Average Recurrence Interval Research Articles

Forecasting excessive rainfall with random forests and a deterministic convection-allowing model

AbstractApproximately seven years of daily initializations from the convection-allowing National Severe Storms Laboratory Weather Research and Forecasting model are used as inputs to train random forest (RF) machine learning models to probabilistically predict instances of excessive rainfall. Unlike other hazards, excessive rainfall does not have an accepted definition, so multiple definitions of excessive rainfall and flash flooding – including flash flood reports and 24-hr average recurrence intervals (ARIs) – are used to explore RF configuration forecast sensitivities. RF forecasts are analogous to operational Weather Prediction Center (WPC) day-1 Excessive Rainfall Outlooks (EROs) and their resolution, reliability, and skill are strongly influenced by rainfall definitions and how inputs are assembled for training. Models trained with 1-y ARI exceedances defined by the Stage-IV (ST4) precipitation analysis perform poorly in the northern Great Plains and southwest U.S., in part due to a high bias in the number of training events in these regions. Increasing the ARI threshold to 2 years or removing ST4 data from training, optimizing forecast skill geographically, and spatially averaging meteorological inputs for training generally results in improved CONUS-wide RF forecast skill. Both EROs and RF forecasts have seasonal skill – poor forecasts in the late fall and winter and skillful forecasts in the summer and early fall. However, the EROs are consistently and significantly better than their RF counterparts, regardless of RF configuration, particularly in the summer months. The results suggest careful consideration should be made when developing ML-based probabilistic precipitation forecasts with convection-allowing model inputs, and further development is necessary to consider these forecast products for operational implementation.

Storm Water Purification in an Urban City of India using a Bio-retention Filter

Bio-retention filtration system is the leading water conservation strategy that makes use of biogeochemical technique within a vegetation ecosystem to retain soil moisture, purify and conserve storm water in urban cities. The present study was aimed at designing a bio-retention filter basin in Kharghar node of Navi Mumbai, Maharashtra, India. The analysis was carried out for both minor (5-year average recurrence interval) and major (100-year average recurrence interval) floods. Total discharge was computed using the rational formula and it was estimated as 0.023 m3/s for minor flood condition and as 0.037 m3/s for major flood condition. The maximum infiltration rate was computed as 0.0047 m3/s considering sandy loam soil as the filter media. A flow width of 1.6 m was considered in designing the bio-retention filter. 100 mm diameter polyvinyl chloride pipe was proposed as they are the best in terms of performance and have advantage over other pipes. No liner is required for filter according to the soil condition of Kharghar. A transition layer of 100 mm gravel was suggested to provide better efficiency and durability for the bio retention system. The vegetation for the bio-retention basin can be Doob or Bermuda grass (Cynodon dactylon) as it has the highest water retention capacity as per Indian conditions.

Do cyclone impacts really matter for the long-term performance of an offshore wind turbine?

With the transition on planning and construction of offshore wind turbine (OWT) from North Europe to other regions like America and East Asia, challenges are proposed for the direct application of international OWT experience to these territories due to disparate natural condition like cyclones. This article is intended to evaluate the impact of cyclone on the long-term performance of an OWT to be installed in cyclone-prone regions. To have a comprehensive consideration on the aero-hydro-structural-soil interaction, an improved decoupled method is proposed and validated for an onshore wind turbine before its application to an OWT. Two cyclone models combined with two wave theories are considered in the fatigue evaluation of an OWT under different working status, and their implications on the final estimation of fatigue damage are compared and discussed. The results obtained from this study indicate that the fatigue life reduction which is caused by cyclone, for an OWT can be conspicuous for a reasonable cyclone strength and average recurrence interval. This implies that potential premature failure of an OWT tower and relevant economic losses can be encountered during its service life if the cyclone contribution to fatigue damage is ignored in the initial conceptual design.

The paleoearthquakes of the Langshan Piedmont fault, North China since late Pleistocene

The Langshan Piedmont fault (LPF) is an active Holocene normal fault that borders Langshan Mountain and the Hetao Graben in the northwest of Ordos Block of China. In this study, paleoseismic trenching was undertaken at three sites and 11 fault outcrops are well exposed. The results show that eight paleoearthquake events occurred on the LPF since 43 ka BP, and six paleoearthquake events are complete since 14 ka BP, the latest event is 2300–2400 a BP; the LPF has the characteristic of quasi-periodic recurrence and the average recurrence interval is 2350 years. Therefore, there is a high probability that the LPF will have another earthquake. The vertical activity rate of the LPF is ~1.12 ​mm/yr since Holocene, and ~0.77 ​mm/yr since 14 ka BP. In this study, it is considered that the LPF is mainly characterized by simultaneous rupture of the whole segment. The vertical displacement of the paleoearthquake events is 0.8–2.5 ​m and the corresponding maximum paleoearthquake magnitude is M 7.4. The seismic hazard of Langshan area should not be ignored. The buildings in Langshan area, especially Wulatehouqi and Qingshan town, should be able to withstand a magnitude 8 earthquake.

Methodology for estimating return intervals for storm demand and dune recession by clustered and non-clustered morphological events

A new methodology is proposed to estimate storm demand and dune recession by clustered and non-clustered events, to determine if the morphological response to storm clusters results in greater beach erosion than that from individual storms that have the same average recurrence interval (ARI) or return period. The method is tested using a numerical morphodynamic model that combines both cross-shore and longshore beach profile evolution processes, forced by a 2D wave transformation model, and is applied as an example within a 20 km long coastal cell at an erosion hotspot at Old Bar, NSW mid-north coast, Australia. Wave and water level data hindcast in previous modelling (Davies et al., 2017) were used to provide two thousand different synthetic wave and tide records of 100 years duration for input to a nested nearshore 2D SWAN model that provides wave conditions at the 12 m depth contour. An open-source shoreline evolution model was used with these wave conditions to model cross-shore and longshore beach profile evolution, and was calibrated and verified against long-term dune recession observations. After a 50 year model spin up, 50 years of storm demand (change in sub-aerial beach volume) and dune toe position were simulated and ranked to form natural estimators for the 50, 25, 16, 12.5 and 10 year return period of individual events, together with confidence limits. The storm demand analysis was then repeated to find the return period of clustered and non-clustered morphological events. Morphological clusters are defined here by considering the response of the beach, rather than the forcing, with a sensitivity analysis of the influence of different recovery thresholds between storms also investigated. The new analysis approach provides storm demand versus return period curves for the combined population of clustered and non-clustered events, as well as a curve for the total population of individual events. In this approach, non-clustered events can be interpreted as the response to isolated storms. For clustered and non-clustered morphological events the expected storm demand for a 50-year return period is approximately 25% greater than that for individual events. Alternatively, for clustered and non-clustered events the magnitude of the storm demand that occurs at a return period of 17 years is the same as that which occurs at a return period of 50 years for individual events. However, further analysis shows that for a 50-year return period, the expected storm demand for the population of non-clustered events is similar to that of the clustered events, although the size of the population of the latter is much greater. Hence, isolated storms can generate the same storm demand as storm clusters, but there is a much higher probability that a given storm demand is generated by a morphologically clustered event.

Prehistoric earthquakes on the Banning strand of the San Andreas fault, North Palm Springs, California

AbstractWe studied a paleoseismic trench excavated in 2017 across the Banning strand of the San Andreas fault and herein provide the first detailed record of ground-breaking earthquakes on this important fault in Southern California. The trench exposed an ~40-m-wide fault zone cutting through alluvial sand, gravel, silt, and clay deposits. We evaluated the paleoseismic record using a new metric that combines event indicator quality and stratigraphic uncertainty. The most recent paleoearthquake occurred between 950 and 730 calibrated years B.P. (cal yr B.P.), potentially contemporaneous with the last rupture of the San Gorgonio Pass fault zone. We interpret five surface-rupturing earthquakes since 3.3–2.5 ka and eight earthquakes since 7.1–5.7 ka. It is possible that additional events have occurred but were not recognized, especially in the deeper (older) section of the stratigraphy, which was not fully exposed across the fault zone. We calculated an average recurrence interval of 380–640 yr based on four complete earthquake cycles between earthquakes 1 and 5. The average recurrence interval is thus slightly less than the elapsed time since the most recent event on the Banning strand. The average recurrence interval on the Banning strand is thus intermediate between longer intervals published for the San Gorgonio Pass fault zone (~1600 yr) and shorter intervals on both the Mission Creek strand of the San Andreas fault (~215 yr) and the Coachella section (~125 yr) of the San Andreas fault.

Probabilistic modelling of multi-phase eruptions found in geological records: An example from Mt. Ruapehu, New Zealand

More than half of explosive volcanic eruptions contain multiple eruption phases with eruption dynamics (i.e., style, intensity, magnitude) varying with eruption progression. While probabilistic eruption forecast models constitute a useful tool for decision making during volcanic crises, the probabilistic forecast of likelihood, style and magnitude of potentially upcoming phase(s) within a multi-phase eruption progression remains a major challenge. Probabilistic eruption forecast models are crucially dependent on the quality of the underlying eruption records and their ability to account for inter-sequence and intra-sequence changes in eruption behaviour. Recent studies examining multi-phase eruption progression have been limited by the amount of historical data available, motivating the investigation into the feasibility of identifying and quantifying multi-phase eruption behaviour in the geological record. Mt. Ruapehu is one of New Zealand's most active volcanoes and its 1800 years-present Tufa Trig Formation comprises at least thirty-one small to moderate explosive eruptions, of which more than half contain more than one phase. An interpolated age model for the past 1800 years is presented and used to model inter-sequence eruption onsets. Four volcanic regimes, distinguished by eruption frequency and magnitude can be identified: (1) A low rate regime with an average of one eruption every 125 years, involving mostly single-phase low to mid-intensity eruptions, (2) two medium rate regimes with a 40 year average recurrence interval and (3) a high frequency regime characterised by decadal-scale reposes, and including the largest multi-phase eruptions of the past 1800 years. Tephra volume estimates are combined with a statistical model for the number of phases to characterise the intra-sequence progression. Eruption progression is consistent with existing multi-phase models developed on historical data, and suggests that tephra volume increases in later phases of an eruption.

Evaluation of different parameter estimation techniques in extreme bushfire modelling for Victoria, Australia

Generalised Extreme Value (GEV) distribution can be used effectually to model extreme climatic events like bushfire. The major predicament of using GEV distribution is accurate determination of three parameters (location, scale, and shape); nevertheless, there are no specific guidelines to identify the most apposite parameter estimation technique of the GEV distribution for bushfire studies. In this study, influence of different GEV parameters estimation techniques were investigated in Victoria, Australia for extreme bushfire event modelling, using annual maximum forest fire danger index (FFDI), which is a combination of manifold climatic and fuel variables to indicate the potential for bushfires to propagate, and withstand suppression. Four GEV parameters estimation methods namely: Maximum Likelihood Estimation (MLE), Generalised Maximum Likelihood Estimation (GMLE), Bayesian and L-moments were used for two different timescale data (full data set and last 10 years of full dataset) to estimate the GEV distribution parameters. The return levels of FFDI for different Average Recurrence Interval (ARI) were estimated using the above mentioned four methods and two timescales. The study demonstrates that Fréchet (type II) extreme value distribution is pertinent for modelling the annual maximum FFDI for most of the selected stations; nonetheless, GEV distribution parameters can vary considerably due to variation in the length of the data series. Several applied statistical parameters namely: Mean square error (MSE) and Mean absolute error (MAE) were used to identify the most pertinent parameter estimation technique of the GEV distribution. The study reveals that L-moments can be used, even in the presence of the smaller data set. In addition, L-moments is the most appropriate parameters estimation technique of GEV distribution because of the presence of the lowest MSE and MAE values for most of the stations. The outcomes of this research are pivotal for Victorian public and private stakeholders to forecast the severity and intensity of imminent bushfire events due to recent bushfire events in fire prone areas.

Kinematics of the exceptionally-short surge cycles of Sít’ Kusá (Turner Glacier), Alaska, from 1983 to 2013

AbstractGlacier surges are periodic episodes of mass redistribution characterized by dramatic increases in ice flow velocity and, sometimes, terminus advance. We use optical satellite imagery to document five previously unexamined surge events of Sít’ Kusá (Turner Glacier) in the St. Elias Mountains of Alaska from 1983 to 2013. Surge events had an average recurrence interval of ~5 years, making it the shortest known regular recurrence interval in the world. Surge events appear to initiate in the winter, with speeds reaching up to ~25 m d−1. The surges propagate down-glacier over ~2 years, resulting in maximum thinning of ~100 m in the reservoir zone and comparable thickening at the terminus. Collectively, the rapid recurrence interval, winter initiation and down-glacier propagation suggest Sít’ Kusá's surges are driven by periodic changes in subglacial hydrology and glacier sliding. Elevation change observations from the northern tributary show a kinematic disconnect above and below an icefall located 23 km from the terminus. We suggest the kinematic disconnect inhibits drawdown from the accumulation zone above the icefall, which leads to a steady flux of ice into the reservoir zone, and contributes to the glacier's exceptionally short recurrence interval.

Dating and interpretation of recent clastic sediments in an urban cave

Capshaw Cave functions as a major stormwater runoff channel for the city of Cookeville, Tennessee, receiving inputs from several large sinkholes. Sediments deposited in the cave reflect the history of erosion and runoff from the city as it grew over the last century. At various locations in the cave, ~1 m thick sequences of flood-deposited, laminated fine sediments were observed along the modern stream. Alternating laminations observed in the upper ~40 cm of the sediment profile varied between 0.5 cm thick (10Y 7/6 yellow, fine sand) and 2.0 cm thick (10Y 3/2 very dark grayish brown silty sand) layers. Based on measurements of 137Cs activity, the upper 35 cm of sediment was deposited between 1963 (the peak year of 137Cs fallout from nuclear testing) and 2013 (the year samples were collected), at an average rate of 0.7 cm/y. A total of 23 alternating pairs of layers indicate an average flood recurrence interval of ~2.2 years between 1963 and 2013. Total Pb concentrations measured in cave sediments showed a peak at the 45 cm depth, suggesting that sediments above this level were deposited after the decline in Pb emissions in the 1970s, and showing general agreement with the timing of deposition suggested by 137Cs. Below 40 cm, the dark silty sand layers were fewer in number and increased in thickness (up to 10 cm), possibly due to changes in cave hydrology or sediment erosion from the surrounding watershed. These findings suggest that, before the 1960s, sedimentation rates were higher and floods were less frequent. After the 1960s, sedimentation rates decreased and floods became more common, probably as a result of urbanization in the watershed.

Assessing the Effectiveness of Mitigation Strategies for Flood Risk Reduction in the Segamat River Basin, Malaysia

Flooding is a frequent, naturally recurring phenomenon worldwide that can become disastrous if not addressed accordingly. This paper aims to evaluate the impacts of land use change and climate change on flooding in the Segamat River Basin, Johor, Malaysia, with 1D–2D hydrodynamic river modeling, using InfoWorks Integrated Catchment Modeling (ICM). The study involved the development of flood maps for four different scenarios: (1) future land use in 2030; (2) the impacts of climate change; (3) three mitigation strategies comprising detention ponds, rainwater harvesting systems (RWHSs), and permeable pavers; and (4) a combination of these three mitigation strategies. The obtained results show increases in the flood peaks under both the land use change and climate change scenarios. With the anticipated increase in development activities within the vicinity up to 2030, the overall impact of urbanization on the extent of flooding would be rather moderate, as the upper and middle parts of the basin would still be dominated by forests and agricultural activities (approximately 81.13%). In contrast, the potential flood-inundated area is expected to increase from 12.25% to 16.64% under storms of 10-, 50-, 100-, and 1000-year average recurrence intervals (ARI). Interestingly, the simulation results suggest that only the detention pond mitigation strategy has a considerable impact on reducing floods, while the other two mitigation strategies have less flood reduction advantages for this agricultural-based rural basin located in a tropical region.

A Historical Earthquake-Induced Landslide Damming Event at the Qiaojia Reach of the Jinsha River, SE Tibetan Plateau: Implication for the Seismic Hazard of the Xiaojiang Fault

In bedrock mountainous areas where active faults and deep river valleys interact, earthquake-induced landslides can be used to explore local seismic hazards. The intersection of the highly active Xiaojiang Fault and the Jinsha River and its main tributaries in southwest China is a site of abundant earthquake-induced landslides. We found some boulders inappropriately scattered on the east bank of the Qiaojia reach of the Jinsha River, where the Qiaojia Segment of the Xiaojiang Fault passes through. We investigated the lithology and topography nearby and confirmed its source area, as well as the existence of a landslide damming event in the field. A high-resolution Digital Surface Model (DSM) generated from Unmanned Aerial Vehicle (UAV) images was used to analyze its characteristics and calculate its parameters. Optically Stimulated Luminescence (OSL) and 14C dating methods on the related dammed lake sand shows the age of the landslide, which is not later than 878 AD. The characteristics of large size with limited depositional extent, spatial relevance between the landslide and Xiaojiang Fault, and temporal-coincidence of the landslide with 624 AD earthquake support the seismic origin of this landslide. Moreover, the 624 AD earthquake was reanalyzed for its magnitude and macro-epicenter based on the coseismic displacement of the Heishui River floodplain. It was calculated to be Mw7.7 or Ms7.9 and relocated to the Qiaojia area. No M ≥ 7 earthquakes have occurred on the Qiaojia Segment for nearly 1,400 years since 624 AD. The elapsed time is close to the average recurrence interval of large earthquakes on the Qiaojia Segment. Therefore, the seismic hazard of the Qiaojia area should be considered in the future.

Assessment of tropical cyclone wave models for engineering applications

Tropical Cyclone (TC) wind and wave models are used to quantify meteorological and oceanographic conditions in the application of offshore engineering design criteria. In regions such as the North West Shelf of Australia, a statistically sound 'risk of failure' design assessment can require historical records far longer than are typically available, even with meteorological datasets of several decades length. To address this mismatch between design requirements and observational history, synthetic tropical cyclone wind and wave datasets can be developed to mimic long records with the objective of estimating extreme event average recurrence intervals of 10,000 years. Modelling large numbers of TC storms in practice requires a trade-off between time (computational efficiency) and accuracy (model skill). The development of the synthetic dataset in this study draws the balance by combining computationally efficient parametric models, and computationally intensive fully dynamic models, with different model grid resolutions. This paper outlines performance differences between the various model approaches and make recommendations for engineering.

Paleoseismologic trenching confirms recent Holocene activity of the major Algeciras fault system in southern Colombia

The Algeciras Fault System (AFS) in Colombia, which is characterized by its predominant dextral strike-slip movement, is part of the major transcurrent fault system known in Ecuador, Colombia and Venezuela as the Eastern Frontal Fault System, that disconnects the North Andean Block (NAB) from the South American plate in a process of tectonic escape. It is responsible for some of the most important seismic events in the seismic history of Colombia that occurred in 1827 with Mw 7.1 that destroyed large part of all settlements in the Huila Department and caused considerable damage and loss of life in the capital of Bogota. More recently another event of Mw 7.0 took place in 1967 that also caused damage in the capital, and in December 2019 an event of Mw 6.0 caused minor damage in various settlements in the Eastern foothills of the Eastern Cordillera. So far, mapping studies based on data obtained from satellite imagery, airphotos and structural field data have outlined the complexity of the AFS and have identified the existence of at least six tectonic basins occurring along the main fault of the system. In 2016, within the framework of activities of the Space Geodesy Research Group of the Geohazards Directorate of the Geological Survey of Colombia (SGC) a program of morphotectonic field studies was carried out in and around the Algeciras pull-apart basin in the Huila Department that led to the opening of two exploratory paleoseismologic trenches. This paper presents the results of the first of these two trenches, located in the center of the Algeciras valley at a place named Lagunillas. It is situated at the rim of a shallow fault-dammed lake formed by an uphill facing scarp generated by the dextral strike-slip displacement of a shortcut fault that traverses the alluvial fill of the basin along its longitudinal axis. The results of the paleoseismologic study prove the occurrence of seven seismic events with magnitudes Mw 7.0 during the Holocene with an average recurrence interval of 1300–1400 years. This constitutes a significant contribution to the study of seismic hazard assessment of the AFS that complements, in a quantitative way, the evidence provided by the data of historic seismicity of this major fault and points out the considerable danger that the fault presents to the country as a whole and in particular to the metropolitan area of Bogota.

Holocene paleoeseismology of the Fodongmiao-Hongyazi Fault along the Northern Tibetan margin (Western China) and implication to intraplate earthquake rupturing pattern

The margins of the Tibetan Plateau are the most recent evolving part of the orogen, where distributed fault systems accumulate intraplate crustal deformation induced by the Indo-Asian collision, and many great earthquakes occur. Understanding the paleoearthquake history of the faults along the Tibetan margins will increase our knowledge of the process of outward growth of the Tibetan Plateau, seismic hazard assessments, and intraplate earthquake patterns. However, until now, few paleoseismic studies were conducted along the northern Tibetan margin, which hampers our understanding of fault activity and seismic hazards posed to the densely populated cities in the region. In this study, we excavated paleoseismic trenches across the Fodongmiao-Hongyazi fault (FHF) along the northern Tibetan margin. Five Holocene events were documented from five trenches based on OSL and radiocarbon-14 dating of trench horizons and careful analysis of stratigraphy and fault structures. These events are FE5 (9.6–7.7 ka), FE4 (7.6–7.0 ka), FE3 (4.4–3.5 ka), FE2 (3.2–1.8 ka), and the 1609 M 71/4 Hongyapu earthquake. The average recurrence interval of the five events is ~2.0 ka. Additionally, combined with morphotectonic features and trench observations, the 1609 Hongyapu earthquake most likely caused the whole fault to rupture with a length of ~95 km. Its moment magnitude was estimated to be 7.2 ± 0.2 based on empirical statistical relationships between the magnitude, surface rupture length, and coseismic offset.

Latest Quaternary Active Faulting and Paleoearthquakes on the Southern Segment of the Xiaojiang Fault Zone, SE Tibetan Plateau

AbstractThe Xiaojiang fault zone (XJFZ) is an important part of the Xianshuihe-Xiaojiang fault system, acting as the eastern boundary of the Chuan-Dian block on the southeastern margin of the Tibetan Plateau and accommodating the lateral extrusion of the block. The faulting activity and paleoseismic history on the southern segment of the XJFZ remain poorly understood. Here, trench excavations and radiocarbon dating revealed that four recent surface-rupturing paleoearthquakes have occurred on the Jianshui fault (JSF) in the southern segment of the XJFZ since ~15370 yr BP. The ages of these events, labeled E4-E1 from oldest to youngest, are limited to the following time ranges: 15360-12755, 10845-6900, 1455-670, and 635-145 yr BP, respectively. The most recent event E1 was most likely the 1606 Jianshui earthquake. These events appear to occur unregularly in time. The time interval between the last two events is 726±235 yr, and the average recurrence interval for all four events is 4589±3132 yr. The deformed strata show that the JSF is characterized kinematically by transtension, which likely respond to the apparent change in the direction of clockwise rotation of the Chuan-Dian block around the eastern Himalayan syntaxis. Combined with the analysis of the neighboring NW-striking faults, our study suggests that the south-southeastward motion of the Chuan-Dian block is likely to be firstly accommodated in part by the right-lateral shear and dip-slip motions of the Qujiang and Shiping faults and continues across the Red River fault zone, then is transmitted southward along the Dien Bien Phu fault. Therefore, the southern segment of the XJFZ plays a dominant role in the tectonic deformation of the southeastern Chuan-Dian block, with a high seismic hazard.

Detailed paleoseismic history of the Hinagu fault zone revealed by the high‐density radiocarbon dating and trenching survey across a surface rupture of the 2016 Kumamoto earthquake, Kyushu, Japan

AbstractThe NE‐trending Hinagu fault zone, length 81 km, is one of the major active faults in Kyushu, Japan. From north to south, it is divided into three segments based on geomorphic features and paleoseismic behavior: the Takano‐Shirahata, Hinagu, and Yatsushiro Sea segments. The 2016 Kumamoto earthquake produced a 6‐km‐long surface rupture with a dextral strike‐slip displacement on the northern part of the Takano‐Shirahata segment. Surface rupture, a faint east‐side‐up flexure with a vertical offset of less than 8 cm, was observed near the middle of the Takano‐Shirahata segment. To examine past surface‐rupturing earthquakes on the Takano‐Shirahata segment, including rupture frequency and timing, we conducted a paleoseismic study with boring and trenching at Yamaide. A trench across the surface rupture exposed multiple fault strands associated with multiple surface‐rupturing events that deformed several strata of fine‐grained sediments. By structural and stratigraphic interpretation, high‐density radiocarbon dating and tephra analysis, and Bayesian modeling, we constrained the timing of seven events, Events 1–7, to 0.84–1.25, 1.31–7.06, 9.99–11.0, 10.8–12.1, 12.0–13.0, 14.2–15.1, and before 14.8 kcal BP. Slip during Events 1–6 was obviously larger than the 2016 slip. The estimated average recurrence interval was about 2596–2860 years, but the interval between Events 2 and 3 was much longer than other intervals. Moreover, the vertical throw associated with Event 2 was larger than that of other events. This implies that the Takano‐Shirahata segment has a period with rare larger earthquakes and a period with frequent smaller earthquakes. Some events might have produced ruptures on both the Takano‐Shirahata and the northern part of the Hinagu segments simultaneously or in a short time. The variety of recurrence intervals suggests that the seismic activity has been affected by one or both activities of the Futagawa fault zone and the Hinagu segment.

A 2600-year-long paleoseismic record for the Himalayan Main Frontal Thrust (western Bhutan)

Abstract. In spite of an increasing number of paleoseismic studies carried out over the last decade along the Himalayan Arc, the chronology of historical and prehistorical earthquakes is still poorly constrained. In this paper, we present geomorphologic and paleoseismic studies conducted over a large river-cut exposure along the Main Fontal Thrust in southwestern Bhutan. The Piping site reveals a 30 m high fault-propagation fold deforming late Holocene alluvial deposits. There, we carried out detailed paleoseismic investigations and built a chronological framework on the basis of 22 detrital charcoal samples submitted to radiocarbon dating. Our analysis reveals the occurrence of at least five large and great earthquakes between 485±125 BCE and 1714 CE with an average recurrence interval of 550±211 years. Coseismic slip values for most events reach at least 12 m and suggest associated magnitudes are in the range of Mw 8.5–9. The cumulative deformation yields an average slip rate of 24.9±10.4 mm yr−1 along the Main Frontal Thrust over the last 2600 years, in agreement with geodetic and geomorphological results obtained nearby.

Impacts of climate change on streamflow and floodplain inundation in a coastal subtropical catchment

Climate change is expected to significantly alter river hydrological regimes throughout the world, affecting water resources and the frequency of floods and droughts. The objectives of this study were to determine the impacts of climate change and sea level rise on streamflow and floodplain inundation in the subtropical Logan-Albert catchment, Australia. An ensemble of 11 high-resolution climate models forced under high (Representative Concentration Pathway 8.5 - RCP8.5) and intermediate-emission (RCP4.5) scenarios was applied. There was considerable variation from the model ensemble result in projections of major flooding events at 5 and 100-year average recurrence intervals (ARIs). The largest events (100-year ARI) tended towards an increase, whereas the smallest (5-year ARI) tended towards a decrease. Floodplain inundation from a 100-year ARI event increased in all simulations and inclusion of sea level rise resulted in increased floodplain inundation area nearly doubling by the end of the century, which has substantial implications for flood risk. Our study highlights the non-linear nature of climate change impacts on streamflow and floodplain inundation, demonstrating the need for a comprehensive assessment at the floodplain scale when informing preparedness for future flooding events.

Displacement Accumulation and Sampling of Paleoearthquakes on Active Normal Faults of Crete in the Eastern Mediterranean

AbstractActive normal faults on the Mediterranean island of Crete form prominent limestone scarps together with basin and range topography. These faults mainly strike E‐ESE and N‐NNE in southern and northern Crete, respectively, with fault sets commonly intersecting and northerly trending faults being a factor of 3 more abundant. Lengths, displacements, and displacement rates have been analyzed for 84 active faults sampled over 2 ± 0.5 Ma (long‐term) and 16.5 ± 2 ka (short‐term) time‐intervals, with half showing no resolvable short‐term activity. Active faults record earthquake processes on timescales of thousands to million years and constrain sampling biases, which can lead to under and over estimates of fault parameters. The available data provide no evidence for fault propagation and support a model in which fault lengths were established early in the development of the fault system. Short‐term displacement rates (0.09–1.2 mm/year) are generally higher than long‐term rates (0.002–0.7 mm/year), with a factor of 4 disparity in the average recurrence intervals for the two time periods (∼2.5 Kyr vs. ∼11 Kyr). We attribute these differences to “clustering” of surface‐rupturing (e.g., >Mw6) earthquakes on individual faults over millennial timescales, and to preferential sampling of the most seismically active faults during the short‐term. Displacement rates are comparable when averaged for each time interval on the longest faults (>10 km), indicating that for these faults earthquake “clustering” spans time‐intervals of <∼16.5 Kyr. Paleoerthquakes > Mw6 on Crete are at least three times more frequent than historical earthquakes since ∼1920, possibly because multi‐fault surface‐rupturing earthquakes are double counted in the paleo‐record.