![]() ![]() Click on a given earthquake to view the detailed event page. This piece has been edited to reflect that revision.Below are recent earthquakes. Note: On March 8, we revised the magnitude of the November 30 Anchorage earthquake upward, from 7.0 to 7.1. Earthquakes outside this small area are not aftershocks from the magnitude 7.1 earthquake-they’re just part of the background seismicity in other areas that haven’t ruptured recently, and should remind us that large earthquakes are possible anywhere and anytime in Southern Alaska. They shake the earth far less than the 7. The epicenter of the Great Alaska Earthquake was about 12 miles north of Prince William Sound and 75 miles east of Anchorage. ANCHORAGE, Alaska (AP) Seven weeks after a massive earthquake rocked Alaska, aftershocks are still shattering 7-year-old Connor Cartwrights sense of safety. A 9.2 on the Moment Magnitude Scale, this was the second largest earthquake in recorded history, generated huge tsunamis, killed 131 people, and cost over 300 million dollars in property damage. Remember, this only applies to the relatively small part of Southcentral Alaska that ruptured during the November 30 earthquake, from south of Point MacKenzie north to around Big Lake. Aftershocks from the quake continued for three weeks. This is a PowerPoint presentation about the 1964 earthquake that hit Alaska on Good Friday, March 27th, at 5:37 pm. Around that time, based on what we’ve seen so far, the aftershocks should blend into the activity we know and expect in that area. In other words, people in Southcentral should expect to keep feeling aftershocks through September, at least. ![]() Our current estimate suggests that aftershocks of magnitude 3 or larger will continue for around 300 days after the November 30 mainshock. The 7.9 Denali Fault, Alaska Earthquake of November 3, 2002: Aftershock Locations, Moment Tensors and Focal Mechanisms from the Regional Seismic Network Data. ![]() As time passes and we collect more data, we can refine this analysis. aftershocks located using teleseismic data from March 28 through December 31. By finding the point where that line crosses a line representing background seismicity (4), we can estimate when the rate of aftershocks will drop below pre-mainshock levels-in other words, when the aftershock sequence will effectively be over. ![]() Geological Survey Geophysicist Paul Caruso said there have been 545 aftershocks since the initial quake. If we also plot seven-day averages of aftershock counts over time (2), we can draw a line representing the rate of decrease in seismicity (3). Aftershocks on Saturday continued to fray nerves in Alaska. A magnitude 6.9 earthquake struck off the coast of Southwest Alaska early Monday in what the Alaska Earthquake Center called an aftershock of an 8. Because of this relationship, we can plot the data on a log/log scale (1). In other words, the declining rate of aftershocks can be graphed as a curve that falls steeply at first and then levels off gradually without ever quite reaching zero. The first 11 of these aftershocks, with magnitude greater than 6.0 on the Richter scale, occurred in the first day in the next three weeks there were 9 more of. Mathematically speaking, the decrease is logarithmic and asymptotic. This is a defining characteristic of all mainshock-aftershock sequences. That rupture changed the distribution of stress in the rock throughout that area. When we look at plots showing the number of magnitude 3 and larger earthquakes each day, we can see that those daily counts start high and decrease rapidly. 30what we call the mainshockruptured an area inside the subducting Pacific plate roughly 20 miles deep and running from south of Point MacKenzie up to Big Lake. Because people mostly want to know when they will stop feeling aftershocks, we’ll estimate when we expect a return to background level for earthquakes greater than magnitude 3. We usually say that aftershocks have stopped when the seismicity in the ruptured area returns to its background level, which is the average rate of earthquakes prior to the mainshock. The burning question on the minds of many residents in Southcentral Alaska is, “When will the aftershocks stop?” This is a tricky question, but enough time has passed since the November 30 magnitude 7.1 earthquake for us to make an informed estimate. ![]()
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