scholarly journals Geomorphic expression and slip rate of the Fairweather fault, southeast Alaska, and evidence for predecessors of the 1958 rupture

Geosphere ◽  
2021 ◽  
Author(s):  
Robert C. Witter ◽  
Adrian M. Bender ◽  
Katherine M. Scharer ◽  
Christopher B. DuRoss ◽  
Peter J. Haeussler ◽  
...  
Keyword(s):  
Active Faults ◽  
Plate Boundary ◽  
Slip Rate ◽  
Strike Slip ◽  
Tectonic Deformation ◽  
Plate Boundaries ◽  
Slip Rates ◽  
Southeast Alaska ◽  
The Past ◽  
Show Evidence

Active traces of the southern Fairweather fault were revealed by light detection and ranging (lidar) and show evidence for transpressional deformation between North America and the Yakutat block in southeast Alaska. We map the Holocene geomorphic expression of tectonic deformation along the southern 30 km of the Fairweather fault, which ruptured in the 1958 moment magnitude 7.8 earthquake. Digital maps of surficial geology, geomorphology, and active faults illustrate both strike-slip and dip-slip deformation styles within a 10°–30° double restraining bend where the southern Fairweather fault steps offshore to the Queen Charlotte fault. We measure offset landforms along the fault and calibrate legacy 14C data to reassess the rate of Holocene strike-slip motion (≥49 mm/yr), which corroborates published estimates that place most of the plate boundary motion on the Fairweather fault. Our slip-rate estimates allow a component of oblique-reverse motion to be accommodated by contractional structures west of the Fairweather fault consistent with geodetic block models. Stratigraphic and structural relations in hand-dug excavations across two active fault strands provide an incomplete paleoseismic record including evidence for up to six surface ruptures in the past 5600 years, and at least two to four events in the past 810 years. The incomplete record suggests an earthquake recurrence interval of ≥270 years—much longer than intervals <100 years implied by published slip rates and expected earthquake displacements. Our paleoseismic observations and map of active traces of the southern Fairweather fault illustrate the complexity of transpressional deformation and seismic potential along one of Earth’s fastest strike-slip plate boundaries.

scholarly journals Morphology, structure, and kinematics of the San Clemente and Catalina faults based on high-resolution marine geophysical data, southern California Inner Continental Borderland (USA)

Geosphere ◽  
2020 ◽  
Vol 16 (5) ◽  
pp. 1312-1335
Author(s):  
Maureen A.L. Walton ◽  
Daniel S. Brothers ◽  
James E. Conrad ◽  
Katherine L. Maier ◽  
Emily C. Roland ◽  
...  
Keyword(s):  
High Resolution ◽  
Southern California ◽  
Active Faults ◽  
Plate Boundary ◽  
Vertical Component ◽  
Slip Rates ◽  
Seismic Reflection Data ◽  
The North ◽  
Reflection Data ◽  
Show Evidence

Abstract Catalina Basin, located within the southern California Inner Continental Borderland (ICB), United States, is traversed by two active submerged fault systems that are part of the broader North America–Pacific plate boundary: the San Clemente fault (along with a prominent splay, the Kimki fault) and the Catalina fault. Previous studies have suggested that the San Clemente fault (SCF) may be accommodating up to half of the ∼8 mm/yr right-lateral slip distributed across the ICB between San Clemente Island and the mainland coast, and that the Catalina fault (CF) acts as a significant restraining bend in the larger transform system. Here, we provide new high-resolution geophysical constraints on the seabed morphology, deformation history, and kinematics of the active faults in and on the margins of Catalina Basin. We significantly revise SCF mapping and describe a discrete releasing bend that corresponds with lows in gravity and magnetic anomalies, as well as a connection between the SCF and the Santa Cruz fault to the north. Subsurface seismic-reflection data show evidence for a vertical SCF with significant lateral offsets, while the CF exhibits lesser cumulative deformation with a vertical component indicated by folding adjacent to the CF. Geodetic data are consistent with SCF right-lateral slip rates as high as ∼3.6 mm/yr and transpressional convergence of <1.5 mm/yr accommodated along the CF. The Quaternary strands of the SCF and CF consistently cut across Miocene and Pliocene structures, suggesting generation of basin and ridge morphology in a previous tectonic environment that has been overprinted by Quaternary transpression. Some inherited crustal fabrics, especially thinned crust and localized, relatively hard crustal blocks, appear to have had a strong influence on the geometry of the main trace of the SCF, whereas inherited faults and other structures (e.g., the Catalina Ridge) appear to have minimal influence on the geometry of active faults in the ICB.

scholarly journals New geodetic constraints on southern San Andreas fault-slip rates, San Gorgonio Pass, California

Geosphere ◽  
2020 ◽  
Author(s):  
Katherine A. Guns ◽  
Richard A Bennett ◽  
Joshua C. Spinler ◽  
Sally F. McGill
Keyword(s):  
Velocity Field ◽  
Southern California ◽  
San Andreas Fault ◽  
Plate Boundary ◽  
Slip Rate ◽  
Fault Slip ◽  
Slip Rates ◽  
San Andreas ◽  
Fault Slip Rates ◽  
Gps Velocity Field

Assessing fault-slip rates in diffuse plate boundary systems such as the San Andreas fault in southern California is critical both to characterize seis­mic hazards and to understand how different fault strands work together to accommodate plate boundary motion. In places such as San Gorgonio Pass, the geometric complexity of numerous fault strands interacting in a small area adds an extra obstacle to understanding the rupture potential and behavior of each individual fault. To better understand partitioning of fault-slip rates in this region, we build a new set of elastic fault-block models that test 16 different model fault geometries for the area. These models build on previ­ous studies by incorporating updated campaign GPS measurements from the San Bernardino Mountains and Eastern Transverse Ranges into a newly calculated GPS velocity field that has been removed of long- and short-term postseismic displacements from 12 past large-magnitude earthquakes to estimate model fault-slip rates. Using this postseismic-reduced GPS velocity field produces a best- fitting model geometry that resolves the long-standing geologic-geodetic slip-rate discrepancy in the Eastern California shear zone when off-fault deformation is taken into account, yielding a summed slip rate of 7.2 ± 2.8 mm/yr. Our models indicate that two active strands of the San Andreas system in San Gorgonio Pass are needed to produce sufficiently low geodetic dextral slip rates to match geologic observations. Lastly, results suggest that postseismic deformation may have more of a role to play in affecting the loading of faults in southern California than previously thought.

Paleoearthquakes on the Húsavík-Flatey Fault in northern Iceland: Where are the large earthquakes?

2021 ◽  
Author(s):  
Remi Matrau ◽  
Yann Klinger ◽  
Jonathan Harrington ◽  
Ulas Avsar ◽  
Esther R. Gudmundsdottir ◽  
...  
Keyword(s):  
Slip Rate ◽  
Late Glacial ◽  
Fault Scarp ◽  
Alluvial Fan ◽  
Tectonic Deformation ◽  
Birch Wood ◽  
Alluvial Deposits ◽  
Slip Rates ◽  
Tephra Layers ◽  
Large Earthquakes

<p>Paleoseismology is key to study earthquake recurrence and fault slip rates during the Late Pleistocene-Holocene. The Húsavík-Flatey Fault (HFF) in northern Iceland is a 100 km-long right-lateral transform fault connecting the onshore Northern Volcanic Zone to the offshore Kolbeinsey Ridge and accommodating, together with the Grímsey Oblique Rift (GOR), ~18 mm/yr of relative motion between the Eurasian and North American plates. Significant earthquakes occurred on the HFF in 1755, 1838 and 1872 with estimated magnitudes of 6.5-7. However, historical information on past earthquakes prior to 1755 is very limited in both timing and size.</p><p>We excavated five trenches in a small basin (Vestari Krubbsskál) located 5.5 km southeast of the town of Húsavík and at 300 m.a.s.l. and one trench in an alluvial fan (Traðargerði) located 0.5 km north of Húsavík and at 50 m.a.s.l. In a cold and wet environment, such as in coastal parts of Iceland, one has to take into account periglacial processes affecting the topsoil to discriminate tectonic from non-tectonic deformation. We used tephra layers in the Vestari Krubbsskál and Traðargerði trenches as well as birch wood samples in Traðargerði to constrain the timing of past earthquakes. Tephra layers Hekla-3 (2971 BP) and Hekla-4 (4331±20 BP) are visible in the top half of all the trenches. In addition, a few younger tephra layers are visible in the top part of the trenches. In Traðargerði several dark layers rich in organic matter are found, including birch wood-rich layers from the Earlier Birch Period (9000-7000 BP) and the Later Birch Period (5000-2500 BP). In Vestari Krubbsskál the lower halves of the trenches display mostly lacustrine deposits whereas in Traðargerði the lower half of the trench shows alluvial deposits overlaying coarser deposits (gravels/pebbles) most likely of late-glacial or early post-glacial origins. In addition, early Holocene tephra layers are observed in some of the trenches at both sites and may correspond to Askja-S (10800 BP), Saksunarvatn (10300 BP) and Vedde (12100 BP). These observations provide good age constraints and suggest that both the Vestari Krubbsskál and Traðargerði trenches cover the entire Holocene.</p><p>Trenches at both sites show significant normal deformation in addition to strike-slip, well correlated with their larger scale topographies (pull-apart basin in Vestari Krubbsskál and 45 m-high fault scarp in Traðargerði). We mapped layers, cracks and faults on all trench walls to build a catalogue of Holocene earthquakes. We identified events based on the upward terminations of the cracks and retrodeformation. Our results yield fewer major earthquakes than expected, suggesting that large earthquakes (around magnitude 7) are probably rare and the more typical HFF earthquakes of magnitude 6-6.5 likely produce limited topsoil deformation.[yk1]  Our interpretation also suggests that the Holocene slip rate [yk2] for the fault section we are studying may be slower than the estimated geodetic slip rate (6 to 9 mm/yr)[yk3]  for the entire onshore HFF, although secondary onshore sub-parallel fault strands could accommodate part of the deformation.</p>

scholarly journals A physics-based approach of deep interseismic creep for viscoelastic strike-slip earthquake cycle models

2019 ◽  
Vol 220 (1) ◽  
pp. 79-95
Author(s):  
Lucile Bruhat
Keyword(s):  
Surface Deformation ◽  
Slip Rate ◽  
Strike Slip ◽  
Dynamic Rupture ◽  
Crust And Upper Mantle ◽  
Slip Rates ◽  
Region I ◽  
Best Fitting ◽  
Time Invariant ◽  
Analytical Expressions

SUMMARY Most geodetic inversions of surface deformation rates consider the depth distribution of interseismic fault slip-rate to be time invariant. However, some numerical simulations show downdip penetration of dynamic rupture into regions with velocity-strengthening friction, with subsequent updip propagation of the locked-to-creeping transition. Recently, Bruhat and Segall developed a new method to characterize interseismic slip rates, that allows slip to penetrate up dip into the locked region. This simple model considered deep interseismic slip as a crack loaded at its downdip end, and provided analytical expressions for stress drop within the crack, slip and slip rate along the fault. This study extends this approach to strike-slip fault environments, and includes coupling of creep to viscoelastic flow in the lower crust and upper mantle. I use this model to investigate interseismic deformation rates along the Carrizo Plain section of the San Andreas fault. This study reviews possible models, elastic and viscoelastic, for fitting horizontal surface rates. Using this updated approach, I develop a physics-based solution for deep interseismic creep which accounts for possible slow vertical propagation, and investigate how it improves the fit of the horizontal deformation rates in the Carrizo Plain region. I found solutions for fitting the surface deformation rates that allow for reasonable estimates for earthquake rupture depth and coseismic displacement and improves the overall fit to the data. Best-fitting solutions present half-space relaxation time around 70 yr, and very low propagation speeds, less than a metre per year, suggesting a lack of creep propagation.

Interseismic stress field variations in Hjalli-Ölfus, SW Iceland

2020 ◽  
Author(s):  
Ingi Th. Bjarnason ◽  
Revathy M. Parameswaran ◽  
Bergthóra S. Thorbjarnardóttir
Keyword(s):  
Plate Boundary ◽  
Strike Slip ◽  
Seismogenic Zone ◽  
Plate Boundaries ◽  
Central Volcano ◽  
Seismic Zone ◽  
Stress Regime ◽  
Mid Atlantic Ridge ◽  
Spatio Temporal ◽  
Earthquake Sequences

<p>Western South Iceland Seismic Zone (SISZ) plate boundary lies adjacent to the Hengill central volcano. The sinistral SISZ connects the two arms of the divergent Mid-Atlantic Ridge (MAR) plate boundaries (Western and Eastern Volcanic Zones; WVZ, EVZ), while Hengill is a part of the WVZ. Seismicity in western SISZ, also known as the Hjalli-Ölfus region, closely interacts with the seismicity and magmatism in Hengill. For instance, the  4 June 1998 Mw 5.4 Hengill earthquake witnessed aftershocks that extended south to meet the Hjalli-Ölfus segment. This segment then hosted the Mw 5.1 Hjalli-Ölfus earthquake that occurred on 13 November 1998; elucidating the Hengill-Ölfus interaction. Relative relocations of earthquakes from July 1991 to December 1999 in Hjalli-Ölfus indicate that the seismogenic zone is predominant at 4-8 km depth, with 80% of the events occuring along an ~ENE-WSW trending seismic zone with lateral extension of ~12 km. The remaining occur along N-S faults, much like the observed norm of dextral faulting along the rest of the SISZ (e.g., 17 June 2000, 29 May 2008 earthquakes; Árnadottir et al., 2001; Brandsdottir et al., 2010). These relocated earthquake sequences were used to perform stress inversions within specified spatio-temporal grids. The results show that from 1994 to 1997, the western part of the Hjalli-Ölfus region exhibits an oblique normal stress regime, while the eastern part remains consistently strike-slip in nature. From mid-1997 to June 1998 western Hjalli-Ölfus shifts from an oblique normal to a strike-slip stress regime, while the eastern part maintains the strike-slip character of the SISZ. However, two months after the 4 June 1998 Hengill earthquake, the western part shifts back to an oblique normal regime, which loses a part of its normal-faulting tendency after the 13 November 1998 Hjalli-Ölfus earthquake. This variation in stress fields between two significant events on conjugately oriented prodominantly strike-slip faults is a clear example of these features influencing one another between seismic episodes. </p>

scholarly journals Propagation of a strike-slip plate boundary within an extensional environment: the westward propagation of the North Anatolian Fault

2016 ◽  
Vol 53 (11) ◽  
pp. 1416-1439 ◽  
Author(s):  
Xavier Le Pichon ◽  
A.M. Celâl Şengör ◽  
Julia Kende ◽  
Caner İmren ◽  
Pierre Henry ◽  
...  
Keyword(s):  
Plate Boundary ◽  
Strike Slip ◽  
Fault System ◽  
Plate Boundaries ◽  
Sea Of Marmara ◽  
The North ◽  
Gulf Of Corinth ◽  
Northern Border ◽  
North Aegean ◽  
Narrow Plate

We document the establishment of the Aegea–Anatolia/Eurasia plate boundary in Pliocene–Pleistocene time. Before 2 Ma, no localized plate boundary existed north of the Aegean portion of the Anatolia plate and the shear produced by the motion of Anatolia–Aegea with respect to Eurasia was distributed over the whole width of the Aegean – West Anatolian western portion. In 4.5 Ma, a shear zone comparable to the Gulf of Corinth was formed in the present Sea of Marmara. The initial extensional basins were cut by the strike-slip Main Marmara Fault system after 2.5 Ma. Shortly after, the plate boundary migrated west of the Sea of Marmara along the northern border of Aegea from the North Aegean Trough, to the Gulf of Corinth area and to the Kefalonia Fault. There, it finally linked with the northern tip of the Aegean subduction zone, completing the system of plate boundaries delimiting the Anatolia–Aegea plate. We have related the change in the distribution of shear from Miocene to Pliocene to the formation of a relatively undeforming Aegea block in Pliocene that forced the shear to be distributed over a narrow plate boundary to the north of it. We attribute the formation of this block to the northeastward progression of the oceanic Ionian slab. We propose that the slab cuts the overlying lithosphere from asthenospheric sources and induces a shortening environment over it.

scholarly journals Extreme Quaternary plate boundary exhumation and strike slip localized along the southern Fairweather fault, Alaska, USA

Geology ◽  
2021 ◽  
Vol 49 (5) ◽  
pp. 602-606 ◽  
Author(s):  
Richard O. Lease ◽  
Peter J. Haeussler ◽  
Robert C. Witter ◽  
Daniel F. Stockli ◽  
Adrian M. Bender ◽  
...  
Keyword(s):  
North America ◽  
Sedimentary Cover ◽  
Plate Boundary ◽  
Slip Rate ◽  
Strike Slip ◽  
Plate Motion ◽  
The North ◽  
Exhumation Rates ◽  
Restraining Bend

Abstract The Fairweather fault (southeastern Alaska, USA) is Earth’s fastest-slipping intracontinental strike-slip fault, but its long-term role in localizing Yakutat–(Pacific–)North America plate motion is poorly constrained. This plate boundary fault transitions northward from pure strike slip to transpression where it comes onshore and undergoes a <25°, 30-km-long restraining double bend. To the east, apatite (U-Th)/He (AHe) ages indicate that North America exhumation rates increase stepwise from ∼0.7 to 1.7 km/m.y. across the bend. In contrast, to the west, AHe age-depth data indicate that extremely rapid 5–10 km/m.y. Yakutat exhumation rates are localized within the bend. Further northwest, Yakutat AHe and zircon (U-Th)/He (ZHe) ages gradually increase from 0.3 to 2.6 Ma over 150 km and depict an interval of extremely rapid >6–8 km/m.y. exhumation rates that increases in age away from the bend. We interpret this migration of rapid, transient exhumation to reflect prolonged advection of the Cenozoic–Cretaceous sedimentary cover of the eastern Yakutat microplate through a stationary restraining bend along the edge of the North America plate. Yakutat cooling ages imply a long-term strike-slip rate (54 ± 6 km/m.y.) that mimics the millennial (53 ± 5 m/k.y.) and decadal (46 mm/yr) rates. Fairweather fault slip can account for all Pacific–North America relative plate motion throughout Quaternary time and indicates stability of highly localized plate boundary strike slip on a single fault where extreme rock uplift rates are persistently localized within a restraining bend.

scholarly journals Latest Quaternary slip rates of the San Bernardino strand of the San Andreas fault, southern California, from Cajon Creek to Badger Canyon

Geosphere ◽  
2021 ◽  
Author(s):  
Sally F. McGill ◽  
Lewis A. Owen ◽  
Ray J. Weldon ◽  
Katherine J. Kendrick ◽  
Reed J. Burgette
Keyword(s):  
Confidence Interval ◽  
San Andreas Fault ◽  
Slip Rate ◽  
Alluvial Fan ◽  
Slip Rates ◽  
San Jacinto Fault ◽  
The Past ◽  
San Andreas ◽  
San Jacinto Fault Zone ◽  
San Bernardino

Four new latest Pleistocene slip rates from two sites along the northwestern half of the San Bernardino strand of the San Andreas fault suggest the slip rate decreases southeastward as slip transfers from the Mojave section of the San Andreas fault onto the northern San Jacinto fault zone. At Badger Canyon, offsets coupled with radiocarbon and optically stimulated luminescence (OSL) ages provide three independent slip rates (with 95% confidence intervals): (1) the apex of the oldest dated alluvial fan (ca. 30–28 ka) is right-laterally offset ~300–400 m yielding a slip rate of 13.5 +2.2/−2.5 mm/yr; (2) a terrace riser incised into the northwestern side of this alluvial fan is offset ~280–290 m and was abandoned ca. 23 ka, yielding a slip rate of 11.9 +0.9/−1.2 mm/yr; and (3) a younger alluvial fan (13–15 ka) has been offset 120–200 m from the same source canyon, yielding a slip rate of 11.8 +4.2/−3.5 mm/yr. These rates are all consistent and result in a preferred, time-averaged rate for the past ~28 k.y. of 12.8 +5.3/−4.7 mm/yr (95% confidence interval), with an 84% confidence interval of 10–16 mm/yr. At Matthews Ranch, in Pitman Canyon, ~13 km northwest of Badger Canyon, a landslide offset ~650 m with a 10Be age of ca. 47 ka yields a slip rate of 14.5 +9.9/−6.2 mm/yr (95% confidence interval). All of these slip rates for the San Bernardino strand are significantly slower than a previously published rate of 24.5 ± 3.5 mm/yr at the southern end of the Mojave section of the San Andreas fault (Weldon and Sieh, 1985), suggesting that ~12 mm/yr of slip transfers from the Mojave section of the San Andreas fault to the northern San Jacinto fault zone (and other faults) between Lone Pine Canyon and Badger Canyon, with most (if not all) of this slip transfer happening near Cajon Creek. This has been a consistent behavior of the fault for at least the past ~47 k.y.

scholarly journals Active faults sources for the Pátzcuaro–Acambay fault system (Mexico): fractal analysis of slip rates and magnitudes <i>M</i><sub>w</sub> estimated from fault length

2018 ◽  
Vol 18 (11) ◽  
pp. 3121-3135
Author(s):  
Avith Mendoza-Ponce ◽  
Angel Figueroa-Soto ◽  
Diana Soria-Caballero ◽  
Víctor Hugo Garduño-Monroy
Keyword(s):  
Time Domain ◽  
Fractal Analysis ◽  
Active Faults ◽  
Slip Rate ◽  
Spatial Domain ◽  
Fault System ◽  
Slip Rates ◽  
Oblique Convergence ◽  
Definition Of ◽  
Intrinsic Definition

Abstract. The Pátzcuaro–Acambay fault system (PAFS), located in the central part of the Trans-Mexican Volcanic Belt (TMVB), is delimited by an active transtensive deformation area associated with the oblique subduction zone between the Cocos and North American plates, with a convergence speed of 55 mm yr−1 at the latitude of the state of Michoacán, Mexico. Part of the oblique convergence is transferred to this fault system, where the slip rates range from 0.009 to 2.78 mm yr−1. This has caused historic earthquakes in Central Mexico, such as the Acambay quake (Ms=6.9) on 19 November 1912 with surface rupture, and another in Maravatío in 1979 with Ms=5.6. Also, paleoseismic analyses are showing Quaternary movements in some faults, with moderate to large magnitudes. Notably, this zone is seismically active, but lacks a dense local seismic network, and more importantly, its neotectonic movements have received very little attention. The present research encompasses three investigations carried out in the PAFS. First, the estimation of the maximum possible earthquake magnitudes, based on 316 fault lengths mapped on a 15 m digital elevation model, by means of three empirical relationships. In addition, the Hurst exponent Hw and its persistence, estimated for magnitudes Mw (spatial domain) and for 32 slip-rate data (time domain) by the wavelet variance analysis. Finally, the validity of the intrinsic definition of active fault proposed here. The average results for the estimation of the maximum and minimum magnitudes expected for this fault population are 5.5≤Mw≤7. Also, supported by the results of H at the spatial domain, this paper strongly suggests that the PAFS is classified in three different zones (western PAFS, central PAFS, and eastern PAFS) in terms of their roughness (Hw=0.7,Hw=0.5,Hw=0.8 respectively), showing different dynamics in seismotectonic activity and; the time domain, with a strong persistence Hw=0.949, suggests that the periodicities of slip rates are close in time (process with memory). The fractal capacity dimension (Db) is also estimated for the slip-rate series using the box-counting method. Inverse correlation between Db and low slip-rate concentration was observed. The resulting Db=1.86 is related to a lesser concentration of low slip-rates in the PAFS, suggesting that larger faults accommodate the strain more efficiently (length ≥3 km). Thus, in terms of fractal analysis, we can conclude that these 316 faults are seismically active, because they fulfill the intrinsic definition of active faults for the PAFS.

Fragmentation of the Sinai Plate indicated by spatial variation in present-day slip rate along the Dead Sea Fault System

2020 ◽  
Vol 221 (3) ◽  
pp. 1913-1940
Author(s):  
Francisco Gomez ◽  
William J Cochran ◽  
Rayan Yassminh ◽  
Rani Jaafar ◽  
Robert Reilinger ◽  
...  
Keyword(s):  
Continental Margin ◽  
Plate Boundary ◽  
Slip Rate ◽  
Dead Sea ◽  
Fault System ◽  
Slip Rates ◽  
Dead Sea Fault System ◽  
The Dead ◽  
Gps Velocities ◽  
Splay Faults

SUMMARY A comprehensive GPS velocity field along the Dead Sea Fault System (DSFS) provides new constraints on along-strike variations of near-transform crustal deformation along this plate boundary, and internal deformation of the Sinai and Arabian plates. In general, geodetically derived slip rates decrease northwards along the transform (5.0 ± 0.2 to 2.2 ± 0.5 mm yr−1) and are consistent with geological slip rates averaged over longer time periods. Localized reductions in slip rate occur where the Sinai Plate is in ∼N–S extension. Extension is confined to the Sinai side of the fault and is associated with prominent changes in transform geometry, and with NW–SE striking, left-lateral splay faults, including the Carmel Fault in Israel and the Roum Fault in Lebanon. The asymmetry of the extensional velocity gradients about the transform reflects active fragmentation of the Sinai Plate along the continental margin. Additionally, elastic block modelling of GPS velocities requires an additional structure off-shore the northern DSF segment, which may correspond with a fault located along the continental margin, suggested by prior geophysical studies.

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