eltanin fracture zone

M. (1997) for the intermediate-period, fundamental-mode surface waves. Lat: Wolfe 2. Symbols, axes and origin of coordinates same as Fig. 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. (1981), Arvidsson & Ekstrm (1998) and Ekstrm et al. Cumulative moment release along that segment is displayed in Fig. . Their length, relative simplicity, 80 mm yr-1, long-term slip rate and the lack of known shocks of Mw > 7 make them a good laboratory for studying quasi-periodic recurrence of earthquakes on a timescale of years to a few decades. 4). 4. 2). D.W. The synthetic waveforms used in the CMT inversion are corrected for lateral heterogeneity using the whole-mantle model of Dziewonski & Woodward (1992) for the body waves and long-period mantle waves, and the phase-velocity maps of Ekstrm et al. A major purpose of our work is to examine the degree of repeatability (or lack thereof) of major earthquakes along various segments of the three Eltanin transforms. For the period 19902009, we rejected only one event, which occurred on 2001 August 6. At least one seamount chain, the New England Seamounts, lies in the northwestern Atlantic. These depths are similar to those determined by Wolfe et al. Our calculations of moment magnitude Mw are compared with determinations of the short-period magnitude mb in Fig. Their poorly determined repeat times range from 13 to 24 yr. Oxford University Press is a department of the University of Oxford. Stewart & Okal (1983) modelled P and reflected body waves for several strike-slip events along the Eltanin system. -Linear spreading on Earth's curved surface. Listen to the audio pronunciation of Eltanin Fracture Zone on pronouncekiwi G. Palaeoseismically determined dates for earthquakes along faults of the San Andreas system are uncertain, whereas exact dates are known for the events we examine along the Eltanin transforms. New Mw corresponds to seismic moment magnitude recomputed for this study. For the larger and more complex 2001 earthquake the rupture initiation depth is 8.9 km, and the centroid depth, taking into account the propagation of the point source in the direction of the directivity vector, is approximately 11 km, about 7 km below the ocean floor. Bathymetric Features 67%. 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. 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. Lamont-Doherty Earth Observatory Contribution 7505. Deep water flow through the trench is from west to east with a rate of 3.6 Sverdrups (million m/s) of 1.57C (34.83F) water. The present application of this method points to a recent change in Pacific plate motion, and. A new analysis of plate cooling models indicates that the properties of oceanic lithosphere may need to be reevaluated, or that additional phenomena beyond the conditions of simple mineral physics plate models are important. 4279 km S of Papeete, French Polynesia / pop: 26,357 / local time: 16:34:59.2 2016-05-02, Distances: 1977km (1228mi) N of Siple, Mount, Antarctica Gordon (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. Nearby ocean bottom seismometers are needed to detect them. The centroid epicentre and time did not shift appreciably in these different inversions, nor did the geometry of the moment tensor change appreciably. Menke Red triangle indicates CMT solution for shock of 1975 April 19. J. Subsequent locations of earthquakes and mapping of bathymetry and magnetic anomalies showed that the Eltanin zone consisted of three en echelon transforms (Molnar et al. We take this along with the distributions of events in time and longitude after 1976 (Fig. Eltanin Fracture Zone. Depths modelled by Wolfe et al. None of our normal-faulting solutions are found adjacent to that part of the Tharp transform. Langenhorst Observed P waves for a normal-faulting event, however, leave close to their maximum radiation on the focal sphere. Our calculations for all events have the advantage of having been corrected for lateral heterogeneity with the same model. A.M. 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). How are fracture zones like the Eltanin created? Okal M.D. The combined three Eltanin transform faults are much more active at the Mw~ 6 level than a comparable length of either the San Andreas Fault in California or other transform systems on land. We first examine an unusual case of repeatability of shocks of nearly the same Mw, 6.0. How are fracture zones like the Eltanin created? D.W. Best-fitting linear relationships are drawn through the dates of earthquakes and the seismic moment that had just been accumulated. Mw is systematically higher than mb for strike-slip events along the three transforms, on average about 0.5 units. They differ in that hypocentres derived using body waves give the location of rupture initiation whereas CMT solutions give centroid locations and origin times. It is one the the major earthquake zones in F. [6] Undersea Features Fishing & Outdoor Fracture Zone Maps: Undersea Features is home to a total of 187 Fracture Zone(s), listed below. 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. R.P. Finally we are left with what accounts for transform segments that rupture with high seismic coupling and those with low coupling. The remarkable quasi-repeatability of events of Mw > 5.9 may be attributed to the isolation of an asperity, that is, a single resisting fault segment that ruptures mainly or solely in earthquakes. The Eltanin Fault System(Eltanin Fracture Zone) is a series of six or seven dextral transform faults that offset the Pacific-Antarctic Ridge, a spreading zone between the Pacific Plateand the Antarctic Plate. The sense of the rotation is such that one or more offsets between parts of the Tharp transform would be short compressional features rather than spreading centres. The Eltanin Fault System (Eltanin Fracture Zone) is a series of six or seven dextral transform faults that offset the Pacific-Antarctic Ridge, a spreading zone between the Pacific Plate and the Antarctic Plate. How that may vary along strike and affect seismic coupling is unknown. A break in the smooth trend of the ridge at latitude 37.5S has been recognized in both bathymetric and altimetric data. [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. E. W. F. Although magmatism was more or less continuous on the ridge during 28-60 Ma, it probably occurred on crust . 2006). The Atlantis Fracture Zone (30 N) is one of the smallest transform faults along the Mid-Atlantic Ridge with a spatial offset of 70 km and an age offset of ~ 6 Ma. 7 includes an earthquake on 1981 June 20 of Mw 5.94, which was located just to the east of the others at a time when relatively few stations were available for calculating a CMT location. G. The Eltanin Fault System (Eltanin Fracture Zone) is a series of six or seven dextral transform faults that offset the Pacific-Antarctic Ridge, a spreading zone between the Pacific Plate and the Antarctic Plate.The affected zone of the Pacific-Antarctic Ridge is about 800 km long, between 56 S, 145 W and 54.5 S, 118.5 W, southwest of Easter Island, and about as far as one can get from . 11 for Mw > 6. Their surface wave magnitudes, Ms, for events before 1969 along the Eltanin system were determined typically from one to a few stations. Their remoteness and rough seas, however, puts a premium on studying them at large distances using seismic waves and various satellite technologies. There are about 300 fracture zones, with an average north-south separation of 55 kilometres (34 mi): two for each degree of latitude. . Woodhouse 3) along the eastern part of the Heezen transform between +100 and +200 km (Fig. 4065 km S of Avarua, Cook Islands / pop: 13,373 / local time: 16:34:59.2 2016-05-02 Only the Heezen transform has been surveyed by swath mapping (Lonsdale 1994). The boat was returning to France after spending a few months on a scientific mission near Cape Horn as part of the first International Polar Year. The Polar and Subantarctic Fronts are observed to pass along the Udinstev Fracture Zone 3 as the jets in the flow are steered by the topography (e.g., Moore et al. Their 1000 km length is greater than that of any other oceanic transforms at fast-spreading plate boundaries. Mammericks C1. Ekstram 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. 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. [4] Table S1 in the Supporting Information lists the formal uncertainties of the revised centroid locations. Experience has shown that deviations of the CMT centroid depth from the true depth occur both randomly and systematically. 4 occurred. 8) includes three events that are much larger than the others in that series. R.A. Phipps Morgan & Forsyth (1988), Shen & Forsyth (1992), Behn (2007), Gregg et al. When the event of Mw 6.3 on 1969 August 18 (Stewart & Okal 1983) is included, the repeat time of the three largest shocks is 19 yr with a COV of 0.37. The two dotted lines in Fig. Fig. 1997, 2005). 2. Numbers for 15 yr period 1976-1990 were multiplied by 20/15. Most of the earthquakes are mislocated systematically to the south of the three transforms as discussed later. They may be regarded as quasi-periodic. Pacific Ocean depth map showing the Heezen Fault and the Tharp Fault as #17. From 1990 to 2009, we selected events in the ISC, PDE, GCMT and surface wave detection (SWE) catalogues with at least one magnitude equal to or greater than 5.5. Eltanin fracture zone fracture zone zone of fracture n. , rock fracture zone Mendocino fracture zone oceanic fracture zone deep fracture zone Charlie Gibbs fracture zone - oceanic floor fracture zone 1975; Lonsdale 1994), which were named for M. Tharp, B. Heezen and C. Hollister . This yielded 84 earthquakes. . 4. The segment between -210 and -241 km consists of a large number of events of Mw > 5.55, one of Mw 6.08, three of 6.15 =Mw= 6.17 and one of Mw 6.3 (Stewart & Okal 1983) on 1973 September 18. In contrast, normal-faulting events of Mw 5-6.5 are common along slower spreading ridges such as those in the Atlantic. As it flows north, it is constrained by numerous obstacles on the seafloor. G. We then examine other segments with fewer but larger earthquakes. What is the labour of cable stayed bridges? 7, several of which are aftershocks and foreshocks, are considered to be noise in ascertaining the quasi-periodic behaviour of the larger shocks. 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. As in Fig. This bias suggests that the models used for CMT and ISC locations are not slow enough to the north and northeast along the East Pacific Rise. 5 contains only two earthquakes of Mw 5.45 and 5.50. Added to Thesaurus in 1989. No thrust earthquake mechanisms, however, were found along the Tharp zone. That Ms was obtained using a single station. Shen Forsyth Our determinations of Mw typically use observations at more stations than those of Ms. Those for Mw also use Love and Rayleigh waves. Sunrise: 06:37AM; Sunset: 05:22PM; Day length: 10h 45m; The local time in Stockholm County is currently the same as the solar time. These species await a formal description and it is not known whether or not they represent communities distinct from those on the northern MAR. J.K. A.M. Ekstram GE was partially supported by NSF grant EAR-09-24694. 4), to constrain their source depths. 3). . 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. We obtained a CMT solution for an additional earthquake of Mw 6.15 in 1979. 7; several were the sites of two or three earthquakes of Mw > 6.15. Figs 4-6 depict the three Eltanin transforms in greater detail.

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