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Long-period ocean-bottom motions in the source areas of large subduction earthquakes.

Nakamura T, Takenaka H, Okamoto T, Ohori M, Tsuboi S - Sci Rep (2015)

Bottom Line: The waveforms and spectrograms demonstrate prolonged and amplified motions that are inconsistent with attenuation patterns of ground motions on land.Simulated waveforms reproducing observed ocean-bottom data demonstrate substantial contributions of thick low-velocity sediment layers to development of these motions.This development, which could affect magnitude estimates and finite fault slip modelling because of its critical period ranges on their estimations, may be common in the source areas of subduction earthquakes where thick, low-velocity sediment layers are present.

View Article: PubMed Central - PubMed

Affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001, Japan.

ABSTRACT
Long-period ground motions in plain and basin areas on land can cause large-scale, severe damage to structures and buildings and have been widely investigated for disaster prevention and mitigation. However, such motions in ocean-bottom areas are poorly studied because of their relative insignificance in uninhabited areas and the lack of ocean-bottom strong-motion data. Here, we report on evidence for the development of long-period (10-20 s) motions using deep ocean-bottom data. The waveforms and spectrograms demonstrate prolonged and amplified motions that are inconsistent with attenuation patterns of ground motions on land. Simulated waveforms reproducing observed ocean-bottom data demonstrate substantial contributions of thick low-velocity sediment layers to development of these motions. This development, which could affect magnitude estimates and finite fault slip modelling because of its critical period ranges on their estimations, may be common in the source areas of subduction earthquakes where thick, low-velocity sediment layers are present.

No MeSH data available.


Related in: MedlinePlus

Estimated peak ground velocity (PGV) versus hypocentral distances.Yellow diamonds and brown circles indicate PGVs at ocean-bottom and land stations, respectively, as a function of hypocentral distance from the source to stations assuming a point source approximation. Black diamonds and circles indicate PGVs at KMD16 and MIEH09, respectively. An empirical attenuation relationship and standard deviation for the velocity component for the period band of 0.1–5 s at a stiff soil site23 as a function of equivalent hypocentral distance are shown by solid and dashed grey lines, respectively. (a) Observed short-period PGV (0.1–5 s). (b) Observed long-period PGV (10–20 s). The purple line indicates the regression line obtained for long-period PGV at land stations. (c) Simulated long-period PGV (10–20 s).
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f3: Estimated peak ground velocity (PGV) versus hypocentral distances.Yellow diamonds and brown circles indicate PGVs at ocean-bottom and land stations, respectively, as a function of hypocentral distance from the source to stations assuming a point source approximation. Black diamonds and circles indicate PGVs at KMD16 and MIEH09, respectively. An empirical attenuation relationship and standard deviation for the velocity component for the period band of 0.1–5 s at a stiff soil site23 as a function of equivalent hypocentral distance are shown by solid and dashed grey lines, respectively. (a) Observed short-period PGV (0.1–5 s). (b) Observed long-period PGV (10–20 s). The purple line indicates the regression line obtained for long-period PGV at land stations. (c) Simulated long-period PGV (10–20 s).

Mentions: Figure 3 illustrates the attenuation of peak ground velocity (PGV), determined from the maximum amplitude in the horizontal velocity waveforms as a function of the hypocentral distance from the source to the station assuming a point source approximation. The PGV in the short-period band of 0.1–5 s was similar at the land and ocean-bottom stations (Fig. 3a). The PGV at both the land and ocean-bottom stations agreed approximately with that predicted by empirical equations23 for stiff soil in the short-period band as a function of the equivalent hypocentral distance. Differences in amplification between the land and ocean-bottom stations gradually appeared in the long-period band of >3 s, based on analysis of the PGV in various central periods (Figure S1).


Long-period ocean-bottom motions in the source areas of large subduction earthquakes.

Nakamura T, Takenaka H, Okamoto T, Ohori M, Tsuboi S - Sci Rep (2015)

Estimated peak ground velocity (PGV) versus hypocentral distances.Yellow diamonds and brown circles indicate PGVs at ocean-bottom and land stations, respectively, as a function of hypocentral distance from the source to stations assuming a point source approximation. Black diamonds and circles indicate PGVs at KMD16 and MIEH09, respectively. An empirical attenuation relationship and standard deviation for the velocity component for the period band of 0.1–5 s at a stiff soil site23 as a function of equivalent hypocentral distance are shown by solid and dashed grey lines, respectively. (a) Observed short-period PGV (0.1–5 s). (b) Observed long-period PGV (10–20 s). The purple line indicates the regression line obtained for long-period PGV at land stations. (c) Simulated long-period PGV (10–20 s).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663758&req=5

f3: Estimated peak ground velocity (PGV) versus hypocentral distances.Yellow diamonds and brown circles indicate PGVs at ocean-bottom and land stations, respectively, as a function of hypocentral distance from the source to stations assuming a point source approximation. Black diamonds and circles indicate PGVs at KMD16 and MIEH09, respectively. An empirical attenuation relationship and standard deviation for the velocity component for the period band of 0.1–5 s at a stiff soil site23 as a function of equivalent hypocentral distance are shown by solid and dashed grey lines, respectively. (a) Observed short-period PGV (0.1–5 s). (b) Observed long-period PGV (10–20 s). The purple line indicates the regression line obtained for long-period PGV at land stations. (c) Simulated long-period PGV (10–20 s).
Mentions: Figure 3 illustrates the attenuation of peak ground velocity (PGV), determined from the maximum amplitude in the horizontal velocity waveforms as a function of the hypocentral distance from the source to the station assuming a point source approximation. The PGV in the short-period band of 0.1–5 s was similar at the land and ocean-bottom stations (Fig. 3a). The PGV at both the land and ocean-bottom stations agreed approximately with that predicted by empirical equations23 for stiff soil in the short-period band as a function of the equivalent hypocentral distance. Differences in amplification between the land and ocean-bottom stations gradually appeared in the long-period band of >3 s, based on analysis of the PGV in various central periods (Figure S1).

Bottom Line: The waveforms and spectrograms demonstrate prolonged and amplified motions that are inconsistent with attenuation patterns of ground motions on land.Simulated waveforms reproducing observed ocean-bottom data demonstrate substantial contributions of thick low-velocity sediment layers to development of these motions.This development, which could affect magnitude estimates and finite fault slip modelling because of its critical period ranges on their estimations, may be common in the source areas of subduction earthquakes where thick, low-velocity sediment layers are present.

View Article: PubMed Central - PubMed

Affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001, Japan.

ABSTRACT
Long-period ground motions in plain and basin areas on land can cause large-scale, severe damage to structures and buildings and have been widely investigated for disaster prevention and mitigation. However, such motions in ocean-bottom areas are poorly studied because of their relative insignificance in uninhabited areas and the lack of ocean-bottom strong-motion data. Here, we report on evidence for the development of long-period (10-20 s) motions using deep ocean-bottom data. The waveforms and spectrograms demonstrate prolonged and amplified motions that are inconsistent with attenuation patterns of ground motions on land. Simulated waveforms reproducing observed ocean-bottom data demonstrate substantial contributions of thick low-velocity sediment layers to development of these motions. This development, which could affect magnitude estimates and finite fault slip modelling because of its critical period ranges on their estimations, may be common in the source areas of subduction earthquakes where thick, low-velocity sediment layers are present.

No MeSH data available.


Related in: MedlinePlus