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Diane I. Doser 《Pure and Applied Geophysics》2006,163(8):1461-1476
I have relocated 18 earthquakes occurring in the south-central Alaska region between 1899 and 1917 using a bootstrap relocation
technique. Locations of events within the Yakutat region suggest that the 1899 sequence began on 4 September with a MS = 7.9 event within the area of the Pamplona fault zone/western Transition fault zone, rupturing the western portion of the
North American/Pacific plate interface. A MS = 7.4 event on 10 September appears to have ruptured the offshore portion of the plate interface to the east of the 4 September
event. This was followed by a MS = 8.0 event that likely ruptured the onshore and down-dip portion of the plate interface. A MS = 7.0 event in 1908 may have ruptured a small portion of the plate interface between the 4 September and 10 September events.
Events occurring between 1911 and 1916 in the Prince William Sound region appear to be slab events occurring in similar locations
to more recent seismicity. Within the Kodiak region the 1900 earthquake of MS = 7.7 has a location consistent with the rupture of the Kodiak asperity which also ruptured during the 1964 great Alaska
earthquake. Other large magnitude Kodiak events appear to be associated with regions of recent seismicity, including the Karluk
Lake area of southwestern Kodiak Island and the Albatross Basin located offshore southeast of Kodiak Island. Space-time seismicity
patterns since 1899 indicate that magnitude 6 to7 events have occurred with regularity in the Kodiak Island region; that there
has been a lack of magnitude ≥ 6 events in the Prince William Sound region since 1964, and that the Yakutat region has remained
notably quiescent at the magnitude ≥ 6 level. 相似文献
2.
The 1964 Prince William Sound earthquake (March 28, 1964;M
w
=9.2) caused crustal deformation over an area of approximately 140,000 km2 in south central Alaska. In this study geodetic and geologic measurements of this surface deformation were inverted for the slip distribution on the 1964 rupture surface. Previous seismologic, geologic, and geodetic studies of this region were used to constrain the geometry of the fault surface. In the Kodiak Island region, 28 rectangular planes (50 by 50 km each) oriented 218°N, with a dip varying from 8o nearest the Aleutian trench to 9o below Kodiak Island, define the rupture surface. In the Prince William Sound region 39 planes with variable dimensions (40 by 50 km near the trench, 64 by 50 km inland) and orientation (218°N in the west and 270°N in the east) were used to approximate the complex faulting. Prior information was introduced to constrain offshore dip-slip values, the strike-slip component, and slip variation between adjacent planes. Our results suggest a variable dip-slip component with local slip maximums occurring near Montague Island (up to 30 m), further to the east near Kayak Island (up to 14 m), and trenchward of the northeast segment of Kodiak Island (up to 17m). A single fault plane dipping 30°NW, corresponding to the Patton Bay fault, with a slip value of 8 m modeled the localized but large uplift on Montague Island. The moment calculated on the basis of our geodetically derived slip model of 5.0×1029 dyne cm is 30% less than the seismic moment of 7.5×1029 dyne cm calculated from long-period surface waves (Kanamori, 1970) but is close to the seismic moment of 5.9×1029 dyne cm obtained byKikuchi andFukao (1987). 相似文献
3.
Monty A. Hampton 《Marine Georesources & Geotechnology》2013,31(2):159-180
Abstract Fine‐grained sedimentary deposits on the Kodiak continental shelf and upper slope comprise three distinct compositional types: terrigenous mud, diatomrich mud, and ash‐rich sandy mud. The sediment types can be distinguished on the basis of geotechnical properties as well as by composition. The terrigenous mud has properties largely within the normal range for fine‐grained marine sediment, except for the low compressibility of many samples. This sediment underlies the walls of canyons that incise the upper slope, and analyses of undrained static and cyclic loading indicate potential instability in the steepest areas. The diatom‐rich mud has high water content, plasticity index, and compression index but low grain specific gravity. The ash‐rich sandy mud is nonplastic and has low water content and compressibility. It has high drained and undrained static strength but is extremely weakened by cyclic loading. Extensive deposits of sedimentary bedrock and coarsegrained glacial sediment in the region apparently are relatively stable, but low sediment strength or high compressibility may be encountered at the local sites of soft sedimentary deposits. 相似文献
4.
Methane seeps occur at depths extending to over 7000 m along the world's continental margins, but there is little information about the infaunal communities inhabiting sediments of seeps deeper than 3000 m. Biological sampling was carried out off Unimak Island (3200–3300 m) and Kodiak Island (4500 m) on the Aleutian margin, Pacific Ocean and along the Florida Escarpment (3300 m) in the Gulf of Mexico to investigate the community structure and nutrition of macrofauna at these sites. We addressed whether there are characteristic infaunal communities common to the deep‐water seeps or to the specific habitats (clam beds, pogonophoran fields, and microbial mats) studied here, and ask how these differ from background communities or from shallow‐seep settings sampled previously. We also investigated, using stable isotopic signatures, the utilization of chemosynthetically fixed and methane‐derived organic matter by macrofauna from different regions and habitats. Within seep sites, macrofaunal densities were the greatest in the Florida microbial mats (20,961 ± 11,618 ind·m−2), the lowest in the Florida pogonophoran fields (926 ± 132 ind·m−2), and intermediate in the Unimak and Kodiak seep habitats. Seep macrofaunal densities differed from those in nearby non‐seep sediments only in Florida mat habitats, where a single, abundant species of hesionid polychaete comprised 70% of the macrofauna. Annelids were the dominant taxon (>60%) at all sites and habitats except in Florida background sediments (33%) and Unimak pogonophoran fields (27%). Macrofaunal diversity (H′) was lower at the Florida than the Alaska seeps, with a trend toward reduced richness in clam bed relative to pogonophoran field or non‐seep sediments. Community composition differences between seep and non‐seep sediments were evident in each region except for the Unimak margin, but pogonophoran and clam bed macrofaunal communities did not differ from one another in Alaska. Seep δ13C and δ15N signatures were lighter for seep than non‐seep macrofauna in all regions, indicating use of chemosynthetically derived carbon. The lightest δ13C values (average of species’ means) were observed at the Florida escarpment (−42.8‰). We estimated that on average animal tissues had up to 55% methane‐derived carbon in Florida mats, 31–44% in Florida clam beds and Kodiak clam beds and pogonophoran fields, and 9–23% in Unimak seep habitats. However, some taxa such as hesionid and capitellid polychaetes exhibited tremendous intraspecific δ13C variation (>30‰) between patch types. Overall we found few characteristic communities or features common to the three deep‐water seeps (>3000 m), but common properties across habitats (mat, clam bed, pogonophorans), independent of location or water depth. In general, macrofaunal densities were lower (except at Florida microbial mats), community structure was similar, and reliance on chemosynthesis was greater than observed in shallower seeps off California and Oregon. 相似文献
5.
《Marine Policy》2015
Scholars and fishermen alike view the privatization of fishing rights as a fundamental driver of social change in fishing communities. This article presents the results of a mixed-methods ethnographic study in Kodiak, Alaska, exploring how fisheries privatization processes remake fishery systems. Findings from this study suggest that a diverse range of fishery participants share core values about the social dimensions of fishery systems. Support or opposition to past privatization processes tended to be articulated in reference to how these core values (e.g., hard work, opportunity, and fairness) were perceived to have been strengthened or eroded by such processes. Data from this study suggest that while still widespread in the Kodiak fishing community, core social values in fishing may be changing as a result of privatization processes. Although ethnographic and survey data showed a range of perspectives on the effects of privatization on fishing and the Kodiak community, study participants tended to talk about privatization as a significant change that had divisive, negative impacts in the community. Crew members and the next generation of fishermen were identified as disproportionately affected by privatization processes. Ethnographic data detail important shifts in the power, status, and livelihoods of crew members. Nearly all Kodiak fishery participants interviewed expressed concern about the future of fisheries access in the community for the next generation, in large part because of the substantial financial barriers to entry generated by privatization of fisheries access. Many discussed the need for more entry-level opportunities necessary for access in all fisheries. 相似文献
6.
The 1964 Alaska earthquake was the second largest seismic events in the 20th century. The aim of this work is the use of surface deformation data to determine asperity and slip distributions on the fault plane of the Alaska earthquake: these distributions are calculated by a Monte Carlo method. To this aim, we decompose the fault plane in a large number of small square asperity units with a side of 25 km; this allows us to obtain plane surfaces with an irregular shape. In the first stage, each asperity unit is allowed to slip a constant amount or not to slip at all, providing the geometry of the dislocation surface that best reproduces the observed displacements. To this purpose, a large number of slip distributions have been tried by the use of the Monte Carlo method. The slip amplitude is the same for all the asperities and is equal to the average fault slip inferred from the seismic moment. In the second stage, we evaluate the slip distribution in the dislocation area determined by the Monte Carlo inversion: in this case, we allow unit cells to undergo different values of slip in order to refine the initial dislocation model. The results confirm the previous finding that the slip distribution of the great Alaska earthquake was essentially made of two dislocation areas with a higher slip, the Prince William Sound and the Kodiak asperities. Analysis of the post-1964 seismicity in the rupture region shows a strong correlation between the larger earthquakes (Mw≥6) and the distribution of locked asperities following the 1964 event, which can be considered as an independent test of the validity of the model. We do not find slip values higher than 25 m for any of the patches, and we determine two separate high-slip zones: one correspondent to the Prince William Sound asperity, and one (18 m slip) to the Kodiak asperity. The slip distribution connected with the 1964 shock appears to be consistent with the following seismicity in the region. 相似文献
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