eltanin fracture zoneeltanin fracture zone

We found that Mo evaluated at 10-km depth is 15 per cent smaller than that calculated at the best-fitting centroid depth (25.7 km). (1993) find that a 10 clockwise rotation of magnetic anomalies north of the Heezen transform occurred within the last 4 Ma, which would put it in extension. 4706 km S of Papeete, French Polynesia / pop: 26,400 / local time: 01:42:15.1 2017-06-15 Sea-surface shape by satellite Pelagic shrimps of the Family Oplophoridae (Crustacea Decapoda) from the Pacific sector of the Southern Ocean: USNS Eltanin Cruises 10, 11, 14-16, 19-21, 24 . 7, many of the smaller events are either aftershocks or foreshocks and are considered to be noise for the purposes of assessing the repeat times of the largest earthquakes. Hence, remote techniques such as seismicity and satellite altimetry provide important constraints on the tectonics, especially for the Tharp and Hollister transforms. Please see the related question for more information. S1 in the Supporting Information shows the revised CMT solutions for 186 earthquakes from 1976 to 2009 on the left and those in the online catalogue on the right. side (rather than on top of or away from one another.) The Eltanin Transform Fault and Fracture Zone is a series of six or seven dextral transform faults along ~800 km of the. Our distributions of earthquakes do not fit other thermal models that we have examined. Nearby asperities, as along the eastern part of the Heezen transform, may break either individually or together. We used a box from 54S to 58S and 140W to 120W to identify earthquakes that might be located on the Eltanin transform system. Forsyth The affected zone of the Pacific-Antarctic Ridge is about 800kmlong, between 56 S, 145 W and 54.5 S, 118.5 W,[1] southwest of Easter Island, and about as far as one can get from land on planet Earth (4852.6S 12323.6W). Solomon [2], The trench has a depth of 7,761m (25,463ft), is 300km (190mi) long and has an average width of 19km (12mi) and allows for a major circulation of deep ocean basin water from the west Atlantic to the east Atlantic basins. These segments contain fewer events of Mw > 5.9 than that in Fig. For the Eltanin events, this bias is unlikely to be larger than 15 per cent, even for the events with the deepest calculated centroids. Explanation: Fracture zones are characterised as structural line View the full answer Transcribed image text: How are fracture zones like the Eltanin created? Some of our largest events occur within about 25 km of the eastern end of the Heezen and the western end of the Hollister transforms (Figs 4 and 6). In contrast, VanDeMark (2006) used few events, a double-difference methodology and a uniform velocity model for Rayleigh waves in calculating revised earthquake locations along the Eltanin transforms. Behn a) reproduction b) controlling an experiment c) growth and development d) maintaining a steady temperature, An equation for the period T of a planet (the time to make one orbit about the Sun) is, T2=42r3/(GM)T ^ { 2 } = 4 \pi ^ { 2 } r ^ { 3 } / ( G M ) Smith They proposed that the Eltanin transforms consisted of small, well-separated asperities that rupture in earthquakes. 3) along the eastern part of the Heezen transform between +100 and +200 km (Fig. Watts L.R. 4814 km S of Papeete, French Polynesia / pop: 26,357 / local time: 08:09:44.3 2016-08-18, Distances: 3385 km SE of Wellington, New Zealand / pop: 381,900 / local time: 14:34:59.2 2016-05-03 Enter your email address to follow this blog and receive notifications of new posts by email. No thrust-faulting solutions were found. North of and parallel to the fracture zone is a transverse ridge which is particularly prominent over hundreds of kilometres east and west of the MAB of the South Atlantic. m3/(kgs2). We thank S. Carbotte and C. Scholz of Lamont and journal reviewers J. McGuire and C. Laederach for critically examining the manuscript and for valuable suggestions and P.G. Strike-slip mechanism in centre is that for 2007 event. For the period 19761989, we selected for analysis all events in the ISC (International Seismological Centre), PDE (Preliminary Determination of Epicentres of the US Geological Survey) and GCMT catalogues, regardless of magnitude. 11 between Mw 5.4 and 6.0 for events from 1991 to 2010. His results support the idea that events along that segment break a single isolated asperity. . 7 for events of Mw > 5.55 (blue) and Mw > 5.9 (red). . (Ages of chrons are from Gee & Kent 2007). Wilson (1965) utilized the observation that earthquakes along the Eltanin fracture zone were confined to the zone between two offset ridge crests in formulating his hypothesis of transform faulting. C.G. Ryan and M. Tolstoy for helpful discussions. This is in accord with the findings of Stewart & Okal (1983) that the Eltanin system has not broken in great events since 1920 and is unlikely to do so. This is an improvement over past formulations where bathymetric offsets were imposed kinematica. Fracture zone evolution is investigated using dynamic models that allow the fault zones to freely slip. Since the 40-km section of the Tharp (Fig. 4699 km SW of Santiago, Chile / pop: 4,837,295 / local time: 15:09:44.3 2016-08-18 We did not use the ISC catalogue for events after 1999. G. M.D. 5) and the 42-km section of the Heezen (Figs 4 and 7) are well isolated from other large shocks along those transforms we took the scatter in locations along them as a measure of L. Our knowledge of L is limited otherwise by the paucity of aftershocks of Mw > 5-5.5. Lonsdale Our knowledge of the Eltanin system is limited by the relatively high magnitude of completeness of events, Mw 5.4, and the paucity of aftershocks and forerunning events. , and M is in kg. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. Solid line indicates Mw=Ms. Boettcher Our new catalogue can be used in testing computer simulations of earthquake recurrence. Available long-period data for events along the three transforms increased from about 15 to 100 global stations as illustrated in Fig. 4. The seismic history of the Eltanin Fracture Zone on the Pacific-Antarctic Ridge for the years 1920-1981 shows that the seismic slip accumulated during this recording interval accounts for only a small fraction (less than 10%) of the amount of slip predicted by kinematic models of plate motion. M.S. The along strike dimensions and perhaps the downdip widths of asperities must be small for parts of the three Eltanin faults that have not ruptured in events larger than Mw 5.0-5.5. Since that segment is adjacent to the one in blue in Fig. 1 for events of Mw 6.2 in 1983 and 2007. COV = 0 and 1.0 correspond to strict periodicity and random occurrence, respectively. Unfortunately, the computed depths of earthquakes along the three Eltanin transforms are not accurate enough to ascertain centroid depths or the downdip width of seismic faulting at the several to 20 km level. The 40Ar39Ar dating of rocks dredged . (2005), McGuire (2008) and Boettcher & McGuire (2009) find that some fault segments are characterized by a predominance of aseismic slip while others are fully coupled. We assume that earthquakes along a given segment of a transform occur on single faults although the distribution of CMT solutions scatters about 15 km perpendicular to the transforms. The point-source depths are about 10-12 km, which suggests that the earthquakes ruptured faults that cross the M discontinuity. Unlike all the other countries in the St. Cecilia Archipelago, Eltanin is only comprised of one island. 4). We interpret it as indicative that only some parts of the three Eltanin transforms are capable of generating shocks of Mw 6.1-6.4 and that events much larger than 6.4, especially events of Mw > 7, are unlikely to occur. Lonsdale (1994) states My interpretation is that mechanical coupling across the transform valley allows eastward drag by the old thick Antarctic lithosphere to impede the westward movement away from the rise crest of a 20-30-km-wide adjacent strip of thin, newly accreted Pacific lithosphere'. Mw is systematically higher than mb for strike-slip events along the three transforms, on average about 0.5 units. Several of those well-coupled segments ruptured quasi-periodically in earthquakes of Mw~5.5-6 and with repeat times shorter than 10 yr. We choose the Eltanin transform faults as another good place to search for these phenomena. The transform valley is 15-20 km wide and 2-4 km deep. How that may vary along strike and affect seismic coupling is unknown. The CMT locations for the Heezen and Hollister transforms and the eastern end of the Tharp are biased to the south of the bathymetric expression of the transforms (Fig. At 14.5W the trough reaches a maximum depth of 2895 fm (5470 m). Fox We chose one of the Eltanin earthquake of (2009 May 7, Mw= 5.6) for which the CMT centroid depth is 25.7 km, and calculated the CMT at various fixed depths, inverting as usual for all the other parameters. The slope of -1.0 for the latter period for Mw 5.4-6.0 is typical of that for earthquakes in many areas of the world. Bergman When Sykes showed his results to M. Ewing, the latter arranged with NSF (US National Science Foundation) for the Research Vessel Eltanin to map the region. 4. G. It moves His relocations along the Heezen transform, with one exception, are more tightly clustered than ours. Turkey. 4 are more tightly clustered in map view. J.K. G. T. In that simple model, earthquakes should extend to greater depths and presumably be larger near the centres of transforms, which is clearly not the case for the Heezen and Tharp faults. The morphology of the Atlantis Fracture Zone is typical of that of slow-slipping transforms. The fault segment between -665 and -680 km (green symbols in Fig. S. Carbotte (written communication, 2011 July 22) notes that the concentration of earthquakes at the eastern end of the Heezen transform corresponds with the region where the inside Corner Rift' of Lonsdale (1994) is found to the north. Major differences in seismic coupling along strike are not in accord with common thermal models of plate cooling but instead are attributed to varying degrees of metamorphism, rock type and effective normal stress and possibly to the presence of short intratransform spreading centres. The average displacement per earthquake is 0.32 m assuming full coupling and an average repeat time of 4 yr. Figs 8-10 show cumulative moment release throughout 2010 for seven additional segments of the three Eltanin faults. J. https://earthquake.usgs.gov/earthquakes/eventpage/us20009msm#executive, http://www.emsc-csem.org/Earthquake/earthquake.php?id=504225, http://earthquake.usgs.gov/earthquakes/eventpage/us100049ce#general_summary, Follow Earth Extremities on WordPress.com, MAGNITUDE6.9KERMADEC ISLANDS, NEWZEALAND, MAGNITUDE5.6SOUTHERN MID-ATLANTIC RIDGE, MAGNITUDE5.6EAST OF SOUTH SANDWICHISLANDS, MAGNITUDE6.9KERMADEC ISLANDS, NEW ZEALAND. Reported values for the ratios KlRb RblSr La/Yb and Sr87 86ISr for fresh material, generally'"hint at a These results suggest that asperities responsible for earthquake release at the Mw > 6 levels vary in size along strike but not much in downdip width. 4. . Map view of CMT locations of earthquakes along Heezen transform and easternmost end of Tharp transform from 1976 to 2010. As in Fig. Hence, it and the two larger events occurred along an off-transform feature. Whether the depths obtained for normal-faulting events, which occurred off the transforms, applies to strike-slip events along the transforms themselves is equivocal since the velocity and thermal structure of the three transforms is not known and close-in observations with ocean bottom instruments have not been made. Their poorly determined repeat times range from 13 to 24 yr. No known large earlier events can be readily attributed to the segment between 122 and 141 km in Fig. A break in the smooth trend of the ridge at latitude 37.5S has been recognized in both bathymetric and altimetric data. The plate boundary is about 1,200 kilometers long along the On the basis of serial hydrographic measurements, the Chain Fracture Zone appears to be separated into several deeper sections. Pacific Ocean Topography 70%. McGuire (2008) examined 16 pairs of Mw= 5.5 earthquakes that occurred along approximately the same segments of transform faults on the East Pacific Rise to the south and north of the equator. Our locations and those of the ISC based on body waves are located systematically about 25 km south of the transforms as mapped in Fig. The new result is well constrained by the surface wave data, which were not included in the original analysis. Earthquakes of Mw > 5.55 were included in each computation. The RSS includes pelagic material from the early Cretaceous (140 Ma) which, coupled with the thickness of the sequence, does not fit with the normal scenario for the opening of the South Atlantic around the Aptian-Albian (125100 Ma). Of the 84 earthquakes from 1976 to 1989, we rejected seven CMT solutions. Nearby ocean bottom seismometers are needed to detect them. Lat: Tolstoy Clearly, a gradient in the maximum size of earthquakes and seismic coupling occurs between the eastern and western ends of the Heezen transform. What is the reflection of the story of princess urduja? Bohnenstiehl A Seabeam reconnaissance of the 400 km-long fast-slipping (88 mm yr-1) Heezen transform fault zone and the 55 km-long spreading center that links it to Tharp transform defined and bathymetrically described several types of ridges built by tectonic uplift and volcanic construction. An up-to-date map of the Antarctic Circumpolar Current (ACC) fronts is constructed from the latest version of mean dynamic topography from satellite altimetry (Park et al., 2019, Observations of the Antarctic Circumpolar Current over the Udintsev Fracture Zone, the narrowest choke point in the . Gordon 1999). Dotted lines denote approximate locations of ridges. For LNADW and AABW, the Romanche and Chain Fracture Zones (just south of the equator) are the only deep passages in the MAR where interbasin exchange is possible. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. It seems unlikely that our CMT location errors would change much over the length of the Tharp transform. . Moment magnitudes are given below each solution. Oxford University Press is a department of the University of Oxford. Figs 4-6 depict the three Eltanin transforms in greater detail. We have combined shipboard and Seasat altimeter derived data in an intergrated geological and geophysical study of the Louisville Ridge; a 3500kmlong seamount chain extending from the Tonga trench to the Eltanin Fracture Zone. Similarly, earthquake recurrence is more difficult to examine for other long oceanic transform faults, such as those in the equatorial Atlantic, that have considerably smaller long-term slip rates. We present a compilation of the seismic properties of the Eltanin Transform Fault (TF) system, compelled by the recent discovery of the Hollister Ridge and the possibility of a change of plate. Given the uncertainty of its CMT location, we think it is reasonably associated with a previous rupture of the same asperity as in Figs 4 and 7. 10) was the site of many earthquakes of Mw > 5.55, two of Mw 6.13 and two of Mw 6.0, the latter two on the same day in 2010. D.L. The random variations can be considered a consequence of the complicated trade-offs that occur when noisy data are fit with synthetic seismograms that do not capture the full complexity of wave propagation in the Earth. We take this along with the distributions of events in time and longitude after 1976 (Fig. 5 contains only two earthquakes of Mw 5.45 and 5.50. Mw determined in this study compared with the surface wave magnitude Ms as computed by either ISC or PDE for periods between about 17 and 22 s. Mw is determined at longer periods. Systematic deviations can occur when the Earth structure in the source area deviates significantly from the structure assumed in the calculation of synthetic seismograms, that is, from PREM (Dziewonski & Anderson 1981). None of the five is reasonably attributed to a small spreading segment along either of those two transforms. Indeed, jets are observed to pass along both the Udinstev and Eltanin Fracture Zones (Gille 1994; Hughes and Ash 2001). Thus, the use of the CMT methodology insured more complete coverage of earthquakes in this very remote area of the Earth. In addition those three oceanic transforms are not as multibranched as many transform zones on continents. The CMT locations for the Tharp transform are rotated several degrees with respect to both the computed transform direction in Fig. Kent J.H. Our findings are in contrast to the widely stated notion that oceanic transform faults, especially those at fast spreading plate boundaries, are poorly coupled with perhaps the presence of occasional stuck patches or asperities. Sykes . T. Seamount chains in the Pacific basin tend to be aligned northwesterly, and several chains are intimately associated with fracture zones; the Eltanin Fracture Zone in the southwestern Pacific is an example.
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