Koji Okumura

Hiroshima University | HU · Division of Geography, Archaeology, and Cultural Heritage Studies

Since Nepal is an earthquake-prone country due to the collision of the Indian and Eurasian plates, it is crucial for its capital of Kathmandu to evaluate ground motion hazards from a future large earthquake. For this purpose, we constructed a realistic scenario earthquake with realistic rupture parameters in a likely location. To obtain the locatio...

We constructed a new distribution of the rupture zones of great historical earthquakes along the Main Himalayan Thrust (MHT) by integrating the distribution in a previous study and the results of recent trench surveys. Additionally, recent Global Navigation Satellite System (GNSS) observations revealed that the boundary between the Indian and Euras...

Fault displacement hazard assessment is based on empirical relationships that are established using historic earthquake fault ruptures. These relationships evaluate the likelihood of coseismic surface slip considering on‐fault and off‐fault ruptures, for given earthquake magnitude and distance to fault. Moreover, they allow predicting the amount of...

Debris avalanches caused by volcano sector collapse often form characteristic depositional landforms such as hummocks. Sedimentological and geomorphological analyses of debris avalanche deposits (DADs) are crucial to clarify the size, mechanisms, and emplacement of debris avalanches. We describe the morphology of hummocks on the northeastern flank...

Fault Displacement Hazard Assessment is based on empirical relationships from historic fault ruptures. These relationships establish the likelihood of co-seismic fault displacements values, for on-fault (i.e. along the primary earthquake fault) and off-fault (i.e. distributed surface rupture off the primary rupture) displacements, for a given earth...

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Debris avalanche caused by the sector collapse of a volcanic mountain often forms characteristic depositional landforms including hummocks. Not only sedimentological but also geomorphological analyses of debris avalanche deposits (DAD) are crucial to clarify the size, mechanisms, and processes of the debris avalanche. We investigate the morphology...

In the last twenty years, the interest of scientific community towards Earthquake Environmental Effects (EEEs) has progressively increased especially in the frame of INQUA - International Union for Quaternary Research. In 2007 the ESI 2007 (Environmental Seismic Intensity scale) was published, a new intensity scale based only on EEEs resulting by a...

With the development of modern techniques, we are able to improve the mapping of faint coseismic or cumulative surface deformation features, potentially enabling detection of blind faults. This also opens the opportunity to improve the empirical relationships relating earthquake magnitude to coseismic surface displacement or fault length towards th...

http://www.isprambiente.gov.it/it/pubblicazioni/periodici-tecnici/memorie-descrittive-della-carta-geologica-ditalia/earthquake-environmental-effect-for-seismic-hazard-assessment-the-esi-intensity-scale-and-the-eee-catalogue In the last twenty years, the interest of scientific community towards Earthquake Environmental Effects (EEEs) has progressive...

The Kumaun Sub-Himalaya region is one of the most active regions falling into Seismic Zone V along the Himalaya. The geomorphology and drainage patterns in the area of active faulting and related growing fold provide significant information on the ongoing tectonic activity. The Kaladungi Fault (KF), an imbricated thrust fault of the Himalayan Front...

The Mw 9.0 Tohoku-oki earthquake and the record of major historical seismic events including the AD 869 Jogan earthquake on the Japan trench illustrate the active tectonic capability on the subduction zone. The recent coastal deformation is revealed by the 2011 coseismic subsidence (up to 1.2 m) and postseismic uplift (up to 20 cm within 1.5 years)...

The strain accumulating between M9-class earthquakes is a major component of the active deformation that contributes to resolve the pattern of seismic cycle at plate boundary zones. Recent geodetic and seismotectonic works constrain the ~ 500-km-long 2011 Tohoku megathrust rupture and related slip distribution. Here, we investigate marine terraces...

The French-Japanese PALET project (ANR-JST Flash program) aims to constrain the seismic cycle and long-term faulting behaviour of the NE Japan subduction zone. The project is three fold: I - The study of marine terraces, benches and notches along the 500 km long coastline affected by the 2011 Mw 9.0 Tohoku-oki earthquake. They indicate that uplift...

Accurate location and geometry of seismic sources are critical to estimate strong ground motion. Complete and precise rupture history is also critical to estimate the probability of the future events. In order to better forecast future earthquakes and to reduce seismic hazards, we should consider over all options and choose the most likely paramete...

The discrepancy between geologic and geodetic slip rate along the North Anatolian fault has been more evident as solid incremental (Kondo et al. 2010) and cumulative (Kozaci et al. 2009, Okumura et al. 2010) slip rate data are accumulated. The strain transient effect (Kozaci et al. 2009) could be a plausible cause for the discrepancy. At the same t...

Completeness of historic earthquake catalogs must be examined by geologic records, though the geologic records are not always more complete and precise than historic records. The historic records on large earthquakes from the North Anatolian fault are tested in trenches on the 1944 segment. Previous results indicated 3 historic and 1 geologic event...

Structural simplicity of a highly-active fault system is a requisite for characteristic recurrence of large earthquakes. Recent paleoseismological studies on timing and repeated slips on the North Anatolian fault and the San Andreas fault have evidenced the condition. Regular recurrent earthquakes of similar size in a fault segment seems to be real...

A light detection and ranging (LiDAR) survey was conducted in a densely built-up area to generate a high-resolution digital elevation model (DEM) to look for active faults. The urban district of Matsumoto City in central Japan is located in a 3-km2 basin along the Itoigawa–Shizuoka Tectonic Line active fault system, one of Japanese onshore fault sy...

Annually laminated carbonates, known as tufas, commonly develop in limestone areas and typically record seasonal patterns of oxygen- and carbon-isotope compositions. δ18O values are principally controlled by seasonal changes of water temperature, whereas δ13C values are the result of complex reactions among the gaseous, liquid, and solid sources of...

Tufas are freshwater carbonates widely developed in limestone areas under temperate and tropical climates. The stable isotopic and the other chemical properties of the tufas changes with climatic conditions. Because of the relatively high depositional rate and development of annual lamination, the tufas can be ideal paleoclimatic archives that supp...

Ten years have past since the first official assessment of the long-term seismic risks of the Itoigawa-Shizuoka tectonic line active fault system (ISTL) in 1996. The disaster caused by the1995 Kobe (Hyogo-ken-Nanbu) earthquake urged the Japanese government to initiated a national project to assess the long-term seismic risks of on-shore active faul...

LiDAR that provides us high-resolution DEM has been successfully applied to the field of active tectonics recently to reveal invisible and obscure active faults, especially in forested areas. Here, we apply the LiDAR to an urban district in which detailed fault mapping is normally difficult due to densely populated buildings and artificial modifica...

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 inver...

The Bam fault zone is a major active fault zone in southeastern Iran. Geomorphic evidence indicates that it has been responsible for repeated faulting events since the late Pleistocene. The 26 December 2003 Bam earthquake was associated with a 14 km fresh surface rupture trending northsouth along the preexisting Bam fault zone. However, an en echel...

Severe ground shaking from Mw 6.5--7.0 blind faulting events as in Kobe 1995, in Bam, Iran 2004 or in Chuetsu, Japan 2004 often causes intensive damages. These unexpected but intensive shocks raised skepticism on long-term earthquake forecasts based on historic and geologic records. This paper aims to examine the validity and limitation of geologic...

Sakhalin Island straddles an active plate boundary between the Okhotsk and Eurasian plates. South of Sakhalin, this plate boundary is illuminated by a series of Mw 7–8 earthquakes along the eastern margin of the Sea of Japan. Although this plate boundary is considered to extend onshore along the length of Sakhalin, the location and convergence rate...

The 1944 Bolu-Gerede earthquake (M-s 7.3) occurred along the North Anatolian fault in northern Turkey and ruptured for about 180 km of the fault. The surface slip distribution and fault geometry, which provide fundamental data on detailed fault segmentation and recurrence of faulting during a multisegment rupture, are poorly known for this event. W...

The Itoigawa-Shizuoka Tectonic Line active fault system in central Japan extends for ca.150 km and it is one of the most active faults on land. It consists of east-dipping reverse faults, north-west trending left-lateral strike-slip faults and west-dipping reverse faults. The Shimotsutaki fault consists of the southeastern portion of the central fa...

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The Bam fault is an active Quaternary fault that runs over 50 km. The segments north and south of the Bam scarp are high-angle faults with small east-side-up component. There are possible offset streams that indicate predominant right-lateral strike-slip offset. The Bam scarp represents an east dipping flexure or monocline on the east wing of an as...

The Bam fault zone is a major active fault zone in southeastern Iran. Geomorphic evidence indicates that it has been responsible for repeated faulting events since late Pleistocene. The December 26, 2003 Bam earthquake was associated with two fresh surface ruptures 5 km apart trending north-south and a 2 km wide zone of hairline fractures developed...

During the December 26th, 2006 Bam earthquake, continuous ruptures with a consistent rightlateral strike-slip of a few centimeters occurred north of Bam. A 3km long strand of ruptures coincides exactly with the trace of the geologic Bam fault. These ruptures were possibly caused by the tectonic slip on the source fault of the 2006 earthquake. The B...

The Kuromatsunai lowland fault zone in southwest Hokkaido is one of the major active faults in Japan. This 30-km-long and 5-km-wide fault zone consists of many N-S-trending, several-km-long thrust faults, which are closely related to the folding structure of the thick sediments of late Miocene to early Pleistocene age. The folding structure has bee...

We excavated four new fault crossing trenches and a complex of fault parallel trenches at Ardicli, 15 km east of Gerede on the 1944 Bolu-Gerede segment of the North Anatolian fault to resolve timing and slip in past earthquakes. A unique large gravel-filled channel (unit 10) was determined to be offset 17 to 20 m. Preliminary age control on the gra...

Paleoseismic studies of two historically aseismic Quaternary faults in Australia confirm that cratonic faults in stable continental regions (SCR) typically have a long-term behavior characterized by episodes of activity separated by quies- cent intervals of at least 10,000 and commonly 100,000 years or more. Studies of the approximately 30-km-long...

The amount of slip per event is one of the most important parameters establishing a recurrence model of large earthquakes. In Japan, previous works have usually exposed only two trench walls, and recognition of faulting events and estimation of holizontal slip have some uncertainty. This study tried to estimate accurate slip per event and identify...

A 180-km-long right-lateral surface rupture associated with the 1944 Bolu-Gerede earthquake (Ms 7.3) was re-examined by interpretation of aerial photographs taken in the 1970's, field observations of tectonic landforms and offset topographic features, and interviews to the villagers. The 1944 rupture is divided into five geometrical or behavioral s...

Though the intensive research on the North Anatolian fault after the 1999 Kocaeli earthquake brought a lot of information on the present and past activity of the fault, our knowledge about the rupture history and the past slips along the entire length of the North Anatolian fault is still very limited. More precise data on the timing and amount of...

The 150-km-long Itoigawa-Shizuoka tectonic line active fault system (ISTL)in central Japan is one of the most active Quaternary fault systems inJapan. Estimated slip-rates on the fault system are as large as 10 m/ka, butthe historic seismicity has been low since 841 A.D. with no largeearthquakes recorded. The high slip rates contrast with the long...

The Median Tectonic Line active fault system (MTL) is one of the most active and longest active faults on land in Japan, and has a potential source of destructive large earthquakes. However, paleoseismological data along the MTL are sparse in Shikoku. The history of surface-rupturing earthquakes, particularly the timing of the latest events, on eac...

Japanese and Turkish researchers on the geology of earthquake are now conducting a joint research on the Kocaeli (or Izmit) earthquake of August 17, 1999. The mission is based on the urgent needs to understand the earthquake itself as well as the past earthquakes in and around the Marmara Sea. This field report introduces the outline of the ongoin...

We have prepared a preliminary active fault map of Sakhalin, Russia, based on an interpretation of aerial photographs and satellite images. Major active structures include 110-km-long active faults along the western margin of the Yuzhno-Sakhalinsk Lowland in southern Sakhalin and 120-km-long active faults along the western margin of the Poronaysk L...

The Bocono fault is a major NE–SW-trending, dextral fault that extends for about 500 km along the backbone of the Venezuelan Andes. Several large historical earthquakes in this region have been attributed to the Bocono fault, and some of these have been recently associated with specific parts through paleoseismologic investigations. A new trench st...

An active fault system extends for about 200 kilometers along the Median Tectonic Line (MTL) in Shikoku, Southwest Japan. Along this fault system, previous studies recognized a 10-km-long gap in the surface trace in the eastern part of the Matsuyama Plain. The gap is the largest so far found in Shi-koku. The authors newly identified very distinct s...

We review progress of geological and geomorphological approaches in paleoseismology in Japan during the this decade. We emphasize the growth of active fault studies since the 1995 Kobe earthquake. Two examples of intensive trenching studies, one on the Itoshizu-Tectonic Line in central Japan, and the other on the Miura Peninsula south of Tokyo, are...

Trenching, microgeomorphic mapping, and tree ring analysis provide information on timing of paleoearthquakes and behavior of the San Andreas fault in the Santa Cruz mountains. At the Grizzly Flat site alluvial units dated at 1640-1659 A.D., 1679-1894 A.D., 1668-1893 A.D., and the present ground surface are displaced by a single event. This was the...

The Itoigawa?Shizuoka tectonic line active fault system (ISTL) is one of the longest and the most complex active fault systems on land in Japan with very high activity. The system comprises the northern (55 km long east dipping reverse faults), the middle (60 km long left-lateral strike-slip faults), and the southern (35 km long west-dipping revers...

Associated with the Hyogo-ken Nanbu earthquake of January 17, 1995 (MJMA 7.2), a 10.5km long surface fault ruptures, the Hokudan Earthquake Fault System, appeared along the Nojima Fault and the Mizukoshi Flexure on the northwest coast of Awaji Island, central Japan. The surface ruptures consist of a NE-SW trending right-lateral fault system with hi...

Tephrochronology of Akan, Kutcharo and intercalating exotic marker tephras innovated the chronology and correlation of Middle to Late Pleistocene marine terraces in eastern Hokkaido. The vertical displacement of M1 and older paleoshorelines along the Okhotsk Sea indicates two distinctive uplift zones of Abashiri and Shiretoko. On the Pacific coast,...

Correction and calibration of radiocarbon dates are indispensable procedures for accurate and precise age estimation. The most significant factors for correction and calibration are reservoir effect isotopic fractionation, and secular variation in atmospheric ¹⁴C-concentration. The correction of the reservoir effect is enabled by carbon-cycle model...

The Shikotsu and Kuttara volcanoes erupted violently during the Late Pleistocene and provided many time-marker tephra layers. These layers are important for the Quaternary tephrochronological studies in the Ishikari Lowland, Hidaka District, and Tokachi Plain. New radiocarbon dates have been obtained by accelerated mass spectrometry. By correlating...

The middle section of the Itoigawa-Shizuoka Tectonic Line (Middle ISTL) is an active fault system that extends NW-SE for 50km from Matsumoto to Kobuchizawa, in central Japan. The Middle ISTL is characterized by high average slip-rate reaching 8 to 10mm/yr during the Late Pleistocene and Holocene. This is one of the highest slip-rate reported from a...

Four modes of mixture of oceanic materials such as cherts, limestones and basalts, and terrigenous trench fill sediments are recognized in the Cretaceous accretionary complexes in southern Sakhalin, Far eastern Pacific margin of the U.S.S.R. The first mode is a thin-skinned stacking of pelagic bedded cherts with black shale, due to duplex formation...

The tephrostratigraphy in eastern Hokkaido is described in this paper in order to summarize recent progress and to show the outline of Quaternary tephras in Hokkaido. The stratigraphy of pyroclastic flow deposits from Akan and Kutcharo volcanoes, which have the longest history of explosive activities in Hokkaido, has been revised and interrelated t...

The Atotsugawa fault extends 60km or more in the northern Hida Mountains of central Japan, linearly running from ENE to WSW, and forms a master active fault system with predominantly right-lateral component of displacement. A historical large earthquake (1858, M≅7.0) occurred in this region, and many small to micro-earthquakes are taking place alon...

The Toya pyroclastic flow deposit is one of the largest tephras of late Pleistocene in northern Japan, covering wide areas of the western part of Hokkaido around the Toya caldera. We have extensively investigated a fine-grained vitric ash layer which has very similar petrographic and chemical properties to the Toya pyroclastic flow deposit in many...

The interglacial climates in northern Japan were slightly warmer to cooler than today, and the relic red soils in Hokkaido were formed under repeated interglacial climates from around 500 000 BP. -from Authors

A catalog for late Quaternary marker-tephras occurring in northern Japan is presented. Characterization of tephras for identification is based on a combination of their features. Stratigraphic and petrographic descriptions are indispensable in correlation of distal tephras with proximal ones. As a result of characterization of tephras in northern J...

The Nara Basin, the eastern rim of which is bordered by N-S trending faults and flexures, is located in the central part of the Kinki Triangle. Terraces have been deformed along the Tenri and Narasaka flexures. These flexures are surface expressions of the reverse faults in bed rocks. The average rate of the vertical component of the deformation is...

A US-Japan team made geoslicer surveys of liquefaction features in the New Madrid seismic zone of the central United States in the fall of 2001, with hopes of improving methods for estimating ground motions from historic and prehistoric earthquakes. Large earthquakes occurred on December 16 (twice), 1811, and on January 23 and February 7, 1812 at t...

Geologists and seismologists in the United States have been compiling and publicizing databases on possible sources of earthquakes including active faults since early 1970s. The ideas about the database and risk assessment have evolved in close response to public demands raised by such unforeseen earthquake hazards in 1989 Loma Prieta earthquake an...