Miura Peninsula Research Articles

Assessing the rescue capabilities of administrative agencies and estimating the scale of rescue team dispatch in the event of tsunami disasters

We propose a method to estimate the rescue team size that should be deployed from outside affected municipalities and thus clarify the success or failure of the rescue response of administrative agencies in the event of a tsunami. Capacity of Rescue was used to quantitatively evaluate the lifesaving capability of each rescue team; Index of Rescue was defined to evaluate whether the number of rescue workers in administrative organizations was sufficient for the number of people in need of rescue in the event of a tsunami. The proposed method was applied to a simulation of the coastal area of the Miura Peninsula in Kanagawa Prefecture. Results indicated that the rescue capabilities of the police and fire departments would be limited by the tsunami in the event of an earthquake exceeding M8.2, and thus require assistance from the Self-Defense Forces (SDF). Estimating a reasonable scale of rescue team dispatch, an M8.7 earthquake with an evacuation rate of 90 % can be handled by dispatching 40,000 SDF personnel within 72 h, whereas a 70 % evacuation rate would require 230,000 personnel, exceeding the scale of the 2011 Tohoku Tsunami. Considering the uncertainty of the occurrence of an earthquake, an evaluation based on the expected value resulted in 35,000 people. This is a more realistic result when considering the total number of personnel in the SDF. The methods and attempts proposed in this study can contribute to disaster relief planning by reducing the burden on the rescue teams.

Differences in Tick Infestation Intensity by Season, Sex, Age Class, and Body Region of Feral Raccoons (Procyon lotor) in the Miura Peninsula, Japan

Differences in Tick Infestation Intensity by Season, Sex, Age Class, and Body Region of Feral Raccoons (Procyon lotor) in the Miura Peninsula, Japan

A new shallow water species of the palaemonid shrimp genus Palaemon Weber, 1795 (Decapoda: Caridea) from Japan.

During a survey of the shallow water decapod fauna in the Miura Peninsula, Kanagawa Prefecture, central Japan, four specimens of a new palaemonid shrimp, Palaemon parvibrachium n. sp., were collected from sea grass beds of Nanozostera japonica (Ascherson & Graebner) Tomlinson & Posluszny, 2001. The new species appears morphologically similar to P. serrifer (Stimpson, 1860), one of the most common representatives of Palaemon Weber, 1795 in Japanese waters, but the short carpus of the second pereopod and the different live colouration readily differentiate the new species from the latter. A DNA barcode (a partial fragment of the mitochondrial CO1 gene), as well as a partial fragment of the mitochondrial 16S rRNA gene, are provided to genetically characterize the new species.

Species richness and status of Red List macrozoobenthos species at Ena Bay on the southern Miura Peninsula in comparison with 9 tidal flats located from Tokyo-Bay to the Kii Peninsula

Species richness and status of Red List macrozoobenthos species at Ena Bay on the southern Miura Peninsula in comparison with 9 tidal flats located from Tokyo-Bay to the Kii Peninsula

Habitat structure and recent environmental changes in intertidal zones of Ena Bay, southern Miura Peninsula, Japan

Habitat structure and recent environmental changes in intertidal zones of Ena Bay, southern Miura Peninsula, Japan

Recurrence and Long-Term Evaluation of Kanto Earthquakes

ABSTRACT The 1923 Taisho Kanto earthquake—an interplate event along the Sagami trough where the Philippine Sea plate subducts beneath the Kanto region—produced ground shaking, crustal deformation, landslides, and tsunamis, and caused the worst earthquake disaster in Japan. Based on seismological and geodetic data, many fault models have been proposed, extending ∼100 km from the epicenter, with a moment magnitude (Mw) of 7.8–8.2, and large slips of ∼8 m located near the epicenter and beneath the Miura Peninsula. The penultimate 1703 Genroku Kanto earthquake produced similar macroseismic effects around Sagami Bay and the Miura Peninsula, but larger coastal uplift and tsunami in the Boso Peninsula. The proposed fault models extend off the Boso Peninsula with Mw of 8.1–8.5. In 2004, the Earthquake Research Committee (ERC) classified the Kanto earthquakes as “Taisho type” and “Genroku type” with recurrence intervals of 200–400 yr and 2300 yr, respectively. In 2014, the ERC revised the long-term evaluation to a recurrence interval of 180–590 yr and a 30 yr probability of 0%–5% based on the Brownian passage time model. With the Cabinet Office, the ERC considered the source area of the maximum possible earthquake of Mw 8.6–8.7. The recent historiographical and paleoseismological studies have identified other candidates for the past Kanto earthquakes in 1495, 1433, 1293, and 878. Various combinations of these candidates give a mean recurrence interval of 210–315 yr, an aperiodicity parameter of 0.04–0.76, and a 30 yr probability of 0.0%–19%. The Cabinet Office has calculated the seismic intensity and tsunami heights of various types of Kanto earthquakes. National and local governments estimate the damage from these hazards. For the Tokyo metropolitan area, the estimated damage and occurrence probability are more significant for M ∼7 earthquakes with various types and depths, and most mitigation efforts are directed at such events.

Geological Controls on Marine Cavernous Landforms along Japanese Pacific-side Rocky Coasts

Marine cavernous landforms, including notches, caves, arches and tunnels, characterize the rocky coast landscape and are strongly influenced by the geology (e.g., rock strength and structure) of sea cliffs. Geological controls on the development and shape of marine cavernous landforms are evaluated based on field investigations along the Pacific coastlines of Honshu Island, Japan. Morphological parameters, width (w), depth (d), and height (h), of cavernous landforms were measured directly or through images taken with an unmanned aerial vehicle, together with geological factors, such as rock types, strength (Schmidt hammer rebound values: R), dips and strikes of bedding, major joints, and fault planes. In total, 76 caves are investigated in six coastal areas: Sanriku Coast, Joban Coast, Boso Peninsula, Miura Peninsula, Izu Peninsula, and Kii Peninsula. According to shape index, d/w, and presence of the open end, cavernous landforms are classified into notches (d/w < 1, closed end), caves (d/w ≥ 1, closed end), arches (d/w < 1, open end), and tunnels (d/w ≥ 1, open end). An analysis shows that the major geological controls differ between notches and the other three forms. Low rock strength (R < 40) and sub-horizontal bedding are, respectively, the primary and secondary controls on the formation of notches, whereas weak rock structures (joints, faults and bedding) with a dip steeper than 30° (vertical or steeply inclined structures) and a strike trending perpendicular to the cliff face are the major controls on the formation of caves, arches and tunnels. Rock strength also affects planar forms defined by the shape index, promoting a deepening of cavernous forms, particularly when the cliff has a medium rock strength (R = 30-50) that provides an optimal balance between erosion force and resisting force. In general, vertical or steep structures contribute to the deepening of holes, whereas horizontal or gentle structures favor widening.

Modern and fossil seawater identification using ground- and pore-water dating from the western coast of the Miura Peninsula, Japan

Deep groundwater flow in coastal areas has attracted considerable attention in the context of radioactive waste disposal and CO2 storage from transportation point of view. It is important to show the stability of groundwater flow for a long time, which relates to identify modern and fossil seawater in coastal area. Borehole investigation was conducted at a coastal area along the west side of the Miura Peninsula in Japan, where is a typical of the accretionary wedge environments. As part of this investigation, groundwater ages have been evaluated based on dating ground- and pore-water samples (obtained by groundwater pumping and rock core squeezing, respectively) from three boreholes of up to 500 m deep. At the borehole locations, the Miura Group, which consists of sandstone and siltstone, is observed to depths of ∼200 m and the Hayama Group, which primarily consists of mudstone, is observed below ∼200 m. In the Miura Group, 14C was abundant; high-Cl samples showed high 14C and low 36Cl/Cl, equivalent to modern seawater. In the underlying Hayama Group, where the low hydraulic conductivity of the formation means that the assessment was based almost solely on porewater samples, the Cl concentration below a depth of 300 m was close to that of seawater and 36Cl/Cl was close to in situ secular equilibrium (as estimated from rock properties). Furthermore, 4He was abundant in the Hayama Group, and an observed shift in δ37Cl is inferred to have been controlled simply by diffusion. The results indicate that the groundwater in the Miura Group is modified modern seawater, while the porewater in the Hayama Group is fossil seawater. Thus, groundwater dating, using a combination of 14C, 36Cl, and 4He, is a useful tool for the identification of modern and fossil seawater in coastal areas.

Geology and fossil cold-seep assemblages in the Kazusa Group on the northern Miura Peninsula, central Japan

房総半島，三浦半島，多摩丘陵などに露出する後期鮮新世-中期更新世の前弧海盆堆積物である上総層群は，鮮新世以降における南関東の地質や地形の発達過程を理解する上で重要な地層である．なかでも三浦半島北部の上総層群下部-中部では近年，岩相層序学的研究および，広域凝灰岩層，石灰質ナノ化石，古地磁気，有孔虫化石の酸素安定同位体比などを用いた年代層序学的研究が盛んに行われている．その成果により，本地域の上総層群では，本邦でも有数の極めて詳細な上部鮮新統-下部更新統の層序が確立しつつあり，それによって房総半島において，いわゆる黒滝不整合により欠落している層準のほぼ連続的な地質記録が残されていることが明らかにされている．さらに本地域の上総層群から数多く産出する，主に二枚貝化石からなるメタン冷湧水性化学合成化石群集についても詳細な記載が行われてきており，プレート境界周辺の海洋底からのメタン湧出が，地質時代における地球環境に与えた影響を評価するうえで重要である．本コースでは，三浦半島北部の上総層群中部-下部を観察し，層序学的研究および，産出する化学合成化石群集についての研究成果について紹介する．

Detection of Ships Cruising in the Azimuth Direction Using Spotlight SAR Images with a Deep Learning Method

Spotlight synthetic aperture radar (SAR) achieves a high azimuth resolution with long integration times. Meanwhile, the long integration times also cause defocused and smeared images of moving objects such as cruising ships This is a typical imaging mechanism for moving objects in Spotlight SAR images. Conversely, ships can be classified as stationary or moving from the amount of smearing, and this classification method is, in general, based on manual observation. This paper proposes an automatic method for detecting cruising ships using deep learning known as the “You Only Look Once (YOLO) v5 model”, which is one of the frameworks of the YOLO family. In this study, ALOS-2/PALSAR-2 L-band Spotlight SAR images over the waters around the Miura Peninsula, Japan, were analyzed using the YOLO v5 model with a total of 53 ships’ images and compared with Automatic Identification System (AIS) data. The results showed a precision of approximately 0.85 and a recall rate of approximately 0.89 with an F-measure of 0.87. Thus, sufficiently high values were achieved in the automatic detection of moving ships using the deep learning method with the YOLO v5 model. As for false detections, images of breakwaters were classified as ships cruising in the azimuth direction. Further, range moving ships were found to be difficult to detect. From the present preliminary study, it was found that the YOLO v5 model is limited to ships cruising predominantly in the azimuth direction.

Specimen-based records of Kyphosus ocyurus (Perciformes: Kyphosidae) from the Miura Peninsula and Hachijo-jima Island, Izu Islands, Japan

Specimen-based records of Kyphosus ocyurus (Perciformes: Kyphosidae) from the Miura Peninsula and Hachijo-jima Island, Izu Islands, Japan

Annotated checklist of marine fishes of the southwestern coast of Miura Peninsula, Kanagawa Prefecture, Japan

Annotated checklist of marine fishes of the southwestern coast of Miura Peninsula, Kanagawa Prefecture, Japan

Stratigraphy and Geological Structures of the Miura Group in the Ubajima Islands, Northernmost Sagami Bay: Multiple Duplexes and Fault-propagation Folds Based on Tracing Tephra Key Beds

Mapping was carried out of well exposed folded and faulted strata in the Ubajima Islands off Chigasaki City, Kanagawa Prefecture, central Japan of the northernmost part of Sagami Bay, where the present Philippine Sea plate subduction boundary extends beneath the central part of the North America plate. The strata were dated with radiolarian fossils as middle to late Miocene, and correlated with part of the Misaki Formation of the Miura Group of the southern Miura Peninsula. The strata are composed of dominant basaltic pyroclastic or volcaniclastic sedimentary rocks with sporadic felsic tephra layers and rare silty sedimentary rocks, and were defined as the Ubajima Formation. Detailed field mapping of the Ubajima Formation verified that the strata are deformed in a complicated way into duplex structures having two stages. The first stage is characterized by bedding parallel to subparallel thrust faults in the SW direction of the horizontal reference frame. This might be of the antiformal stack type known by many parallel repetitions of the same horizons. At the second stage, the same parts are further duplicated into other antiformal stack-type duplex structures, forming multi-duplex structures. Finally those structures are folded and faulted by a fault-propagation fold system that has strong shear zones at propagation fault zones. The Ubajima Formation is thought to be deposited on the forearc area of the Izu volcanic arc, then accreted to the Honshu side by accretionary prism formation. These structures represent good examples of accretionary prism toes along subduction zones.

Site conditions of herbaceous communities on the rocky coast of the Miura Peninsula, Kanagawa Prefecture, eastern Japan

Site conditions of herbaceous communities on the rocky coast of the Miura Peninsula, Kanagawa Prefecture, eastern Japan

Does screening for prostate cancer improve cancer-specific mortality in Asian men? Real-world data in Yokosuka City 15 years after introducing PSA-based population screening.

Studies of prostate-specific antigen (PSA)-based population screening have been conducted in western countries, but there is little data in Asian populations. The objective of this study was to determine the efficacy of PSA screening in Asian men using real-world data over a period of 15 years after introducing population screening in Yokosuka City, Japan. We investigated patients with pathologically diagnosed prostate cancer at four hospitals and two clinics across the Yokosuka area (Miura peninsula) between April 2001 and March 2015. Patients were divided into two groups; the S group consisted of those diagnosed by PSA-based population screening in Yokosuka City and the NS group consisted of those diagnosed by methods other than screening. Cancer-specific survival (CSS) and overall survival (OS) rates were calculated using the Kaplan-Meier method with the log-rank test to compare survival between the two groups. Clinical and pathological factors for cancer-specific mortality were assessed with Cox regression analyses to calculate the hazard ratio (HR) and 95% confidence interval (CI). A total of 3094 patients had been diagnosed with prostate cancer over the 15-year period. The median follow-up period was 77 months. The S group and the NS group consisted of 977 and 2117 patients, respectively. Patients in the S group were younger (age: 71 years vs 73 years, P < .001) and had a lower Charlson comorbidity index (CCI) with favorable oncological factors, such as lower initial PSA, Gleason score (GS), and risk category. Kaplan-Meier curves for OS and CSS revealed significant differences between the two groups (OS: P < .001, CSS: P < .001). Analysis with Cox proportional hazards model indicated the NS group (HR: 1.584, 95% CI, 1.065-2.356, P = .023), a CCI > 4 (HR: 1.552, 95% CI, 1.136-2.120, P = .006), a GS ≥ 8 (HR: 4.869, 95% CI, 2.631-9.001, P < .001), and nonlocalized cancer (locally advanced; HR: 2.632, 95% CI, 1.676-4.133, P < .001, advanced; HR: 9.468, 95% CI, 6.279-14.278, P < .001) as independent risk factors for cancer-specific mortality. PSA-based population screening of prostate cancer might be useful in the Japanese population.

Stratigraphy and duplexes in new outcrops of Aburatsubo Member of Upper Misaki Formation, Miura Group, Sajima, Miura Peninsula, Japan

Stratigraphy and duplexes in new outcrops of Aburatsubo Member of Upper Misaki Formation, Miura Group, Sajima, Miura Peninsula, Japan

三浦半島第四系宮田層中の不整合と挟在する“船久保タフ(Fn）”のFt, U-Pb, K-Ar 年代

三浦半島第四系宮田層中の不整合と挟在する“船久保タフ(Fn）”のFt, U-Pb, K-Ar 年代

三浦市南部における3 種の熱帯・亜熱帯性海岸植物の 実生の生育状況

三浦市南部における3 種の熱帯・亜熱帯性海岸植物の 実生の生育状況

Combined analysis of sulfur and carbon contents, and foraminifer as paleoenvironmental indicators in tidal flat sediments on Miura Peninsula, Japan

Reconstruction of natural hazards from tidal flat sediments is essential for assessment of coastal hazards, and is based on knowledge of recent sediments. This study therefore examined recent sediments deposited on a narrow, muddy tidal flat on Miura Peninsula, metropolitan Tokyo, Japan, by means of sedimentological analysis, C, N, and S elemental analysis, carbonate content, 137Cs dating, and analysis of benthic foraminifera (species composition and degree of preservation). 137Cs profiles of four sediment cores of ∼20 cm in length showed that the sediments were deposited after the release of 137Cs by the accident at the Fukushima No. 1 Nuclear Power caused by the Tohoku-oki tsunami at March 2011. Results of C/S ratios of mud fractions indicated that the intertidal deposits in the central bay are characterized by low C/S ratios (4.9–11.4) and the bayhead deposits of the upper intertidal and supratidal zones by higher ratios (13.9–24.9). A fluid–mud layer identified in the central bay had the same C/S ratios and carbonate contents as marine sediments, indicating that the fluid-mud deposits probably resulted from resuspension of mud caused by storm-wave action after March 2011. Faunal analysis of benthic foraminifera showed that very low density of foraminifera can be regarded as one of the defining characteristics of fluid-mud deposits.

Scrobiculosides A and B from the deep-sea sponge Pachastrella scrobiculosa.

Two new steroidal saponins, scrobiculosides A and B, were isolated from the deep-sea sponge Pachastrella scrobiculosa, collected at a depth of 200m off Miura Peninsula, Japan. The aglycones of scrobiculosides A and B feature a vinylic cyclopropane and a ∆24,25 exomethylene on the side chains, respectively. Both saponins have a common sugar moiety composed of β-D-galactopyranosyl-(1 → 2)-6-acetyl-β-D-glucopyranoside, with the exception of an acetyl group on C6″ in scrobiculoside A. Scrobiculoside A exhibited cytotoxicity against HL-60 and P388 cells, with IC50 values of 52 and 61μM, respectively.