Table of Content
Though volcanic activity causes only a small proportion of Alaska's earthquakes, these earthquakes often warrant more detailed analysis. Ten-hour seismograms from a seismic station on Atka Island on August 6 & 7, 2008. The sudden appearance of numerous earthquakes was an early sign of an eruption that began later in the day on August 7. Not all swarms of earthquakes indicate eruptions; but nearly all eruptions are preceded by vigorous seismic activity. The Alaska Earthquake Center exists to minimize our risks by understanding where earthquakes occur and why. Tracking the earthquakes that occur each day provides clues about the earthquakes that are likely in the future.
The earthquake prompted tsunami warnings and advisories for Alaska, British Columbia, Washington, Oregon, California, and Hawaii. Residents in low-lying areas along the Gulf of Alaska and in British Columbia were evacuated to shelters and higher ground. The Pacific Tsunami Warning Center later cancelled most of the alerts within four hours of the earthquake, due to the apparent lack of tsunami.
Anchorage earthquake left crumbling buildings, collapsed roofs and damaged roads
The Alaska Earthquake Information Center categorized the shaking as light. The time between the siren sounding and the all-clear was tense, and his son and daughter were scared. "But in the main, I think people kind of knew what they needed to do and just waited for information," he said. Elsewhere in the United States, Washington state, Oregon, California and Hawaii were under tsunami watches, which eventually were lifted. The International Seismological Centre has a bibliography and/or authoritative data for this event.
The Pacific Plate subducts, or sinks, beneath the North American Plate at a deep-sea trench that defines the Alaska-Aleutian subduction zone on the seafloor, about 90 km to the northwest of the Jan. 23 earthquake epicenter. The easternmost megathrust earthquake was the March 28, 1964 M9.2 Prince William Sound earthquake, currently the second largest recorded earthquake in the world. The event had a rupture length of roughly 700 km extending from Prince William Sound in the northeast to the southern end of Kodiak Island in the southwest.
Damage
The weather rolling in will slow down our response, but we will continue to work on repairs alongside our dedicated contractors. Every single bridge affected by this quake will be inspected by bridge engineers and a plan will be developed to address any repairs needed. After an initial assessment of all bridges, engineers will return for more thorough inspections of each bridge. The main goal when building new bridges or retrofitting old ones is to prevent collapse, which helps ensure your safety when traveling. Alaska’s bridges are designed in specific ways to stay standing during an earthquake.
The Alaska mainland is crosscut by numerous fault systems that accommodate this compression and shearing. In the popular cruise-ship town of Seward, about 110 miles south of Anchorage, Fire Chief Eddie Athey said the quake felt like a gentle rattle that lasted for up to 90 seconds. By the time customers started arriving, the excitement had passed and people just sat around quietly eating their meals, speaking little of the quake. In the nearby Matanuska-Susitna Borough, multiple roads were closed, collapsed and cracked. Two of the city’s main hospitals were damaged, but their emergency rooms remained open.
Tsunami Hazard Map Tool
Even though a Village Inn had been damaged, they got breakfast there. They visited with an Anchorage friend and headed home around 2 p.m. Sulczynski said a passerby offered them a ride on to the airport. Last week, he wasn’t able to get confirmation from the Anchorage Police or local towing companies that his vehicle will be removed from the road. Alaska Public Media later reported that a towing company recovered his car.
Maintenance crews have completed the grinding and grading at MP 19 Spur Highway. The other two locations on Spur will be ground and bladed by end of day. Finish work and paving will take place in the spring when asphalt plants are operational again. All DOT&PF bridge inspectors are now in Southcentral Alaska and are conducting technical bridge inspections. At this point, 44 high priority structures have been inspected. DOT&PF has documented approximately 50 potential damage sites.
Earthquake
Most of these earthquakes—and all major earthquakes—can be traced to the movement of tectonic plates. The Alaska Department of Transportation and Public Facilities moved quickly to inspect bridges and begin road repairs. Despite not normally paving during winter, area asphalt plants were restarted and within days sufficient repairs were made to reopen several heavily damaged roads. The first major aftershocks occurred 20 minutes after the earthquake.
Extensive damage was recorded in Kenai, Moose Pass, and Kodiak but significant shaking was felt over a large region of Alaska, parts of western Yukon Territory, and British Columbia, Canada. Property damage was the largest in Anchorage, as a result of both the main shock shaking and the ensuing landslides. This megathrust earthquake also triggered a devastating tsunami that caused damage along the Gulf of Alaska, the West Coast of the United States, and in Hawaii. Although damage from earthquake shaking was not severe locally, tsunami run-up heights were recorded as high as 42 m on Unimak Island and tsunami waves in Hilo, Hawaii also resulted in casualties. The slow rupture of this event has made it difficult to constrain the focal mechanism and depth of the earthquake, though it is thought to have been an interplate thrust earthquake. Communities on Kodiak Island and other coastal areas on the Gulf of Alaska and Cook Inlet were evacuated after warning sirens were activated.
Earthquake aftershocks are continuing to contribute to settling and cracking. Glenn Highway southbound traffic, just south of the Knik River at the Old Glenn Highway, is down to one lane. We are working at eight of the highest priority sites out of the 50 damaged locations on state-maintained infrastructure identified so far.
The paving work will help level the areas between the bridge and abutment that buckled. Check 511.Alaska.Gov or dial to check the status of specific roads. Travel 511 Traveler Alaska Marine Highway Visitor information Alaska Railroad Aviation & Airports Active Transportation Commercial Vehicles Highway Construction Ports & Harbors Road Weather More travel links... During the statewide conference, Anchorage hospitals reported no surge in need. He said staff at the Harbormaster’s office evacuated shortly after the initial quake.
This is a different mechanism than megathrust faults in the region, which do occur on the plate boundary itself. This faulting in the Pacific Plate is caused by downward bending while the plate is being forced under Alaska. Southern Alaska lies at the eastern end of the Aleutian Trench, where the Pacific Plate is subducting beneath the North American Plate. Near Anchorage, the plates are converging at a rate of 57 mm per year. The region has experienced severe earthquakes in the past, including several megathrust earthquakes. The 1964 earthquake, with a magnitude of 9.2, was the largest earthquake in American history and the second largest to ever be recorded anywhere in the world.
Subduction zone quakes have the potential to generate very strong ground shaking, and accompanying dangerous tsunamis as occurred in 1964. The western Aleutians, stretching from the western end of the Rat Islands in the east to the Commander Islands, Russia, in the west, is tectonically different from the central and eastern portions of the arc. Additionally, this portion of the subduction zone has not hosted large earthquakes or megathrust events in recorded history. Instead, the largest earthquakes in this region are generally shallow, predominantly strike-slip events with magnitudes between M5-6. Any strong earthquake shaking could potentially dislodge submarine landslides and trigger a deadly local tsunami. The next megathrust earthquake occurred along the central portion of the Aleutian arc near the Andreanof Islands on March 9, 1957, with a magnitude of M8.6.
No comments:
Post a Comment