Average Recurrence Interval Research Articles

Mapping TRMM TMPA into Average Recurrence Interval for Monitoring Extreme Precipitation Events

AbstractA prototype online extreme precipitation monitoring system is developed from the TRMM TMPA near-real-time precipitation product. The system utilizes estimated equivalent average recurrence interval (ARI) for up-to-date precipitation accumulations from the past 1, 2, 3, 5, 7, and 10 days to locate locally severe events. The mapping of precipitation accumulations into ARI is based on local statistics fitted into generalized extreme value (GEV) distribution functions. Initial evaluation shows that the system captures historic extreme precipitation events quite well. The system provides additional rarity information for ongoing precipitation events based on local climatology that could be used by the general public and decision makers for various hazard management applications. Limitations of the TRMM ARI due to short record length and data accuracy are assessed through comparison with long-term high-resolution gauge-based rainfall datasets from the NOAA Climate Prediction Center and the Asian Precipitation–Highly-Resolved Observational Data Integration Toward Evaluation of Water Resources (APHRODITE) project. TMPA-based extreme climatology captures extreme distribution patterns from gauge data, but a strong tendency to overestimate from TMPA over regimes of complex orography exists.

Paleoseismic study on active normal faults in the southeastern Weihe Graben, central China

Field investigations and trench excavations can provide direct and indirect geological evidence for the occurrence of paleo-earthquakes. In this study, we present geological and topographical evidence for the occurrence of great paleo-earthquakes produced by active normal faults in the southeastern Weihe Graben, central China. Field and trench observations, in combination with radiocarbon ages, reveal that: (i) four surface-faulting events occurred in the past 4000years with an average recurrence interval of ∼1000years, which is in contrast with the previously estimated interval of ∼2000–2900years; (ii) the most recent fault event is correlated to the 1556 M∼8.5 Huaxian earthquake; (iii) an alluvial terrace riser that formed at ∼5300yr B.P. has been vertically offset by 9–11m, indicating an average vertical slip rate of 1.7–2.1mm/yr in the late Holocene. Our results confirm that normal faults in the southeastern Weihe Graben have been active in the late Holocene as source seismogenic faults, and that these faults have the potential to trigger large earthquakes of M>7 in the future. Therefore, it is important to urgently reevaluate the seismic potential and seismic hazard in the densely populated Weihe Graben region.

Late Pleistocene–Holocene paleoseismology of the Batang fault (central Tibet plateau, China)

The Yushu segment of the Ganzi–Yushu fault system (central Tibet plateau) is mainly composed by the Yushu fault and the Batang fault. The 2010 Ms 7.1 Yushu earthquake occurred on the Yushu fault, causing huge loss of lives and widespread damages to the densely populated Yushu area. So far, much effort has been devoted to the surface rupture and paleoseismology of the Yushu fault, while the late Quaternary activity of the Batang fault has not received much attention. The Batang fault has a clear geomorphic expression with fault scarps, sag ponds, push-ups, systematic offset of fluvial terraces, and alluvial fans along its trace. Integrated methods of geomorphological mapping, outcrop analysis, trench excavation and logging, optically stimulated luminescence (OSL), and radiocarbon (14C) dating are employed to study the latest Pleistocene and Holocene paleoseismology of the Batang fault. Several paleoearthquakes are identified from geomorphic and stratigraphic evidence between 22ka and after 2.7ka. The oldest event (E1) occurred after 22kaBP, E2 prior to 14kaBP, E3 within 14 and 9.5kaBP, E4 within 8.0–7.8kaBP, E5 prior to 6.7kaBP, the penultimate event (E6) occurred within 4.3–4.0kaBP, and the most recent event (E7) occurred after 2.7kaBP. The average recurrence interval of paleoearthquakes for the Batang fault is about 2000a in the last ~8kaBP, and the relapse time of the latest paleoearthquake is <2.7ka. Co-seismic displacement of the most recent surface-rupturing event is about 3m, as deduced from the offsets of the youngest terrace risers and of small gullies. Empirical equations between co-seismic displacement and earthquake magnitude reveal that the average magnitude of these events is about 7.3. This study contributes important information for the seismic hazard assessment of the densely populated Yushu area.

Coseismic Displacement and Recurrence Interval of the 1973 Ragay Gulf Earthquake, Southern Luzon, Philippines

The 1973 Ragay Gulf earthquake produced an onshore surface rupture approximately 30 km in length along the Guinayangan segment of the Philippine fault in southern Luzon Island. Through geologic mapping and paleoseismic trenching, we have characterized the amount of coseismic offsets, the average recurrence interval, and the slip rate of the segment. The coseismic offsets we identified in the field were fairly constant along the fault, ranging from 1 to 2 m. Paleoseismic trenching at the Capuluan Tulon site exposed stratigraphic evidence for three or possibly four surfacerupturing events after the deposition of strata dated at AD 410–535. The average recurrence interval was calculated to be 360–780 years, which is close to that for the Digdig fault, the source fault of the 1990 central Luzon earthquake. The slip rate, based on the calculated recurrence interval and offsets during the 1973 earthquake, has been calculated to be 2.1–4.4 mm/yr. This rate is significantly smaller than the geodetic slip and creep rates of 20–25 mm/yr estimated for the Philippine fault on the islands of Masbate and Leyte. The slip rate deficit may be explained by the possibilities of underestimation of the recurrence interval due to possible missing paleoseismic events within the stratigraphic records, the occurrence of larger earthquakes in the past, and the aseismic fault creep between the surface-rupturing earthquakes.

Single lot on site detention requirements in New South Wales Australia and its relation to holistic storm water management

Abstract Storm water run-off from urban developments need to be controlled to minimize its impacts on the quality and hydrodynamics of receiving waters. Holistic management strategies and treatment at the source have been introduced in Australia to mitigate the effects of run-off from urban developments on waterways. The adoption of conventional storm water quality and quantity controls and Water Sensitive Urban Design (WSUD) principles by councils, developers, industry and catchment managers assist in mitigating this impact. Pending on local council requirements, lot scale (re)development may include a combination of a rainwater tank, an On Site Detention (OSD) system and possibly an infiltration or bio-retention system, with overflows discharging to the existing drainage systems. It is argued in this paper that designing these systems independently may result in over-design, increasing development costs. This paper considers the effect of rainwater tanks on water quantity discharges on a lot scale, and how this can affect the design of OSD systems. This major research study, conducted in Western Sydney, indicated that where planning development controls require that storm water management be implemented to ensure run-off flow rates do not increase as a result of the development, a reduction can be applied to the OSD design, if a rainwater tank is installed on the same site as the OSD and is connected to multiple end-uses. This combination of systems can contain up to the 1-year Average Recurrence Interval (ARI) runoff in the rainwater tanks, thereby significantly reducing the OSD volume and orifice size.

Abrupt change in runoff on the north slope of the Catskill Mountains, NY, USA: Above average discharge in the last two decades

Abstract Study region Schoharie Creek, Catskills Mountains, New York, USA. Study focus Total annual flow in Schoharie Creek, Catskills Mountains, was above the long-term average for most of the last two decades. We hypothesize that the end of the 20th century and early 21st century mark a change in the streamflow in the Schoharie watershed. To test this, we evaluated annual flow, center-volume (CV) and winter–spring center-volume (WSCV) dates, and average daily flow within four comparison periods purposefully selected to represent: average conditions, below average, above average and recent conditions Recurrence intervals of the 2-yr, 5-yr, and 10-yr daily maximum flow calculated for the comparison periods suggested that these event magnitudes were larger during the last decade. New hydrological insights for the region The increase in high-frequency event magnitude was most pronounced at the 5-yr daily maximum flow in the lower Schoharie. During the last decade the 5-yr event magnitude exceeded the record-long 10-yr daily maximum flow magnitude. Changes to peak daily flow implies more flow in the lower Schoharie more frequently. Seasonal differences drive above average winter runoff, shortened peak runoff in spring and in several cases below average summer and late summer flow. This flow pattern is not just a matter of more water all the time, but more water during the high-flow period and less water during the low-flow period, intensifying annual extremes.

A 21-Event, 4,000-Year History of Surface Ruptures in the Anza Seismic Gap, San Jacinto Fault, and Implications for Long-term Earthquake Production on a Major Plate Boundary Fault

Paleoseismic work completed at Hog Lake on the San Jacinto Fault (SJF) near Anza, California, indicates that at least 21 surface ruptures have occurred in the Anza Seismic gap over the past 4,000 years. The ages of the ruptures are constrained by 111 radiocarbon dates, 97 of which fall in stratigraphic order. The average recurrence interval for all ruptures for this period is about 185 ± 105 years, although some ruptures, such as occurred in the April 1918 earthquake, caused only minor displacement. We rate the expression of each interpreted event in each of the twelve developed field exposures presented in this work by assigning numeric values for the presence of different criteria that indicate rupture to a paleo-ground surface. Weakly expressed ruptures, for example the deformation we interpret to be the result of the historical 1918 earthquake, received low scores and are interpreted as smaller earthquakes. From this analysis, we infer that at least fifteen of the identified ruptures are indicative of large earthquakes similar to the penultimate earthquake, inferred to be the M w 7.3 22 November 1800 earthquake. The adjusted recurrence interval for large earthquakes lengthens to approximately 254 years. Comparison with the rupture history at the Mystic Lake paleoseismic site on the Claremont strand indicates that it is plausible that several of the large ruptures identified at Hog Lake could have jumped the Hemet step-over at Mystic Lake and continued on the Claremont strand (or vice versa), but most of the event ages do not match between the two sites, indicating that most ruptures do not jump the step. Finally, comparison with San Andreas Fault ruptures both to the north and south of its juncture with the SJF suggest that some northern SJF ruptures identified at Mystic Lake may correlate with events identified at Wrightwood, but that these northern ruptures have no match at Hog Lake and can not indicate rupture of the entire SJF onto the SAF.

Determining change points in data completeness for the Holocene eruption record

Changes in data completeness for the Smithsonian Institution’s “Volcanoes of the World” (VOTW) eruption catalogue, by region and for selected countries, are determined and utilised to estimate average eruption recurrence intervals. In the VOTW database, the number of documented volcanic eruptions has increased markedly since the middle of the last millennium. This is largely attributed to population expansion, geological investigation and improvements in detection and recording technologies, rather than an increase in volcanic activity. Simple methods, such as break-in-slope or stationarity tests, can be used to determine changes in data completeness, but often require subjective choices, introducing additional uncertainty. A Markov chain Monte Carlo simulation method for assessing and determining changes in the completeness of natural hazard event catalogues is adapted to determine the completeness of the database. Data completeness is assumed to follow a step-change model, where the probability of documenting an eruption is Volcanic Explosivity Index-dependent before the change point date and 100 % after. A distribution of candidate change point dates is obtained for each region and country subset which allows uncertainty in the data completeness date to be quantified, and for uncertainty in eruption frequencies to be expressed and propagated through statistical models.

Modern depositional processes in a confined, flood-prone setting: Benches on the Shoalhaven River, NSW, Australia

Past research has suggested that in-channel alluvial landforms, often termed benches, are associated with flow events with specific return periods and that such landforms are inset within terraces, floodplains, or higher bench surfaces. Chronostratigraphic analysis and hydraulic modelling in a bedrock-confined reach of the lower Shoalhaven River show that they have been extensively eroded and at least partially reformed during the historical period. Lower benches are inundated by flood events with average recurrence intervals (ARI) of 2 or less years, middle benches by events ca. 5years ARI, and upper benches by events ca. 10years ARI. The lower benches commonly share over- or onlapping stratigraphic units, demonstrating that deposition can occur on multiple bench surfaces simultaneously. This is in contrast to earlier suggestions of discrete bench surfaces being associated with, and formed by, events that have a specific return period. In the Shoalhaven River, Pleistocene and Holocene terraces determine the large alluvial channel geometry for a wide range of discharges up to the 50-year return interval with benches forming temporary sediment storages within this larger channel. The large channel dimensions and associated hydraulics and high annual flood variability (flash flood magnitude index of 0.53) for the Shoalhaven River facilitate the construction of multiple bench surfaces across a range of elevations. Benches are formed of a wide range of facies from decimetre-thick massive sand units through interbedded sands and silts.

Comparison of Runoff Quality and Quantity from a Commercial Low-Impact and Conventional Development in Raleigh, North Carolina

Urbanization and its associated increased impervious footprint lead to stream impairment through erosion, flooding, and augmented pollutant loads. Low-impact development (LID) focuses on disconnecting impervious areas, increasing infiltration and evapotranspiration, and treating storm water on site through the use of storm water control measures (SCMs). In this study, a conventional development (centralized storm-water management) and an adjoining infiltration-based LID commercial site in Raleigh, North Carolina, were compared with respect to hydrology and water quality. The conventional development [2.76 ha, 61% directly connected impervious area (DCIA)] and the LID (2.53 ha, 84% DCIA) had underlying hydrologic soil group B soils. The LID was treated by a mix of green (aboveground) and grey (underground) infrastructure including an underground detention chamber and infiltration gallery, underground and aboveground cisterns, and aboveground swales and bioretention; the conventional development was treated with a dry detention basin and swales. Inflow and outflow runoff volumes and peak flows were normalized by DCIA. For the 47 hydrologic storms monitored, runoff coefficients of 0.02 at the LID site and 0.49 at the conventional site were recorded. The conventional development had an 11-fold higher median peak flow rate than the LID site. For the three storms more intense than the 10-year, 5-min average recurrence interval (ARI) event, the conventional site Qp was an average of 7.7 times higher than that of the LID. Flow proportional, composite water-quality samples were analyzed for total nitrogen (TN), total phosphorus (TP), total Kjeldahl nitrogen (TKN), total ammoniacal nitrogen (TAN), nitrite-nitrate nitrogen (NOX), organic nitrogen (ON), orthophosphate (Ortho-P), and total suspended solids (TSS). Generally, no significant difference in pollutant event mean concentrations (EMCs) was observed between sites. For the 20 water-quality storms sampled, the LID site produced pollutant loadings that were less than 5% of those at the conventional site for all species studied. Results demonstrated highly effective and space-saving solutions when green and grey infrastructure are merged, which is often the case when constructing on high land-cost properties. The exceptional results from this LID were due to (1) an overdesigned system capable of capturing the 77-mm storm, rather than a typical 25-mm storm, and (2) the high infiltration capacity of the type B soils coupled with a high driving head (∼3 m).

Stratigraphic and microfossil evidence for a 4500-year history of Cascadia subduction zone earthquakes and tsunamis at Yaquina River estuary, Oregon, USA

We infer that each buried soil represents a Cascadia subduction zone earthquake because the soils are laterally extensive and abruptly overlain by sandy deposits and mud. Preservation of coseismically buried soils occurred from 4500 yr ago until ~500–600 yr ago, after which preservation was compromised by cessation of gradual relative sea-level rise, which in turn precluded drowning of marsh soils during instances of coseismic subsidence. Based on grain-size and microfossil data, sandy deposits overlying buried soils accumulated immediately after a subduction zone earthquake, during tsunami incursion into Sallys Bend. The possibility that the sandy deposits were sourced directly from landslides triggered upstream in the Yaquina River basin by seismic shaking was discounted based on sedimentologic, microfossil, and depositional site characteristics of the sandy deposits, which were inconsistent with a fluvial origin. Biostratigraphic analyses of sediment above two buried soils—in the case of two earthquakes, one occurring shortly before 1541–1708 cal. yr B.P. and the other occurring shortly before 3227–3444 cal. yr B.P.—provide estimates that coseismic subsidence was a minimum of 0.4 m. The average recurrence interval of subduction zone earthquakes is 420–580 yr, based on an ~3750–4050-yr-long record and seven to nine interearthquake intervals.

Analysis of the 15 June 2013 isolated extreme rainfall event in Springfield, Missouri

An isolated extreme rainfall event occurred across portions of the Springfield, Missouri, area on 15 June 2013, causing substantial flooding of several small headwater tributaries of the James River. Heavy, nearly stationary thunderstorm activity developed along an outflow boundary after 1500 UTC. This area of thunderstorms trained over southern Springfield before dissipating around 1845 UTC. Post-event analysis of rainfall amounts indicated both gauge observations and radar-derived estimates exceeding the 100-yr event (1% annual chance equivalent). Local storm reports from the National Weather Service (NWS) forecast office in Springfield were supplemented with additional reports derived from news media and social media. Flash flood nowcasting techniques such as NWS gridded flash flood guidance (GFFG), rainfall average recurrence interval (ARI) estimates, the distributed hydrologic model-threshold frequency (DHM-TF), and the flooded locations and simulated hydrographs (FLASH) project were compared to local storm reports of flash flooding. A timeline of output from each of these techniques was compared to the time of reported flooding to evaluate the usefulness of each tool in the context of NWS operations. It was found that GFFG underestimated the scope of the flash flooding and would not have provided an estimate of flash flood severity. Rainfall ARI estimates, DHM-TF, and FLASH each suggested a significant flash flood event; however, DHM-TF output would have been available too late for forecasters and FLASH output would have provided several areas of false alarms. Rainfall ARI estimates provided the best balance of detecting areas of flash flooding, correctly estimating flash flood severity, and being available in a timely manner to NWS forecasters.

Spatial and temporal variation of palaeoseismic activity at an intraplate, historically quiescent structure: The Concud fault (Iberian Chain, Spain)

Several faults in the Teruel and Jiloca grabens (Iberian Chain, NE Spain), particularly the targeted Concud fault, show evidences of recent, continuous activity, despite their scarce instrumental and historic seismic record.Three trenches are studied in two locations (central and southeastern sectors of the Concud fault, respectively). After comparing with previous works, we reconstruct a palaeoseismic succession with nine events distributed along a maximum time lapse bracketed between 81.6 and 14.0ka. This succession involves an average recurrence interval of 7.4±2.8ka, with individual interseismic periods between 4 and 11ka. The calculated coseismic displacements range from 0.6 to 2.7m, with an average value of 1.9m that results in a slip rate of 0.26mm/a. Due to the incomplete sedimentary record for Holocene times, we cannot affirm that the youngest event detected was actually the last one. We conjecture that some other events may have occurred during the period between 15.0 and 3.4ka.Temporal and spatial variations have been detected in palaeoseismic activity, specifically in the distribution of coseismic displacements. First, a non-steady slip rate is evidenced during Plio-Pleistocene times: a long-term tendency towards increasing slip rate is modulated in detail by the occurrence of minor cycles, as the sequence of increasing/decreasing activity recorded within the studied time window suggests. Secondly, an asymmetric distribution of coseismic slip along the fault trace is observed, paralleling the distribution of total fault throw, which shows an absolute maximum close to the southeastern tip. A combination of factors is proposed to explain this: branching of the main fault; dominant, remote-stress-driven slip towards N 220° E on the NW–SE fault segment; guided movement on the passive, NNW–SSE segment giving rise to an oblique roll-over monocline; and decoupling of the hanging-wall block owing to the transverse Los Mansuetos–Valdecebro fault zone.

Possible slip history scenarios for the Hyuga‐nada region and Bungo Channel and their relationship with Nankai earthquakes in southwest Japan based on numerical simulations

AbstractThe Nankai earthquakes are great interplate earthquakes with recurrence intervals of 100–200 years, occurring along the Nankai Trough, southwestern Japan. New geological evidences suggest that the rupture area of the 1707 earthquake (one of the largest) extended farther westward than previously thought, and similar magnitude events may have recurrence intervals of several hundred years. West of the Nankai earthquake segments, in the Bungo Channel region, slow slip events (SSEs) have occurred with recurrence intervals of several years since 1980. Farther westward, no M ≥ 7.5 interplate earthquakes have occurred except for one in 1968 in the northern Hyuga‐nada region, near the Bungo Channel. We numerically simulated the generation cycles of Nankai earthquakes, Hyuga‐nada earthquakes, and Bungo Channel SSEs to obtain possible slip histories in these regions, particularly during 1707–1980. We showed that the Nankai and Hyuga‐nada earthquakes occur mostly independently, with average recurrence intervals of 151 and 117 years, respectively. An SSE patch slipped coseismically during both the Nankai and Hyuga‐nada earthquakes. The rupture of the Nankai earthquakes extended to the Hyuga‐nada region every ~500–600 years and was followed by quiescence of SSEs for more than 200 years. Subsequently, SSEs occurred repeatedly every 8 years. Current observational findings are generally consistent with the characteristics obtained from our scenarios, except regarding the recurrence intervals of Hyuga‐nada earthquakes, for which few observations are available. Further evidence of the slip history in these regions will be required to use information from such simulations to forecast future earthquakes.

Modeling of a lot scale rainwater tank system in XP-SWMM: A case study in Western Sydney, Australia

Lot scale rainwater tank system modeling is often used in sustainable urban storm water management, particularly to estimate the reduction in the storm water run-off and pollutant wash-off at the lot scale. These rainwater tank models often cannot be adequately calibrated and validated due to limited availability of observed rainwater tank quantity and quality data. This paper presents calibration and validation of a lot scale rainwater tank system model using XP-SWMM utilizing data collected from two rainwater tank systems located in Western Sydney, Australia. The modeling considers run-off peak and volume in and out of the rainwater tank system and also a number of water quality parameters (Total Phosphorus (TP), Total Nitrogen (TN) and Total Solids (TS)). It has been found that XP-SWMM can be used successfully to develop a lot scale rainwater system model within an acceptable error margin. It has been shown that TP and TS can be predicted more accurately than TN using the developed model. In addition, it was found that a significant reduction in storm water run-off discharge can be achieved as a result of the rainwater tank up to about one year average recurrence interval rainfall event. The model parameter set assembled in this study can be used for developing lot scale rainwater tank system models at other locations in the Western Sydney region and in other parts of Australia with necessary adjustments for the local site characteristics.

A 3400-year-long paleoseismologic record of earthquakes on the southern segment of Anninghe fault on the southeastern margin of the Tibetan Plateau

The Anninghe fault (ANHF) is an active left-lateral strike-slip fault along the southeastern margin of the Tibetan Plateau. Previous studies suggested the ANHF was divided into two segments, which herein we named the northern and southern segments respectively. Multiple trenches were excavated on the northern segment, revealing well-constrained paleoseismic events by radiocarbon ages. However, until now there is no paleoseismic result on the southern segment, which terminates at the Zemuhe fault (ZMHF) around Xichang where there were multiple historical records of large earthquakes. In this paper, we used high-resolution images for mapping fault traces on the southern segment of the ANHF and found a small depression. Through trenching in the depression, five paleoseismic events are identified and named E1 through E5 from youngest to oldest at 1750AD-present, 1430–1870AD, 940–1150AD, 700–1000AD, and 1400–500BC respectively. Comparing with the historical record earthquakes around Xichang, we suggest that the latest event E1 is associated with one of the 1850AD and 1952AD events, and event E2 is interpreted as the 1536AD earthquake; event E4 is possibly associated with the 814AD earthquake. The average recurrence interval of earthquakes on the southern segment is about 600–800yr, the interval between E1 and E2 is 416yr or 314yr, and 386–596yr between E2 and E3. The interval between E3 and E4 is shorter at 126–336yr, but much longer at 1314–2214yr between E4 and E5. These surface-faulting events on the southern segment of the ANHF appear to be unevenly spaced in time. Furthermore, integrating the paleoseismic sequence of the northern segment of the ANHF, the two segments appear to be ruptured individually or interactively triggered within a narrow time range, or co-ruptured during one paleoseismic event, indicating that the ANHF possibly shows a cascading rupturing behavior.

Complete seismic release of tectonic strain and earthquake recurrence in the Apennines (Italy)

AbstractHere I compare estimates of tectonic strain rates from dense Global Positioning System measurements with the seismicity released in the last ~500 years in the Apennines (Italy). The rates of seismic moment accumulation from geodesy and of historical seismic release by earthquakes agree within the uncertainties, ruling out significant aseismic deformation. Within the considered 400 km long section of the Apennines, this balance yields an average recurrence interval of 30–75 years forMW≥6.5 events without requiring a future earthquake larger than those observed historically (MW~7). A minimum estimate of unreleased strain allowsMW≥6.5 andMW≥6.9 events to be released in ~35%and ~10%of the central‐southern Apennines, respectively. The definition of the seismic potential for smaller events is more uncertain, and their occurrence remains a significant threat throughout the Apennines.

Late Quaternary paleoseismic sedimentary archive from deep central Gulf of Corinth: time distribution of inferred earthquake-induced layers

&lt;p&gt;A sedimentary archive corresponding to the last 17 cal kyr BP has been studied by means of a giant piston core retrieved on board R/V MARION-DUFRESNE in the North Central Gulf of Corinth. Based on previous methodological improvements, grain-size distribution and Magnetic Susceptibility Anisotropy (MSA) have been analysed in order to detect earthquake-induced deposits. We indentified 36 specific layers -Homogenites+Turbidites (HmTu) - intercalated within continuous hemipelagictype sediments (biogenic or bio-induced fraction and fine-grained siliciclastic fraction). The whole succession is divided into a non-marine lower half and a marine upper half. The “events” are distributed through the entire core and they are composed of two terms: a coarse-grained lower term and an upper homogeneous fine-grained term, sharply separated. Their average time recurrence interval could be estimated for the entire MD01-2477 core. The non-marine and the marine sections yielded close estimated values for event recurrence times of around 400 yrs to 500 yrs.&lt;/p&gt;

Seismic velocity variations at TCDP are controlled by MJO driven precipitation pattern and high fluid discharge properties

Using seismic noise based monitoring techniques we find that seismic velocity variations (dv/v) observed with the borehole array of the Taiwan Chelungpu-fault Drilling Project (TCDP) are controlled by strong precipitation events associated with the Madden–Julian Oscillation (MJO), a dynamic intraseasonal atmospheric pattern in the tropical atmosphere. High-frequency noise (>1 Hz) excited by steady anthropogenic activity in the vicinity of the TCDP allows daily resolution of dv/v time series. Relatively large fluid discharge properties control the equilibration of the ground water table and hence seismic velocities on time scales smaller than the average precipitation recurrence interval. This leads to the observed synchronous 50–80 day periodicity in dv/v and rainfall records in addition to the dominant annual component. Further evidence for the governing role of hydraulic properties is inferred from the similarity of observed dv/v timing, amplitude, and recovery properties with dv/v synthetics generated by a combined model of ground water table changes and diffusive propagation of seismic energy. The lapse time (τ) dependent increase of dv/v amplitudes is controlled by the sensitivity of the diffuse wave field sampled at 1100 m depth to shallower water level fluctuations. The significant vertical offset between stations and water level explains the direct τ dependence which is opposite to the trend previously inferred from measurements at the surface.

Quasi-periodicity of large avalanches in the long-range connective sandpile models and its implication in natural earthquakes

In this study, we investigated the quasi-periodicity of large avalanches using a new modification of sandpile models, i.e., the long-range connective sandpile (LRCS) model. The LRCS model considers the random distant connection between two separated, instead of neighboring, cells and shows interesting precursory behavior before large avalanches. We explore the statistics of recurrence intervals between large events and find a strong dependence on the size L of the sandpile. In the LRCS model, the average recurrence interval W of large avalanches follows the relationship . Having the recurrence intervals of many earthquake fault systems around the world, we propose an empirical rule between those intervals and the corresponding earthquakes' magnitudes and provide evidence of the quasi-periodic behavior of natural earthquakes.