Joined: 01 Jan 2005
Yes, I saw that earlier today, quite a surprise to where I'd have expected further activity. It actually made the international news, even though earthquakes on the east coast are more usual in comparison to the center, but I guess there's larger populations.
What I had wondered was if there would be more activity around Yellowstone.
USGS have updated their summary of the event.
The magnitude 5.3 southern Colorado earthquake of 23 August 2011 occurred in a region that has experienced numerous small and moderate shocks in the last decade. Since August 2001, eight shocks of magnitude greater than 4.0 have occurred, with the previous largest having been a shock of magnitude 5.0 that occurred in August 2005. Many of the shocks have occurred in episodes of activity known as seismic "swarms", in which more than one earthquake occurred at nearly the same location within a period of several days and in which the largest shock occurred after the beginning of the sequence and was not greatly larger than the preceding or following events of the swarm. The USGS conducted a detailed study of an earthquake swarm in this region that occurred in 2001; a report is available on-line. The shock of 23 August 2011 also occurred within a swarm of smaller shocks that began on the previous day. The 2001 and 2011 swarms notwithstanding, it should be noted that some shocks that have occurred within the southern Colorado source region in the last decade that have not been part of seismic swarms.
The shock of 23 August 2011 occurred as the result of normal faulting, at a shallow depth of focus. The preliminary location, depth, and style of faulting for the 2011 earthquake are very similar to the earthquakes in the previously-cited 2001 swarm. The 2001 swarm did not occur on a mapped geologic fault. The north or north-northeast strike of the causative faults of the largest 2001 and 2011 earthquakes are consistent with the east-west extension that has formed the Rio Grande rift to the west of the epicentral region.
Prior to the onset of earthquake activity in 2001, events had occurred in the Trinidad region in 1966 and 1973. A widely felt magnitude 4.6 earthquake occurred on October 2, 1966, and was felt over a 38,400 km˛ (15,000 mi˛) area. The published location for the 1966 event is northeast of Trinidad, and detailed analysis of this event indicates that it likely did not occur in the same area as the 2001 swarm or the 2011 M 5.3 earthquake. However in September 1973, a swarm of six earthquakes within a period of five days was felt in and around Segundo, Colorado (which is near the epicenter of the M 5.3 quake), and the two largest events had magnitudes of 3.1 and 4.2. The published locations of these two earthquakes are directly northwest of Trinidad Lake, but their exact locations are uncertain by at least ±10 km (±6 miles). Considering the location uncertainty and the felt report information, the 1973 earthquake swarm could have originated from the same source area as the 2001 and 2011 swarms.
USGS report for Virginia
The Virginia earthquake of 2011 August 23 occurred as reverse faulting on a north or northeast-striking plane within a previously recognized seismic zone, the "Central Virginia Seismic Zone." The Central Virginia Seismic Zone has produced small and moderate earthquakes since at least the 18th century. The previous largest historical shock from the Central Virginia Seismic Zone occurred in 1875. The 1875 shock occurred before the invention of effective seismographs, but the felt area of the shock suggests that it had a magnitude of about 4.8. The 1875 earthquake shook bricks from chimneys, broke plaster and windows, and overturned furniture at several locations. A magnitude 4.5 earthquake on 2003, December 9, also produced minor damage.
Previous seismicity in the Central Virginia Seismic Zone has not been causally associated with mapped geologic faults. Previous, smaller, instrumentally recorded earthquakes from the Central Virginia Seismic Zone have had shallow focal depths (average depth about 8 km). They have had diverse focal mechanisms and have occurred over an area with length and width of about 120 km, rather than being aligned in a pattern that might suggest that they occurred on a single causative fault. Individual earthquakes within the Central Virginia Seismic Zone occur as the result of slip on faults that are much smaller than the overall dimensions of the zone. The dimensions of the individual fault that produced the 2011 August 23 earthquake will not be known until longer-term studies are done, but other earthquakes of similar magnitude typically involve slippage along fault segments that are 5 - 15 km long.
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).
_________________ The important thing is knowing who owns the fence
What is the maximum distance for an earthquake to be felt? Say if there was an earthquake in Chile or something that measured like 10.5(probably impossible), would you be able to feel it like at san francisco, or how far would you be able to feel it from the epicenter?
there were some spam like links here ...
Last edited by sharoony on Sat Oct 01, 2011 1:02 am; edited 1 time in total
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum