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1.
On March 11th 2011 a M w 9.0 mega-thrust interface subduction earthquake, the Great East Japan Earthquake, occurred 130 km off the northeast coast of Japan in the Pacific Ocean at the Japan Trench, triggering tsunami which caused damage along 600 km of coastline. Observations of damage to buildings (including vertical evacuation facilities) and coastal defences in Tōhoku are presented following investigation by the Earthquake Engineering Field Investigation Team (EEFIT) at 10 locations in Iwate and Miyagi Prefectures. Observations are presented in the context of the coastal setting and tsunami characteristics experienced at each location. Damage surveys were carried out in Kamaishi City and Kesennuma City using a damage scale for reinforced concrete (RC), timber and steel frame buildings adapted from an earlier EEFIT tsunami damage scale. Observations show that many sea walls and breakwaters were overtopped, overturned, or broken up, but provided some degree of protection. We show the extreme variability of damage in a local area due to inundation depth, flow direction, velocity variations and sheltering. Survival of many RC shear wall structures shows their high potential to withstand local earthquake and significant tsunami inundation but further research is required into mitigation of scour, liquefaction, debris impact, and the prevention of overturning failure. Damage to steel and timber buildings are also discussed. These observations are intended to contribute to mitigation of future earthquake and tsunami damage by highlighting the key features which influence damage level and local variability of damage sustained by urban coastal infrastructure when subjected to extreme tsunami inundation depths.  相似文献   

2.
Evaluating Tsunami Hazard in the Northwestern Indian Ocean   总被引：1，自引：0，他引：1  
We evaluate here the tsunami hazard in the northwestern Indian Ocean. The maximum regional earthquake calculated from seismic hazard analysis, was used as the characteristic earthquake for our tsunami hazard assessment. This earthquake, with a moment magnitude of M w 8.3 and a return period of about 1000 years, was moved along the Makran subduction zone (MSZ) and its possible tsunami wave height along various coasts was calculated via numerical simulation. Both seismic hazard analysis and numerical modeling of the tsunami were validated using historical observations of the Makran earthquake and tsunami of the 1945. Results showed that the possible tsunami may reach a maximum height of 9.6 m in the region. The distribution of tsunami wave height along various coasts is presented. We recommend the development of a tsunami warning system in the region, and emphasize the value of education as a measure to mitigate the death toll of a possible tsunami in this region.  相似文献   

3.
The new scale Mt of tsunami magnitude is a reliable measure of the seismic moment of a tsunamigenic earthquake as well as the overall strength of a tsunami source. This Mt scale was originally defined by Abe (1979) in terms of maximum tsunami amplitudes at large distances from the source. A method is developed whereby it is possible to determine Mt at small distances on the basis of the regional tsunami data obtained at 30 tide stations in Japan. The relation between log H, maximum amplitude (m) and log Δ, a distance of not less than 100 km away from the source (km) is found to be linear, with a slope close to 1.0. Using three tsunamigenic earthquakes with known moment magnitudes Mw, for calibration, the relation, Mt = log H + log Δ + D, is obtained, where D is 5.80 for single-amplitude (crest or trough) data and 5.55 for double-amplitude (crest-to-trough) data. Using a number of tsunami amplitude data, Mt is assigned to 80 tsunamigenic earthquakes that occurred in the northwestern Pacific, mostly in Japan, during the period from 1894 to 1981. The Mt values are found to be essentially equivalent to Mw for 25 events with known Mw. The 1952 Kamchatka earthquake has the largest Mt, 9.0. Of all the 80 events listed, at least seven unusual earthquakes which generated disproportionately-large tsunamis for their surface-wave magnitude Ms are identified from the relation. From the viewpoint of tsunami hazard reduction, the present results provide a quantitative basis for predicting maximum tsunami amplitudes at a particular site.  相似文献   

4.
— T waves recorded at hydrophone and seismic stations following the Papua New Guinea earthquake of 17 July 1998 and its aftershocks show that a small event at 09:02 GMT featured source properties incompatible with an elastic dislocation of appropriate body-wave magnitude (m b=4.4). These include an exceptional duration (47 s at the Wake Island hydrophone station WK31), a spectrum rich in high frequencies (7 to 12 Hz), and a generally low spectral amplitude. These characteristics can be explained by the model of an underwater slump, accelerating from a standstill and eventually slowing down. The relocation of the 09:02 event is compatible with its location within an amphitheater inside which shipboard cruises in 1998 and 1999 documented the presence of a 4 – km3 geologically fresh slump. We propose that the slump took place at 09:02 on 17 July 1998, i.e., 13 minutes after the mainshock, and that it generated the locally catastrophic tsunami, whose properties (amplitude and distribution of runup; timing) could not be explained by a dislocation model.  相似文献   

5.
Field Survey of the 27 February 2010 Chile Tsunami   总被引：1，自引：0，他引：1  
On 27 February 2010, a magnitude M w?=?8.8 earthquake occurred off the coast of Chile??s Maule region causing substantial damage and loss of life. Ancestral tsunami knowledge from the 1960 event combined with education and evacuation exercises prompted most coastal residents to spontaneously evacuate after the earthquake. Many of the tsunami victims were tourists in coastal campgrounds. The international tsunami survey team (ITST) was deployed within days of the event and surveyed 800?km of coastline from Quintero to Mehuín and the Pacific Islands of Santa María, Mocha, Juan Fernández Archipelago, and Rapa Nui (Easter). The collected survey data include more than 400 tsunami flow depth, runup and coastal uplift measurements. The tsunami peaked with a localized runup of 29?m on a coastal bluff at Constitución. The observed runup distributions exhibit significant variations on local and regional scales. Observations from the 2010 and 1960 Chile tsunamis are compared.  相似文献   

6.
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   

7.
根据构造相似条件分析,琉球海沟与日本海沟、智利海沟、印尼巽他海沟一样具备发生9级罕遇超巨大地震的可能。在对近几年来全球发生的超巨大地震参数及构造对比分析的基础上,设定琉球海沟9.0级地震参数,并将其引发的海啸进行数值模拟研究。结果表明,该地震可引发初始波高为8m的海啸,台湾东北部半小时后遭受10m以上海啸,3~4小时左右传至浙南、闽北沿岸,近岸各处波高在1~2m;5小时左右传至浙北、粤北沿岸,浙江近岸各处波高在2m左右,广东沿海、台湾海峡由于台湾岛的正面阻挡,海啸波高低于50cm;8小时后靠近上海海岸线,最大波高约1m。海啸的上岸高度与海岸附近的海深和海岸线的形态密切相关,我国东南海域地形变化复杂、海湾众多,对海啸波有放大作用,模拟结果可能比实际海啸偏小。我国沿海地区分布着不少已建和在建的核电厂,在核电设计时未考虑海啸,一旦发生这种罕遇地震海啸则影响不可忽视,尤其是若与风暴潮、天文大潮叠加则可能出现严重后果。由于核电安全要求万无一失,故须制订有效预警和应对措施。  相似文献   

8.
Twin Tsunamis Triggered by the 12 January 2010 Haiti Earthquake   总被引：2，自引：0，他引：2  
On 12 January 2010, a magnitude M w 7.0 earthquake occurred 25 km west–southwest of Haiti’s capital Port-au-Prince causing an estimated 316,000 fatalities, thereby exceeding any previous loss of life from a similar size earthquake. In addition, tsunami waves triggered by the earthquake caused at least three fatalities at Petit Paradis due to a complete lack of tsunami awareness. The International Tsunami Survey Team (ITST) was deployed within weeks of the event and covered the greater Bay of Port-au-Prince and more than 100 km of Hispaniola’s southern coastline. The collected survey data include more than 21 tsunami heights along with observations of coastal land level change. Maximum tsunami heights of 3 m have been measured for two independently triggered tsunamis.  相似文献   

9.
Mechanism of tsunami earthquakes   总被引：1，自引：0，他引：1  
  相似文献   

10.
—Whereas the coast of Peru south of 10°S is historically accustomed to tsunamigenic earthquakes, the subduction zone north of 10°S has been relatively quiet. On 21 February 1996 at 21:51 GMT (07:51 local time) a large, tsunamigenic earthquake (Harvard estimate M w = 7.5) struck at 9.6°S, 79.6°W, approximately 130 km off the northern coast of Peru, north of the intersection of the Mendaña fracture zone with the Peru–Chile trench. The likely mechanism inferred from seismic data is a low-angle thrust consistent with subduction of the Nazca Plate beneath the South American plate, with relatively slow rupture characteristics. Approximately one hour after the main shock, a damaging tsunami reached the Peruvian coast, resulting in twelve deaths. We report survey measurements, from 7.7°S to 11°S, on maximum runup (2–5m, between 8 and 10°S), maximum inundation distances, which exceeded 500 m, and tsunami sediment deposition patterns. Observations and numerical simulations show that the hydrodynamic characteristics of this event resemble those of the 1992 Nicaragua tsunami. Differences in climate, vegetation and population make these two tsunamis seem more different than they were. This 1996 Chimbote event was the first large (M w >7) subduction-zone (interplate) earthquake between about 8 and 10°S, in Peru, since the 17th century, and bears resemblance to the 1960 (M w 7.6) event at 6.8°S. Together these two events are apparently the only large subduction-zone earthquakes in northern Peru since 1619 (est. latitude 8°S, est. M w 7.8); these two tsunamis also each produced more fatalities than any other tsunami in Peru since the 18th century. We concur with Pelayo and Wiens (1990, 1992) that this subduction zone, in northern Peru, resembles others where the subduction zone is only weakly coupled, and convergence is largely aseismic. Subduction-zone earthquakes, when they occur, are slow, commonly shallow, and originate far from shore (near the tip of the wedge). Thus they are weakly felt, and the ensuing tsunamis are unanticipated by local populations. Although perhaps a borderline case, the Chimbote tsunami clearly is another wake-up example of a "tsunami earthquake."  相似文献   

11.
Tsunamis are most destructive at near to regional distances, arriving within 20–30 min after a causative earthquake; effective early warning at these distances requires notification within 15 min or less. The size and impact of a tsunami also depend on sea floor displacement, which is related to the length, L, width, W, mean slip, D, and depth, z, of the earthquake rupture. Currently, the primary seismic discriminant for tsunami potential is the centroid-moment tensor magnitude, M w CMT , representing the product LWD and estimated via an indirect inversion procedure. However, the obtained M w CMT and the implied LWD value vary with rupture depth, earth model, and other factors, and are only available 20–30 min or more after an earthquake. The use of more direct discriminants for tsunami potential could avoid these problems and aid in effective early warning, especially for near to regional distances. Previously, we presented a direct procedure for rapid assessment of earthquake tsunami potential using two, simple measurements on P-wave seismograms—the predominant period on velocity records, T d , and the likelihood, T 50 Ex , that the high-frequency, apparent rupture-duration, T 0, exceeds 50–55 s. We have shown that T d and T 0 are related to the critical rupture parameters L, W, D, and z, and that either of the period–duration products T d T 0 or T d T 50 Ex gives more information on tsunami impact and size than M w CMT , M wp, and other currently used discriminants. These results imply that tsunami potential is not directly related to the product LWD from the “seismic” faulting model, as is assumed with the use of the M w CMT discriminant. Instead, information on rupture length, L, and depth, z, as provided by T d T 0 or T d T 50 Ex , can constrain well the tsunami potential of an earthquake. We introduce here special treatment of the signal around the S arrival at close stations, a modified, real-time, M wpd(RT) magnitude, and other procedures to enable early estimation of event parameters and tsunami discriminants. We show that with real-time data currently available in most regions of tsunami hazard, event locations, m b and M wp magnitudes, and the direct, period–duration discriminant, T d T 50 Ex can be determined within 5 min after an earthquake occurs, and T 0, T d T 0, and M wpd(RT) within approximately 10 min. This processing is implemented and running continuously in real-time within the Early-est earthquake monitor at INGV-Rome (http://early-est.rm.ingv.it). We also show that the difference m b  ? log10(T d T 0) forms a rapid discriminant for slow, tsunami earthquakes. The rapid availability of these measurements can aid in faster and more reliable tsunami early warning for near to regional distances.  相似文献   

12.
On 11 March 2011, a moment magnitude M w = 9.0 earthquake occurred off the Japan Tohoku coast causing catastrophic damage and loss of human lives. In the immediate aftermath of the earthquake, we conducted the reconnaissance survey in the city of Rikuzentakata, Japan. In comparison with three previous historical tsunamis impacting the same region, the 2011 event presented the largest values with respect to the tsunami height, the inundation area and the inundation distance. A representative tsunami height of 15 m was recorded in Rikuzentakata, with increased heights of 20 m around rocky headlands. In terms of the inundation area, the 2011 Tohoku tsunami exceeded by almost 2.6 times the area flooded by the 1960 Chilean tsunami, which ranks second among the four events compared. The maximum tsunami inundation distance was 8.1 km along the Kesen River, exceeding the 1933 Showa and 1960 Chilean tsunami inundations by factors of 6.2 and 2.7, respectively. The overland tsunami inundation distance was less than 2 km. The tsunami inundation height linearly decreased along the Kesen River at a rate of approximately 1 m/km. Nevertheless, the measured inland tsunami heights exhibit significant variations on local and regional scales. A designated “tsunami control forest” planted with a cross-shore width of about 200 m along a 2 km stretch of Rikuzentakata coastline was completely overrun and failed to protect the local community during this extreme event. Similarly, many designated tsunami shelters were too low and were overwashed by tsunami waves, thereby failing to provide shelter for evacuees—a risk that had been underestimated.  相似文献   

13.
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   

14.
Following the 2007, August 15th, M w 8.0, Pisco earthquake in central Peru, Sladen et al. (J Geophys Res 115: B02405, 2010) have derived several slip models of this event. They inverted teleseismic data together with geodetic (InSAR) measurements to look for the co-seismic slip distribution on the fault plane, considering those data sets separately or jointly. But how close to the real slip distribution are those inverted slip models? To answer this crucial question, the authors generated some tsunami records based on their slip models and compared them to DART buoys, tsunami records, and available runup data. Such an approach requires a robust and accurate tsunami model (non-linear, dispersive, accurate bathymetry and topography, etc.) otherwise the differences between the data and the model may be attributed to the slip models themselves, though they arise from an incomplete tsunami simulation. The accuracy of a numerical tsunami simulation strongly depends, among others, on two important constraints: (i) A fine computational grid (and thus the bathymetry and topography data sets used) which is not always available, unfortunately, and (ii) a realistic tsunami propagation model including dispersion. Here, we extend Sladen’s work using newly available data, namely a tide gauge record at Callao (Lima harbor) and the Chilean DART buoy record, while considering a complete set of runup data along with a more realistic tsunami numerical that accounts for dispersion, and also considering a fine-resolution computational grid, which is essential. Through these accurate numerical simulations we infer that the InSAR-based model is in better agreement with the tsunami data, studying the case of the Pisco earthquake indicating that geodetic data seems essential to recover the final co-seismic slip distribution on the rupture plane. Slip models based on teleseismic data are unable to describe the observed tsunami, suggesting that a significant amount of co-seismic slip may have been aseismic. Finally, we compute the runup distribution along the central part of the Peruvian coast to better understand the wave amplification/attenuation processes of the tsunami generated by the Pisco earthquake.  相似文献   

15.
We use a viscous slide model of Jiang and LeBlond (1994) coupled with nonlinear shallow water equations to study tsunami waves in Resurrection Bay, in south-central Alaska. The town of Seward, located at the head of Resurrection Bay, was hit hard by both tectonic and local landslide-generated tsunami waves during the M W 9.2 1964 earthquake with an epicenter located about 150 km northeast of Seward. Recent studies have estimated the total volume of underwater slide material that moved in Resurrection Bay during the earthquake to be about 211 million m3. Resurrection Bay is a glacial fjord with large tidal ranges and sediments accumulating on steep underwater slopes at a high rate. Also, it is located in a seismically active region above the Aleutian megathrust. All these factors make the town vulnerable to locally generated waves produced by underwater slope failures. Therefore it is crucial to assess the tsunami hazard related to local landslide-generated tsunamis in Resurrection Bay in order to conduct comprehensive tsunami inundation mapping at Seward. We use numerical modeling to recreate the landslides and tsunami waves of the 1964 earthquake to test the hypothesis that the local tsunami in Resurrection Bay has been produced by a number of different slope failures. We find that numerical results are in good agreement with the observational data, and the model could be employed to evaluate landslide tsunami hazard in Alaska fjords for the purposes of tsunami hazard mitigation.  相似文献   

16.
We assess the tsunami hazard posed to New Zealand by the Kermadec and southern New Hebrides subduction margins. Neither of these subduction zones has produced tsunami large enough to cause significant damage in New Zealand over the past 150?years of well-recorded history. However, as this time frame is short compared to the recurrence interval for major tsunamigenic earthquakes on many of the Earth’s subduction zones, it should not be assumed that what has been observed so far is representative of the long term. For each of these two subduction zones we present plate kinematic and fault-locking results from block modelling of earthquake slip vector data and GPS velocities. The results are used to estimate the current rates of strain accumulation on the plate interfaces where large tsunamigenic earthquakes typically occur. We also review data on the larger historical earthquakes that have occurred on these margins, as well as the Global CMT catalogue of events since 1976. Using this information we have developed a set of scenarios for large earthquakes which have been used as initial conditions for the COMCOT tsunami code to estimate the subsequent tsunami propagation in the southwest Pacific, and from these the potential impact on New Zealand has been evaluated. Our results demonstrate that there is a significant threat posed to the Northland and Coromandel regions of New Zealand should a large earthquake (M w ?8.5) occur on the southern or middle regions of the Kermadec Trench, and that a similarly large earthquake on the southern New Hebrides Trench has the potential to strongly impact on the far northern parts of New Zealand close to the southern end of the submarine Three Kings Ridge. We propose logic trees for the magnitude–frequency parameters of large earthquakes originating on each trench, which are intended to form the basis for future probabilistic studies.  相似文献   

17.
— On the evening of 17 July 1998, on th e Aitape Coast of Papua New Guinea, a strongly felt earthquake was followed some 10–25 minutes later by a destructive tsunami. The tsunami comprised three waves, each estimated to be about 4 m high. The second of the three waves rose to a height of 10–15 m above sea level after it had crossed the shoreline and caused most damage. Maximum wave heights and the greatest damage were recorded along a 14-km sector of coast centered on Sissano Lagoon. In this sector the wavefronts moved from east to west along the coast; all structures were destroyed, and in the two main villages 20–40 percent of the population was killed. Partial destruction extended 23 km to the southeast and 8 km to the northwest, and effects of the tsunami were felt as far as 250 km to the west–northwest, beyond the international border. More than 1600 people are known to have died, with some estimates as high as 2200; 1000 were seriously injured, and 10,000 survivors were displaced. This paper presents information from interviews with eye-witnesses and from mapping of damage and inundation, and includes new information on the height, shape and timing of the waves; on the possible escape of petroleum and other gases from beneath the seafloor before and during the tsunami; on unusual sound effects that preceded the waves, and lighting effects that followed; on possible deep circulation (to 250 m) of sea water in the waves; on subsidence of the order of 50–70 cm at the coastal sand barrier; and on the resilience and potential protective capacity of certain species of trees. Eye-witness accounts indicate that the tsunami reached the shore at between 09:00 and 09:08 UT, which is earlier than is proposed in published models of the timing and location of the source of the tsunami.  相似文献   

18.
A numerical model of the wave dynamics in Chenega Cove, Alaska during the historic M w 9.2 megathrust earthquake is presented. During the earthquake, locally generated waves of unknown origin were identified at the village of Chenega, located in the western part of Prince William Sound. The waves appeared shortly after the shaking began and swept away most of the buildings while the shaking continued. We model the tectonic tsunami in Chenega Cove assuming different tsunami generation processes. Modeled results are compared with eyewitness reports and an observed runup. Results of the numerical experiments let us claim the importance of including both vertical and horizontal displacement into the 1964 tsunami generation process. We also present an explanation for the fact that arrivals of later waves in Chenega were unnoticed.  相似文献   

19.
On November 15, 2006, Crescent City in Del Norte County, California was hit by a tsunami generated by a M w 8.3 earthquake in the central Kuril Islands. Strong currents that persisted over an eight-hour period damaged floating docks and several boats and caused an estimated $9.2 million in losses. Initial tsunami alert bulletins issued by the West Coast Alaska Tsunami Warning Center (WCATWC) in Palmer, Alaska were cancelled about three and a half hours after the earthquake, nearly five hours before the first surges reached Crescent City. The largest amplitude wave, 1.76-meter peak to trough, was the sixth cycle and arrived over two hours after the first wave. Strong currents estimated at over 10 knots, damaged or destroyed three docks and caused cracks in most of the remaining docks. As a result of the November 15 event, WCATWC changed the definition of Advisory from a region-wide alert bulletin meaning that a potential tsunami is 6 hours or further away to a localized alert that tsunami water heights may approach warning- level thresholds in specific, vulnerable locations like Crescent City. On January 13, 2007 a similar Kuril event occurred and hourly conferences between the warning center and regional weather forecasts were held with a considerable improvement in the flow of information to local coastal jurisdictions. The event highlighted the vulnerability of harbors from a relatively modest tsunami and underscored the need to improve public education regarding the duration of the tsunami hazards, improve dialog between tsunami warning centers and local jurisdictions, and better understand the currents produced by tsunamis in harbors.  相似文献   

20.
—On October 4, 1994, an earthquake of magnitude M w = 8.2 occurred in the western part of the Kurile Islands, generating a tsunami that has been well recorded along the entire coast of Japan. Previous works have shown that this earthquake does not represent a low angle thrust event, normally expected in a subduction zone, rather an intra-plate event rupturing through the slab. On the basis of the accepted mechanism, two fault models, representative of the nodal plane ambiguity, have been suggested. The goal of this work is to verify whether the tsunami simulations are able to rule out one of the two proposed fault models. Taking into account both fault models together with a heterogeneous slip along the fault, we have performed numerical simulations of the tsunami. All source models produce tide-gauge records in agreement with the observed ones. The limit of resolution of the performed simulations, estimated by means of a perturbed bathymetry, does not allow us to distinguish the best source model.  相似文献   

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