Facing the Japan Trench, where the Pacific tectonic plate subducts, Sanriku is an important area because, as the so-called origin of the Japanese archipelago, it contains a continuous geological record extending back 500 million years. It is also a region that has experienced several historically strong earthquakes and resulting tsunamis, including the Tohoku Earthquake and Tsunami in March 2011. At the Sanriku Geopark, young people are taught the history of the Earth and about the area’s natural disasters. Jodogahama Beach, which is located at the central part of the Sanriku Coast, is a place where you can sense an active nature of the Earth. The form of the cape and the white rocks are characteristic features of Jodogahama beach. The landscape is so beautiful that it has been named Pure Land Beach, and it has become a representative scenic spot of the Sanriku Coast. In addition to the scenic beauty of Oku-Jodogahama and Usuki-Yama along the walking trails at Jodogahama, traces of magma flows, showing the flow structure before the magma cooled and hardened, can also be observed in the rocky outcrops. Furthermore, geological formations and scenic beauty can be observed at close proximity to the sea when taking sightseeing cruises and Sappa boat trips. (Photograph and explanation: Shinichi SUGIMOTO)
Changing land use patterns are clarified from time and space points of view. Relationships are revealed between changing land-use patterns and port functions in the Kaigan area of the Tokyo waterfront, Minato Ward, Tokyo Metropolis. After Tokyo port opened in 1941, the Tokyo waterfront area was used mainly for logistics facilities, such as warehouses and port facilities. However, since the 1960s, the logistics system in the port has been changed by containerization. Port facilities in the Tokyo waterfront area became outdated. In response, the Tokyo waterfront area was redeveloped in the mid-1980s. As a result, significant changes to land use occurred in the Tokyo waterfront area. This study selects three target years, 1985, 1996, and 2012. A mesh analysis is conducted of land use in the Kaigan area, Minato Ward, Tokyo district. From 1985 to 1996, the port policy changed land use in the port district away from logistics facilities, including warehouses and port facilities. From 1985 to 1996, vacant land for redevelopment increased during the period of the asset inflation-led bubble economy. In comparison with the period from 1985 to 1996, during the period of from 1996 to 2012, land use changes in the port district ceased and changes outside the port district continued. These are connected to changing port functions. Since the 2000s, the number of passenger ships using Takeshiba pier has increased, promoting changes to urban land use in the surrounding area. On the other hand, at Shibaura pier, the number of the cargo ships entering remains unchanged, and land in the vicinity has continued to be used for logistics facilities such as warehouses and port facilities. Consequently, relationships are suggested between changing land-use patterns and port functions.
The Sanriku coast was believed to have followed an uplifting trend in the geological time-scale on the basis of it being a flat surface interpreted as a Pleistocene marine terrace. On the contrary, geodetic and tide-gauge data show a rapid trend of this area subsiding during the last several decades. This area also experienced extensive subsidence during the 2011 Tohoku-oki earthquake (Mw 9.0). The discrepancy between long-term uplift and short-term subsidence has been pointed out by several researchers, but remains unresolved. Knowledge of sedimentary facies and deposition ages of the Holocene sequence is required to consider this problem. The depositional process of the Holocene sequence and crustal movement is discussed on the basis of coastal geology. A sediment core, KO1, was acquired from the lower reach of the Kesennuma Okawa Plain, southern Sanriku coast. Core sediments show typical deltaic succession influenced by Holocene sea-level change. Relative sea-level (RSL) at 9.6 to 10.1 cal BP is estimated to be −37 to −34 m based on the depositional surface of tidal flat deposits including molluscan shells living in the intertidal zone. Estimated RSL is lower than the theoretical RSL without tectonic effects. A probable cause of this discrepancy is Holocene tectonic subsidence in the area studied. Unlike previous arguments for a long-term uplift, particularly in northern Sanriku, the results of this study reinforce the theory that the south Sanriku coast subsided in the geologic time-scale.
This study is based on an Internet survey of prospective tourists visiting the Sanriku Geopark, which was conducted to understand their travel habits, impressions of the Sanriku coastal area, general awareness of the Geopark, and motivations for travelling. A principal component analysis (PCA) is also performed using a multivariate analysis technique to examine the characteristics of tourists and images of travel destinations they would want to visit in the future. The results demonstrate low awareness of the Sanriku Geopark, especially in metropolitan areas. The majority of respondents do not have a definitive image of the Geopark. The results also indicate that tourists visiting the Sanriku coast are primarily from neighboring prefectures, such as Miyagi and Aomori, as well as from the Tokyo metropolitan area. This suggests that increasing informational awareness of the Sanriku Geopark in these areas would be effective way for attracting more visitors. Regarding their travel habits, the respondents' answers indicate that they mostly go on two-day family trips in a private vehicle. In the majority of cases, their purpose for travelling is “to feel refreshed” or “to eat delicious food.” Based on these data, a PCA employing variance-covariance matrices reveals that tourists are basically seeking “extraordinary” and “healing” experiences from their travels. The principal component scores from the PCA are used and the average scores of each gender are calculated. A t-test reports no significant difference between genders with regard to seeking an “extraordinary” experience, but it identifies a trend among women of seeking “healing” experiences more actively than men (p < 0.10) at a level of 0.1%. On the other hand, regarding the tourists' impressions of the Sanriku coastal area, the results of the multivariate analysis suggest that prospective visitors tend to perceive the coastal area comprehensively in terms of both “nature and scenery” and “local area and culture” to the same degree as those who have previously visited the place. For the area to be resuscitated as a tourist destination, it is important to construct a regional brand and devise strategies that will lead to the region's rebirth as a top travel destination. This can be achieved by offering higher quality experiences and services without destroying the traditional image of the Sanriku coast.
Hummocks are conically shaped mounds, which occur following catastrophic sector collapses, and are mainly observed around volcanoes. Empirical relationships of hummocks proposed by Yoshida et al. (2012) are basically applicable if hummocks now distributed on a debris avalanche depositional area do not have remarkable disturbances due to topographical barriers or modifications after deposition. Using these empirical relationships, the Old Yotei volcano, whose mega-collapse in the Late Pleistocene has not been clarified yet, is examined. The results show that the size-distance relationship of hummocks (N=297), distributed west of the volcano can be expressed by an exponential function as, A=α exp (−β D), where A is the average area of a hummock within a certain span and D is the average distance from the source. For the Old Yotei volcano, the values of coefficients α and β of the fitted curve are 170286.4 and 0.000429, respectively. Based on a geomorphological interpretation of both α and β values, it can be concluded that the collapse volume of the Old Yotei volcano is ca.1.3 km3, and the equivalent coefficient of friction of the debris avalanche is 0.129. The latter also reveals a high probability that the pre-collapse summit of the Old Yotei volcano reached 1700 m a.s.l. Thus, the image of the flank collapse of the Old Yotei volcano has been restored more decisively by the distribution of hummocks.
The Miocene collision of the Izu-Bonin arc with the Honshu arc in Japan is thought to have initiated eastward bending of the Median Tectonic Line (MTL) from an approximate E-W strike to an ENE-WSW strike in the Ise area of the easternmost Kii Peninsula. However, the exact surface trace of the MTL in the Ise area remains poorly defined because of Quaternary sediment cover and the development of urban areas. Determination of the surface trace of the MTL is important to evaluate the characteristics of seismic motion upon the paired metamorphic belts divided by the MTL, which reflects the subsurface geology, and to better explain the curvature of the MTL in central Japan. This paper presents the results of petrographic observations from several localities in the Ise area, including Tamaki Town and Ise City: boring cores at (1) the factory building of Miwa Lock Co., Ltd., in Tamaki Town, which overlie the MTL, (2) Ise City Hall, (3) Ise City Tourism and Culture Hall, as well as additional boring data from Ise City. The depth of pre-Neogene basement increases eastward from the Gokatsura area, ranging from 6-12 m in the Sanbagawa belt near Ise City Hall to greater than 30m in the Ryoke Belt. A geological survey of rare exposures, including the Ryoke rocks of the Ooike pond area in Tamaki Town, Miocene conglomerate along the Miyagawa River in the Ryoke belt, and Sanbagawa schists in Ise City, have helped to constrain the exact location of the MTL in Ise City. Through this study we have also signalized the potential of investigated sites in Ise city to be used as prospect geosites in future. After proper development and promotion these sites can become important points of attention to be seen by visitors and geologists and provide various opportunities for local economy growth.
The Uemachi fault zone extends north to northeast for about 51 km across metropolitan Osaka, southwest Japan. We conducted paleseismological surveys along the fault zone to estimate the timing of recent faulting events. We identified two reverse faulting events in the northern section of the fault zone, including the latest event, which occurred after ca. 2400 yr BP. In the southern section, the timing of the most recent event is estimated to be ca. 2200–2300 yr BP or later. The timing of the latest events in the northern and southern sections is coincident, implying that the most recent event was a multi-segment rupture through the whole Uemachi fault zone. We also examined geomorphic changes around the fault zone resulting from the most recent faulting event, based on previously reported archaeological and geological studies. As a result, we found: 1) coastal uplift occurred in the Osaka Castle Town archaeological site on the hanging wall side of the fault zone at the end of the middle Yayoi period; and, 2) numerous archaeological sites around the old Lake Kawachi were abruptly submerged at the end of the middle Yayoi period, and the submerged area had not been in residence again until around the final stage of the Yayoi period. These major, simultaneous geomorphic changes can be explained only by crustal movements resulting from a faulting event in the Uemachi fault zone. Thus, the timing of the most recent faulting event is estimated to be at the end of the middle Yayoi period. To evaluate the total risk due to active faulting, we have to understand not only tectonic landforms and coseismic surface ruptures, but also related regional abrupt geomorphic changes such as coseismic broader submergence in the Kawachi Plain from the perspectives of tectonic geomorphology and paleoseismology.
The overall configuration of the Cretaceous subduction-related arc-trench system in Japan is preserved in the current distribution of the relevant orogenic components; i.e., the coeval set of accretionary complexes formed at the trench (Sanbosan and North Shimanto belts) , high-P/T meta-ACs along the Wadati–Benioff zone (Sanbagawa and Shimanto metamorphic belts) , arc batholiths (Ryoke–Sanyo and San-in belts) , and fore-arc basin strata (Ryoseki–Monobegawa and Izumi groups) . To document the sediment distributary pattern within the Cretaceous arc-trench system and the composition of relevant provenance, detrital zircon dating was conducted for the Upper Cretaceous sandstones (Atogura and Tochiya formations) from the northern Kanto Mountains. These strata occur immediately to the south of Median Tectonic Line of SW Japan, and as klippe with unknown origin. The results of U-Pb dating by LA-ICPMS show that three sandstones have common age spectra with four major age groups; i.e., 120–150 Ma (Early Cretaceous) , 170–200 Ma (Jurassic) , 250–300 Ma (Permian) , and 1600–2200 Ma (Paleoproterozoic) , with minor amounts of much older grains up to 2900 Ma (Archean) . These age spectra are unique, when compared to other coeval Cretaceous fore-arc and/or intra-arc sandstones in Japan. The Early Cretaceous grains were obviously derived from a proximal source to the depositional site, probably the Cretaceous volcanic arc of the Ryoke–Sanyo belt in SW Japan. The dominant grains of the Jurassic and Permian ages were probably derived from coeval plutonic belts in the provenance, whereas the Paleoproterozoic grains were probably derived from continental blocks in East Asia with crusts of corresponding ages, such as the North and South China blocks. Except for the Cretaceous arc source, Jurassic and Permian granitoids are extremely rare in major parts of Japan, and the Paleoproterozoic crust is totally absent. The only exception to the occurrence of Jurassic and Permian granitoids exists in the Hida belt of SW Japan. The age spectra of the analyzed Upper Cretaceous sandstones differ remarkably from those of other coeval fore-arc sandstones, whereas they clearly show similarities to Cretaceous sandstones in the Hida belt. This suggests that the analyzed Upper Cretaceous sandstones were primarily deposited in a domain far from the present position but with a close link to the Hida belt, which is located more than 100 km away to the northwest. Tectonic emplacement onto the present position immediately above the Cretaceous high-P/T meta-ACs probably took place during the Paleogene and Neogene, likely in relation to Miocene rifting of the Japan Sea. This study provides the first evidence of the across-arc geotectonic link between back-arc and fore-arc domains of Cretaceous Japan.
There are two emerged abrasion platforms on Enoshima Island, Kanagawa Prefecture, Southern Kanto district: the 4.0-meter-high Ryoshimachi surface, and the 1.0–1.3-meter-high Iwaya surface. Both emerged prior to the 1703 Genroku Earthquake. Considering uplift due to the 1923 Taisho Kanto Earthquake and non-seismic subsidence since the Genroku Era, uplift due to the 1703 Genroku Earthquake was 0.7 m or less, assuming that the height of Ryoshimachi surface before the Genroku Earthquake was 3 m or higher. This indicates that uplift of the Genroku Earthquake at Enoshima was smaller than that of the Taisho Earthquake, and the focal regions of the two earthquakes were different in the Sagami Bay. These two earthquakes are not repeating earthquakes at the Sagami Bay area.
A total of 27 beachrock and consolidated samples were collected from Ie Island, Okinawa, to determine their accumulation ages and/or formation of beachrock. They were radiocarbon dated and their stable carbon isotope ratios (δ13C) were measured to correct radiocarbon ages. Beachrocks were formed from ca. 4,600 cal BP until around 690 cal BP. Nyateya-gama cave is a sea-cave whose floor sediments have been partially consolidated since ca. 3,600 cal BP. The characteristics of the deposits resemble beachrock; however, they do not indicate a typical cuesta topography.