nph=390, Dmin=57.9 km, Rmss=1.17 sec, Gp= 47, M-type=regional
moment magnitude (Mw), Version=6 Source Magnitude: USGS NEIC
(WDCS-D) Location: USGS NEIC (WDCS-D) Event IDusc0005ild
Magnitude5.8 Date-Time Tuesday, August 23, 2011 at 17:51:04 UTC
Tuesday, August 23, 2011 at 01:51:04 PM at epicenter Time of
Earthquake in other Time Zones Location37.936N, 77.933W Depth6 km
(3.7 miles) RegionVIRGINIA Distances 8 km (5 miles) SSW (195) from
Mineral, VA 11 km (7 miles) SSE (148) from Louisa, VA 29 km (18
miles) NE (45) from Columbia, VA 61 km (38 miles) NW (317) from
Richmond, VA 135 km (84 miles) SW (217) from Washington, DC
Location Uncertainty horizontal +/- 2.3 km (1.4 miles); depth +/-
3.1 km (1.9 miles) Parameters NST= 22, Nph= 23, Dmin=50 km,
Rmss=0.44 sec, Gp= 79, M-type=centroid moment magnitude (Mw),
Version=B Source Southeast U.S. Seismic Network Event IDse082311a
Initial EstimateSix hours after earthquake
Slide 5
Virginia earthquake history EARTHQUAKES IN THE CENTRAL VIRGINIA
SEISMIC ZONE Since at least 1774, people in central Virginia have
felt small earthquakes and suffered damage from infrequent larger
ones. The largest damaging earthquake (magnitude 4.8) in the
seismic zone occurred in 1875. Smaller earthquakes that cause
little or no damage are felt each year or two. Earthquakes in the
central and eastern U.S., although less frequent than in the
western U.S., are typically felt over a much broader region. East
of the Rockies, an earthquake can be felt over an area as much as
ten times larger than a similar magnitude earthquake on the west
coast. A magnitude 4.0 eastern U.S. earthquake typically can be
felt at many places as far as 100 km (60 mi) from where it
occurred, and it infrequently causes damage near its source. A
magnitude 5.5 eastern U.S. earthquake usually can be felt as far as
500 km (300 mi) from where it occurred, and sometimes causes damage
as far away as 40 km (25 mi). FAULTS Earthquakes everywhere occur
on faults within bedrock, usually miles deep. Most bedrock beneath
central Virginia was assembled as continents collided to form a
supercontinent about 500-300 million years ago, raising the
Appalachian Mountains. Most of the rest of the bedrock formed when
the supercontinent rifted apart about 200 million years ago to form
what are now the northeastern U.S., the Atlantic Ocean, and Europe.
At well-studied plate boundaries like the San Andreas fault system
in California, often scientists can determine the name of the
specific fault that is responsible for an earthquake. In contrast,
east of the Rocky Mountains this is rarely the case. The Central
Virginia seismic zone is far from the nearest plate boundaries,
which are in the center of the Atlantic Ocean and in the Caribbean
Sea. The seismic zone is laced with known faults but numerous
smaller or deeply buried faults remain undetected. Even the known
faults are poorly located at earthquake depths. Accordingly, few,
if any, earthquakes in the seismic zone can be linked to named
faults. It is difficult to determine if a known fault is still
active and could slip and cause an earthquake. As in most other
areas east of the Rockies, the best guide to earthquake hazards in
the seismic zone is the earthquakes themselves.
Slide 6
Thrust mechanism is estimated for this earthquake by
quake.usgs.gov
Slide 7
Slide 8
Immediately following earthquake 6 hours after earthquake