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1.
The Mw = 9.3 megathrust earthquake of December 26, 2004 off the northwest coast of Sumatra in the Indian Ocean generated a catastrophic tsunami that was recorded by a large number of tide gauges throughout the World Ocean. Part 1 of our study of this event examines tide gauge measurements from the Indian Ocean region, at sites located from a few hundred to several thousand kilometers from the source area. Statistical characteristics of the tsunami waves, including wave height, duration, and arrival time, are determined, along with spectral properties of the tsunami records.  相似文献   

2.
Energy Decay of the 2004 Sumatra Tsunami in the World Ocean   总被引：1，自引：0，他引：1  
The catastrophic Indian Ocean tsunami generated off the coast of Sumatra on 26 December 2004 was recorded by a large number of tide gauges throughout the World Ocean. This study uses gauge records from 173 sites to examine the characteristics and energy decay of the tsunami waves from this event in the Indian, Atlantic and Pacific oceans. Findings reveal that the decay (e-folding) time of the tsunami wave energy within a given oceanic basin is not uniform, as previously reported, but depends on the absorption characteristics of the shelf adjacent to the coastal observation site and the time for the waves to reach the site from the source region. In general, the decay times for island and open-ocean bottom stations are found to be shorter than for coastal mainland stations. Decay times for the 2004 Sumatra tsunami ranged from about 13 h for islands in the Indian Ocean to 40–45 h for mainland stations in the North Pacific.  相似文献   

3.
The 2010 Mentawai earthquake (magnitude 7.7) generated a destructive tsunami that caused more than 500 casualties in the Mentawai Islands, west of Sumatra, Indonesia. Seismological analyses indicate that this earthquake was an unusual “tsunami earthquake,” which produces much larger tsunamis than expected from the seismic magnitude. We carried out a field survey to measure tsunami heights and inundation distances, an inversion of tsunami waveforms to estimate the slip distribution on the fault, and inundation modeling to compare the measured and simulated tsunami heights. The measured tsunami heights at eight locations on the west coasts of North and South Pagai Island ranged from 2.5 to 9.3 m, but were mostly in the 4–7 m range. At three villages, the tsunami inundation extended more than 300 m. Interviews of local residents indicated that the earthquake ground shaking was less intense than during previous large earthquakes and did not cause any damage. Inversion of tsunami waveforms recorded at nine coastal tide gauges, a nearby GPS buoy, and a DART station indicated a large slip (maximum 6.1 m) on a shallower part of the fault near the trench axis, a distribution similar to other tsunami earthquakes. The total seismic moment estimated from tsunami waveform inversion was 1.0 × 1021 Nm, which corresponded to Mw 7.9. Computed coastal tsunami heights from this tsunami source model using linear equations are similar to the measured tsunami heights. The inundation heights computed by using detailed bathymetry and topography data and nonlinear equations including inundation were smaller than the measured ones. This may have been partly due to the limited resolution and accuracy of publically available bathymetry and topography data. One-dimensional run-up computations using our surveyed topography profiles showed that the computed heights were roughly similar to the measured ones.  相似文献   

4.
On the evening of March 28, 2005 at 11:09?p.m. local time (16:09 UTC), a large earthquake occurred offshore of West Sumatra, Indonesia. With a moment magnitude (M w) of 8.6, the event caused substantial shaking damage and land level changes between Simeulue Island in the north and the Batu Islands in the south. The earthquake also generated a tsunami, which was observed throughout the source region as well as on distant tide gauges. While the tsunami was not as extreme as the tsunami of December 26th, 2004, it did cause significant flooding and damage at some locations. The spatial and temporal proximity of the two events led to a unique set of observational data from the earthquake and tsunami as well as insights relevant to tsunami hazard planning and education efforts.  相似文献   

5.
In the last 15 years there have been 16 tsunami events recorded at tide stations on the Pacific Coast of Canada. Eleven of these events were from distant sources covering almost all regions of the Pacific, as well as the December 26, 2004 Sumatra tsunami in the Indian Ocean. Three tsunamis were generated by local or regional earthquakes and two were meteorological tsunamis. The earliest four events, which occurred in the period 1994–1996, were recorded on analogue recorders; these tsunami records were recently re-examined, digitized and thoroughly analysed. The other 12 tsunami events were recorded using digital high-quality instruments, with 1-min sampling interval, installed on the coast of British Columbia (B.C.) in 1998. All 16 tsunami events were recorded at Tofino on the outer B.C. coast, and some of the tsunamis were recorded at eight or more stations. The tide station at Tofino has been in operation for 100 years and these recent observations add to the dataset of tsunami events compiled previously by S.O. Wigen (1983) for the period 1906–1980. For each of the tsunami records statistical analysis was carried out to determine essential tsunami characteristics for all events (arrival times, maximum amplitudes, frequencies and wave-train structure). The analysis of the records indicated that significant background noise at Langara, a key northern B.C. Tsunami Warning station located near the northern end of the Queen Charlotte Islands, creates serious problems in detecting tsunami waves. That station has now been moved to a new location with better tsunami response. The number of tsunami events observed in the past 15 years also justified re-establishing a tide gauge at Port Alberni, where large tsunami wave amplitudes were measured in March 1964. The two meteorological events are the first ever recorded on the B.C. coast. Also, there have been landslide generated tsunami events which, although not recorded on any coastal tide gauges, demonstrate, along with the recent investigation of a historical catastrophic event, the significant risk that landslide generated tsunami pose to coastal and inland regions of B.C.  相似文献   

6.
The Hokkaido-Nansei-Oki earthquake (M w 7.7) of July 12, 1993, is one of the largest tsunamigenic events in the Sea of Japan. The tsunami magnitudeM t is determined to be 8.1 from the maximum amplitudes of the tsunami recorded on tide gauges. This value is larger thanM w by 0.4 units. It is suggested that the tsunami potential of the Nansei-Oki earthquake is large forM w . A number of tsunami runup data are accumulated for a total range of about 1000 km along the coast, and the data are averaged to obtain the local mean heightsH n for 23 segments in intervals of about 40 km each. The geographic variation ofH n is approximately explained in terms of the empirical relationship proposed byAbe (1989, 1993). The height prediction from the available earthquake magnitudes ranges from 5.0–8.4 m, which brackets the observed maximum ofH n , 7.7 m, at Okushiri Island.  相似文献   

7.
The fault parameters of the Guam earthquake of August 8, 1993 are estimated from seismological analyses, and the possibility of identifying the actual fault plane from tsunami waveforms is tested. The Centroid Moment Tensor solution of long-period surface waves shows one nodal plane shallowly dipping to the north and the other nodal plane steeply dipping to the south. The seismic moment is 3.5×1020 Nm and the corresponding moment magnitude is 7.7. The Moment Tensor Rate Function inversion ofP waves also yields a similar focal mechanism and seismic moment. The point source depth is estimated as 40–50 km.This earthquake generated tsunamis that propagated toward the Japanese coast along the Izu-Bonin-Mariana ridge system. The tsunamis are recorded on ocean bottom pressure gauges and tide gauges. Numerical computation of tsunamis shows that the computed waveforms from the two possible fault planes match well with the observed tsunami waveforms. The numerical computation also shows that the tsunami waveforms at Guam Island, just above the fault, should contain useful information regarding the identification of the actual fault plane. However, the current sampling rate of the tide gauges is so small that the records cannot help the identification.  相似文献   

8.
The major (M w = 8.8) Chilean earthquake of 27 February 2010 generated a trans-oceanic tsunami that was observed throughout the Pacific Ocean. Waves associated with this event had features similar to those of the 1960 tsunami generated in the same region by the Great (M w = 9.5) 1960 Chilean Earthquake. Both tsunamis were clearly observed on the coast of British Columbia. The 1960 tsunami was measured by 17 analog pen-and-paper tide gauges, while the 2010 tsunami was measured by 11 modern digital coastal tide gauges, four NEPTUNE-Canada bottom pressure recorders located offshore from southern Vancouver Island, and two nearby open-ocean DART stations. The 2010 records were augmented by data from seven NOAA tide gauges on the coast of Washington State. This study examines the principal characteristics of the waves from the 2010 event (height, period, duration, and arrival and travel times) and compares these properties for the west coast of Canada with corresponding properties of the 1960 tsunami. Results show that the 2010 waves were approximately 3.5 times smaller than the 1960 waves and reached the British Columbia coast 1 h earlier. The maximum 2010 wave heights were observed at Port Alberni (98.4 cm) and Winter Harbour (68.3 cm); the observed periods ranged from 12 min at Port Hardy to 110–120 min at Prince Rupert and Port Alberni and 150 min at Bamfield. The open-ocean records had maximum wave heights of 6–11 cm and typical periods of 7 and 15 min. Coastal and open-ocean tsunami records revealed persistent oscillations that “rang” for 3–4 days. Tsunami energy occupied a broad band of periods from 3 to 300 min. Estimation of the inverse celerity vectors from cross-correlation analysis of the deep-sea tsunami records shows that the tsunami waves underwent refraction as they approached the coast of Vancouver Island with the direction of the incoming waves changing from an initial direction of 340° True to a direction of 15° True for the second train of waves that arrived 7 h later after possible reflection from the Marquesas and Hawaiian islands.  相似文献   

9.
We modeled a tsunami from the West Papua, Indonesia earthquakes on January 3, 2009 (M w?=?7.7). After the first earthquake, tsunami alerts were issued in Indonesia and Japan. The tsunami was recorded at many stations located in and around the Pacific Ocean. In particular, at Kushimoto on Kii Peninsula, the maximum amplitude was 43?cm, larger than that at Manokwari on New Guinea Island, near the epicenter. The tsunami was recorded on near-shore wave gauges, offshore GPS sensors and deep-sea bottom pressure sensors. We have collected more than 150 records and used 72 stations?? data with clear tsunami signals for the tsunami source modeling. We assumed two fault models (single fault and five subfaults) which are located to cover the aftershock area. The estimated average slip on the single fault model (80?×?40?km) is 0.64?m, which yields a seismic moment of 1.02?×?1020?Nm (M w?=?7.3). The observed tsunami waveforms at most stations are well explained by this model.  相似文献   

10.
The 1963 great Kurile earthquake was an underthrust earthquake occurred in the Kurile?CKamchatka subduction zone. The slip distribution of the 1963 earthquake was estimated using 21 tsunami waveforms recorded at tide gauges along the Pacific and Okhotsk Sea coasts. The extended rupture area was divided into 24 subfaults, and the slip on each subfault was determined by the tsunami waveform inversion. The result shows that the largest slip amount of 2.8?m was found at the shallow part and intermediate depth of the rupture area. Large slip amounts were found at the shallow part of the rupture area. The total seismic moment was estimated to be 3.9?×?1021?Nm (Mw 8.3). The 2006 Kurile earthquake occurred right next to the location of the 1963 earthquake, and no seismic gap exists between the source areas of the 1963 and 2006 earthquakes.  相似文献   

11.
—The 1994 great Kuril earthquake generated an unusual tsunami that was observed at five tide gauges on the Hokkaido coast of the Okhotsk Sea. The tsunami arrived at tide gauges considerably earlier than the expected time, calculated on the assumption that the tsunami source area coincides with the aftershock area. Numerical simulation of the tsunami shows that the first wave of the tsunami in the Okhotsk Sea was generated by the significant subsidence north of the Kuril Islands. It is assumed that this subsidence is due to the earthquake. The coseismic deformation area of the ocean bottom extended over a vastly larger area than the aftershock area or the rupture area for the Kuril earthquake. The numerical simulation also shows that the tsunami observed at Utoro during the first hour after the origin time of the earthquake was mainly generated by the horizontal movement of the sloping ocean bottom near the Shiretoko Peninsula.  相似文献   

12.
On December 12, 1992 a large earthquake (M s 7.5) occurred just north of Flores Island, Indonesia which, along with the tsunami it generated, killed more than 2,000 people. In this study, teleseismicP andSH waves, as well asPP waves from distances up to 123°, are inverted for the orientations and time histories of multiple point sources. By repeating the inversion for reasonable values of depth, time separation and spatial separation, a 2-fault model is developed. Next, the vertical deformation of the seafloor is estimated from this fault model. Using a detailed bathymetric model, linear and nonlinear tsunami propagation models are tested. The data consist of a single tide gauge record at Palopo (650 km to the north), as well as tsunami runup height measurements from Flores Island and nearby islands. Assuming a tsunami runup amplification factor of two, the two-fault model explains the tide gauge record and the tsunami runup heights on most of Flores Island. It cannot, however, explain the large tsunami runup heights observed near Leworahang (on Hading Bay) and Riangkroko (on the northeast peninsula). Massive coastal slumping was observed at both of these locations. A final model, which in addition to the two faults, includes point sources of large vertical displacement at these two locations explains the observations quite well.  相似文献   

13.
Bottom pressure gauges deployed in bays of Shikotan Island (South Kuril Islands) recently recorded two tsunamis: the Simushir (Kuril Islands) tsunami of January 13, 2007 generated by a local earthquake with magnitude M w = 8.1 and the Peruvian tsunami of August 15, 2007 generated by a distant earthquake, M w = 8.0. The records enabled us to investigate the properties of these two tsunamis and to estimate the effect of the regional and nearshore topography on arriving tsunami waves. Eigen periods and spatial structure of resonant oscillations in particular bays were examined based on results of numerical modeling. Significant amplification of the fundamental (Helmholtz) resonant modes in Malokurilskaya Bay (19 min) and in Krabovaya Inlet (29 min) and some secondary modes was caused by the Simushir tsunami. The considerably different geometry and bottom topography of these bays, located on the inner coast of the island, determine the differences in their eigen periods; the only mutual peak, which was found in both basins, had a period of 5 min and was probably related to the source features. The Peruvian tsunami was clearly recorded by the bottom pressure gauge in Tserkovnaya Bay on the outer (oceanic) coast of the island. Three dominant periods in the tsunami spectrum at this bay were 60, 30 and 19 min; the latter period was found to be related to the fundamental mode of the bay, while the other two periods appear to be associated with the shelf resonant amplification of tsunami waves arriving in the region of the South Kuril Islands. The prevalence of low-frequency components in the observed tsunami spectrum is probably associated with the large extension of the initial source area and faster decay of short period waves during the long trans-oceanic tsunami propagation.  相似文献   

14.
快速准确的海啸源模型是近场海啸精确预警的关键.尽管目前还没有办法直接对其进行正演定量计算,但是可以通过多源地震、海啸观测数据进行反演或联合反演推算.不同的海啸源可能导致不同的预警结论,了解不同类型海啸源适用性、评估海啸源特征差异对近场海啸的影响,无论对于海啸预警还是海啸模拟研究尤为重要.本文评估分析了6种不同同震断层模型对2011年3月11日日本东北地震海啸近场数值预报的影响,重点对比分析了有限断层模型与均一滑动场模型对近场海啸产生、传播、淹没特征的影响及各自的误差.研究表明:近场海啸波能量分布主要取决于海啸源分布特征,特别是走向角的差异对海啸能量分布影响较大;有限断层模型对海啸灾害最为严重的39°N以南沿岸地区的最大海啸爬坡高度明显优于均一滑动场模型结果;综合对比DART浮标、GPS浮标及近岸潮位站共32个站次的海啸波幅序列结果发现有限断层模型整体平均绝对/相对误差比均一滑动场模型平均误差要低,其中Fujii海啸源的平均绝对/相对误差最小,分别是0.56m和26.71%.UCSB海啸源的平均绝对/相对误差次之.3个均一滑动场模型中USGSCMT海啸源模拟精度最高.相对于深海、浅海观测站,有限断层模型比均一滑动场模型对近岸观测站计算精度更高.海啸源误差具有显著的方向性,可能与反演所采用的波形数据的代表性有关;谱分析结果表明Fujii海啸源对在12至60min主频波谱的模拟要优于UCSB海啸源.海啸源中很难真实反映海底地震破裂过程,然而通过联合反演海啸波形数据推算海啸源的方法可以快速确定海啸源,并且最大限度的降低地震破裂过程与海啸产生的不确定性带来的误差.  相似文献   

15.
M TSU : Recovering Seismic Moments from Tsunameter Records   总被引：1，自引：0，他引：1  
We define a new magnitude scale, MTSU, allowing the quantification of the seismic moment M0 of an earthquake based on recordings of its tsunami in the far field by ocean-bottom pressure sensors (``tsunameters') deployed in ocean basins, far from continental or island shores which are known to affect profoundly and in a nonlinear fashion the amplitude of the tsunami wave. The formula for MTSU, MTSU = log10 M0 − 20 = log10 X (ω) + CDTSU + CSTSU + C0, where X (ω) is the spectral amplitude of the tsunami, CDTSU a distance correction and CSTSU a source correction, is directly adapted from the mantle magnitude Mm introduced for seismic surface waves by Okal and Talandier. Like Mm, its corrections are fully justified theoretically based on the representation of a tsunami wave as a branch of the Earth's normal modes. Even the locking constant C0, which may depend on the nature of the recording (surface amplitude of the tsunami or overpressure at the ocean floor) and its units, is predicted theoretically. MTSU combines the power of a theoretically developed algorithm, with the robustness of a magnitude measurement that does not take into account such parameters as focal geometry and exact depth, which may not be available under operational conditions in the framework of tsunami warning. We verify the performance of the concept on simulations of the great 1946 Aleutian tsunami at two virtual gauges, and then apply the algorithm to 24 records of 7 tsunamis at DART tsunameters during the years 1994–2003. We find that MTSU generally recovers the seismic moment M0 within 0.2 logarithmic units, even under unfavorable conditions such as excessive focal depth and refraction of the tsunami wave around continental masses. Finally, we apply the algorithm to the JASON satellite trace obtained over the Bay of Bengal during the 2004 Sumatra tsunami, after transforming the trace into a time series through a simple ad hoc procedure. Results are surprisingly good, with most estimates of the moment being over 1029 dyn-cm, and thus identifying the source as an exceptionally large earthquake.  相似文献   

16.
The tsunami caused by the 2007 Peru earthquake (Mw 8.0) provoked less damage than by the seismic shaking itself (numerous casualties due to the earthquake in the vicinity of Pisco). However, it propagated across the Pacific Ocean and small waves were observed on one tide gauge in Taiohae Bay (Nuku Hiva, Marquesas, French Polynesia). We invert seismological data to recover the rupture pattern in two steps. The first step uses surface waves to find a solution for the moment tensor, and the second step uses body waves to compute the slip distribution in the source area. We find the slip distribution to consist of two main slip patches in the source area. The inversion of surface waves yields a scalar moment of 8.9 1020 Nm, and body-wave inversion gives 1.4 1021 Nm. The inversion of tsunami data recorded on a single deep ocean sensor also can be used to compute a fault slip pattern (yielding a scalar moment of 1.1 1021 Nm). We then use these different sources to model the tsunami propagation across the Pacific Ocean, especially towards Nuku Hiva. While the source model taken from the body-wave inversion yields computed tsunami waves systematically too low with respect to observations (on the central Pacific Ocean DART buoy as on the Polynesian tide gauge), the source model established from the surface-wave inversion is more efficient to fit the observations, confirming that the tsunami is sensitive to the low frequency component of the source. Finally we also discuss the modeling of the late tsunami arrivals in Taiohae Bay using several friction coefficients for the sea bottom.  相似文献   

17.
We report the statistical and wavelet analyses of the 21 May 2003 tsunami produced by an M w 6.8–6.9 thrust earthquake in the western Mediterranean Sea using 19 tide gauge records. The largest trough-to-crest wave height was 196 cm recorded at the Sant Antoni station in the lee of the incoming tsunami wave. Except at one station, the first wave was not the largest wave at all the analyzed stations, and the largest wave arrived several hours after the first arrival. In addition, the tsunami waves persisted for more than 1 day at most stations. As the spectra of coastal tide gauge stations are strongly influenced by topographic features, special care was taken here while interpreting the results of spectral and wavelet analysis. Our wavelet analysis shows that only a peak at around 23 min is persistent for long duration, and other peaks at 14, 30, 45, and 60 min appeared at short durations. The 23-min signal is possibly associated with the width of the source fault whereas the fault length contributed to the 45-min signal. Based on these dominant periods, the tsunami source dimensions are estimated as 95 km × 45 km. The statistical and wavelet analyses performed here provide some new insights into the characteristics of the tsunami that was generated and propagated in the western Mediterranean basin.  相似文献   

18.
Based on the tsunami data in the Central American region, the regional characteristic of tsunami magnitude scales is discussed in relation to earthquake magnitudes during the period from 1900 to 1993. Tsunami magnitudes on the Imamura-Iida scale of the 1985 Mexico and 1992 Nicaragua tsunamis are determined to bem=2.5, judging from the tsunami height-distance diagram. The magnitude values of the Central American tsunamis are relatively small compared to earthquakes with similar size in other regions. However, there are a few large tsunamis generated by low-frequency earthquakes such as the 1992 Nicaragua earthquake. Inundation heights of these unusual tsunamis are about 10 times higher than those of normal tsunamis for the same earthquake magnitude (M s =6.9–7.2). The Central American tsunamis having magnitudem>1 have been observed by the Japanese tide stations, but the effect of directivity toward Japan is very small compared to that of the South American tsunamis.  相似文献   

19.
A nonlinear shallow water model in cylindrical polar coordinate system is developed, using an explicit finite difference scheme with a very fine resolution, to compute different aspects of tsunami at North Sumatra and the adjacent island Simeulue in Indonesia, and the Penang Island in Peninsular Malaysia. The pole of the frame is placed on the mainland of Penang (100.5°E) and the model area extends up to the west of Sumatra (87.5°E). The model is applied to simulate the propagation of tsunami wave towards North Sumatra, Simeulue and Penang Islands associated with Indonesian tsunami of 26 December 2004. The model is also applied to compute water levels along the coastal belts of those islands. Computed and observed water level data are found to be in good agreement and North Sumatra is found to be vulnerable for very high surges. The computed and observed arrival times of high surges are also in reasonable agreement everywhere. Further studies are carried out to investigate the effect of convective terms and it is found that their effects are insignificant in tsunami propagation and weakly significant for wave amplitude very near to the coast.  相似文献   

20.
Two remote tsunamis were recorded on the Pacific coast of Russia: a relatively weak Samoan tsunami of September 29, 2009 and a much stronger Chilean tsunami of February 28, 2010. In the area of the South Kuril Islands, records were obtained using autonomous bottom pressure gauges of the Institute of Marine Geology and Geophysics (IMGG). Additionally, for the oceanic coast of the Kamchatka Peninsula, Paramushir, and Bering Islands we used data transmitted from coastal tide gauges of the Russian Tsunami Warning Service (TWS). The maximum trough-to-crest heights of the Samoan tsunami were about 30–40 cm, and were recorded about 3 h after the first tsunami arrival. The maximum Chilean tsunami trough-to-crest wave heights were 218 cm at Severo-Kurilsk, 187 cm at Tserkovnaya Bay (Shikotan Island), and 140 cm at Khodutka Bay (Kamchatka Peninsula). The time between first and maximum waves reached 4 h. Strong sea level oscillations for both events range for a long time: about 15–17 h. The Samoan tsunami induced high-frequency oscillations; a considerable increase in spectral energy in the tsunami spectrum was observed at periods of 4–20 min. In contrast, the Chilean tsunami induced low-frequency oscillations; the dominant periods were 30–80 min. A probable reason for these differences is the different extensions of the source areas (the Chilean source was much larger than the Samoan source) and the different energy radiation directions from the sources. Local topography resonant effects were the main reason of well-expressed peaks in power spectra in different areas: with a period of 10 min (Khodutka Bay), 19–20 min (Malokurilskaya and Tserkovnaya bays), 29 min (Krabovaya Inlet), and 43 min (Avachinskaya Guba and Nikolskoe).  相似文献   

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