Matsumoto Basin Research Articles

Shallow S-wave seismic reflection profiling across the northern section of the East Matsumoto Basin fault in the Itoigawa–Shizuoka tectonic line active fault system, central Japan

Shallow S-wave seismic reflection profiling across the northern section of the East Matsumoto Basin fault in the Itoigawa–Shizuoka tectonic line active fault system, central Japan

Community Structure of Aquatic Insects Adapted to Lentic Water Environments, and Fine-Scale Analyses of Local Population Structures and the Genetic Structures of an Endangered Giant Water Bug Appasus japonicus.

Environments such as floodplains and the marshlands of rivers, lakes and ponds, are important habitats for aquatic insects adapted to lentic water conditions. In addition, ponds and paddy fields artificially created for agriculture are also important alternative habitats for lotic water-dependent wildlife. In this study, we focused on aquatic insects in ponds in the Matsumoto Basin, located in the center of Japan. Although this is an urbanized area, aquatic animals adapted to floodplains inhabit it at a relatively high density for Japan. We conducted a multifaceted evaluation of the environments of the 33 ponds in this region and conducted a survey of the aquatic insect fauna inhabiting them. In this study, we conducted quantitative sampling, focusing on two insect orders adapted to large-scale lentic water environments (i.e., Heteroptera and Coleoptera), and observed five species of three families and 16 species of five families from the Matsumoto Basin, respectively. Within these species, eight endangered species were included. Furthermore, we carried out a genetic structure analysis for the giant water bug, Appasus japonicus, inhabiting these ponds in high density, and conducted a comparative evaluation of their genetic diversity between these ponds. A total of 530 specimens of A. japonicus were genetically analyzed for the mitochondrial DNA COI region, and 26 haplotypes were observed. The degree of genetic diversity between the ponds was clearly demonstrated. In addition, we discussed the wintering possibilities for the giant water bugs based on their corresponding surrounding environmental factors, and comprehensively discussed their “source−sink” relationships in this region. Therefore, this is a comprehensive study focused on the relevant environmental factors, diversification of their community structures, their population structures, and their genetic structure at a fine scale.

Potentially of Winter Weed Vegetation to Control the Sand-dust Storm in the Agricultural Area of Southwestern Matsumoto Basin

Potentially of Winter Weed Vegetation to Control the Sand-dust Storm in the Agricultural Area of Southwestern Matsumoto Basin

松本盆地南東部,高ボッチ山西麓に発達する"崖の湯断層群"( 内陸盆地の構造と形成プロセス)

松本盆地南東部,高ボッチ山西麓に発達する"崖の湯断層群"( 内陸盆地の構造と形成プロセス)

Planting to Control the Sand-dust Storm in the Agricultural Area of Southwestern Matsumoto Basin

Planting to Control the Sand-dust Storm in the Agricultural Area of Southwestern Matsumoto Basin

Concealed faults in southern part of the Matsumoto Basin. An example of underground imaging by microtremor array survey (SPAC method).

Concealed faults in southern part of the Matsumoto Basin. An example of underground imaging by microtremor array survey (SPAC method).

The Coating Materials to Control the Sand-dust Storm in the Agricultural Area of Southwestern Matsumoto Basin

The Coating Materials to Control the Sand-dust Storm in the Agricultural Area of Southwestern Matsumoto Basin

Concealed faults in central part of the Matsumoto Basin. An example of underground imaging defined by microtremor array survey (SPAC method).

Concealed faults in central part of the Matsumoto Basin. An example of underground imaging defined by microtremor array survey (SPAC method).

Investigating the role of the Itoigawa-Shizuoka tectonic line towards the evolution of the Northern Fossa Magna rift basin

Abstract The Itoigawa-Shizuoka tectonic line (ISTL) fault system is considered to have one of the highest probabilities for a major inland earthquake occurrence in the whole of Japan. It is a complex fault system with the dip directions of the local fault segments changing from north to south between an east-dipping low-angle thrust fault, a strike slip fault and a west-dipping thrust fault. The tectonic relations between the different parts of the fault system and the surrounding geological units are yet to be fully explained. This study aims to reveal the juncture of the northern and central parts of the ISTL and investigate its contribution towards the shaping of the Northern Fossa Magna rift basin. We conducted 3 deployments of 1 or 2 linear arrays of seismic stations across the central and northern ISTL regions and observed local micro-earthquakes for a period of 3 years. Each deployment recorded continuous waveform data for approximately 3 months. Using arrival times of 1193 local earthquakes, we jointly determined earthquake locations and a 3D velocity model, applying the tomography method. We were able to image the regional crustal structures from the surface to a depth of 20 km with a spatial resolution of 5 km. Subsequently, we used the obtained 3D velocity model to relocate the background local seismicity from 2003 to 2009. The juncture of the northern and central parts of the ISTL was well constrained by our results. The depth extension of the northern parts of the ISTL fault segments follows the bottom of the Miocene Northern Fossa Magna rift basin (NFM) and forms an east-dipping low-angle fault. In contrast, the central parts of the ISTL fault segments are estimated to lie along the eastern boundary of the Matsumoto basin forming an oblique strike slip fault (Fig. 1).

糸魚川-静岡構造線活断層帯中部,松本盆地南部・塩尻峠および諏訪湖南岸断層群の変動地形の再検討

糸魚川-静岡構造線活断層帯中部,松本盆地南部・塩尻峠および諏訪湖南岸断層群の変動地形の再検討

Distributional Change and Epidemic Introgression in Overlapping Areas of Japanese Pond Frog Species Over 30 Years

Pelophylax nigromaculatus, P. porosus porosus, and P. p. brevipoda are three pond frog species distributed in Japan. Their distributions overlap at two basins in central Japan (P. nigromaculatus and P. p. porosus in the Matsumoto basin, and P. nigromaculatus and P. p. brevipoda in the Ina basin), and hybrid descendants have been found in these areas. To clarify the distribution areas and hybrid zones of the frogs, and to understand the mode of introgressive hybridization and its impact on the frog populations, we conducted exhaustive sampling at each basin and performed allozyme and mtDNA analyses of 233 individuals. Analysis using genetic markers clearly detected nine F1 hybrids and 94 hybrid descendants of P. nigromaculatus and P. porosus from the overlapping areas of both basins. Allozyme and mtDNA data suggest directional hybridization between female P. p. porosus and male P. nigromaculatus in the Matsumoto basin. Over the past 30 years, the distribution of P. p. porosus has been narrowed and fragmented by the invasion of P. nigromaculatus, seemingly because of directional hybridization in the Matsumoto basin. In the Ina basin, the "pure" P. p. brevipoda (n = 8) population was extremely reduced by gene introgression from P. nigromaculatus, yet its distribution was barely changed compared to the Matsumoto basin. Consequently, this study shows that P. porosus populations are threatened by interspecific hybridization with P. nigromaculatus, and that introgressive hybridization damaged P. porosus populations by different means in each basin.

名水を訪ねて（99）松本盆地周辺の名水

名水を訪ねて（99）松本盆地周辺の名水

A Study of Wind Erosion in a Agricultural Area of the Southwestern Matsumoto Basin

A Study of Wind Erosion in a Agricultural Area of the Southwestern Matsumoto Basin

長野県松本盆地のGPS観測(1992-1996)

長野県松本盆地のGPS観測(1992-1996)

Newly-found Surface Faulting Event on the North-central Portion of the Itoigawa-Shizuoka Tectonic Line Active Fault System

The 150 km long Itoigawa-Shizuoka Tectonic Line Active Fault System (ISTL) in central Japan is one of the most active fault systems in Japan. Paleoseismologcal studies 1980s have revealed that the most recent event and the average recurence interval of the ISTL. The approximately 7 km long portion of the fault system between Matsumoto and Okaya has been regarded as a gap without any active fault trace. The gap namely the “Shiojiri Pass Gap” has long been taken as a segment boundary owing to the geometric discontinuity. Recent geomorphological analyses of the gap have demonstrated a through-going left-lateral slip assocaited with recent earthquakes in this area, based on aerial photograph interpretation and excavation studies. Excavation study on this portion revealed that the latest faulting event occurred between 1,700 cal. B.P. to 1,310 cal. B.P. (255 A.D. -645 A.D.). The timing of the last faulting event at this study area coincides with the timing in the Gofukuji fault and Okaya fault. The active faults extending from the Matsumoto basin as far as the northwestern margin of the Suwa basin display the evidence for its recent reactivation at the same time.

Evaluation of seed banks for plant community recovery in abandoned rice fields of Matsumoto Basin, Nagano, Japan

Evaluation of seed banks for plant community recovery in abandoned rice fields of Matsumoto Basin, Nagano, Japan

A Root Cause of Sandy-Dust Storm Occurring in a Agricultural Area of the South West Matsumoto Basin

A Root Cause of Sandy-Dust Storm Occurring in a Agricultural Area of the South West Matsumoto Basin

微動探査と地震波干渉法による松本盆地のＳ波速度構造の推定

糸魚川─静岡構造線（以下，糸静線）は，わが国で最も活発な断層帯の一つとされ，M８クラスの地震が発生する可能性があり，その周辺地域では強震動予測が行われている。より精度の高い予測には信頼性の高い地下構造の情報が必要となる。本研究では，糸静線近傍に位置する長野県松本盆地内の8地点において，微動のアレイ観測を実施し，レイリー波の位相速度を求めた。さらに，それらの逆解析から表層から地震基盤までの1次元Ｓ波速度構造を明らかにした。また，同盆地内の2地点において70日間微動観測を行い，その上下成分に地震波干渉法を適用し2点間のグリーン関数を求め，そのレイリー波の群速度を求めた。さらに，その逆解析から地震基盤までの1次元S波速度構造を明らかにした。この結果は，微動探査による結果とよく一致しており，松本盆地において地震波干渉法の適用が可能であることが分かった。さらに，微動観測記録の水平成分に対しても地震波干渉法への適用も試み，ラブ波の群速度やレイリー波の楕円率も推定することができた。これらの表面波の特徴も微動探査の結果で説明することができた。

Spatial separation of groundwater flow paths from a multi‐flow system by a simple mixing model using stable isotopes of oxygen and hydrogen as natural tracers

Stable isotopes of oxygen and hydrogen have the potential to serve as tracers for both source and flow paths in a groundwater system. The ratios of stable isotopes of oxygen (δ18O) and hydrogen (δD) can be used as natural tracer parameters to separate multiflow groundwater paths by applying a simple inversion analysis method to determine the differences between observed and calculated δ18O and δD data in a simple mixing model. The model presented here assumes that the distribution of natural tracers in the steady state is governed by simple mixing between flow paths with a normal distribution of flow rate. When the inversion analysis and simple mixing model were applied to the multiflow system of the Matsumoto Basin, which is surrounded by Japanese alpine ranges, the end‐members of the relationship between observed δ18O and δD could be separated spatially into specific groundwater flow paths in the multiflow system of shallow and deep groundwater flow paths.

糸魚川‐静岡構造線活断層系・松本盆地東縁断層南部に沿う左横ずれ変位地形

The East Matsumoto Basin faults (EMBF) consist of the northern segment of the Itoigawa-Shizuoka Tectonic Line active fault system (ISTL), central Japan, and extend for ca. 30 km along the eastern margin of the Matsumoto Basin. The faults have been considered to be eastdipping reverse faults, which were re-activated sometime after the tectonic inversion event during the middle Miocene in central Japan. However, we found geomorphic evidence of strikeslip movement on the EMBF, such as systematic left-lateral offsets of abandoned channels and scissoring vertical offsets on the fan surface, which were probably formed during the Nara era. These offsets were measured as left-lateral displacements of 6 to 7 m with a slight vertical component, and were probably formed in association with the most recent faulting event of EMBF. In this case, the style and the amount of slip per event are comparable with those of the neighboring Gofukuji fault, which has one of the highest probabilities of seismic risk calculated among active faults on land in Japan. These refined geomorphic features indicate that the principal slip component on the southern portion of EMBF is not merely dip-slip but left-lateral slip, taking account of the cumulative vertical displacement inferred from uplifted hills since Miocene to Plio-Pleistocene at the eastern side of the fault traces. These facts and presumptions are consistent with the deformation pattern around the ISTL revealed by recent continuous GPS observations. In addition, these new findings allow us to understand that the subsidence in the Matsumoto urban district can be explained as a pull-apart basin related to a 1.5-km-wide left-step between the EMBF and Gofukuji faults. Su8rface geometry, style, and amount of faulting of both faults suggest that this left-step does not seem to be a significant enough segment boundary of the ISTL to arrest rupture propagation. Thus, the portion between the southern EMBF and Gofukuji fault is appropriately a single fault segment.