Slip Rate Variation During the Last ∼210 ka on a Slow Fault in a Transpressive Regime: The Carrascoy Fault (Eastern Betic Shear Zone, SE Spain)

Fault slip rate variability over time is a crucial aspect for understanding how single faults interact among each other in fault systems. Several studies worldwide evidence the occurrence of high activity periods with clustering of events and synchronization among faults, followed by long periods of low activity (super-cycles). The increasing gathering of evidence of these phenomena is making fault hazard models quickly evolving and challenging seismic hazard assessment. However, in moderately active fault systems, a determination of fault slip rates can present large uncertainties, that have to be carefully considered when slip rate histories are determined. In this work, we estimate the variation of slip rate in the last ∼210 ky of the NE segment of the left-lateral reverse Carrascoy Fault, one of the main faults forming the Eastern Betic Shear Zone in SE Spain. We study two selected field sites where we have been able to measure offsets and date the sediments along with uncertainties. The first site shows a progressive discordance drawn by different calcretes developed on alluvial deposits. The vertical throw is calculated by modeling the growth of the discordance. The vertical slip rates are estimated dating the deformed calcretes by Uranium Series and by comparing them with a complete regional calcrete dates database compiled from the literature. On the second site, we analyze the geomorphology of different Upper Pleistocene alluvial fans, where three incised channels are offset by the fault, providing the net slip for the last ∼124 ky. We discuss the influence of different factors on the estimate of net slip rates using data from different sources. This analysis highlights the importance of determining an accurate fault geometry and how local data can provide misleading deformation rates. Our results suggest the existence of long periods of low activity disturbed by short high activity periods. Such a pattern of activity along time is defined for the first time in the Eastern Betic Shear Zone, with interesting implications in the seismogenic behavior of the rest of the slow faults within the region.

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

Geosphere ◽

10.1130/ges02239.1 ◽

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.

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

10.5194/egusphere-egu21-13998 ◽

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

Paleoseismology is key to study earthquake recurrence and fault slip rates during the Late Pleistocene-Holocene. The H&#250;sav&#237;k-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 Gr&#237;msey 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.We excavated five trenches in a small basin (Vestari Krubbssk&#225;l) located 5.5 km southeast of the town of H&#250;sav&#237;k and at 300 m.a.s.l. and one trench in an alluvial fan (Tra&#240;arger&#240;i) located 0.5 km north of H&#250;sav&#237;k 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 Krubbssk&#225;l and Tra&#240;arger&#240;i trenches as well as birch wood samples in Tra&#240;arger&#240;i to constrain the timing of past earthquakes. Tephra layers Hekla-3 (2971 BP) and Hekla-4 (4331&#177;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 Tra&#240;arger&#240;i 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 Krubbssk&#225;l the lower halves of the trenches display mostly lacustrine deposits whereas in Tra&#240;arger&#240;i 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 Krubbssk&#225;l and Tra&#240;arger&#240;i trenches cover the entire Holocene.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 Krubbssk&#225;l and 45 m-high fault scarp in Tra&#240;arger&#240;i). 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]&#160; Our interpretation also suggests that the Holocene slip rate [yk2]&#160;for the fault section we are studying may be slower than the estimated geodetic slip rate (6 to 9 mm/yr)[yk3]&#160; for the entire onshore HFF, although secondary onshore sub-parallel fault strands could accommodate part of the deformation.

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A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: The South Malawi Active Fault Database

10.5194/se-2020-104 ◽

2020 ◽

Author(s):

Jack N. Williams ◽

Hassan Mdala ◽

Åke Fagereng ◽

Luke N. J. Wedmore ◽

Juliet Biggs ◽

...

Keyword(s):

Seismic Hazard ◽

Active Fault ◽

Slip Rate ◽

Fault Slip ◽

Slip Rates ◽

Scaling Relationships ◽

Regional Strain ◽

Earthquake Scaling ◽

Recurrence Intervals ◽

Fault Slip Rate

Abstract. Seismic hazard is frequently characterised using instrumental seismic records. However, in regions where the instrumental record is short relative to earthquake repeat times, extrapolating it to estimate seismic hazard can misrepresent the probable location, magnitude, and frequency of future large earthquakes. Although paleoseismology can address this challenge, this approach requires certain geomorphic settings and carries large inherent uncertainties. Here, we outline how fault slip rates and recurrence intervals can be estimated through an approach that combines fault geometry, earthquake-scaling relationships, geodetically derived regional strain rates, and geological constraints of regional strain distribution. We then apply this approach to the southern Malawi Rift where, although no on-fault slip rate measurements exist, there are theoretical and observational constraints on how strain is distributed between border and intrabasinal faults. This has led to the development of the South Malawi Active Fault Database (SMAFD), the first database of its kind in the East African Rift System (EARS) and designed so that the outputs can be easily incorporated into Probabilistic Seismic Hazard Analysis. We estimate earthquake magnitudes of MW 5.4–7.2 for individual fault sections in the SMAFD, and MW 6.0–7.8 for whole fault ruptures. These potentially high magnitudes for continental normal faults reflect southern Malawi's 11–140 km long faults and thick (30–35 km) seismogenic crust. However, low slip rates (intermediate estimates 0.05–0.8 mm/yr) imply long recurrence intervals between events: 102–105 years for border faults and 103–106 years for intrabasinal faults. Sensitivity analysis indicates that the large range of these estimates can be reduced most significantly from an improved understanding of the rate and partitioning of rift-extension in southern Malawi, earthquake scaling relationships, and earthquake rupture scenarios. Hence these are critical areas for future research. The SMAFD provides a framework for using geological and geodetic information to characterize seismic hazard in low strain rate settings with few on-fault slip rate measurements, and could be adapted for use elsewhere in the EARS or globally.

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36Cl exposure dating of post-glacial features along the Mt Vettore Fault (Central Apennines, Italy) constraining fault slip rate and last glacial advance.

10.5194/egusphere-egu21-12653 ◽

2021 ◽

Author(s):

Lea Pousse-Beltran ◽

Lucilla Benedetti ◽

Jules Fleury ◽

Paolo Boncio ◽

Valery Guillou ◽

...

Keyword(s):

Slip Rate ◽

Fault Slip ◽

Fault System ◽

Central Apennines ◽

Climate Conditions ◽

Last Glacial ◽

Exposure Dating ◽

Fault Systems ◽

Fault Slip Rate ◽

Exposure Ages

In the Central Apennines (Italy), up to now, no absolute dating directly based on the moraines has been carried out to constrain glacial oscillation. However, climatic constrains are often used in the Central Apennine to estimate long term (> 10 ka) fault slip rate. In addition slip rate assessments based on offset morphotectonic markers on the main branches of fault systems and encompassing several seismic cycles (> 10 ka) are sparse. This is particularly true for the Monte Vettore-Monte Bove fault system which triggered the 2016-2017 seismic sequence. We thus provide new assessment for the vertical slip rates along the Mt Vettore-Mt Bove fault system. &#160;Offset measurements were made using a 5-cm resolution DEM obtained through a drone survey and constrain a fault scarp height of 15.5 &#177; 1.4 m and a cumulative offset of 32-40.5 m. Samples were collected from the Valle Lunga terminal moraine at 1710 m asl and yield 36Cl exposure ages of 12.7 + 2.2/-1.9 ka while the flat, abraded surface located on top of the tectonic scarp yield 36Cl exposure ages of 23.4 + 5.3/-4.3 ka. Assuming the offset started to accumulate when climate conditions allow its preservation, thus once the surface was abandoned, we constrain a vertical slip rate of 1.2 &#177; 0.2 mm/yr along the master branch of the Mt Vettore normal fault. &#160;This rate is higher than the ones previously obtained from trenches along secondary splays of the Mt Vettore-Mt Bove and on the Norcia fault systems. Besides, the yielded chronology for the last glacial maximum in that area at ~23 ka is in good agreement with the timing previously proposed for the LGM in the Apennines.

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INVERTING FAULT SLIP RATES ON COMPLEX FAULT SYSTEMS TO OBTAIN THE OPTIMAL SPATIAL DISTRIBUTION OF EARTHQUAKES

10.1130/abs/2020am-353817 ◽

2020 ◽

Author(s):

Eric L. Geist ◽

◽

Tom Parsons

Keyword(s):

Spatial Distribution ◽

Fault Slip ◽

Slip Rates ◽

Fault Systems ◽

Fault Slip Rates ◽

Complex Fault

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HOLOCENE FAULT SLIP RATES INDICATE LOCALIZATION OF EASTERN CALIFORNIA SHEAR ZONE DEFORMATION BETWEEN RIDGECREST AND BARSTOW

10.1130/abs/2020cd-347493 ◽

2020 ◽

Author(s):

Elizabeth K. Haddon ◽

◽

David M. Miller ◽

Victoria E. Langenheim ◽

Shannon A. Mahan

Keyword(s):

Shear Zone ◽

Fault Slip ◽

Slip Rates ◽

Eastern California Shear Zone ◽

Fault Slip Rates ◽

Zone Deformation

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Slip rate determined from cosmogenic nuclides on normal-fault facets

Geology ◽

10.1130/g47644.1 ◽

2020 ◽

Vol 49 (1) ◽

pp. 66-70

Author(s):

Jim Tesson ◽

Lucilla Benedetti ◽

Vincent Godard ◽

Catherine Novaes ◽

Jules Fleury ◽

...

Keyword(s):

Slip Rate ◽

Normal Fault ◽

Time Frame ◽

Fault Slip ◽

Normal Faults ◽

Slip Rates ◽

Topographic Features ◽

The Past ◽

Data Inversion ◽

Fault Slip Rates

Abstract Facets are major topographic features built over several 100 k.y. above active normal faults. Their development integrates cumulative displacements over a longer time frame than many other geomorphological markers, and they are widespread in diverse extensional settings. We have determined the 36Cl cosmogenic nuclide concentration on limestone faceted spurs at four sites in the Central Apennines (Italy), representing variable facet height (100–400 m). The 36Cl concentration profiles show nearly constant values over the height of the facet, suggesting the facet slope has reached a steady-state equilibrium for 36Cl production. We model the 36Cl buildup on a facet based on a gradual exposure of the sample resulting from fault slip and denudation. Data inversion with this forward model yields accurate constraints on fault slip rates over the past 20–200 k.y., which are in agreement with the long-term rate independently determined on some of those faults over the past 1 m.y. 36Cl measurements on faceted spurs can therefore constrain fault slip rate over time spans as long as 200 k.y., a time period presently undersampled in most morphotectonic studies.

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