Factors of Variability and Measures for the Shakeability of Long-Period Ground Motion

Yuzawa, Yutaka; Nagumo, Hideki

doi:10.5610/jaee.12.2_41

Cited by 6 publications

(5 citation statements)

References 8 publications

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“…The dominant period of the observed LP waves in the Kanto Basin ranged from 3 to 10 s (e.g., Furumura & Hayakawa, 2007;Yoshimoto & Takemura, 2014), which is roughly proportional to the basement depth; however, the period also varies with the earthquake magnitude (i.e., the source spectrum) and the incident direction of the surface waves to the 3-D basin structure (e.g., Denolle et al, 2013;Furumura, 2014aFurumura, , 2014bYuzawa & Nagumo, 2012).…”

Section: Observed Lp Ground Motions Of the 2007mentioning

confidence: 99%

Early Forecast of Long‐Period Ground Motions via Data Assimilation of Observed Ground Motions and Wave Propagation Simulations

Furumura

Maeda

Oba

2019

Geophysical Research Letters

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We propose an efficient approach for the early forecast of long‐period (> 3–10 s) ground motions generated in sedimentary basins by large earthquakes based on the data assimilation of observed ground motions and finite‐difference method simulations of seismic wave propagation in a 3‐D heterogeneous structure. This approach uses the dense K‐NET and KiK‐net nationwide networks in Japan and a high‐performance supercomputer to perform forecasts using the assimilated wavefields at speeds much faster than the actual wave propagation speed. Therefore, an early alert can be issued prior to the occurrence of strong motions in basins due to large, distant earthquakes. We validated the effectiveness of this data‐assimilation‐based forecast approach via numerical tests for the early forecast of long‐period ground motions in central Tokyo using the observed waveform data from the Mw6.6 2007 Off Niigata and Mw9.0 2011 Off Tohoku earthquakes.

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Section: Observed Lp Ground Motions Of the 2007mentioning

confidence: 99%

Early Forecast of Long‐Period Ground Motions via Data Assimilation of Observed Ground Motions and Wave Propagation Simulations

Furumura

Maeda

Oba

2019

Geophysical Research Letters

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“…The excitation and propagation of significant later arrivals with a predominant period of 5 s during the 2011 event were not affected by the trenchlike structure of the Kanto Basin. Yuzawa and Nagumo (2012) studied the shakability of long-period ground motion in Kanto Basin and pointed out that its variability is due to source region. They interpreted the amplitude variation as due to the distance that the surface wave travels through sedimentary layers.…”

Section: Effects Of Source Region Velocity Structurementioning

confidence: 99%

“…Both epicenters were located northwest of Tokyo Bay, and the distances from Tokyo Bay were comparable. Usually, ground motion characteristics are estimated based on source parameters, path distance, and site conditions (e.g., Kanno et al 2006;Yokota et al 2011;Yuzawa and Nagumo 2012). Considering this, although the ground motions observed in the Tokyo Bay area during these two events should have shown similar characteristics, their seismograms showed some differences.…”

Section: Introductionmentioning

confidence: 99%

Effects of subsurface structures of source regions on long-period ground motions observed in the Tokyo Bay area, Japan

Uetake

2017

Earth Planets Space

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We compared the long-period ground motion observed in the Tokyo Bay area during two shallow M6.7 earthquakes that occurred in northern Nagano Prefecture, Japan, on March 12, 2011, and November 22, 2014. The magnitudes, focal depths, and source mechanisms of these events were almost identical, but their seismograms were quite different. Significant long-period later arrivals with a predominant period of 5 s were recognized in the velocity traces of the 2011 event, but there were no such remarkable later arrivals in the 2014 event traces. The ground motions at stations located outside the basin area were studied as incident waves to the Kanto Basin. A large wave packet with a predominant period of 5 s was recognized in the velocity traces of the 2011 event, but there was no significant wave packet in the 2014 event traces. Based on particle motion, this wave packet was hypothesized to be a Rayleigh wave. The source regions of the two events have quite different subsurface structures. The different characteristics in longperiod ground motion in the Tokyo Bay area during the two events were due to different Rayleigh wave excitations in the source regions.

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“…However, the propagation and amplification of the LP ground motions in large basins are significantly influenced by the heterogeneous 3‐D subsurface structures along long propagation paths and cause strong focusing and defocusing (e.g., Denolle et al, 2013; Frankel et al, 2018; Furumura & Hayakawa, 2007; Mukai et al, 2018; Wirth et al, 2019). For example, the amplification of the LP ground motions in the Kanto basin was shown to have large variations with respect to the incident angle of the LP surface waves to the basin edge; the amplification was larger for the earthquakes occurring in the north to southwest of Tokyo, whereas it is much weaker for the earthquakes occurring in the northeast (e.g., Furumura, 2014; Uetake, 2017; Yuzawa & Nagumo, 2012). Also, the earthquakes occurring in the Nankai Trough are usually characterized by longer durations of LP ground motions after traversing the accretionary wedge of the Nankai Trough subduction zone (Furumura et al, 2008; Hayakawa et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Data Assimilation‐Based Early Forecasting of Long‐Period Ground Motions for Large Earthquakes Along the Nankai Trough

2020

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Long-period (LP) ground motions with periods of~2-10 s caused by large earthquakes are strongly amplified in sedimentary basins, posing serious threats to modern cities to cause resonance and damage to skyscrapers, oil storage tanks, long-span bridges, and other structures with long natural periods. Since the LP ground motions are composed of surface waves traveling for longer distances with much slower speeds than body waves, an alert could be issued by detecting the spread of strong ground motion near the source and before large ground motions occur in distant basins. In this study, an early forecasting of LP ground motions is proposed based on data assimilation of observed ground motions obtained by high-density, nationwide seismic networks and a computer simulation of the seismic wave propagation using a high-resolution subsurface structure model. The shaking of the LP ground motions in the distant basins is immediately forecasted by high-speed supercomputers from current data-assimilated wavefield. In addition, the forecasting speed is significantly improved by using Green's functions, representing the wave propagation response from the data assimilation stations to a forecast target site. The effectiveness of this data assimilation-based forecasting of LP ground motions in conjunction with using Green's functions is demonstrated by numerical tests using the observed strong motion records from the 2004 Off Kii Peninsula earthquake in Japan (Mw 7.4) together with synthetic seismograms of anticipated large earthquake scenarios in the Nankai Trough.

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Factors of Variability and Measures for the Shakeability of Long-Period Ground Motion

Cited by 6 publications

References 8 publications

Early Forecast of Long‐Period Ground Motions via Data Assimilation of Observed Ground Motions and Wave Propagation Simulations

Early Forecast of Long‐Period Ground Motions via Data Assimilation of Observed Ground Motions and Wave Propagation Simulations

Effects of subsurface structures of source regions on long-period ground motions observed in the Tokyo Bay area, Japan

Data Assimilation‐Based Early Forecasting of Long‐Period Ground Motions for Large Earthquakes Along the Nankai Trough

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