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1.
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   

2.
国际海啸预警系统(ITWS)   总被引：5，自引：2，他引：5  
介绍了国际海啸预警系统的构成、地震与海啸信息的检测、海啸预警信息的发布，并介绍了太平洋海啸预警中心和阿拉斯加海啸预警中心。  相似文献   

3.
The coast of California was significantly impacted by two recent teletsunami events, one originating off the coast of Chile on February 27, 2010 and the other off Japan on March 11, 2011. These tsunamis caused extensive inundation and damage along the coast of their respective source regions. For the 2010 tsunami, the NOAA West Coast/Alaska Tsunami Warning Center issued a state-wide Tsunami Advisory based on forecasted tsunami amplitudes ranging from 0.18 to 1.43 m with the highest amplitudes predicted for central and southern California. For the 2011 tsunami, a Tsunami Warning was issued north of Point Conception and a Tsunami Advisory south of that location, with forecasted amplitudes ranging from 0.3 to 2.5 m, the highest expected for Crescent City. Because both teletsunamis arrived during low tide, the potential for significant inundation of dry land was greatly reduced during both events. However, both events created rapid water-level fluctuations and strong currents within harbors and along beaches, causing extensive damage in a number of harbors and challenging emergency managers in coastal jurisdictions. Field personnel were deployed prior to each tsunami to observe and measure physical effects at the coast. Post-event survey teams and questionnaires were used to gather information from both a physical effects and emergency response perspective. During the 2010 tsunami, a maximum tsunami amplitude of 1.2 m was observed at Pismo Beach, and over $3-million worth of damage to boats and docks occurred in nearly a dozen harbors, most significantly in Santa Cruz, Ventura, Mission Bay, and northern Shelter Island in San Diego Bay. During the 2011 tsunami, the maximum amplitude was measured at 2.47 m in Crescent City Harbor with over $50-million in damage to two dozen harbors. Those most significantly affected were Crescent City, Noyo River, Santa Cruz, Moss Landing, and southern Shelter Island. During both events, people on docks and near the ocean became at risk to injury with one fatality occurring during the 2011 tsunami at the mouth of the Klamath River. Evaluations of maximum forecasted tsunami amplitudes indicate that the average percent error was 38 and 28 % for the 2010 and 2011 events, respectively. Due to these recent events, the California tsunami program is developing products that will help: (1) the maritime community better understand tsunami hazards within their harbors, as well as if and where boats should go offshore to be safe, and (2) emergency managers develop evacuation plans for relatively small “Warning” level events where extensive evacuation is not required. Because tsunami-induced currents were responsible for most of the damage in these two events, modeled current velocity estimates should be incorporated into future forecast products from the warning centers.  相似文献   

4.
The authors recently proposed a new method for detecting tsunamis using high-frequency (HF) radar observations, referred to as “time-correlation algorithm” (TCA; Grilli et al. Pure Appl Geophys 173(12):3895–3934, 2016a, 174(1): 3003–3028, 2017). Unlike standard algorithms that detect surface current patterns, the TCA is based on analyzing space-time correlations of radar signal time series in pairs of radar cells, which does not require inverting radial surface currents. This was done by calculating a contrast function, which quantifies the change in pattern of the mean correlation between pairs of neighboring cells upon tsunami arrival, with respect to a reference correlation computed in the recent past. In earlier work, the TCA was successfully validated based on realistic numerical simulations of both the radar signal and tsunami wave trains. Here, this algorithm is adapted to apply to actual data from a HF radar installed in Tofino, BC, for three test cases: (1) a simulated far-field tsunami generated in the Semidi Subduction Zone in the Aleutian Arc; (2) a simulated near-field tsunami from a submarine mass failure on the continental slope off of Tofino; and (3) an event believed to be a meteotsunami, which occurred on October 14th, 2016, off of the Pacific West Coast and was measured by the radar. In the first two cases, the synthetic tsunami signal is superimposed onto the radar signal by way of a current memory term; in the third case, the tsunami signature is present within the radar data. In light of these test cases, we develop a detection methodology based on the TCA, using a correlation contrast function, and show that in all three cases the algorithm is able to trigger a timely early warning.  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.
We explained spectra of distant tsunamis observed in enclosed basins by applying the synthesis method based on joint analysis of tsunami and background spectra from a number of stations. This method is the generalization of the method proposed by Rabinovich (J. Geopys. Res. 102, 12663-12676, 1997) to separate source and topography effects in recorded tsunami waves. The source function is extracted by inversion of the tsunami/background spectra averaged from many observational sites. The method is applied to the 2009 Papua tsunami observed at the Owase tide station in southwest Japan, a region with complicated topography and numerous bays and inlets. The synthesized spectrum explains the observed spectral amplitudes for each frequency component. It is shown that averaging of tsunami and background from various tide gauge stations in semi-enclosed basins is an efficient approach to extract the source function.  相似文献   

7.
The Alaska Tsunami Warning Center has the responsibility of providing timely tsunami warning services for Alaska and the west coasts of Canada and the United States. Recently, the ATWC implemented a new microcomputer system which is used for both automatic and interactive earthquake processing, and for disseminating critical information to the Tsunami Warning System recipients.Real-time seismic wave form data from 23 short-period and 9 long-period sites in Alaska, the lower 48 States, and Hawaii, are continually computer-monitored for the occurrence of an earthquake. Once detected from the short-period wave form data, pre- and post-earthquake data are displayed on a graphics terminal along with an indicator to identify the time of the onset of theP waves (P-picks). TheP-picks can easily be changed during or after data collection via a mouse. Magnitudes (M b ,M l ,M B ,M S ) are automatically computed from appropriate short- and long-period wave form data concurrently with the above processing. A second graphics terminal displays cycle-by-cycle long-period wave form data that was used to compute an earthquake'sM B andM S magnitudes.An earthquake's parametric data and other information are available and printed within tens of seconds after theP wave arrivals are recorded at the first 5 sites, then 7 sites, 9 sites, and a final parametric computation using all collected data. Three video display monitors are used for displaying the parameters, procedural aids, and a map showing the epicenter. Additionally, selected event parameters are immediately transmitted by VHF radio to alphanumeric beepers which are carried by standby duty personnel during those times that the Center is not manned.Using a dedicated video display terminal and printer, the interactive system can use data and parameters resulting from the automatic processes for concurrent parameter recomputations; perform additional computations; disseminate critical information; and generate procedural aids for duty geophysicists to facilitate an earthquake/tsunami investigation.  相似文献   

8.
We apply a recently developed and validated numerical model of tsunami propagation and runup to study the inundation of Resurrection Bay and the town of Seward by the 1964 Alaska tsunami. Seward was hit by both tectonic and landslide-generated tsunami waves during the $M_{\rm W}$ 9.2 1964 megathrust earthquake. The earthquake triggered a series of submarine mass failures around the fjord, which resulted in landsliding of part of the coastline into the water, along with the loss of the port facilities. These submarine mass failures generated local waves in the bay within 5?min of the beginning of strong ground motion. Recent studies estimate the total volume of underwater slide material that moved in Resurrection Bay to be about 211?million m3 (Haeussler et?al. in Submarine mass movements and their consequences, pp 269?C278, 2007). The first tectonic tsunami wave arrived in Resurrection Bay about 30?min after the main shock and was about the same height as the local landslide-generated waves. Our previous numerical study, which focused only on the local landslide-generated waves in Resurrection Bay, demonstrated that they were produced by a number of different slope failures, and estimated relative contributions of different submarine slide complexes into tsunami amplitudes (Suleimani et?al. in Pure Appl Geophys 166:131?C152, 2009). This work extends the previous study by calculating tsunami inundation in Resurrection Bay caused by the combined impact of landslide-generated waves and the tectonic tsunami, and comparing the composite inundation area with observations. To simulate landslide tsunami runup in Seward, we use a viscous slide model of Jiang and LeBlond (J Phys Oceanogr 24(3):559?C572, 1994) coupled with nonlinear shallow water equations. The input data set includes a high resolution multibeam bathymetry and LIDAR topography grid of Resurrection Bay, and an initial thickness of slide material based on pre- and post-earthquake bathymetry difference maps. For simulation of tectonic tsunami runup, we derive the 1964 coseismic deformations from detailed slip distribution in the rupture area, and use them as an initial condition for propagation of the tectonic tsunami. The numerical model employs nonlinear shallow water equations formulated for depth-averaged water fluxes, and calculates a temporal position of the shoreline using a free-surface moving boundary algorithm. We find that the calculated tsunami runup in Seward caused first by local submarine landslide-generated waves, and later by a tectonic tsunami, is in good agreement with observations of the inundation zone. The analysis of inundation caused by two different tsunami sources improves our understanding of their relative contributions, and supports tsunami risk mitigation in south-central Alaska. The record of the 1964 earthquake, tsunami, and submarine landslides, combined with the high-resolution topography and bathymetry of Resurrection Bay make it an ideal location for studying tectonic tsunamis in coastal regions susceptible to underwater landslides.  相似文献   

9.
基于日本南海海槽地震活动性和历史海啸事件记载的分析,本文对日本南海海槽发生MW9.1罕遇地震情况下的海啸进行了数值模拟研究.结果表明:该地震可引发初始波幅约10 m的海啸,6个小时后传至浙江沿海,近岸各处波幅为1—2 m;8个小时后靠近上海海岸线,最大波幅约2 m,受地形影响局地爬高至近3 m;11个小时后抵达苏北黄海沿岸,预计波幅普遍在1 m左右.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.我国近岸海域地形变化复杂,海湾众多,对海啸波有放大作用,该模拟结果可能比实际传播到近岸时偏小,因此综合评估日本海啸影响我国华东地区的规模m可达1—2级左右.一旦日本南海发生罕遇地震对我国的影响不容忽视,尤其遇上风暴潮与天文大潮叠加,则可能会造成一定程度的海啸灾害.   相似文献   

10.
The Method of Splitting Tsunamis (MOST) model adapted by National Oceanic and Atmospheric Administration (NOAA) for tsunami forecasting operations is praised for its computational efficiency, associated with the use of splitting technique. It will be shown, however, that splitting the computations between \(x\) and \(y\) directions results in specific sensitivity to the treatment of land–water boundary. Slight modification to the reflective boundary condition in MOST caused an appreciable difference in the results. This is demonstrated with simulations of the Tohoku-2011 tsunami from the source earthquake to Monterey Bay, California, and in southeast Alaska, followed by comparison with tide gage records. In the first case, the better representation of later waves (reflected from the coasts) by the modified model in a Pacific-wide simulation resulted in twice as long match between simulated and observed tsunami time histories at Monterey gage. In the second case, the modified model was able to propagate the tsunami wave and approach gage records at locations within narrow channels (Juneau, Ketchikan), to where MOST had difficulty propagating the wave. The modification was extended to include inundation computation. The resulting inundation algorithm (Cliffs) has been tested with the complete set of NOAA-recommended benchmark problems focused on inundation. The solutions are compared to the MOST solutions obtained with the version of the MOST model benchmarked for the National Tsunami Hazard Mitigation Program in 2011. In two tests, Cliffs and MOST results are very close, and in another two tests, the results are somewhat different. Very different regimes of generation/disposal of water by Cliffs and MOST inundation algorithms, which supposedly affected the benchmarking results, have been discussed.  相似文献   

11.
The Ligurian coast, located at the French–Italian border, is densely populated as well as a touristic area. It is also a location where earthquakes and underwater landslides are recurrent. The nature of the local tsunamigenesis is therefore a legitimate question, because no tsunami warning system can resolve tsunami arrival times of a few minutes, which is the case for the area. As far as the seismicity of the area is concerned, the frequent recurrent earthquakes are generally of moderate magnitude: most of them are lower than M w 5. However, the relatively large M w 6.9 earthquake (Larroque et al., in Geophys J Int, 2012. doi:10.1111/j.1365-246X.2012.05498.x) that occurred on the February 23, 1887, offshore of Imperia (Italian Riviera) is quite emblematic. This unusual event for the region merits a complete study: the quantification of its rupture mechanism is essential (1) to understand the regional active deformation, but also (2) to evaluate its tsunamigenesis potential by deriving relevant rupture scenarios obtained from our knowledge of the event; for that purpose the event is extensively described here. The first point has been the subject of quite a few studies based on the seismotectonics of the area. The last documented approach has been completed by Larroque et al. (Geophys J Int, 2012. doi:10.1111/j.1365-246X.2012.05498.x) who proposed a rupture scenario involving a reverse faulting along a north dipping fault and favoring a M w 6.9 magnitude. In the present paper (1) we study the accuracy of their solutions in relation to the computational grid spacing and the dispersive/nondispersive parameterization, (2) based on an uncertainty on the recorded wave amplitude of the Genoa tide gauge they used, we propose a M w 6.7 earthquake magnitude solution for the event (the kinematics is unchanged), co-existing with the M w 6.9, (3) we evaluate the tsunami coastal impact of the 1887 event, and (4) we test a range of possible ruptures that local faults may undergo in order to propose a synoptic mapping of the tsunami threat in the area. The spatial distribution of the maximum wave height (MWH) is provided with a tentative identification of the processes that are responsible for it. This latter issue is imperative in order to make our mapping as generic as possible in the framework of our deterministic approach (based on realistic scenarios and not on ensemble statistics). The predictions suggest that the wave impact is mostly local, considering the relatively moderate size of the rupture planes. Although the present-day seismicity in this region is moderate, stronger earthquakes (M > 6.5) have occurred in the past. The studied scenarios show that for such events specific localities along the French–Italian Riviera may experience very significant MWH related to the shallow focal depth tested for such scenarios. We may reasonably conclude that the tsunami threat is relatively significant and uniform at the Italian side of the Riviera (from Ventimiglia to Imperia), while it is more localized (sporadic) at the French side from Antibes to Menton with, however, higher local level of inundation, e.g., Nice city center.  相似文献   

12.
On 15 July 2009, a Mw 7.8 earthquake occurred off the New Zealand coast, which by serendipitous coincidence occurred while the International Tsunami Symposium was in session in Novosibirsk, Russia. The earthquake generated a tsunami that propagated across the Tasman Sea and was detected in New Zealand, Australia and as far away as the US West coast. Small boats close to the epicenter were placed in jeopardy, but no significant damage was observed despite a measured run-up height of 2.3 m in one of the Sounds in close proximity to the source (Wilson in GNS Science Report 46:62 2009). Peak-to-trough tsunami heights of 55 cm were measured at Southport, Tasmania and a height of 1 m was measured in Jackson Bay, New Zealand. The International Tsunami Symposium provided an ideal venue for illustration of the value of immediate real-time assessment and provided an opportunity to further validate the real time forecasting capabilities with the scientific community in attendance. A number of agencies with responsibility for tsunami forecast and/or warning, such as the NOAA Center for Tsunami Research, the Pacific Tsunami Warning Center, GNS Science in New Zealand, the Australian Bureau of Meteorology and the European Commission Joint Research Centre were all represented at the meeting and were able to demonstrate the use of state of the art numerical models to assess the tsunami potential and provide warning as appropriate.  相似文献   

13.
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   

14.
Tsunami Forecasting and Monitoring in New Zealand   总被引：1，自引：0，他引：1  
New Zealand is exposed to tsunami threats from several sources that vary significantly in their potential impact and travel time. One route for reducing the risk from these tsunami sources is to provide advance warning based on forecasting and monitoring of events in progress. In this paper the National Tsunami Warning System framework, including the responsibilities of key organisations and the procedures that they follow in the event of a tsunami threatening New Zealand, are summarised. A method for forecasting threat-levels based on tsunami models is presented, similar in many respects to that developed for Australia by Allen and Greenslade (Nat Hazards 46:35?C52, 2008), and a simple system for easy access to the threat-level forecasts using a clickable pdf file is presented. Once a tsunami enters or initiates within New Zealand waters, its progress and evolution can be monitored in real-time using a newly established network of online tsunami gauge sensors placed at strategic locations around the New Zealand coasts and offshore islands. Information from these gauges can be used to validate and revise forecasts, and assist in making the all-clear decision.  相似文献   

15.
The 25 April 1992 Cape Mendocino earthquake generated a tsunami characterized by both coastal trapped edge wave and non-trapped tsunami modes that propagated north and south along the U.S. West Coast. Both observed and synthetic time series at Crescent City and North Spit are consistent with the zero-order edge wave mode solution for a semi-infinite sloping beach depth profile. Wave amplitudes at Crescent City were about twice that observed at North Spit, in spite of the fact that the source region was three times farther from Crescent City than North Spit. The largest observed amplitude was due to an edge wave which arrived almost three hours after the initial onset of the tsunami; since such waves are highly localized nearshore, this suggests that the enhanced responsiveness at Crescent City is at least partly due to local dynamic processes. Furthermore, the substantially delayed arrival of this wave, which was generated at the southern end of the Cascadia Subduction Zone, has significant implications for hazard mitigation efforts along the entire U.S. West Coast. Specifically, this study demonstrates that slow-moving but very energetic edge wave modes could be generated by future large tsunamigenic earthquakes in the CSZ, and that these might arrive unexpectedly at coastal communities several hours after the initial tsunami waves have subsided.  相似文献   

16.
The M w=9.3 megathrust earthquake of December 26, 2004 off the coast of Sumatra in the Indian Ocean generated a catastrophic tsunami that caused widespread damage in coastal areas and left more than 226,000 people dead or missing. The Sumatra tsunami was accurately recorded by a large number of tide gauges throughout the world's oceans. This paper examines the amplitudes, frequencies and wave train structure of tsunami waves recorded by tide gauges located more than 20,000 km from the source area along the Pacific and Atlantic coasts of North America.  相似文献   

17.
Sea level variability along the US West Coast is analyzed using multi-year time series records from tide gauges and a high-resolution regional ocean model, the base of the West Coast Ocean Forecast System (WCOFS). One of the metrics utilized is the frequency of occurrences when model prediction is within 0.15 m from the observed sea level, F. A target level of F?=?90% is set by an operational agency. A combination of the tidal sea level from a shallow water inverse model, inverted barometer (IB) term computed using surface air pressure from a mesoscale atmospheric model, and low-pass filtered sea level from WCOFS representing the effect of coastal ocean dynamics (DYN) provides the most straightforward approach to reaching levels F>80%. The IB and DYN components each add between 5 and 15% to F. Given the importance of the DYN term bringing F closer to the operational requirement and its role as an indicator of the coastal ocean processes on scales from days to interannual, additional verification of the WCOFS subtidal sea level is provided in terms of the model-data correlation, standard deviation of the band-pass filtered (2–60 days) time series, the annual cycle amplitude, and alongshore sea level coherence in the range of 5–120-day periods. Model-data correlation in sea level increases from south to north along the US coast. The rms amplitude of model sea level variability in the 2–60-day band and its annual amplitude are weaker than observed north of 42 N, in the Pacific Northwest (PNW) coast region. The alongshore coherence amplitude and phase patterns are similar in the model and observations. Availability of the multi-year model solution allows computation and analysis of spatial maps of the coherence amplitude. For a reference location in the Southern California Bight, relatively short-period sea level motions (near 10 days) are incoherent with those north of the Santa Barbara Channel (in part, due to coastal trapped wave scattering and/or dissipation). At a range of periods around 60 days, the coastal sea level in Southern California is coherent with the sea surface height (SSH) variability over the shelf break in Oregon, Washington, and British Columbia, more than with the coastal SSH at the same latitudes.  相似文献   

18.
Tsunami Warning Centers issue rapid and accurate tsunami warnings to coastal populations by estimating the location and size of the causative earthquake as soon as possible after rupture initiation. Both US Tsunami Warning Centers have therefore been using Mwp to issue Tsunami Warnings 5–10 min after Earthquake origin time since 2002. However, because Mwp (Tsuboi et al., Bulletin of the Seismological society of America 85:606–613, 1995) is based on the far-field approximation to the P-wave displacement due to a double couple point source, we should only very carefully apply Mwp to data obtained in the near field, at distances of less than a few wavelengths from the fault. On the other hand, the surface waves from Great Earthquakes, including those that occur just offshore of populated areas, such as the 2011 Tohoku earthquake, clip seismographs located near the fault. Because the first arriving P-waves from such large events are often on scale, Mwp should provide useful information, even for these Great Earthquakes. We therefore calculate Mwp from 18 unclipped STS-1 broadband P-wave seismograms, recorded at 2–15° distance from the Tohoku epicenter to determine if Mwp can usefully estimate Mw for this earthquake, using data obtained close to the epicenter. In this case there should be a good chance to get reliable Mwp values for stations at epicentral distances of 9–10°, since the source duration for the Tohoku earthquake is less than 200 s and the time window used to estimate Mwp is 120 s in duration. Our analysis indicates that Mwp does indeed give reliable results (Mw ~ 9.1) beginning at about 11° distance from the epicenter. The values of Mwp from seismic waveforms obtained at 11–15° epicentral distance from the Mw 9.1 off the east coast of Tohuku earthquake of March 11, 2011 fell within the range 9.1–9.3, and were available within 4–5 min after origin time. Even the Mwp values of 7.7–8.4, obtained at less than 5° epicentral distance, exceed the PTWC’s threshold of Mw 7.6 for issuing a regional tsunami warning to coastal populations within 1,000 km of the epicenter, and of Mw 6.9 for issuing a local tsunami warning to the coastal populations of Hawaii.  相似文献   

19.
— Surface-wave amplitudes from explosion sources show less variation for a given event han body wave amplitudes, so it is natural to expect that yield estimates derived from surface waves will be more accurate than yield estimates derived from body waves. However, yield estimation from surface waves is complicated by the presence of tectonic strain release, which acts like one or more earthquake sources superimposed on top of the explosion. Moment-tensor inversion can be used to remove the tectonic component of the surface waves, however moment-tensor inversion for shallow sources is inherently non-unique so the explosion isotropic moment cannot be determined with the necessary accuracy by this means. Explosions on an island or near a mountain slope can exhibit anomalous surface waves similar to those caused by tectonic strain release. These complications cause yield estimates derived from surface waves to be less accurate than yield estimates from body waves recorded on a well-calibrated network with good coverage. Surface-wave amplitudes can be expressed as a surface-wave magnitude M s , which is defined as the logarithm of the amplitude plus a distance correction, or as a path corrected spectral magnitude, log $M^{\prime}_0$ , which is derived from the surface-wave spectrum. We derive relations for M s vs. yield and log $M^{\prime}_0$ vs. yield for a large data set and estimate the accuracy of these estimates.  相似文献   

20.
We reviewed joint inversion studies of the rupture processes of significant earthquakes, using the definition of a joint inversion in earthquake source imaging as a source inversion of multiple kinds of datasets (waveform, geodetic, or tsunami). Yoshida and Koketsu (Geophys J Int 103:355–362, 1990), and Wald and Heaton (Bull Seismol Soc Am 84:668–691, 1994) independently initiated joint inversion methods, finding that joint inversion provides more reliable rupture process models than single-dataset inversion, leading to an increase of joint inversion studies. A list of these studies was made using the finite-source rupture model database (Mai and Thingbaijam in Seismol Res Lett 85:1348–1357, 2014). Outstanding issues regarding joint inversion were also discussed.  相似文献   

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