The fault segment between -665 and -680 km (green symbols in Fig. Gee Hence, a variety of rupture behaviours, repeat times and maximum observed magnitudes is associated with the active parts of the three transforms. Strike-slip faulting with moment magnitudes Mw up to 6.4 characterizes most of these events. Distances in kilometres same as in Fig. The CMT centroid depths for events along the Eltanin system are not accurate enough to define the depths or range of seismic faulting at the level of several to 20 km. The Romanche Fracture Zone offsets the Mid-Atlantic ridge by 900 km (560 mi), making it the largest equatorial fracture zone in the Atlantic. Map view of CMT locations of earthquakes along Heezen transform and easternmost end of Tharp transform from 1976 to 2010. The point source depth of 10.4 km places the 2007 earthquake 6-7 km below the ocean floor. 4. The new CMT catalogue that we obtained is more complete than older versions. GE was partially supported by NSF grant EAR-09-24694. This partitioning of slip likely results from changes during the last few million years in the Euler pole for relative motion between the Antarctic and Pacific plates. 2006). 4 and red symbols in Fig. Bohnenstiehl et al. If we assume that all of the true depths of these earthquakes are shallow, what size error or bias should we expect in estimates of Mo? 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). The smallest is likely to be an underestimate, since several patches within what we take to be the seismically active part of the Hollister transform were not active at the Mw= 5.9 level. Eltanin is an island located in the South Pacific Ocean, following the contours of the Eltanin Fracture Zone. We first examine an unusual case of repeatability of shocks of nearly the same Mw, 6.0. The two dotted lines in Fig. J.J. Solomon [1], Lower North Atlantic Deep Water (LNADW) is found around 3,6004,000 metres (11,80013,100ft) below sea level and flows from the Greenland and Norwegian seas; it brings high salinity, oxygen, and freon concentrations towards the equator. (2009). The absence of known earthquakes on the three transforms beyond their bounding ridge crests and the spacing of magnetic anomalies, however, indicate that the Pacific and Antarctic plates are intact today beyond the active parts of those transforms and that the lengths of the transforms are not continuing to grow. Nearby asperities, as along the eastern part of the Heezen transform, may break either individually or together. The San Andreas fault is part of a fault zone known as a transform Haiti is situated on a transform boundary also known as a strike In those circumstances the use of longer period Rayleigh and Love waves, as in the CMT methodology, can lead to those events being identified confidently as earthquakes. Molnar Listen to the audio pronunciation of Eltanin Fracture Zone on pronouncekiwi fracture zones and transform faults flashcards quizlet. 2). Nearby ocean bottom seismometers are needed to detect them. 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). J.H. J.K. Smith The series includes two events of 6.17 and 6.18 and one of less certain Mw of 6.5 (Stewart & Okal 1983) on 1971 April 4 that are much larger than the other three. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. 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. (2005). What are mid-ocean ridges? Fielding Pacific Ocean Topography 70%. Individual ridge segments trend, how- ever, up to a few tens of degrees from the smooth trend. . 4). Regardless of the cause of the deviation of the centroid depth from the true depth, the question arises whether an incorrect centroid depth can cause the scalar seismic moment, Mo, estimate to differ from the true moment in a systematic way. Ekstram This is not surprising since all stations are at large teleseismic distances. The transform valley is 15-20 km wide and 2-4 km deep. . The T-axis of a normal-faulting event in that area of Mw 5.4 in 1978 is inclined about 45 to the transform (Fig. 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. 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 . Lamont-Doherty Earth Observatory Contribution 7505. If those segments are not fully coupled, our calculations of downdip width, of course, are minimum estimates. J.J. Map view of CMT locations of earthquakes along Tharp transform from 1976 to 2010. Richards, W.B.F. One exception to this general observation is the earthquake on 2000 October 4. Stewart If the 1981 shock were mislocated at least 12 km eastwards, the length of the repeating segment would be about 30 km. Wolfe et al. E. W. F. We find or confirm two anomalous characteristics: the . Boettcher Thermal models with constant and variable mineral physics properties are formally analyzed for fits against recently filtered databases for heat flow and topography. We used a box from 54S to 58S and 140W to 120W to identify earthquakes that might be located on the Eltanin transform system. Others related faults include the Vacquier Transform Fault, the Menard Transform Fault, and the Udintsev Fault.[3]. Bathymetric Features 67%. The axes are each rotated with respect to the Euler rotation pole of DeMets et al. If you are interested in visiting one of these Fracture Zone(s) in Undersea Features always contact the local Office of Natural Resources to gather all the regulations for fishing and outdoor adventures in the area. Those P waves left hypocentres close to the intersection of the two nodal planes (B-axis) where their amplitude is very small. Menard The average of the three intervals since 1967 is 12.8 yr with a COV of 0.36. 2. -Linear spreading on Earth's curved surface. The western part of the transverse ridge consists of fragments of uplifted oceanic crust and upper mantle. Maternovskaya The normal-faulting event of 2001 August 6 is larger than that of any of the strike-slip events along the three Eltanin transforms. 7; several were the sites of two or three earthquakes of Mw > 6.15. This is an improvement over past formulations where bathymetric offsets were imposed kinematica. Sykes . That view comes in large part from assuming that the downdip (vertical) width of seismic faulting extends to about the 600 C isotherm as calculated using simple conductive plate cooling models where temperature at a given location along the transform is taken as the average on its two sides. The shaded area is the "Hollister region" whose seismicity is detailed in Fig. 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. 4. His relocations are shown in Figs 4-6 in green. We refer to the magnitudes derived from those moment tensors as either new or recomputed Mws. Fig. 4699 km SW of Santiago, Chile / pop: 4,837,295 / local time: 15:09:44.3 2016-08-18 6). H.W. Archived seismicity, satellite altimetry, and older geophysical traverses extend these descriptions . Elevation map for localities Click for legend, zoom in for elevation lines Routing error m , | Map style: OpenTopoMap ( CC-BY-SA) 4. For the Eltanin events, this bias is unlikely to be larger than 15 per cent, even for the events with the deepest calculated centroids. (2002) used nearby hydroacoustic stations to locate very small events and aftershocks along a number of oceanic transform faults. . 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. The Udintsev Fracture Zone is a suitable site for a long-term monitoring of the Antarctic Circumpolar Current 1 Introduction The Antarctic Circumpolar Current (ACC) forms a continuous near-zonal band of eastward flow. A.M. 3 and studied separately. Undersea Features Fishing & Outdoor Fracture Zone Maps: Undersea Features is home to a total of 187 Fracture Zone(s), listed below. The catalogue for the latter period appears to be complete for Mw > 5.4-5.5 whereas the earlier period is not complete for Mw < 6.0. Data for the reanalysis were collected from all the main global digital networks that have operated since 1976. 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. Moment magnitudes are given below each solution. 4706 km S of Papeete, French Polynesia / pop: 26,400 / local time: 01:42:15.1 2017-06-15 Recurrence of events along nearly the same fault segment is much more difficult to determine for transform faults on land, such as the San Andreas, where large to great earthquakes typically have repeat times of 100 yr or longer and instrumental data and exact dates for more than one earthquake along a fault segment are rare or non-existent. They may be regarded as quasi-periodic. . Hirth Equidistant polar diagram out to distance of 135 centred on our study area, the Eltanin transform system, illustrating distribution of stations that contributed data to CMT solutions. Eltanin has a maritime climate in the transition region between the tundra and subarctic zones (Kppen classification) which is characterised by . 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. L.R. Eltanin fracture zone Scope Notes: SE Pacific. 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 . 2. Earthquakes of Mw 6.2-6.4 occur along each transform but larger events are confined to the eastern half of the Heezen, two parts of the Tharp and segments of the Hollister. T2=42r3/(GM), m3/(kgs2)m ^ { 3 } / \left( k g \cdot s ^ { 2 } \right) Boettcher Distances along the transform are calculated from an arbitrary origin of coordinates at 55.4 S, 125.0 W. 4 occurred. . This transform migration was preceded by a process 2517 Ma during which the Miocene shallow-water platform mentioned above reached sea level as the transverse ridge was first uplifted, then deformed, and finally buried under the sea. 2. It is formed by a transform boundary. We show in detail, however, that some segments of the three transforms are aseismic at the Mw > 5.4 level whereas others are more strongly coupled. The segment of the Heezen transform between 29 and 71 km (Fig. That Ms was obtained using a single station. Our determinations of Mw typically use observations at more stations than those of Ms. Those for Mw also use Love and Rayleigh waves. E.A. The earthquakes were analysed using the standard Global CMT (GCMT) algorithm as described in Dziewonski et al. Shimazaki J.J. Red triangle indicates CMT solution for shock of 1975 April 19. Dziewonski Anderson Shen 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. (1997) for the intermediate-period, fundamental-mode surface waves. Dziak R.L. The presence of large events just to its west and the variety of Mws, however, suggest that it does not always rupture as a single asperity. Larson No known large earlier events can be readily attributed to the segment between 122 and 141 km in Fig. 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. 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 . We choose to use a greater number of stations as time proceeded rather than use a few common stations as he did. stand on one side of it, the other side appears to move to the The horizontal axis is parallel to computed transform directions; the vertical is perpendicular to it. 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. That may account for the variety of Mws along it. McGuire The few involving normal faulting are located up to 40 km on either side of the transforms and involve extension nearly normal to the transforms. R. Map view of CMT locations of earthquakes along Hollister transform fault from 1976 to 2010. 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. For the four seismically active fault segments in Table 1 we obtain similar downdip widths of seismic faulting of about 5 km assuming coupling at the full plate rate. 1975; Lonsdale 1994), which were named for M. Tharp, B. Heezen and C. Hollister . Turkey. Examine the figure above. VanDeMark 1975; Lonsdale 1994), which were named for M. Tharp, B. Heezen and C. Hollister (Fig. The segment of the Heezen from 179 to 200 km has the next smallest T, 7.1 yr, Mw 5.89-6.5 and six events. We also used the same 3-D velocity model for our new CMT solutions. 1988). 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). Eltanin Fracture Zone on the Elevation Map. Weissel Ryan 5. 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. . 8, interaction between the two may well occur. what makes muscle tissue different from other tissues? Figs 4-6 depict the three Eltanin transforms in greater detail. Behn Available long-period data for events along the three transforms increased from about 15 to 100 global stations as illustrated in Fig. In studies of transforms along the ultra-fast spreading East Pacific Rise just to the south of the equator, McGuire et al. Wolfe et al. Lonsdale (1994) mapped a small nearby series of short spreading centres along the Heezen transform, one along the Raitt transform farther north and the Udintsev farther south. None of the five is reasonably attributed to a small spreading segment along either of those two transforms. 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'. (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. The summit of the transverse ridge is capped by Miocene shallow water limestones that reached above sea level 20 Ma before subsiding abnormally fast. Wilson S. Carbotte (written communication, 2011 July 22) notes, however, that some of the shocks along the eastern end of the Tharp transform might fall within a zone of deformed/rotated seafloor south of the transform that looks quite similar to the zone of deformation north of the Heezen transform described by Lonsdale (1994) and seen in Fig. Wolfe et al. Finally we are left with what accounts for transform segments that rupture with high seismic coupling and those with low coupling. I cover many earth extremities ranging from Earthquakes, Quake Swarms, Volcanic Activity/Eruptions, CME's Coronal Mass Ejections, Solar Flares, Geomagnetic Storms, Magnetosphere Pressure plus other solar related radiation pulses, Asteroid/Meteorite Threats, Solar System Threats, Landslides, Flooding, Sink Holes, Hurricanes, Typhoons, Storms, Tsunami's, prolonged Snowfall/Ice, Heatwaves, Drought, Nuclear Fallout/Leak, Viruses, Deceases, Epidemics, Dead Mammals/Birds/Animals, Pollution Threat Levels and many more events. 5 contains only two earthquakes of Mw 5.45 and 5.50. [8], Coordinates: .mw-parser-output .geo-default,.mw-parser-output .geo-dms,.mw-parser-output .geo-dec{display:inline}.mw-parser-output .geo-nondefault,.mw-parser-output .geo-multi-punct{display:none}.mw-parser-output .longitude,.mw-parser-output .latitude{white-space:nowrap}000N 1800W / 0.000N 18.000W / 0.000; -18.000, "Dolomite formation in pelagic limestone and diatomite, Romanche Fracture Zone, Equatorial Atlantic", 10.1175/1520-0485(1998)028<1929:MITRFZ>2.0.CO;2, "Lower Cretaceous to Eocene sedimentary transverse ridge at the Romanche Fracture Zone and the opening of the equatorial Atlantic", "Hydrothermal activity on the southern Mid-Atlantic Ridge: Tectonically- and volcanically-controlled venting at 45S", "Transport of Bottom Water in the Romanche Fracture Zone and the Chain Fracture Zone", 10.1175/1520-0485(1998)028<0779:TOBWIT>2.0.CO;2, "Biodiversity and biogeography of hydrothermal vent species: thirty years of discovery and investigations", https://en.wikipedia.org/w/index.php?title=Romanche_Trench&oldid=1090955796, This page was last edited on 1 June 2022, at 10:32. If those short spreading centres are very young, they may not have had enough time to become oriented perpendicular to the transform. 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. McGuire (2008) also found that 1-d aftershock zones extended 30-50 km along strike for Mw~ 6 main shocks for transforms of the East Pacific Rise near the equator. The three sets of large events have a repeat time of 13 yr and a COV of 0.13. Four of them have T-axes nearly perpendicular to those transforms while the smallest of Mw 5.3 in 1982 is oriented about 45 to the Tharp. What is the labour of cable stayed bridges? G. The four estimates of W in Table 1 range from 3.9 to 6.0 km. Three normal-faulting events were found with T-axes nearly perpendicular to the Heezen transform (Fig. The fracture along blocks of crust (tectonic plates) is called a 11 between Mw 5.4 and 6.0 for events from 1991 to 2010. Farther west activity decreases to a maximum of Mw 5.9-6.1 between +30 and +100 km along the fault and then again to a maximum of Mw 5.6-5.8 between +10 and 30 km. 10) was the site of events of Mw 6.39, 6.03 and 6.36 in 1984.4, 1997.4 and 2005.98, respectively. The centroids of events of larger Mw are found at least 35 km eastwards along the Heezen transform and those to its west are relatively small. Gordon 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. Atwater Tolstoy The feature was then named the Eltanin fracture zone. Although magmatism was more or less continuous on the ridge during 28-60 Ma, it probably occurred on crust . D.W. Search for: Recent Posts. These are very small, typically 3-15 km for the earliest events and 1-2 km for earthquakes since 2000. Thus, the use of the CMT methodology insured more complete coverage of earthquakes in this very remote area of the Earth. Bivalve communities have been reported around vents further south. N.N. . The precision of epicentral locations in his study was improved considerably by using data from new seismic stations in Antarctica that were installed during the International Geophysical Year, 1957-1958, and computer programs for analysing P and PKP arrival times. Somewhat smaller estimates of W are obtained using a value of appropriate to the uppermost mantle. One 30-42-km-long segment of the Heezen transform that appears to be an isolated well-coupled asperity has ruptured in eight earthquakes of Mw 5.9-6.1 quasi-periodically with a coefficient of variation of 0.26 every 4.0 1.0 yr. Other well-coupled fault segments, which were sites with earthquakes up to Mw 6.39 and fewer events since 1976, have average repeat times of about 7-24 yr. 6) indicates that it may be a single fault. How are fracture zones like the Eltanin created? From 1995-2003, Eltanin fracture zone was used with Antarctic Ocean and/or Pacific Ocean. The two largest (Mw 6.7 and 5.9) occurred well to the north of the transform in 2001 and 2007. His results support the idea that events along that segment break a single isolated asperity. m3/(kgs2). The repeat times of those largest events are longer but uncertain since they are based on few earthquakes. 3) along the eastern part of the Heezen transform between +100 and +200 km (Fig. His values and ours of COV = 0.26 imply quasi-periodic behaviour. M.S. G. The inversion procedure follows the method of Ekstrm (1989) and leads to estimates of the earthquake focal mechanism, source-time function and point-source depth that are consistent with both the P-wave data and the CMT results. For the period 19902009, we rejected only one event, which occurred on 2001 August 6. It is one the the major earthquake zones in 4065 km S of Avarua, Cook Islands / pop: 13,373 / local time: 16:34:59.2 2016-05-02 4786 km SE of Avarua, Cook Islands / pop: 13,400 / local time: 01:42:15.1 2017-06-15, http://www.emsc-csem.org/Earthquake/earthquake.php?id=524555, Distances: 4676 km SE of Wellington, New Zealand / pop: 381,900 / local time: 06:09:44.3 2016-08-19 Menard The Eltanin Transform Fault and Fracture Zone is a series of six or seven dextral transform faults along ~800 km of the Pacific-Antarctic Ridge that offset it ~1600 km. Events of Mw > 5.9 account for 70 per cent of the moment in Fig. 2. Fox Excluding it does not change the average repeat time for events of Mw > 5.9; it increases the SD and COV slightly. The five largest shocks have a repeat time of about 8 yr and a COV of 0.43. In the Atlantic Ocean most fracture zones originate from the Mid-Atlantic Ridge, which runs from north to south, and are therefore west to east oriented in general. Four segments of the Tharp transform (Fig. New Mw corresponds to seismic moment magnitude recomputed for this study. Seabeam and SeaMARC II swath-mapping surveys, with ancillary magnetic and gravity profiling, describe the fast-slipping (84-86 mm year1) 380 km-long Heezen transform (56 S) and the 145 km-long Raitt transform (54 S), together with the youngest parts of their rise-flank fracture zones. Hence, remote techniques such as seismicity and satellite altimetry provide important constraints on the tectonics, especially for the Tharp and Hollister transforms. Decide for yourself which test is easiest to use, but dont forget the preliminary test. 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. 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. Watts et al. LOUISVILLE RIDGE AND ELTANIN FRACTURE ZONE 3053 west to isolated peaks superimposed on ridge segments in the southeast. 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 most recent data show, for example, that the Eltanin fracture zone system in the South Pacific is much longer than previously thought, according to Marsh. For example, if it is known that an earthquake occurred at a depth of 10 km, and the CMT was calculated at 25 km, is there a corresponding bias in the CMT estimate of Mo? 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. (1993) and Lonsdale (1994) describe three short spreading centres with a total length of about 6 km along the seismically quiet part of the Heezen transform between 125.5 and 126 W (Fig. 7, several of which are aftershocks and foreshocks, are considered to be noise in ascertaining the quasi-periodic behaviour of the larger shocks. Wolfe et al. 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. Best-fitting linear relationships are drawn through the dates of earthquakes and the seismic moment that had just been accumulated. (PAR), immediately south of the Eltanin Fracture Zones (FZs). Similarly, the series between 95 and 121 km (blue in Fig.