Longer Recurrence Intervals Research Articles

How Does the Onset of Offset Influence Geologic Slip Rates?

Abstract Geologic slip rates are typically based on the displacement accrued by a geomorphic or stratigraphic feature and the age of the offset feature. Because slip rates are commonly calculated by dividing the displacement of a faulted marker by its age, they contain two open time intervals: the elapsed time between the age of an offset feature and the age of the earthquake that displaced the feature, and the time between the present-day and the most recent earthquake. Here, we explore the influence of including unconstrained open intervals in geologic slip rate calculations. We test the degree to which these open intervals affect geologic slip rates and their uncertainties, and we find that their influence depends primarily on mean earthquake recurrence intervals (RIs). Slip rates on faults with longer RIs, such as the Wasatch fault, can be greatly influenced by an increase of up to 20% when accounting for open intervals. In contrast, slip rates on faults with shorter RIs, such as the San Andreas fault, are only slightly influenced by the assumption that slip rates calculated over open intervals approximate those calculated over closed intervals. Our analyses indicate that faults with moderate slip rates (∼0.2–5 mm/yr) are sensitive to both open interval effects themselves, as well as methods to quantify and account for these effects. We re-evaluate how slip rates are calculated and defined in displacement–time space using published deformation records. We explore the utility of assigning a probability distribution to the initiation of offset of the oldest faulted feature and the timing of the most recent earthquake (MRE). We find that calculating geologic slip rates without using probability distributions that capture the timing of the MRE and the onset of offset of the oldest faulted feature, especially on slow-to-moderate slip rate faults, can lead to systematic underestimation of average geologic slip rates.

Risk factors for recurrence of suicide attempt via overdose: A prospective observational study

BackgroundAlthough the prevalence of drug overdose has gradually increased worldwide, the risk factors associated with the recurrence of suicide attempts via drug overdose have not been well elucidated. In this study, we investigated the clinical course of patients with drug overdose and whether or not patients reattempted suicide via overdose, using telephone interviews, to evaluate the risk factors associated with overdose recurrence. MethodsThis prospective observational study enrolled patients who attempted suicide by drug overdose and were transferred to a tertiary emergency hospital in Japan between January 1, 2015 and July 30, 2021. Recurrence of overdose within 1 year of admission for overdose was designated as the primary outcome. Multivariable logistic regression analysis was performed to assess the independent risk factors for the recurrence of overdose. Furthermore, we compared the difference in the recurrence interval between patients with and without cohabitants using the log-rank test. ResultsA total of 94 patients were identified, and recurrence of overdose was observed in 28 patients (29.8%). The median recurrence interval was 6.0 months [IQR (interquartile range), 4.0–7.0 months]. The recurrence rate was significantly higher in patients with a history of schizophrenia than that in patients without a history of schizophrenia (58.3% vs 25.6%, p = 0.048), and significantly lower in patients with cohabitants than that in patients without cohabitants (22.6% vs 43.8%, p = 0.015). The presence of a cohabitant was significantly associated with a longer recurrence interval (p = 0.049). The effect of psychiatric intervention during hospitalization and psychiatric visits after discharge could not be found in this study. ConclusionsA history of schizophrenia was an independent risk factor for the recurrence of overdose, and the presence of a cohabitant was significantly associated with a lower risk of recurrence. Large-scale, long-term studies are required to confirm the results of this study.

Faricimab for Diabetic Macular Edema in Patients Refractory to Ranibizumab or Aflibercept.

Background and Objectives: Faricimab is the first intravitreal injection of vascular endothelial growth factor-A and angiopoietin-2 bispecific monoclonal antibody. Here, we evaluate the functional and anatomical outcomes of faricimab treatment in patients with diabetic macular edema (DME) that was refractory to ranibizumab or aflibercept. Materials and Methods: We performed a retrospective, observational, consecutive-case study of patients who had DME that was refractory to treatment with ranibizumab or aflibercept and were treated with faricimab between July 2022 and January 2023 under a pro re nata regimen. All the participants were followed for ≥4 months after the initiation of faricimab. The primary outcome was a recurrence interval of ≥12 weeks, and the secondary outcomes were the changes in best-corrected visual acuity (BCVA) and central macular thickness (CMT). Results: We analyzed 18 eyes of 18 patients. The mean recurrence interval of previous anti-VEGF injection was 5.8 ± 2.5 weeks, which was significantly extended to 10.8 ± 4.9 weeks (p = 0.0005) by the switch to faricimab. Eight patients (44.4%) achieved a recurrence interval of ≥12 weeks. A history of subtenon injection of triamcinolone acetonide (p = 0.0034) and the presence of disorganization of the retinal inner layers (p = 0.0326) were found to be significantly associated with a recurrence interval of <12 weeks. The mean BCVAs were 0.23 ± 0.28 logMAR and 0.19 ± 0.23 logMAR, and the mean CMTs were 473.8 ± 222.0 µm and 381.3 ± 219.4 µm at baseline and 4 months, respectively, but these changes were not statistically significant. None of the patients experienced serious adverse events. Conclusions: Faricimab may extend the treatment interval for patients with DME that is refractory to ranibizumab or aflibercept. DME previously treated with the subtenon injection of triamcinolone acetonide or associated with disorganization of the retinal inner layers may be less likely to be associated with a longer recurrence interval after switching to faricimab.

A Continuous 13.3-Ka Paleoseismic Record Constrains Major Earthquake Recurrence in the Longmen Shan Collision Zone

Thrust collision zones with low slip rates along the plate boundary are significant areas of stress accumulation and prone to develop more destructive earthquakes with longer recurrence intervals. Such regions are often classified as low seismic risk if they lack continuous records of large earthquakes, such as the eastern Tibetan Plateau before the 2008 Mw 7.9 Wenchuan earthquake. Here, we provide a continuous seismic record in the Longmen Shan thrust fault zone spanning 13,000 years based on detailed investigation of the soft-sediment deformation structures and seismites in the Lixian lacustrine sequence. The recurrence time of large earthquakes (M ≥ 8.1) is 1,200 years, which is significantly shorter than the previous estimate of 2,000–6,000 years. The Maoxian-Wenchuan fault is the main fault that triggered the deformation in the Lixian lacustrine sediments. In addition, earthquake recurrence in the warm period is more frequent than that in the cold period, which should arouse our attention for the seismic study of tectonically active regions.

Factors leading to slope failure on a sediment-starved margin: The southwestern continental margin of the East Sea, Korea

Submarine landslides are common geomorphological features of continental margins. Some of the largest submarine landslides occurred on low-angle (< 4°), sediment-starved margins, yet their preconditioning and trigger mechanisms are still largely unconstrained. The southwestern continental margin of the East Sea (between 37.5°N and 38.0°N), Korea, occupies a narrow shelf (< 10 km), is characterized by low sedimentation rates (~3–7 cm /ka) with an average gradient of less than 2°. Here, we investigate submarine landslides using newly collected datasets including multibeam echosounder (MBES), chirp sub-bottom profiler, multichannel seismic (MCS) data and ten piston cores. MBES data from the margin reveal at least four major submarine landslides initiated at depths of 400 m to over 600 m. These landslides left clear headwall scarps on the seafloor with reliefs reaching over ~130 m and extend for over 40 km. MCS data show that some of the failures have resulted in the complete disintegration of the failed mass, while others have resulted in the deposition of well-defined hummocky debris flows. Sediments recovered downslope of the headwall scarps contain slides and debris flow deposits and turbidites that are overlain by bioturbated hemipelagic layers. Radiocarbon dating from hemipelagic units overlying MTDs within the headwall scarps reveal that major failures occurred at ca. 11 to 19 ka, coinciding with the time of the Last Glacial Maximum (LGM) to early deglaciation. Since then, hemipelagic sedimentation has prevailed throughout the sediment starved slope. Slope stability analyses based on geotechnical properties of sediments indicate that all areas are stable under static, and even stable under loads derived from earthquakes in instrumental records, but there were probably earthquakes in pre-historical records (i.e., with a longer recurrence interval) of potentially significant larger magnitude. We suggest that the preferential occurrence of major failures adjacent to the major faults on the lower slope may ultimately be tectonic-controlled although other factors may have contributed as well. Our work shows that coarse-grained clastic sediments are abundant in the shallow subsurface and that these higher-permeability units, often identified as weak layers, would focus fluid flow and could act as slip planes for slope failure. Our data also indicate that tectonic steepening and gas charging are other key parameters for controlling instability in sediment-starved margins.

Determination of local active tectonics regime in central and northern Greece, using primary geodetic data

Numerous active fault zones are detected into the central and northern part of Greece, while some of them are associated with destructive seismic events. Geometrically, the fault zone characteristics differentiate, showing both extensional and compressional tectonic features. The geodetic data used, recorded by permanent GPS/GNSS stations, provides a precise analysis the tectonic setting. In particular, 58 permanently installed GPS/GNSS stations are located into the study area, having collected primary data for 7 consecutive year time-period. The calculation of the East and North velocity components and their errors, respectively, derived from each GPS/GNSS station, was carried out implementing the triangulation methodology, based on the combination of three different GPS/GNSS stations each time. The dense GPS/GNSS stations network led to the construction of 1092 different triangles, while the centroid of each triangle was extracted. For each centroid, the following parameters were determined: (1) maximum horizontal extension, (2) minimum horizontal extension, (3) total velocity, (4) maximum shear strain, (5) area strain and (6) rotation. The extracted values were geostatistically processed (interpolation—grid pattern), showing low to medium values, especially north of the extension of the North Aegean Fault System, while the same parameters are high at the southern part of Greece. Therefore, the geological and seismological data are confirmed showing that Central–Northern Greece is tectonically less active than Southern Greece. However, it is mentioned that the neotectonic fault length can be related to the production of significant earthquakes, albeit in longer recurrence intervals.

The role of debris flow on total denudation in small basins of the Ashio Mountains, Japan

Total and continuing denudation rates were estimated using cosmogenic nuclides and intensive field observations of sediment transport in two small basins (C3 and S3) from the Ashio Mountains, Japan. The C3 basin underlain by Triassic bedded chert, while the S3 basin has evolved in altered Jurassic sandstone-shale. Continuing denudation rates were estimated from the records of coarse sediment transport and stream discharge for 6 years (2004–2009), soil grain-size distribution, and dissolved load in stream water. A debris flow was observed and the volume was measured in C3 (chert). Concentrations of cosmogenic 10Be and 26Al in fluvial sand were measured to determine spatially-averaged total denudation rates for these basins on the basis of steady-state assumption. Continuing denudation rate for C3 (chert) basin excluding the debris-flow mass accounted for ~75% of the total denudation rate as measured from the cosmogenic nuclides. Assuming a difference between the total and continuing denudation rates indicates the impact of repeat debris flows, the debris flows with the observed magnitude (the mass of 24 t) occur with the recurrence intervals of 100–550 years (mean 167 years) for C3 (chert) basin. For S3 (sandstone) basin, the continuous denudation rates were significantly smaller than the total rates, where debris flow had not occurred for at least 17 years. The large gap in the denudation rates with different time scales shows contribution of higher magnitude debris-flow events with longer recurrence intervals.

Assessment of Continuous Wet Day Rainfall Frequency Distribution in the Intermediate Zone of Sri Lanka

Changes in rainfall distribution patterns around the world have caused fluctuations in thoseclimate regimes. Agriculture is particularly vulnerable to climatic conditions and it is chiefamong the systems that are expected to undergo changes as a consequence of climate change.This study analyses the climate change variability through the fluctuation in precipitationpattern and evaporation, in low country intermediate zone (IL1a) agro ecological region basedon Gumbel’s frequency distribution analysis on wet day rainfall data. Focusing on a cascadeagricultural system in the Katupotha divisional secretariat division of the Kurunegala districtthat is located in the IL1a, the climate change variability was analysed using daily rainfall dataof fifty years (1961-2010) together with long term evaporation data. Experimentalmethodology considered a day to be wet only if the rainfall exceeded its evaporation. Thiswas considered as the precipitation amount that could potentially be used by the crops.Gumbel’s frequency analysis was employed to derive the variability in continuous wet dayrainfall distribution at 25 year time intervals (1961-1985 and 1986-2010). The totalcontinuous wet day rainfall and seasonal total continuous wet day rainfall frequencydistributions were analysed using the technique. Results of the analysis show an increasingtrend in magnitude of the total continuous wet day precipitations from 1961-2010. Thisincreasing trend is observed beyond 2.2 years recurrence interval. At longer recurrenceintervals (20 years) a 50 mm increase is experienced during the last 25 years (1986-2010)while at shorter recurrence intervals (2.2 years), a 6 mm increase is evident. A distinctincreasing trend in the total continuous wet day precipitation from 1961-2010 was observedduring the second inter-monsoon which was a 165 mm increase at a 10 year recurrenceinterval. In contrary, the south-west monsoon, first inter-monsoon and north-east monsoonrecorded decreasing trends in the total continuous wet day precipitation from 1961-2010.

Modeling the activity of short‐term slow slip events along deep subduction interfaces beneath Shikoku, southwest Japan

We developed a model of short‐term slow slip events (SSEs) on the 3‐D subduction interface beneath Shikoku, southwest Japan, considering a rate‐ and state‐dependent friction law with a small cutoff velocity for the evolution effect. We assume low effective normal stress and small critical displacement at the SSE zone. On the basis of the hypocentral distribution of low‐frequency tremors, we set three SSE generation segments: a large segment beneath western Shikoku and two smaller segments beneath central and eastern Shikoku. Using this model, we reproduce events beneath western Shikoku with longer lengths in the along‐strike direction and with longer recurrence times compared with events beneath central and eastern Shikoku. The numerical results are consistent with observations in that the events at longer segments have longer recurrence intervals. The activity of SSEs is determined by nonuniform frictional properties at the transition zone. We also attempt to model the very low frequency (VLF) earthquakes that accompany short‐term SSEs, on a 2‐D thrust fault. We consider a local patch in which the friction parameters are varied. In the case that critical displacement is very small at the patch, fast multiple slips occur at the patch. In the case that the effective normal stress is high at the patch, the patch acts as a barrier to SSEs; when it ruptures, however, rapid slip occurs. Because the source time functions of these cases are somewhat different, it would be possible in the future to assess if either case is an appropriate model for VLF earthquakes.

表層堆積物の変形構造からみた深谷断層系綾瀬川断層北部の後期更新世以降の活動史

The northern Ayasegawa fault is a part of the Fukaya fault system, which is the longest active fault in the Kanto district. The paleoseismology of the northern Ayasegawa fault was revealed by a combination of arrayed boring and ground penetrating radar (GPR) survey. The northern Ayasegawa fault produced a fold scarp with the NW-SE direction running along the boundary between the Oomiya 2 (O2) surface and fluvial lowland. The O2 was formed in Marine Isotope Stage 5a, and was slightly deformed with a wide warping zone. Sixteen sediment cores arrayed across the warping zone contain a series of tephra layers such as Hk-TP (ca. 60-65 ka), KMP, AT (26-29 ka), As-BP group (20-25 ka), and As-YP (15-16.5 ka). These key beds except Hk-TP were deposited and deformed parallel to each other, suggesting that no faulting events occurred between KMP and As-VP fall. The timing of the last faulting event is after the As-YP fall, and is probably younger than 10 ka based on an interpretation of GPR profiles and 14C ages. KMP should be deposited horizontally because it intervened in the peaty silt layer, which accumulated conformably on lacustrine deposits overlapping the fold scarp. Thus, the KMP horizon roughly indicates the vertical offset produced by the events occurred after the As YP fall. The events were probably singular, and the last one formed a vertical offset of more than 4 m. The older event occurred at around 70 ka between Hk-TP fall and O2 formation. Vertical deformation of the O2 was at least 7 m, indicating the possibility that the vertical offset caused by the penultimate event is at least 3 m. The vertical slip per event might reach 5 m, and the average vertical slip rate is nearly 0.1 mm/yr because the warping zone detected by the arrayed boring above is within the flexure zone shown by the P-wave seismic profile. The northern Ayasegawa fault is considered to be a single behavioral segment because of its longer recurrence interval and lower slip rate of 0.1 mm/yr in comparison with those of the other part of the Fukaya fault system.

Surface Slip Associated with the 2004 Parkfield, California, Earthquake Measured on Alinement Arrays

Although still continuing, surface slip from the 2004 Parkfield earth- quake as measured on alinement arrays appears to be approaching about 30-35 cm between Parkfield and Gold Hill. This includes slip along the main trace and the Southwest Fracture Zone (SWFZ). Slip here was higher in 1966 at about 40 cm. The distribution of 2004 slip appears to have a shape similar to that of the 1966 event, but final slip is expected to be lower in 2004 by about 3-15 cm, even when continuing slip is accounted for. Proportionately, this difference is most notable at the south end at Highway 46, where the 1966 event slip was 13 cm compared to the 2004 slip of 4 cm. Continuous Global Positioning System and creepmeters suggest that significant surface coseismic slip apparently occurred mainly on the SWFZ and perhaps on Middle Mountain (the latter possibly caused by shaking) (Langbein et al., 2005). Creepmeters indicate only minor (0.2 cm) surface coseismic slip occurred on the main trace between Parkfield and Gold Hill. We infer that 3-6 cm slip accumulated across our arrays in the first 24 hr. At Highway 46, slip appears complete, whereas the remaining sites are expected to take 2-6 years to reach their background creep rates. Following the 1966 event, afterslip at one site persisted as much as 5-10 years. The much longer recurrence intervals between the past two Parkfield earthquakes and the decreasing slip per event may suggest that larger slip deficits are now growing along the Parkfield segment.

Recurrence intervals of characteristic M4.8±0.1 earthquakes off-Kamaishi, NE Japan—Comparison with creep rate estimated from small repeating earthquake data

We examined the cause of the fluctuation in recurrence intervals of an M4.8±0.1 ‘characteristic earthquake’ sequence off-Kamaishi, NE Japan by comparing the recurrence intervals with creep (quasi-static slip) rates around the asperity estimated from small repeating earthquake data. The eight recurrence intervals (5.52 yrs on average) of the sequence are almost constant but have small fluctuations (standard deviation of 0.68 yrs) characterized by a longer recurrence interval following a shorter one. From the analysis of small repeating earthquakes from 1990 to 2003, we found a significant acceleration of creep on the plate boundary during and after an earthquake swarm in 1992 to the east of the M4.8±0.1 event. The acceleration seems to have migrated from east (shallower part of the plate boundary) to west (deeper part) over about 80 km in 2 yrs to reach the asperity of the M4.8±0.1 events. The 1995 event that occurred with the shortest recurrence interval was probably advanced by this acceleration of creep in around 1994. We also found similar earthquake swarms prior to the 1962 and 1973 ‘characteristic’ events that occurred after the second and third shortest recurrence intervals respectively. Therefore it is possible that the 1962 and 1973 events were also advanced by creep accelerations. The three pairs of longer and shorter recurrence intervals we observed suggest the existence of creep deceleration following the acceleration. We conclude that the recurrence interval fluctuations of the M4.8±0.1 events are mainly controlled by temporal changes of creep around its asperity.

Inconsistent patterns of historical seismicity and earthquake-triggered landsliding in southeastern Sicily: an alarm bell?

In southeastern Sicily, the distribution pattern of earthquake-triggered landslides is inconsistent with historically known seismic activity. In particular, historical seismicity has been stronger in the eastern sector, while earthquake-triggered landsliding is much more developed in the western sector, and this contrasts with expectations. This paper describes the patterns of seismicity and landsliding, and tackles the problem of whether greater landsliding in the western sector may be due (a) to seismicity of the eastern sector or (b) to a high-magnitude, low-recurrence seismicity generated in the western sector itself. It is statistically shown that lithostructural characteristics of rock masses and geometry of hillslopes cannot justify, either singly or jointly, greater landsliding in the western sector if triggering earthquakes are generated in the eastern sector. As a consequence, it is possible that landsliding of the western sector is due to earthquakes generated locally, but having higher magnitude and longer recurrence intervals than historically observed.