Investigating a tsunamigenic megathrust earthquake in the Japan Trench

The 2011 Tohoku-oki earthquake occurred in the Japan Trench 10 years ago, where devastating earthquakes and tsunamis have repeatedly resulted from subduction of the Pacific plate. Densely instrumented seismic, geodetic, and tsunami observation networks precisely recorded the event, including seafloor observations. A large coseismic fault slip that unexpectedly extended to a shallow part of megathrust fault was documented. Strong lateral variations of the coseismic slip near the trench were recorded from marine geophysical studies, along with a possible cause of these variations. The seismic activities in east Japan are still higher than those before the earthquake, and crustal deformation is still occurring. Although the recurrence probability of a great earthquake (magnitude = ~9) in the Japan Trench in the near future is very low, a large normal fault earthquake seaward of the Japan Trench is a concerning possibility.

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Tsunamigenic Ratio of the Pacific Ocean earthquakes and a proposal for a Tsunami Index

Natural Hazards and Earth System Science ◽

10.5194/nhess-12-175-2012 ◽

2012 ◽

Vol 12 (1) ◽

pp. 175-185 ◽

Cited By ~ 16

Author(s):

A. Suppasri ◽

F. Imamura ◽

S. Koshimura

Keyword(s):

Pacific Ocean ◽

Focal Depth ◽

Earthquake Magnitude ◽

Great Earthquake ◽

Tsunami Generation ◽

Tsunami Height ◽

Support Tool ◽

The Pacific ◽

Submarine Earthquakes ◽

The Pacific Ocean

Abstract. The Pacific Ocean is the location where two-thirds of tsunamis have occurred, resulting in a great number of casualties. Once information on an earthquake has been issued, it is important to understand if there is a tsunami generation risk in relation with a specific earthquake magnitude or focal depth. This study proposes a Tsunamigenic Ratio (TR) that is defined as the ratio between the number of earthquake-generated tsunamis and the total number of earthquakes. Earthquake and tsunami data used in this study were selected from a database containing tsunamigenic earthquakes from prior 1900 to 2011. The TR is calculated from earthquake events with a magnitude greater than 5.0, a focal depth shallower than 200 km and a sea depth less than 7 km. The results suggest that a great earthquake magnitude and a shallow focal depth have a high potential to generate tsunamis with a large tsunami height. The average TR in the Pacific Ocean is 0.4, whereas the TR for specific regions of the Pacific Ocean varies from 0.3 to 0.7. The TR calculated for each region shows the relationship between three influential parameters: earthquake magnitude, focal depth and sea depth. The three parameters were combined and proposed as a dimensionless parameter called the Tsunami Index (TI). TI can express better relationship with the TR and with maximum tsunami height, while the three parameters mentioned above cannot. The results show that recent submarine earthquakes had a higher potential to generate a tsunami with a larger tsunami height than during the last century. A tsunami is definitely generated if the TI is larger than 7.0. The proposed TR and TI will help ascertain the tsunami generation risk of each earthquake event based on a statistical analysis of the historical data and could be an important decision support tool during the early tsunami warning stage.

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A Survey of the State of the Power Engineering Profession in the Pacific Northwest and what Working Professionals are Defining as Priorities for Preparing Students to Fill Present and Near-Future Vacancies

10.18260/p.26453 ◽

2016 ◽

Author(s):

Donald Peter

Keyword(s):

Pacific Northwest ◽

The State ◽

Power Engineering ◽

Engineering Profession ◽

The Pacific ◽

Near Future

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Subsidence by liquefaction-fluidization in man-made strata around Tokyo bay, Japan: from geological survey on damaged part at the 2011 off the Pacific Coast of Tohoku Earthquake

Proceedings of the International Association of Hydrological Sciences ◽

10.5194/piahs-372-221-2015 ◽

2015 ◽

Vol 372 ◽

pp. 221-226

Author(s):

O. Kazaoka ◽

S. Kameyama ◽

K. Shigeno ◽

Y. Suzuki ◽

M. Morisaki ◽

...

Keyword(s):

Pacific Coast ◽

Tohoku Earthquake ◽

Geological Survey ◽

Japan Meteorological Agency ◽

Tokyo Bay ◽

Great Earthquake ◽

Reclaimed Land ◽

Chiba Prefecture ◽

Detailed Classification ◽

The Pacific

Abstract. Geological disaster by liquefaction-fluidization happened on southern part of the Quaternary Paleo-Kanto submarine basin at the 2011 Earthquake off the Pacific Coast of Tohoku. Liquefaction-fluidization phenomena occurred mainly in man-made strata over shaking 5+ intensity of Japan Meteorological Agency scale. Many subsided spots, 10–50 m width, 20–100 m length and less than 1 m depth, by liquefaction-fluidization distributed on reclaimed land around northern Tokyo bay. Large amount of sand and groundwater spouted out in the terrible subsided parts. But there are little subsidence and no jetted sand outside the terrible subsided part. Liquefaction-fluidization damaged part at the 1987 earthquake east off Chiba prefecture re-liquefied and fluidized in these parts at the 2011 great earthquake. The damaged area were more wide on the 2011 earthquake than the 1987 quake. Detailed classification maps of subsidence by liquefaction-fluidization on the 2011 grate earthquake were made by fieldwork in Chiba city around Tokyo bay. A mechanism of subsidence by liquefaction-fluidization in man-made strata was solved by geological survey with continuous large box cores on the ACE Liner and large relief peals of the cores at a typical subsided part.

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Identification of Paleoearthquakes and Coseismic Slips on a Normal Fault Using High-Precision Quantitative Morphology: Application to the Jiaocheng Fault in the Shanxi Rift, China

Lithosphere ◽

10.2113/2021/2550879 ◽

2021 ◽

Vol 2021 (Special 2) ◽

Author(s):

Junjie Zou ◽

Honglin He ◽

Yusuke Yokoyama ◽

Adam D. Sproson ◽

Yoshiki Shirahama ◽

...

Keyword(s):

Active Faults ◽

Normal Fault ◽

Seismic Events ◽

Quantitative Morphology ◽

Coseismic Slip ◽

Slip History ◽

Absolute Dating ◽

Future Work ◽

Shanxi Rift

Abstract The quantitative morphology of bedrock fault surfaces combined with aerial surveys and field identification is a useful approach to identify paleoearthquakes, obtain coseismic slips, and evaluate the seismogenic capacity of active faults in bedrock areas where traditional trenching methods are not applicable. Here, we report a case study of the Jiaocheng Fault (JCF) in the Shanxi Rift, China. Although several studies have been conducted on the JCF, its coseismic slip history and seismogenic capacity are still unclear. To address these problems, we investigated two bedrock fault surfaces, Sixicun (SXC) and Shanglanzhen (SLZ), on the JCF’s northern segment using quantitative morphological analysis together with aerial and field surveys. Quantitative fractal analysis based on the isotropic empirical variogram and moving window shows that both bedrock fault surfaces have the characteristics of vertical segmentation, which is likely due to periodic earthquakes, the coseismic slip of which can be determined by the height of the segments. Three seismic events at SXC, with a coseismic vertical slip of 1.74, 1.65, and 1.99 m, and three seismic events at SLZ, with a coseismic vertical slip of 1.32, 2.35, and 1.88 m, are identified. Compared with the previous studies, these three seismic events may occur in the Holocene, but it requires absolute dating ages to support, which is also the focus of our future work. Considering the seismologic capability (M>7.5) and the relationship between the recurrence interval of ~2.6 kyr and elapsed time of more than 3 kyr, the seismic hazard of the northern and middle segments of the JCF requires immediate attention.

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Routine location of T-phase sources in the Pacific

Bulletin of the Seismological Society of America ◽

10.1785/bssa0560010109 ◽

1966 ◽

Vol 56 (1) ◽

pp. 109-118 ◽

Cited By ~ 1

Author(s):

Rockne H. Johnson

Keyword(s):

Peak Power ◽

Power Level ◽

Earthquake Magnitude ◽

Origin Time ◽

Arrival Times ◽

Early Results ◽

The Pacific ◽

Least Squares Fit ◽

The Kuril Islands ◽

T Phase

abstract A program for the routine location of T-phase sources in the Pacific is described. Data for this program are supplied principally by the Pacific Missile Range hydrophone network. Arrival times and power levels are read at Honolulu for processing by an IBM 7040 computer. The solution for location and origin time is the least-squares fit to all hydrophone arrivals which are weighted according to their distribution in azimuth and their distance from the T-phase source. The velocities for the program are obtained from algebraic functions of latitude and longitude which are based upon shot calibrations and upon hydrographic measurements. A T-phase strength is computed from readings of peak power level in a manner analogous to earthquake magnitude. Early results for the r.m.s. difference between T-phase source locations and the corresponding earthquake epicenters were 0.6° in the Aleutians and 1.1° in the Kuril Islands.

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Near-future levels of ocean acidification do not affect sperm motility and fertilization kinetics in the oyster <i>Crassostrea gigas</i>

Biogeosciences ◽

10.5194/bg-6-3009-2009 ◽

2009 ◽

Vol 6 (12) ◽

pp. 3009-3015 ◽

Cited By ~ 83

Author(s):

J. N. Havenhand ◽

P. Schlegel

Keyword(s):

Ocean Acidification ◽

Sperm Motility ◽

Crassostrea Gigas ◽

Power Analysis ◽

Early Life History ◽

Marine Species ◽

The Pacific ◽

Sperm Swimming Speed ◽

Near Future ◽

Fertilization Kinetics

Abstract. An increasing number of studies are now reporting the effects of ocean acidification on a broad range of marine species, processes and systems. Many of these are investigating the sensitive early life-history stages that several major reviews have highlighted as being potentially most susceptible to ocean acidification. Nonetheless there remain few investigations of the effects of ocean acidification on the very earliest, and critical, process of fertilization, and still fewer that have investigated levels of ocean acidification relevant for the coming century. Here we report the effects of near-future levels of ocean acidification (≈−0.35 pH unit change) on sperm swimming speed, sperm motility, and fertilization kinetics in a population of the Pacific oyster Crassostrea gigas from western Sweden. We found no significant effect of ocean acidification – a result that was well-supported by power analysis. Similar findings from Japan suggest that this may be a globally robust result, and we emphasise the need for experiments on multiple populations from throughout a species' range. We also discuss the importance of sound experimental design and power analysis in meaningful interpretation of non-significant results.

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