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‘Ewa Beach, HI, United States

Becker N.C.,Pacific Tsunami Warning Center | Fryer P.,University of Hawaii at Manoa | Moore G.F.,University of Hawaii at Manoa
Geochemistry, Geophysics, Geosystems | Year: 2010

Six-channel seismic reflection data reveal a magma chamber reflector beneath the Malaguana-Gadao Ridge, the southernmost segment of the spreading center in the Mariana Trough. For most of its length the spreading center in this active back-arc basin is morphologically similar to slow spreading mid-ocean ridges, having a deep central graben flanked by a zone of abyssal hill fabric. This southernmost segment, however, has a broad, smooth cross section, lacks a deep central graben, and is thus similar in morphology to fast spreading ridges (e.g., the East Pacific Rise). We identify a magma chamber at 1.5 s two-way travel time below the crest of the ridge. Observations from remotely operated vehicles along the ridge reveal not only fresh pillows, lobate, and sheet lava flows but also an abundance of volcaniclastic debris and intense hydrothermal activity. These observations, together with the "fast spreading" morphology of the ridge, suggest that this segment has a considerably higher magma supply than is typical in the Mariana Trough. We suggest that the volcanic arc or enhanced melting of a hydrated mantle is supplying volatile-rich magma as evidenced by a highly negative coefficient of reflection, -0.42, for this MCR and the presence of evolved, highly vesicular lava and volcaniclastic materials. The southeastern Mariana back-arc basin spreading ridge does not compare readily with mechanical models for global mid-ocean ridge data sets because of marked asymmetry in both volcanism and deformation that may be the consequence of slab-related geometry in this part of the convergent margin system. Copyright 2010 by the American Geophysical Union.

Fryer G.J.,Pacific Tsunami Warning Center
Earth-Science Reviews | Year: 2011

With any handheld GPS unit and a modest investment of time, typically about one hour per kilometer, it is possible to walk along the debris line and so map the inundation limit of a tsunami. These measurements are not adequate to define runup, but with an accuracy of three meters or better (one meter with simple processing) they are quite adequate for all scientific uses of inundation. The same data are invaluable to emergency managers planning recovery efforts. This short note uses the examples of Amanave and Tula in American Samoa, both affected by the 2009 South Pacific tsunami, to encourage the routine collection of such data in future post-tsunami surveys. © 2011.

Butler R.,University of Hawaii at Manoa | Burney D.,National Tropical Botanical Garden | Walsh D.,Pacific Tsunami Warning Center
Geophysical Research Letters | Year: 2014

The Hawaiian Islands' location in the middle of the Pacific Ocean is threatened by tsunamis from great earthquakes in nearly all directions. Historical great earthquakes Mw > 8.5 in the last 100 years have produced large inundations and loss of life in the islands but cannot account for a substantial (≤ 600 m3) paleotsunami deposit in the Makauwahi sinkhole on the Island of Kaua'i. Using high-resolution bathymetry and topography we model tsunami inundation of the sinkhole caused by an earthquake with a moment magnitude of Mw ~9.25 located in the eastern Aleutians. A preponderance of evidence indicates that a giant earthquake in the eastern Aleutian Islands circa 1425-1665 A.D. - located between the source regions of the 1946 and 1957 great tsunamigenic earthquakes - created the paleotsunami deposit in Kaua'i. A tsunami deposit in the Aleutians dated circa 1530-1660 A.D. is consistent with this eastern Aleutian source region. Key Points A Kaua'i tsunami deposit is linked to Mw 9+ earthquake in the eastern AleutiansPaleotsunami evidence in the Aleutians and West Coast U.S. corroborates the timeInundations would be greater than any experienced by Hawai'i in historic times ©2014. American Geophysical Union. All Rights Reserved.

JUNEAU, Alaska A powerful 7.1 magnitude earthquake struck remote southern Alaska early on Sunday, unleashing shudders felt several hundred miles (km) from the tremor's lakefront epicenter at the far end of Cook Inlet from Anchorage, the state's largest city. No injuries were reported, but several neighborhoods in the town of Kenai - roughly halfway between the quake's center and Anchorage - were temporarily evacuated after a gas explosion damaged four homes several hours later, a city spokesman said. As of Sunday night, local utility company Enstar was still investigating whether the earthquake triggered a gas leak believed to have caused the blast, company spokesman John Sims said. There were also reports of brief power outages in Anchorage, about 160 miles (257 km) southwest of the epicenter, and cities immediately to the north and south. The quake, initially reported at a 7.3 magnitude, struck at 1:30 a.m. about 30 miles (48 km) east-southeast of Pedro Bay on the shore of Iliamna Lake, at the foot of a mountain chain just west of Cook Inlet, the U.S. Geological Survey (USGS) reported. The quake was felt as far away as Whitehorse, the capital of Canada's Yukon Territory more than 600 miles (966 km) east of Anchorage, according to the USGS. It was recorded 79 miles (128 km) beneath the surface, a depth that helped keep damage to a minimum, said Dara Merz, a research technician with the Alaska Earthquake Center in Fairbanks. "If you take into account how deep it was, that's a lot of earth and rock that seismic waves have to work through to get to the surface," Merz said. The Fairbanks agency reported a series of aftershocks reaching magnitudes of up to 4.7, though Merz said even larger tremors could follow. Alaska, a seismically active state, records anywhere from 80 to 100 quakes daily, most of them hardly ever noticed. One of the more powerful quakes to hit Alaska in recent years was a 7.9 magnitude temblor that struck beneath the ocean floor near the Aleutian Islands chain in June 2014, but it caused no injuries or major damage. Following Sunday's quake, jittery Anchorage residents and hotel guests who briefly fled their buildings took to social media sites to share their experiences. Some posted photos of stores with aisles littered by fallen merchandise knocked off shelves to the floor. The quake produced no tsunami threat, according to the U.S. Pacific Tsunami Warning Center.

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Site: www.reuters.com

SANTIAGO A strong, 6.9 magnitude earthquake struck off the coast of Chile on Tuesday night, but there were no immediate reports of damage, the Chilean emergency office said. The U.S. Geological Survey said the quake, initially reported as magnitude 6.8 and then 6.6, was at a very shallow depth of 6.2 miles (10 km) under the seabed. Its epicenter was 58 miles (93 km) northwest of Coquimbo and 290 miles (466 km) northwest of Santiago. The earthquake did not trigger a tsunami, the Pacific Tsunami Warning Center said. Chile's ONEMI emergency office said there were no preliminary reports of damage, while Chile's navy said the quake was not strong enough to generate a tsunami. Chile is prone to earthquakes and was hit in 2010 by a powerful 8.8 magnitude earthquake and in 1960 by the largest earthquake ever recorded, at magnitude 9.5.

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