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. Forsyth The time-predictable model (not shown), in which the time to the next earthquake is proportional to the size of the preceding large event, also fits the data, though slightly less well. The CMT methodology and format of the catalogue are described in Dziewonski (1981) and Ekstram (2005). Distances in kilometres same as in Fig. T. D.F. We conclude that strike-slip and normal faulting along the three Eltanin transforms are partitioned so that strike-slip faulting takes place along the transforms themselves and normal faulting occurs nearby but just off the transforms. If the anomalous trend is real, having one group of events (east or west) off the primary transform then almost becomes a necessary interpretation. Hence, it and the two larger events occurred along an off-transform feature. We report the unique occurren 9 for two sequences of earthquakes along the Tharp transform. Eltanin fracture zone Scope Notes: SE Pacific. They found that all depths were less than 20 and a few better determined solutions were shallower than 5 km below the seafloor. The Romanche and Chain Fracture Zones creates a huge gap in the MAR and can act as a "Subsea Berlin Wall" segregating the North Atlantic communities from those in other oceans. Others related faults include the Vacquier Transform Fault, the Menard Transform Fault, and the Udintsev Fault.[3]. 4. Examine the figure above. They are the scars on the seafloor basalt that are created by offsets in the mid-ocean ridge. This technique has the potential to rigorously assess hotspot fixity and to locate extinct hotspots. Lonsdale (1994) concludes that a zone of extension north of the Heezen transform developed following a Pliocene change in relative plate motion. The new result is well constrained by the surface wave data, which were not included in the original analysis. Depths modelled by Wolfe et al. side (rather than on top of or away from one another.) Although magmatism was more or less continuous on the ridge during 28-60 Ma, it probably occurred on crust . 2). His relocations are shown in Figs 4-6 in green. The 40Ar39Ar dating of rocks dredged . Nine earthquakes from 1969 to 1975 are shown at their body wave locations of the International Seismological Centre (ISC). The five largest shocks have a repeat time of about 8 yr and a COV of 0.43. Fig. Searle P. We find that seismic coupling is not merely a function of relative plate velocity, location along the transform and transform length. We obtained a CMT solution for an additional earthquake of Mw 6.15 in 1979. Cumulative moment release is shown in Fig. Hence, with its inclusion, the series appears to be complete from at least 1981 to 2010. R.P. 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 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. [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",, This page was last edited on 1 June 2022, at 10:32. 11 displays the log of the cumulative number of events per 20 yr as a function of decreasing Mw for the periods 1976-1990 and 1991-2010. According to the normal scenario for the opening of the South Atlantic, it is spreading at a rate of 1.75cm/year (0.69in/year) and began forming about 50 Ma. ISC located an earthquake along that segment of Ms 6.1 on 1967 September 9. C. 2. They proposed that the Eltanin transforms consisted of small, well-separated asperities that rupture in earthquakes. E.A. "zone of fracture" in Chinese : , ; ; ,; ; "amsterdam fracture zone" in Chinese : "aseismic fracture zone" in Chinese : 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? Observed P waves for a normal-faulting event, however, leave close to their maximum radiation on the focal sphere. Eltanin has a maritime climate in the transition region between the tundra and subarctic zones (Kppen classification) which is characterised by . The 30- to 42-km length that we used for the repeating events along the Heezen transform in Fig. . Wolfe 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. Swarms of hydrothermal shrimps reminiscent of those found from northern MAR vent-sites have been found on the northern part of the southern MAR. From the scatter of locations perpendicular to the Eltanin transforms, the standard deviation of locations would be around 15 km, after allowing for a constant regional bias. W. . 'dextrally' (also known as right-laterally) which means if you Duncan Jordan 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. The CMT locations for the Tharp transform are rotated several degrees with respect to both the computed transform direction in Fig. 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? J. 4. Approximate slopes are denoted by dashed lines. We find that one isolated asperity along the Heezen transform ruptures about every 4.0 1.0 yr. Archived seismicity, satellite altimetry, and older geophysical traverses extend these descriptions . 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. A large iceberg interfered with one scientific mapping (Lonsdale 1994). 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. This completeness can be seen as well by the slope of 1.0 of the LogNMw relationship in Fig. 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. 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 . The continuity in smooth trend of the ridge and the Eltanin Fracture Zone suggests some relationship between them. , and M is in kg. Moment release in earthquakes of Mw= 6.08 is about 60 per cent of that for Mw > 5.55. The surface wave catalogue (Ekstram 2006) starts in 1990, and the magnitude that is associated with events in that catalogue is usually very close to the Mw obtained in a CMT analysis. The fracture along blocks of crust (tectonic plates) is called a trench to the Eltanin Fracture Zone. He concluded that a major fracture zone intersected the mid-oceanic ridge at that location, much like those mapped by Menard (1960) farther north. 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. Decide for yourself which test is easiest to use, but dont forget the preliminary test. The axes are each rotated with respect to the Euler rotation pole of DeMets et al. Show that the equation is dimensionally correct. L.R. Computed CMT depths in Table S1 in the Supporting Information range from 12 to 26 km, with 12 being the smallest constrained depth. Bergman D.W. The eastern part of the transverse ridge, however, consists of a thick sequence of stratified material called the Romanche Sedimentary Sequence (RSS). [1] The two major faults in the Eltanin Fracture Zone are the Heezen Fault and the Tharp Fault. Earth Extremities 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 . Our work using much greater numbers of stations and earthquakes confirms the general findings of Stewart and Okal about the abundance of aseismic slip and the presence of asperities. We find one segment of the Heezen transform has ruptured quasi-periodically since 1976 in eight shocks of Mw 5.9-6.1 with an average repeat time of 4 yr. We recomputed centroid moment tensor (CMT) solutions for 190 earthquakes along and close to the three transforms of the Eltanin system from 1976 to 2010. This yielded 110 earthquakes for that period. 7; several were the sites of two or three earthquakes of Mw > 6.15. The transform valley is 15-20 km wide and 2-4 km deep. This includes the HGLP, SRO and ASRO networks in the 1970s, the SRO, ASRO, DWWSSN, CDSN and Geoscope networks for the 1980s, and the IRIS/USGS GSN, Geoscope, GEOFON and MedNet networks since the 1990s. Their surface wave magnitudes, Ms, for events before 1969 along the Eltanin system were determined typically from one to a few stations. Enter your email address to follow this blog and receive notifications of new posts by email. They represent a good laboratory for examining fault segments that slip aseismically, others that are well coupled, and the short recurrence times of earthquakes. We note that our revised catalogue with its additions of more solutions, especially of Mw 5.5-6.0, is more complete than the existing CMT catalogue. 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. This attests to the very thin lithosphere at fast spreading ridges. Explanation: Fracture zones are characterised as structural line View the full answer Transcribed image text: How are fracture zones like the Eltanin created? The point source depth of 10.4 km places the 2007 earthquake 6-7 km below the ocean floor. Sykes & Menke (2006) calculated maximum-likelihood estimates of COV that were 0.3 or smaller for a number of large-to-great earthquakes that ruptured nearly the same segments of strike-slip and subduction zone faults. [3], Series of faults that offset the Pacific-Antarctic Ridge. These depths are similar to those determined by Wolfe et al. The linearity of the CMT locations along the shorter Hollister transform (Fig. Map view of CMT locations of earthquakes along Hollister transform fault from 1976 to 2010. 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. 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. These are too small to represent the actual uncertainties. Distances along the transform are calculated from an arbitrary origin of coordinates at 55.4 S, 125.0 W. R. Thus, the use of the CMT methodology insured more complete coverage of earthquakes in this very remote area of the Earth. Who is Jason crabb mother and where is she? The Romanche Fracture Zone offsets the Mid-Atlantic ridge by 900 km (560 mi), making it the largest equatorial fracture zone in the Atlantic. 4, between 75 and 125 km). The point-source depths are about 10-12 km, which suggests that the earthquakes ruptured faults that cross the M discontinuity. 4699 km SW of Santiago, Chile / pop: 4,837,295 / local time: 15:09:44.3 2016-08-18 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. This yielded 84 earthquakes. Ryan J. Fox Solid line indicates Mw=mb. (1993) attribute it to one of those small spreading centres. Fig. As AABW flows through the Romanche Fracture Zone, salinity and temperature increase significantly. They obtained a depth in the range 8-14 km below the seafloor for the 1978 earthquake off the Heezen fault, and approximately 10 km below the seafloor for the 1989 earthquake off the Tharp transform. In the basin on the eastern side of the MAR the Walvis Ridge blocks the northward passage. 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. How that may vary along strike and affect seismic coupling is unknown. H.W. It is that region where three of the four normal faulting earthquakes in Fig. 1999). In relocating earthquakes along the East Pacific Rise and Pacific-Antarctic Ridge, Sykes (1963) found that the pattern of epicentres was offset about 1000 km near 55 S. Moment magnitudes are given below each solution. Ekstram Our new catalogue can be used in testing computer simulations of earthquake recurrence. C.G. [6] Symbols, axes and origin of coordinates same as Fig. We postpone a discussion of reasons why various segments were the sites of shocks of differing Mw until the Discussion (Section 5). . The two dotted lines in Fig. G. 4786 km SE of Avarua, Cook Islands / pop: 13,400 / local time: 01:42:15.1 2017-06-15,, Distances: 4676 km SE of Wellington, New Zealand / pop: 381,900 / local time: 06:09:44.3 2016-08-19 (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. It is the only example of a very short time interval between large shocks along segments of the Eltanin transforms. Listen to the audio pronunciation of Eltanin Fracture Zone on pronouncekiwi This shock of mb 5.6 in the PDE catalogue occurred only 4 min after the Mw 6.7 normal-faulting event near the Heezen transform, and the waveforms are not sufficiently separated to make a CMT analysis possible. The average repeat time for the eight events of Mw > 5.9 is 4.0 1.0 (1 SD) yr. Wolfe et al. The ridge segments and transform faults of the East Pacific Rise and Pacific-Antarctic ridge are the sites of the fastest rates of the seafloor spreading and relative plate motion in the world. 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. If so, their repeat time was about 16 yr but is based on only three events. Woodward Dziak 1 for events of Mw 6.2 in 1983 and 2007. Forsyth . 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 red series in Fig. [5], The hydrothermal vents of the MAR support many life forms. If those segments are not fully coupled, our calculations of downdip width, of course, are minimum estimates. 2). Langenhorst Experience has shown that deviations of the CMT centroid depth from the true depth occur both randomly and systematically. We determined a CMT solution for it using seven digital stations and obtained a Mw of 6.1, a strike-slip mechanism and a location (red triangle) about 20 km west of the group indicated in Fig. For example, the caridean shrimp Alvinocaris muricola inhabits cold seeps in both the Gulf of Mexico and the Gulf of Guinea, which clearly suggests a gene flow across the Atlantic, but the amount of data is very limited and dispersal pathways are not fully understood. The centroid epicentre and time did not shift appreciably in these different inversions, nor did the geometry of the moment tensor change appreciably. Neither Okal & Langenhorst (2000) nor we found any normal faulting earthquakes along spreading ridges adjacent to the Eltanin fault system. Stewart & Okal (1983) concluded that earthquakes along the Eltanin zone from 1920 to 1981 accounted for less than 10 per cent of the slip predicted by kinematic models of plate motion and cooling. Formed around Antarctica, the AABW is cold, has low salinity, and high silicate concentration. Atwater We take this along with the distributions of events in time and longitude after 1976 (Fig. (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. Boettcher Argus S. Carbotte kindly computed the bathymetric map in Fig. . Events of Mw > 5.9 account for 70 per cent of the moment in Fig. 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. As in Fig. 3 and studied separately. His relocations along the Heezen transform, with one exception, are more tightly clustered than ours. 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 D.K. Lynn R. Sykes, Gran Ekstrm, Earthquakes along Eltanin transform system, SE Pacific Ocean: fault segments characterized by strong and poor seismic coupling and implications for long-term earthquake prediction, Geophysical Journal International, Volume 188, Issue 2, February 2012, Pages 421434, 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 . What are mid-ocean ridges? Specifically, in the study of the Eltanin earthquakes, we have obtained depths ranging from the shallowest used in the CMT algorithm (12 km) to 26 km. "zone" in Chinese : n. 1. () 2. 3. . The San Andreas fault is part of a fault zone known as a transform n=02+(1)nn2+7\sum_{n=0}^{\infty} \frac{2+(-1)^{n}}{n^{2}+7}n=0n2+72+(1)n, Which is an example of homeostasis? 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. Watts et al. 2 shows the areal distribution of strike-slip earthquakes Mw > 5.5 as a function of their recomputed magnitude, Mw, in red along the three transform faults of the Eltanin system. They were generally too small to generate stable CMT results. 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. By chron 28 (63-64 Ma) about 750 km of the present 1000 km offset had accumulated across them. [1] The two major faults in the Eltanin Fracture Zone are the Heezen Fault and the Tharp Fault. (1981), Arvidsson & Ekstrm (1998) and Ekstrm et al. Nakata This is not surprising since all stations are at large teleseismic distances. Wilson 10.17882/59800. Montesi 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. DeMets 7, however, since it is located just to the east of other large shocks along the Heezen transform. McGuire This is a consequence of the continuity of displacement eigenfunctions for surface waves across discontinuities, and the dependence of the excitation on these displacements. 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. The 2004 Parkfield earthquake of Mw 6.0 had a rupture length of 20-25 km (Johanson et al. Hirth 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. 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. VanDeMark Solutions for new earthquakes of Mw > 5.5 were not found after early 2002. Their remoteness and rough seas, however, puts a premium on studying them at large distances using seismic waves and various satellite technologies. Moment release over 35 yr per unit length along strike for each of those segments is 3.5 0.7 1014 N m m-1. 8. M.S. GE was partially supported by NSF grant EAR-09-24694. . 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 used a box from 54S to 58S and 140W to 120W to identify earthquakes that might be located on the Eltanin transform system. 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. The total length of the three en echelon faults is nearly 1000 km; each is characterized by fast long-term rates of displacement of about 80 mm yr-1. Search for: Recent Posts. Cumulative seismic moment release for shocks of Mw > 5.55 from 1976 to 2010 along two segments of Hollister transform fault as indicated in Fig. Bohnenstiehl New Mw corresponds to seismic moment magnitude recomputed for this study. . None of the five is reasonably attributed to a small spreading segment along either of those two transforms. Best-fitting linear relationships are drawn through the dates of earthquakes and the seismic moment that had just been accumulated. slip fault zone between the Caribbean and North American 3292km (2046mi) WSW of Puerto Natales, Chile transform faults fracture zones and the kinematics of. -Linear spreading on Earth's curved surface. Boettcher [4] C1. J.J. Tolstoy 11 between Mw 5.4 and 6.0 for events from 1991 to 2010. T. Wolfe et al. J.H. Eltanin Fracture Zone System: IHO-IOC GEBCO Gazetteer of Undersea Feature Names : English: Eltanin Fracture Zone: US BGN Advisory Committee on Undersea Features (ACUF) PlaceType: Fracture Zone : Latitude: 54 8' 16.8" S (-54.137999) Longitude: 127 32' 7.3" W (-127.53537) Min. 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. Strike-slip CMT solutions from 1976 to 2010 as a function of longitude along the entire Eltanin transform system. 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. Since the 40-km section of the Tharp (Fig. . 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. 1975; Lonsdale 1994), which were named for M. Tharp, B. Heezen and C. Hollister (Fig. Is the singer Avant and R Kelly brothers? What causes the formation of offsets in the mid-ocean ridge system? S.M. Our determinations of Mw typically use observations at more stations than those of Ms. Those for Mw also use Love and Rayleigh waves. Oxford University Press is a department of the University of Oxford. Ekstram Search for other works by this author on: Earthquake slip on oceanic transform faults, Global CMT analysis of moderate earthquakes, Mw For full access to this pdf, sign in to an existing account, or purchase an annual subscription. Hence, we suspect that the events at the western end of the Tharp transform are anomalous in some sense. . We find or confirm two anomalous characteristics: the . . This term has multiple hierarchies. The average of the three intervals since 1967 is 12.8 yr with a COV of 0.36. Fig. 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. At faster separating parts of the Pacific-Antarctic boundary, and on most of the rest of the EPR, fracture zone structure is mainly inherited from the variable arrangement of volcanic ridges and tectonic uplifts at the risecrest intersections, rather than from structures formed at the transform valley. A transform fault may occur in the portion On the basis of serial hydrographic measurements, the Chain Fracture Zone appears to be separated into several deeper sections. 3315km (2060mi) WSW of Punta Arenas, Chile 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. J.S. Map view of CMT locations of earthquakes along Tharp transform from 1976 to 2010. which two plates create the eltanin fracture zone quizlet; Well Inspection using ROV at Kondashetti Halli, Bangalore Fielding Nettles 8) contains six events of Mw= 5.89 since 1971. where is and what is eltanin transform fault and fracture. It moves 7 for events of Mw > 5.55 (blue) and Mw > 5.9 (red). 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.
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