Late Holocene Earthquakes Research Articles

Late Holocene earthquakes on the Papatea Fault and its role in past earthquake cycles, Marlborough, New Zealand

ABSTRACT The north-striking sinistral reverse Papatea Fault ruptured with a very large (up to 12 m) oblique slip as part of the 2016 M W 7.8 Kaikōura earthquake in the northeastern South Island. Paleoseismic studies were undertaken at three sites along the Papatea Fault, named Murray’s roadcut, Jacqui’s Gully (both on the main strand), and Wharekiri trench (western strand). These sites provide evidence for up to three Late Holocene paleoearthquakes prior to 2016 (=E0) on this previously unmapped active fault, with preferred OxCal-modelled timings of 98–149 (E1), 546–645 cal yr BP (E2), and >738 cal yr BP (E3). Event correlations between the sites are generally consistent across these past events, implying that the two strands of the Papatea Fault link at depth and rupture together co-seismically as in 2016. Comparisons of its paleoseismic record with the Kekerengu Fault and uplift data from Waipapa Bay and Kaikōura, suggest that the Papatea Fault may have three distinct rupture modes: (i) Kaikōura-type multi-fault ruptures with multi-metre, anelastic block displacements and associated major landscape change; (ii) multi-fault earthquake ruptures with other regional fault combinations; and (iii) single-fault Papatea ruptures with metre-scale displacement. OxCal models offer the possibility that the E1 fault rupture occurred in 1855 CE.

Late Holocene rupture history of the Ash Hill fault, Eastern California Shear Zone, and the potential for seismogenic strain transfer between nearby faults

AbstractUnderstanding how fault systems interact and transfer strain over seismogenic timescales (seconds to ka) requires temporal records of past ruptures along adjacent and intersecting fault networks. Here we document the record of Late Holocene ruptures as recorded in the geomorphology of alluvial deposits along the Ash Hill fault, in the Eastern California Shear Zone (ECSZ). We leverage a multi‐faceted approach to evaluate the relative timing of Ash Hill fault ruptures to those of nearby faults in the ECSZ. We determine the number and timing of Late Holocene earthquakes on the Ash Hill fault using high‐resolution tectono‐geomorphic mapping, a locally calibrated alluvial fan stratigraphy, feldspar luminescence dating, and fault offset analysis from field observations, LiDAR, and drone‐based digital surface elevation models. We find evidence for three surface‐rupturing earthquakes that have occurred since ~4 ka, each with ~1.0 ± 0.2 m of oblique slip per event (Mw ~ 6.9–7.0), and we constrain the timing of these earthquakes by dating deposits that bracket each event. The timing of these three ruptures is similar to the paleoseismic record along the adjacent range‐bounding fault in southern Panamint Valley. Specifically, the two adjacent faults exhibit similar numbers of earthquakes during the Late Holocene, with similar recurrence intervals and rupture timing. These data suggest that it is possible that these two faults have ruptured in the same or closely temporally related events throughout the Late Holocene. Similar spatio‐temporal clustered earthquakes have been recognized in both historic and paleoseismic records in the region, and such behaviour may be common in complexly interlinked fault networks, like those that exist in the ECSZ.

Holocene Faulting and Earthquake Recurrence along the Northern Agua Tibia–Earthquake Valley Fault Zone and Implications for Slip Distribution in Southern California

ABSTRACTSlip rates determined along the Elsinore and San Jacinto faults indicate that south of 33.5° N, the slip rate along the Elsinore fault decreases by ∼2.5 mm/yr, whereas the slip rate along the San Jacinto fault increases by nearly 6 mm/yr. A transfer of slip from the Elsinore to the San Jacinto faults is the likely explanation, but a fault with Holocene activity had yet to be identified to support this hypothesis. We report the results of new mapping and paleoseismic work along the Earthquake Valley fault, the eastern strand of the Elsinore fault, in Warner basin. Our paleoseismic investigation at Big Lake documents three stratigraphic horizons at which there is evidence of coeval shattering and displacements. The uppermost interpreted event breaks up to within 20 cm of a historical horizon and suggests a very young surface rupture. We attribute this event (E1) to either the 1890 or 1892 earthquakes. The ages of the two previous earthquakes are constrained to be between 486 C.E. and 1125 C.E., and between 158 B.C.E. and 235 C.E. These data suggest individual interevent recurrence intervals of 1106 ± 340 yr (E1–E2) and 760 ± 406 yr (E2–E3), respectively. The minimum slip rate of 1.95 ± 0.4 mm/yr is estimated for the Earthquake Valley fault from the offset of two main drainages that cut into the sedimentary fill of Warner basin, which contains the Bishop tuff. We propose that with its geomorphological expression, late Holocene earthquake record, and slip rate estimate, the Earthquake Valley fault is the main structure responsible for transferring slip from the northern Elsinore fault to the southern San Jacinto fault. Given the recency of a surface rupture and our recurrence interval calculations, however, a large earthquake along the Earthquake Valley fault in the near future is unlikely, if time dependence is considered.

Late Glacial and postglacial seismicity in the Northeastern Fennoscandian Shield: tectonic position and age of paleo-earthquakes near Murmansk

Earthquake-induced deformations located near Murmansk City were investigated for information on the age, tectonic position and spatial occurrence of paleo-earthquakes. The main earthquake-generating zone is identified to be the system of strike slip faults and reverse-oblique faults trending NNW along the Kola River valley. We used radiocarbon analysis and paleogeographic reconstructions and revealed three episodes of increased seismic activity: from 9500 to 10500 cal BP, from 892 to 1182 cal BP, and from 200 to 300 cal BP. Based on the peak ground velocity estimation method we suggest that an earthquakes with a maximum moment magnitude up to Mw ≈ 6.0–6.5 may have taken place in the studied area. The recorded location of seismogenic deformation near faults indicates area of strong Late Glacial and Holocene earthquakes occurring in the northern Kola Peninsula; this is also consistent with observations concerning the historical events of 1772 and 1873, which took place near the area.Combined with previous data on palaeoseismicity in Kola region, our studies indicate a longer lasting and more complex spatial and temporal history of postglacial seismicity in the Northeastern Fennoscandian Shield area. In contrast to the generally accepted opinion, strong seismic events occurred not only during the deglaciation period or immediately after it, but continued until the late Holocene and the last centuries. Glacial isostasy as a factor giving rise to stresses has become minimal by the present time, while the tectonic factor continues to be felt.

New trenching results along the \u0130znik segment of the central strand of the North Anatolian Fault (Turkey): an integration with preexisting data

This paper provides a new contribution to the construction of the complex and fragmentary mosaic of the Late Holocene earthquakes history of the İznik segment of the central strand of the North Anatolian Fault (CNAF) in Turkey. The CNAF clearly displays lower dextral slip rates with respect to the northern strand however, surface rupturing and large damaging earthquakes (M > 7) occurred in the past, leaving clear signatures in the built and natural environments. The association of these historical events to specific earthquake sources (e.g., Gemlik, İznik, or Geyve fault segments) is still a matter of debate. We excavated two trenches across the İznik fault trace near Mustafali, a village about 10 km WSW of İznik where the morphological fault scarp was visible although modified by agricultural activities. Radiocarbon and TL dating on samples collected from the trenches show that the displaced deposits are very recent and span the past 2 millennia at most. Evidence for four surface faulting events was found in the Mustafali trenches. The integration of these results with historical data and previous paleoseismological data yields an updated Late Holocene history of surface-rupturing earthquakes along the İznik Fault in 1855, 740 (715), 362, and 121 CE. Evidence for the large M7 + historical earthquake dated 1419 CE generally attributed to this fault, was not found at any trench site along the İznik fault nor in the subaqueous record. This unfit between paleoseismological, stratigraphic, and historical data highlights one more time the urge for extensive paleoseismological trenching and offshore campaigns because of the high potential to solve the uncertainties on the seismogenic history (age, earthquake location, extent of the rupture and size) of this portion of NAFZ and especially on the attribution of historical earthquakes to the causative fault.

The morphosedimentary record of glacial to postglacial environmental changes in fjord-lake Mékinac and adjacent areas (southeastern Canadian Shield)

Fjords can transition from marine embayments to lacustrine waterbodies under glacio-isostatic change following their deglaciation. However, little is known on how a transition from fjord to lake is influenced by glacial dynamics and how it influences sedimentation in and around the basin. Here, we analyse swath bathymetry imagery and subbottom profiles pri in Lake Mékinac (southern Québec) as well as glacial landforms from LiDAR imagery around the lake to document the evolution of a fjord basin into a lacustrine body during the transition from the Late Pleistocene to the Holocene. These analyses helped refine local glacial history and show that the study area was probably under the up-ice reach of the St. Lawrence Ice Stream during full glacial conditions. The mapping of moraines in and around Lake Mékinac shows that deglaciation of the study area was marked by stabilization of the ice-margin during the Mars-Batiscan Event, which is traditionally correlated to the climate deterioration at the end of the Younger Dryas. The architecture of acoustic facies in the lake indicates a transition from glacial conditions (U1), to proglacial-paraglacial (U2) and to postglacial conditions (U3). The bottom of Lake Mékinac also contains multiple mass movement deposits related to progradation of the Du-Milieu River delta and probably to late-Holocene earthquakes. The acoustic architecture of sediments within the lake indicates that the sedimentation regime was most dependant on the sediment input regime and that the transition from fjord to lake did not significantly influence sedimentation during deglaciation of the watershed. Further work on dating the mass movement deposits that characterise the sediment architecture should provide a better assessment of natural hazard associated with seismological events.

Late Holocene uplift of a coastal terrace near the Akatore Fault, southern New Zealand

ABSTRACT Late Holocene earthquake activity on the reverse Akatore Fault of southeastern South Island has caused uplift along >20 km of nearby coastline, with the last major earthquake event c. 800 years ago. Fault-related uplift has exposed a prominent rocky and sandy terrace along the coastline. We used a combination of approaches including land-based observations, LIDAR remote sensing, and radiocarbon dating of shell deposits, to reveal the extent and nature of past uplift in the region. Cumulative uplift of this terrace varies laterally from <1 m at the northern and southern ends to possibly exceed 5 m in the central portion. The coastal terrace lies below a steep fossil sea cliff. Caves at the base of this cliff contain shells with radiocarbon ages <500 years old, implying persistence of large wave incursion right across the terrace after uplift. A major uplift event of ∼2 m along the whole 20 km of shoreline caused extirpation of some intertidal kelps that now have genetically distinct lineages in the uplift zone.

Active Thrusting in an Intermontane Basin: The Kumysh Fault, Eastern Tian Shan

AbstractFaulting and folding on the margins of intermontane basins play important roles in accommodating the Cenozoic deformation of the Tian Shan, an intracontinental orogen in central Asia. In the eastern Tian Shan, the southern margin of the elongated Kumysh Basin is bounded by a NE dipping thrust fault, the Kumysh Fault. We report the first investigation of the slip rate of this fault, which is constrained at two sites by profiling the faulted topography and dating the abandoned alluvial fan surfaces. We obtained the topographic data using the satellite stereo imagery and dated geomorphic units using cosmogenic nuclide (10Be) exposure ages and optically stimulated luminescence methods. The results from Monte Carlo simulations of the data suggest an average dip‐slip rate of ~0.35 mm/yr on the Kumysh Fault since 50–60 ka. The “best fit” models indicate an increase after ~5 ka, which may be apparent or caused by the most recent earthquakes. Structural analysis of the displaced strata on a trench wall suggest at least 2.8 m dip offset caused by the late Holocene earthquakes, which is similar to the heights of fault scarps (1.8–2.9 m) on the second youngest alluvial fans (5.6–5.2 ka). Using the dip angle of ~25–40°, we estimate ~0.31 mm/yr shortening rate across the Kumysh Fault during the late Quaternary. By comparing our results with other estimates published in the easternmost Tian Shan, we suggest that deformation within intermontane basins may accommodate up to 50% of the total late Quaternary shortening rate between the Junggar and Tarim blocks, with only the remaining half accommodated by the main, range‐bounding thrusts.

Testing quartz and feldspar luminescence dating to determine earthquake and tsunami recurrence in the area of the giant 1960 Chile earthquake

Abstract Coasts on active subduction zones are recurrently affected by great earthquakes and associated tsunamis. Deposits resulting from both tidal inundation after coseismic subsidence and from tsunamis can be radiocarbon dated to infer patterns of earthquake and tsunami recurrence. Yet, finding suitable plant material for radiocarbon dating is not always easy. Luminescence dating provides a more ubiquitously applicable approach, but in such settings remains challenging due to three main reasons: (i) The quartz and feldspar minerals formed on active subduction zones tend to show inadequate luminescence properties; (ii) tsunami deposits may be affected by incomplete resetting of luminescence signals; and (iii) the dosimetry in sequences of tsunami and tidal sand sheets intercalated in marsh soils is often complicated. To evaluate the impact of these factors on luminescence dating accuracy, we re-date previously historically-constrained and radiocarbon dated tsunami and post-earthquake tidal deposits marking some predecessors of the giant 1960 Chile earthquake. While the impact of complex dosimetry on luminescence ages was negligible for both quartz and feldspar, the selection of an appropriate luminescence signal and aliquot size was crucial for generating robust chronologies. Due to unstable luminescence signals, quartz optically stimulated luminescence (OSL) ages and fading corrected infrared-stimulated (IR50) feldspar ages significantly underestimate the control ages. Only post-infrared-infrared (pIRIR150) signals of feldspar provide ages without any systematic age underestimation. Incomplete signal resetting was successfully addressed by using small aliquots in combination with the bootstrapped minimum age model. Remaining remnant ages of a few decades to a few centuries for the historical 1960 and 1575 tsunami sand sheets reflect a combination of laboratory residuals and incomplete signal resetting. Our results show that low-temperature pIRIR dating of feldspar is a valuable tool for reconstructing late Holocene earthquake chronologies in regions where quartz is geologically young, volcanic in origin, and holds few transportation cycles, as it occurs in active subduction zones. Although relatively large residual doses introduce dating uncertainties for sediments younger than a few centuries, feldspar pIRIR dating appears to be a good alternative to radiocarbon dating. On the contrary, quartz OSL and feldspar infrared ages were associated with systematic age underestimation, making them problematic for obtaining adequate chronologies in this type of geologic setting.

A 2000 Yr Paleoearthquake Record along the Conway Segment of the Hope Fault: Implications for Patterns of Earthquake Occurrence in Northern South Island and Southern North Island, New Zealand

Abstract Paleoseismic trenches excavated at two sites reveal ages of late Holocene earthquakes along the Conway segment of the Hope fault, the fastest-slipping fault within the Marlborough fault system in northern South Island, New Zealand. At the Green Burn East (GBE) site, a fault-perpendicular trench exposed gravel colluvial wedges, fissure fills, and upward fault terminations associated with five paleo-surface ruptures. Radiocarbon age constraints indicate that these five earthquakes occurred after 36 B.C.E., with the four most recent surface ruptures occurring during a relatively brief period (550 yr) between about 1290 C.E. and the beginning of the historical earthquake record about 1840 C.E. Additional trenches at the Green Burn West (GBW) site 1.4 km west of GBE reveal four likely coseismically generated landslides that occurred at approximately the same times as the four most recent GBE paleoearthquakes, independently overlapping with age ranges of events GB1, GB2, and GB3 from GBE. Combining age constraints from both trench sites indicates that the most recent event (GB1) occurred between 1731 and 1840 C.E., the penultimate event GB2 occurred between 1657 and 1797 C.E., GB3 occurred between 1495 and 1611 C.E., GB4 occurred between 1290 and 1420 C.E., and GB5 occurred between 36 B.C.E. and 1275 C.E. These new data facilitate comparisons with similar paleoearthquake records from other faults within the Alpine–Hope–Jordan–Kekerengu–Needles–Wairarapa (Al-Hp-JKN-Wr) fault system of throughgoing, fast-slip-rate (≥10 mm/yr) reverse-dextral faults that accommodate a majority of Pacific–Australia relative plate boundary motion. These comparisons indicate that combinations of the faults of the Al-Hp-JKN-Wr system may commonly rupture within relatively brief, ≤100-year-long sequences, but that full “wall-to-wall” rupture sequences involving all faults in the system are rare over the span of our paleoearthquake data. Rather, the data suggest that the Al-Hp-JKN-Wr system may commonly rupture in subsequences that do not involve the entire system, and potentially, at least sometimes, in isolated events.

HOLOCENE FAULTS ACTIVITY IN THE SOUTH-EASTERN PART OF WESTERN SIBERIA AND ITS INFLUENCE ON RELIEF AND STRUCTURE OF ALLUVIAL DEPOSITS

The structure of flood plain alluvial deposits in one of the river valleys in the south-eastern part of Western Siberia represents numerous forms of wave-type and flexural deformations and liquefaction (intralayer folding). The river valley corresponds to fault identified on remote images and extended 150 km in north-eastern direction. These deformations indicate the middle or late Holocene earthquake, which causes local displacements of flood-plain surface.

Holocene paleo-earthquakes recorded at the transfer zone of two major faults: The Pastores and Venta de Bravo faults (Trans-Mexican Volcanic Belt)

We present evidence of five late Holocene earthquake ruptures observed at two paleoseismological trenches in the Laguna Bani sag pond (Trans-Mexican Volcanic Belt, central Mexico). The trenches exposed two fault branches of the western termination of the Pastores fault, one of the major fault systems within the central Trans-Mexican Volcanic Belt. The site was studied by combining geomorphological and structural approaches, volcanic mapping, ground-penetrating radar, and paleoseismological analysis. The study revealed that coseismic surface rupture was noncharacteristic, and that the exposed fault branches had not always moved simultaneously. The fault tip has ruptured at least 5 times within the past 4 k.y., and the rupture events followed and preceded the deposition of an ignimbrite. The close temporal relationship of the seismic rupture with the volcanic activity of the area could be the result of volcanism triggered by faulting and its associated seismicity. The relatively high recurrence of seismic events (1.1–2.6 k.y.) and the noncharacteristic fault behavior observed at this tip of the Pastores fault suggest that the fault might have been active as a primary fault rupturing along segments of variable length or depth, and/or that the fault ruptured eventually as a secondary fault. The secondary ruptures would likely be related to earthquakes produced at major neighboring faults such as the Acambay fault, which moved during the 1912 Acambay earthquake, or the Venta de Bravo fault. A relatively large slip rate estimated for this fault branch (0.23–0.37 mm/yr) leads us to contemplate the possible connection at depth between the Pastores and the Venta de Bravo faults, increasing the maximum expected magnitude for central Mexico.

Straightening of the Northern San Jacinto Fault, California, as Seen in the Fault-Structure Evolution of the San Jacinto Valley Stepover

Abstract We investigate a releasing stepover between the Casa Loma and Claremont strands of the northern San Jacinto fault zone to evaluate the late Quaternary structural evolution of the fault zone, and to assess the likelihood of a rupture jumping across the stepover. Our new cone penetration test (CPT) and trench observations along the Claremont fault at Mystic Lake indicate that the main strand of the Claremont fault has jumped nearly a half kilometer westward into the San Jacinto releasing stepover during the late Quaternary. Multiple faults are inferred from the CPT data within a small sag at the northeast side of the stepover that cuts through younger stratigraphy to the west of the basin‐bounding fault near Mystic Lake. Previous seismic‐reflection data also suggest the presence of a young fault that cuts basin strata beneath the middle of Mystic Lake farther west of our study area. Numerous tectono‐geomorphic features observed in satellite and Light Detection and Ranging Digital Elevation Model (LiDAR DEM) imagery are interpreted to delineate the location of the currently active faults, including a zone of faults that cut across the basin from the northern end of the Casa Loma fault to the Claremont fault. Seismicity observations suggest the presence of many faults within the stepover zone. Finally, new paleoseismic data from the Mystic Lake site suggest that some late Holocene earthquakes may have jumped the stepover. All of these observations suggest that the San Jacinto stepover, which has been used as the primary basis for segmenting the northern San Jacinto fault zone, is being bypassed and that the fault zone may now be capable of larger earthquakes than previously expected.

Repeated Folding during Late Holocene Earthquakes on the La Cal Thrust Fault near Mendoza City (Argentina)

In 1861, one of the most destructive earthquakes in the history of Argentina destroyed the city of Mendoza (currently 1 million inhabitants). The magnitude M S∼7.0 earthquake is inferred to have occurred on the 31‐km‐long La Cal thrust fault, which extends from Mendoza to the north, where it offsets an alluvial fan and small inset terraces along a well‐preserved fault scarp. A trench excavated on a terrace that is vertically offset by ∼2.5 m exposes two main stratigraphic units separated by an erosional unconformity. The coarse‐grained upper unit is deformed by three east‐vergent folds ( F 1– F 3). Retrodeformation of these folds yields total displacements of ∼2.0 m, ∼2.4 m, and ∼0.5 m on the underlying fault splays, respectively. The displacement of ∼2.0 m recorded by fold F 1 is interpreted as the result of the fault rupture that caused the 1861 earthquake. F 2 and F 3 were presumably generated during the penultimate event with an inferred magnitude of M w∼7.0, although formation during two distinct ruptures cannot be excluded. Finite‐element modeling shows that coseismic folding above the tip of a blind thrust fault is a physically plausible mechanism to generate these folds. A published luminescence age of 770±76 years, which is interpreted to date the formation of the deformed terrace, indicates that the two (or possibly three) scarp‐forming events occurred during the last ∼800 years. The fine‐grained sediments below the erosional unconformity—that contain evidence for at least one older earthquake—are dated at ∼12 kyr. Our results indicate that elastic strain energy, which is accumulating at the front of the Precordillera today as shown by Global Positioning System (GPS) data, was repeatedly released during earthquakes on the La Cal fault in the past. Hence, the La Cal thrust fault poses a serious threat to the city of Mendoza.

Holocene tectonics and fault reactivation in the foothills of the north Cascade Mountains, Washington

We use LiDAR imagery to identify two fault scarps on latest Pleistocene glacial outwash deposits along the North Fork Nooksack River in Whatcom County, Washington (United States). Mapping and paleoseismic investigation of these previously unknown scarps provide constraints on the earthquake history and seismic hazard in the northern Puget Lowland. The Kendall scarp lies along the mapped trace of the Boulder Creek fault, a south-dipping Tertiary normal fault, and the Canyon Creek scarp lies in close proximity to the south-dipping Canyon Creek fault and the south-dipping Glacier Extensional fault. Both scarps are south-side-up, opposite the sense of displacement observed on the nearby bedrock faults. Trenches excavated across these scarps exposed folded and faulted late Quaternary glacial outwash, locally dated between ca. 12 and 13 ka, and Holocene buried soils and scarp colluvium. Reverse and oblique faulting of the soils and colluvial deposits indicates at least two late Holocene earthquakes, while folding of the glacial outwash prior to formation of the post-glacial soil suggests an earlier Holocene earthquake. Abrupt changes in bed thickness across faults in the Canyon Creek excavation suggest a lateral component of slip. Sediments in a wetland adjacent to the Kendall scarp record three pond-forming episodes during the Holocene—we infer that surface ruptures on the Boulder Creek fault during past earthquakes temporarily blocked the stream channel and created an ephemeral lake. The Boulder Creek and Canyon Creek faults formed in the early to mid-Tertiary as normal faults and likely lay dormant until reactivated as reverse faults in a new stress regime. The most recent earthquakes—each likely M w > 6.3 and dating to ca. 8050–7250 calendar years B.P. (cal yr B.P.), 3190–2980 cal. yr B.P., and 910–740 cal. yr B.P.—demonstrate that reverse faulting in the northern Puget Lowland poses a hazard to urban areas between Seattle (Washington) and Vancouver, British Columbia (Canada).

Late Holocene earthquake geology in Sweden

Abstract As a function of the rapid rate of glacial isostatic uplift, deglacial palaeoseismicity in Sweden was exceptionally high, in magnitude as well as frequency. Today, seismic activity is low to moderately low with occasional events reaching M 4–5. In the Late Holocene, 11 events in the order of M 6–7 are recorded. These palaeoseismic events seem also to be recorded in several old place names, as in the tale of the Fenris Wolf. Some of the events generated local to regional tsunamis. The palaeoseismic activity recorded in Late Holocene time implies that our short-term seismic hazard assessment must include the possibility of future events in the order of up to M 7. For long-term hazard assessment, repeating glacial/deglacial phases, we must work with magnitudes of M 8 to 9.

Investigation of late Quaternary fault block uplift along the Motagua/Swan Islands fault system: Implications for seismic/tsunami hazard for the Bay of Honduras

Uplifted and warped coastal landforms (fossil coral reef and beachrock, wave-cut and beach terraces) on the western part of Roatan Island off the northern Honduran coast record at least two late Holocene earthquakes that we estimate to have had magnitudes of > M7. Uplift has been primarily related to a fault that follows the southern coast of western Roatan, herein termed the “Flowers Bay fault”, a subsidiary fault of the Motagua/Swan Islands Fault System which marks the boundary between the North American and Caribbean plates. Using electron spin resonance (ESR) and radiocarbon ages of calcium carbonate samples and a late Quaternary sea level elevation curve that is compatible with Caribbean sea level data, we constrain the ages and long-term uplift rates of the displaced landforms on Roatan caused by the vertical component of slip on the Flowers Bay fault. The fossil reef that is uplifted along the fault grew between 43 and 34 ka, and the beachrock horizon and lowest uplifted terrace along the southern and western coasts developed between 1000 and 1700 AD. We describe evidence of one earthquake that raised the south coast ~ 3 m (as much as 5 m locally) and that post-dates 1700 AD. We interpret this event to be the great earthquake of August 1856 that generated a tsunami which ran as much as 24 km onto the mainland. Another earthquake circa 900 AD produced a similar amount of uplift as the 1856 event and likely generated a similar tsunami. The age and elevation of the fossil reef suggest a long-term uplift rate of 3 mm/year, consistent with a recurrence interval of ~ 1000 years for these large earthquakes.

Quantifying subaqueous slope stability during seismic shaking: Lake Lucerne as model for ocean margins

Lakes can be used as model basins to investigate subaqueous slope stability under static and dynamic loading conditions. This study combines geophysical, sedimentological and in situ geotechnical methods with limit equilibrium calculations in order to discuss (i) the geological and sedimentological processes acting on submerged non-deltaic lateral slopes in perialpine, fjord-type Lake Lucerne (Central Switzerland); (ii) their control on physical and geotechnical properties that eventually affect the subaqueous stability conditions and slope failure initiation, and (iii) the quantitative assessment of subaqueous slope stability. Three detailed case studies are presented to describe and quantitatively reconstruct stability conditions of slopes that failed during a well-documented historic earthquake in 1601 A.D. and during a prehistoric Late Holocene earthquake around 2220 cal yr BP (both M w > 6). Glacio-lacustrine sedimentation dominated by suspension settling from meltwater plumes and slight overconsolidation from ice-grounding during small readvances of a generally retreating glacier lead to a peculiar glacial-to-postglacial lithologic slope succession that eventually was buried by the Holocene sediment drape. During past earthquake shaking, the slopes that were stable under static loading conditions (factor of safety of 1.5–2) failed along planar sliding surfaces that developed at the lithological boundary between fine-grained, thinly-laminated, slightly underconsolidated cyclic plume deposits with low undrained shear strength values above and overconsolidated, glacially-deformed, glacio-lacustrine deposits with excessive formation pore pressure below. Measured in situ shear strength characteristics and sediment geometries were implemented into limit equilibrium models that allow for quantitative reconstruction of critical ground accelerations of past earthquakes in Central Switzerland. Results reveal seismic peak ground acceleration (PGA) of ∼ 0.08 g and ∼ 0.14 g for the historic 1601 A.D. M w ∼ 6.2 earthquake and the prehistoric, ∼ 2220 cal yr B.P. earthquake, respectively. Additionally, results reveal that stability conditions change over relative short geological time scales because the postglacial sedimentation rate, which mainly controls the static weight of the slope sediment acting on the critical lithological boundary, turns out to be a key parameter in “charging” slopes susceptible to sliding.

Late Holocene earthquakes in southern Apennine: paleoseismology of the Caggiano fault

Although southern Apennines are characterized by the strongest crustal earthquakes of central-western Mediterranean region, local active tectonics is still poorly known, at least for seismogenic fault-recognition is concerned. Research carried out in the Maddalena Mts. (southeast of Irpinia, the region struck by the Mw=6.9, 1980 earthquake) indicates historical ruptures along a 17-km-long, N120° normal fault system (Caggiano fault). The system is characterized by a bedrock fault scarp carved in carbonate rocks, which continues laterally into a retreating and eroded smoothed scarp, affecting the clayey-siliciclastic units, and by smart scarps and discontinuous free-faces in Holocene cemented slope-debris and in modern alluvial fan deposits. The geometry of the structure in depth has been depicted by means of electrical resistivity tomography, while paleoseismic analysis carried out in three trenches revealed surface-faulting events during the past 7 ky BP (14C age), the latest occurred in the past 2 ky BP (14C age) and, probably, during/after slope-debris deposition related to the little ice age (∼1400–1800 a.d.). Preliminary evaluation accounts for minimum slip rates of 0.3–0.4 mm/year, which is the same order of rates estimated for many active faults along the Apennine chain. Associated earthquakes might be in the order of Mw=6.6, to be compared to the historical events occurred in the area (e.g., 1561 and 1857 p.p. earthquakes).

Late Pleistocene and Holocene Paleoearthquake Activity of the Olinghouse Fault Zone, Nevada

Paleoseismic trenching and fault surface trace mapping indicate that the Olinghouse fault zone, a northeast trending, left-lateral strike-slip fault located in the northern Walker Lane, Nevada, has been the source of multiple latest Pleistocene and Holocene surface-rupturing earthquakes. A trench exposure near the eastern end of the fault records two, and possibly three, earthquakes after 3360 ± 190 cal. yr B.P. and two trenches at the western end of the fault contain evidence for two earthquakes after 19,800 ± 630 cal. yr B.P., with the most recent earthquake occurring after 1935 ± 70 cal. yr B.P. The apparent higher frequency of recent earthquakes at the eastern end of the fault may reflect triggered slip on the Olinghouse fault zone due to earthquakes on the conjugate northwest-trending, right-lateral Pyramid Lake fault. Repeated late Pleistocene and Holocene earthquakes on the Olinghouse fault zone demonstrate that northwest-directed, right-lateral shear of the northern Walker Lane is accommodated in part by northeast-trending left-lateral faults.