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1.
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   

2.
The tsunami generated by the 2011 Tohoku Earthquake (M w = 9.0) reached maximum heights of about 5 m along the coast of the Kuril Islands. The most essential feature of this event was sea ice about 0.5 m thick moved by the ocean water. The tsunami did not cause any essential damage on the Kuril Islands, but significantly affected coastal zones and produced interesting effects. The problem of a tsunami accompanied by marine ice is discussed and illustrated with photos.  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.
We investigate spatio-temporal properties of earthquake patterns in the San Jacinto fault zone (SJFZ), California, between Cajon Pass and the Superstition Hill Fault, using a long record of simulated seismicity constrained by available seismological and geological data. The model provides an effective realization of a large segmented strike-slip fault zone in a 3D elastic half-space, with heterogeneous distribution of static friction chosen to represent several clear step-overs at the surface. The simulated synthetic catalog reproduces well the basic statistical features of the instrumental seismicity recorded at the SJFZ area since 1981. The model also produces events larger than those included in the short instrumental record, consistent with paleo-earthquakes documented at sites along the SJFZ for the last 1,400 years. The general agreement between the synthetic and observed data allows us to address with the long-simulated seismicity questions related to large earthquakes and expected seismic hazard. The interaction between m ≥ 7 events on different sections of the SJFZ is found to be close to random. The hazard associated with m ≥ 7 events on the SJFZ increases significantly if the long record of simulated seismicity is taken into account. The model simulations indicate that the recent increased number of observed intermediate SJFZ earthquakes is a robust statistical feature heralding the occurrence of m ≥ 7 earthquakes. The hypocenters of the m ≥ 5 events in the simulation results move progressively towards the hypocenter of the upcoming m ≥ 7 earthquake.  相似文献   

5.
Data are presented from deep seismic sounding along the strike of the Balearic Islands carried out in 1976. The interpretation of the data gives the following results: A sedimentary cover of 4 km around Ibiza to 7 km under Mallorca overlies the crystalline basement. This basement with a P-wave velocity of 6.0 km/s at the top reaches a depth of at least 15 km under Ibiza and 17 km under Mallorca with an increase to 6.1 km/s at these depths. The crust-mantle boundary lies at a depth of 20 km and 25 km, respectively. A well documented upper-mantle velocity of 7.7 km/s is found along the entire profile. The Moho rises to a depth of 20 km about 30 km north of Mallorca and probably continues rising towards the center of the North Balearic Sea. The newly deduced crustal structure together with previously determined velocity-depth sections in the North Balearic Sea as well as heat flow and aeromagnetic data can be interpreted as an extended rift structure caused by large-scale tensional processes in the upper mantle. The available data suggest that the entire zone from the eastern Alboran Sea to the area north of the Balearic Islands represents the southeastern flank of this rift system. In this model the provinces of Spain along the east coast would represent the northwestern rift flank.  相似文献   

6.
热层大气密度是空间大气环境的重要参数,经过多年的研究已开发了多种大气模式,但其误差普遍较大,尤其在磁暴期间偏差值甚至超过100%.本文利用中国星载大气密度探测器和CHAMP卫星加速度计在轨获得的连续探测数据,针对近10年(2003—2014)中多次强磁暴事件和多次中等强度扰动事件,即2003年11月、2004年7月和2005年8~9月多次强磁暴事件(Kp值均达到9),2006年4月、2012年4月的两次中等强度磁暴事件(Kp值分别达到7和6),分析和比对不同强度磁扰事件期间不同高度全球大气密度就位探测值与模式值(NRLMSISE00)之间的差别.在2005年8月24日强磁扰事件中,560 km高度中国卫星就位探测值上涨幅度约2~3倍,扰动区中的增变比高达5.7倍,375 km高度CHAMP卫星就位探测值上涨幅度约0.8倍,扰动区中增变比达4.0倍,期间大气密度模式值不仅没有出现明显的涨落,更没有出现强烈的区域扰动;在2003年11月和2004年7月的强磁扰事件中,CHAMP卫星就位探测值均有显著涨变和强烈扰动变化,而模式值无明显扰动变化;在中等强度磁扰事件中,高度560 km附近就位探测值在北、南半球高纬地区显著上涨,远高于模式值,高度350 km附近就位探测值在地球阴影区域显著上涨,上涨幅度也大于模式值.分析结果表明现有大气模式对地磁扰动(尤其是强磁暴事件)期间全球热层大气密度的响应并不明显,需要进一步改善.  相似文献   

7.
Interannual modulation of mesoscale eddy activity at the intraseasonal timescale in the southeastern tropical Indian Ocean and its relation to the Indian Ocean dipole mode (IOD) events are investigated using results from a high-resolution ocean general circulation model. The model reproduces observed characteristics of the intraseasonal variability and its interannual modulation fairly well, with large variances of the intraseasonal variability during the 1994 and 1997/1998 IOD events. Large negative temperature anomaly off the coasts of Java and the Lesser Sunda Islands in boreal summer, due to seasonal variation and interannual anomaly, extended further to the east in 1994, and the associated strong Indonesian throughflow enhanced the baroclinic instability in the upper layer, generating anomalously large mesoscale eddy activity. The eddy heat transport, in turn, significantly affected decaying phase of the 1994 IOD event. On the other hand, the development of the cold region off the Java Island associated with the 1997/1998 IOD event occurred in boreal winter, causing weaker baroclinic instability and hence weaker eddy activity off Java. This led to little influence on the heat budget in the southeastern tropical Indian Ocean for the 1997/1998 IOD event.  相似文献   

8.
Low Visibility Formation and Forecasting on the Northern Coast of Brazil   总被引：1，自引：0，他引：1  
Visibility analysis and forecast at the Maceio International Airport in the Brazilian Northeast (NEB) was the principal goal of this investigation. Surface meteorological data of the Maceio International Airport were used for low visibility frequency study. Low visibility in NEB was provoked more frequently by light fog (LF) formation (1,098 or 92 h month?1 on average). Haze and fog were very rare (81 h and one event per year, respectively on average). Light fog with a visibility less than 2 km usually was detected together with rain or drizzle. Low visibility was observed more frequently at night and during the rainy season. Applications of the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model for light fog forecast were tested. Thermodynamic processes were studied by vertical profile, elaborated by: (1) National Centers for Environmental Prediction (NCEP) reanalysis data for Maceio (because of some radiosonde absence) and (2) forecast vertical temperature and humidity profiles were produced, using Air Parcels Trajectories of the HYSPLIT model at the pattern levels. The synoptic situations before and during low visibility phenomena were analyzed using different products of NCEP reanalysis, the high resolution (10 km) ETA model and infrared satellite images. Wave disturbance in the trade winds field, localized on the northwest periphery of the South Atlantic subtropical High, usually accompanied the phenomena. A humidity advection, weak ascendant movement and thermal inversion absence at the low levels were created by these waves. The middle level’s descendent movement provoked the humidity accumulation at levels below. Satisfactory results of the HYSPLIT model applications for light fog forecast were obtained with 12 h antecedence. In particular, stable level forecast by the ETA model was forecast satisfactorily with 12 h antecedence; vertical movements were predicted better with up to 48 h antecedence. The PSU/NCAR mesoscale model (MM5) and PAFOG models were tested for analysis and forecast of an intensive fog event. Intensive fog provoked a fatal accident of a small airplane near the Maceio Airport in 2007. These fog formation processes were studied by NCEP reanalysis data, the high resolution regional model MM5, and satellite and radar data. Fog formation was simulated by PAFOG model and satisfactory results were obtained with 10 h antecedence.  相似文献   

9.
The announced October 2006 nuclear test explosion in the Democratic People’s Republic of Korea (DPRK) has been the first real test regarding the technical capabilities of the verification system built up by the Vienna-based Provisional Technical Secretariat (PTS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to detect and locate a nuclear test event. This paper enhances the resolution of the DPRK events’ xenon source reconstruction published by Saey et al. (2007, “A long distance measurement of radioxenon in Yellowknife, Canada, in late October 2006”, GRL, Vol. 34, L20802) that was based solely on radio-xenon measurements taken at the remote radionuclide station in Yellowknife, Canada by involving additional measurements taken by a mobile noble gas system deployed quite close to the event location in the Republic of Korea (ROK). Moreover the horizontal resolution of the forward and backward atmospheric transport modelling methods applied for the source scenario reconstruction has been enhanced appropriately to reflect the considerably shorter source-receptor distances examined in comparison to the previously published source reconstruction. It is shown that the 133Xe measurements in Yellowknife could register 133Xe traces from the nuclear explosion during the first 3 days after the event, while the mobile measurements were rather sensitive to releases during days 2–4 after the explosion. According to the analysis, the most likely source scenario would consist of an initial (possibly up to 21 h delayed) venting of 1 × 10?15 Bq 133Xe during the first 24 h, followed by a two orders of magnitude weaker seepage during the following 3 days. Both measurements corroborate the scenario of a rather rapid venting and soil diffusion of the 133Xe yielded during the explosion. While the Swedish mobile measurements were crucial to enhancement of the reconstruction of the source scenario, given the installation status of the IMS xenon network at the time of the event, a sensitivity analysis revealed that the fully developed network would have been able to detect 133Xe traces from the Korean explosion at a number of stations and allowed for an even better constraint on the release function. The station Ussuriysk, Russia, being in operation in 2006, would have registered 133Xe within 1 day and with a three orders of magnitudes stronger signal compared to the detection at Yellowknife.  相似文献   

10.
Alberni Inlet is a long and narrow fjord adjacent to Barkley Sound on the Pacific Coast of Vancouver Island, Canada. Port Alberni, at the head of the inlet, was affected in 1964 by the largest Pacific tsunami waves in Canadian history. We use observations and results from two numerical models to investigate the resonant characteristics of the region and amplification of tsunami waves in Barkley Sound and Alberni Inlet. The first model (A) was forced at its open boundary with a stationary autoregressive signal, similar to the observed background noise. The second model (B) used an initial sea-level deformation from a potential earthquake off California in the southern segment of the Cascadia Subduction Zone, producing transient tsunami waves. Spectral, cross-spectral and frequency-time (f-t) analyses of the observations were used to examine the resonant properties and topographic response of the local area. The respective results show large admittance functions over a wide 0.5–0.9 cph frequency band, implying a low Q factor but high amplification of arriving waves. This unusual behavior is a result of two effects: A quarter-wave resonance of the system for its fundamental Helmholtz mode and amplification due to the narrowing of the channel cross section from Barkley Sound to Alberni Inlet. The model A numerical results agree favorably with the observations, indicating an energetic resonant mode at frequency of ~0.53 cph (112 min), with its nodal line located near the entrance to Barkley Sound and amplification factor value close to 12. The results from the tsunami propagation model (B) yield spectral characteristics similar to those from the model A and from the observations. The maximum tsunami current speed for this scenario is 2.4 ms?1 in Sproat Narrows, which divides Alberni Inlet into two parts, while the largest computed wave height is 1.6 m in the northern Alberni Inlet, in the area of Port Alberni.  相似文献   

11.
Seismic activity, ground deformation, and soil and fumarole temperatures acquired during 2004–2007 at Vulcano (Aeolian Islands) are analysed and the time relations among the different time series are discussed. Changes in temperature of fumarolic gases took place during four “anomalous” periods (November 2004–March 2005; October 2005–February 2006; August–October 2006; July–December 2007) at the same time as an increasing number of volcano-seismic events. In particular, the temperatures at high temperature vents and at steam heated soil ranged in time from 180 to 440°C and from 20 to 90°C, respectively. The maximum daily number of volcano-seismic events was 57, reached during the second anomalous period. This seismicity, characterised by focal depth generally lower than 1?km below sea level (b.s.l.) and composed of different kinds of events associated to both resonance and shear failure processes, is related to the shallow dynamics of the hydrothermal system. During the analysed period, very few volcano-tectonic earthquakes took place and tilt recordings showed no sharp or important changes. In light of such observations, the increases in both temperature and volcano-seismic events number were associated to increases in the release of gas from a deep and stable magma body, without magma intrusions within the shallow hydrothermal system. Indeed, a greater release of gas from depth leads to increased fluid circulation, that can promote increases in volcano-seismic events number by both fracturing processes and resonance and vibration in cracks and conduits. The different trends observed in the measured geochemical and geophysical series during the anomalous periods can be due to either time changes in the medium permeability or a changing speed of gas release from a deep magma body. Finally, all the observed variations, together with the changing temporal distribution of the different seismic event kinds, suggest that the hydrothermal system at Vulcano can be considered unsteady and dynamic.  相似文献   

12.
The 1771 Yaeyama tsunami is successfully reproduced using a simple faulting model without submarine landslide. The Yaeyama tsunami (M 7.4), which struck the southern Ryukyu Islands of Japan, produced unusually high tsunami amplitudes on the southeastern coast of Ishigaki Island and caused significant damage, including 12,000 casualties. Previous tsunami source models for this event have included both seismological faults and submarine landslides. However, no evidence of landslides in the source has been obtained, despite marine surveying of the area. The seismological fault model proposed in this study, describing a fault to the east of Ishigaki Island, successfully reproduces the distribution of tsunami runup on the southern coast of the Ryukyu Islands. The unusual runup heights are found through the numerical simulation attributable to a concentration of tsunami energy toward the southeastern coast of Ishigaki Island by the effect of the shelf to the east. Thus, the unusual runup heights observed on the southeastern coast of Ishigaki Island can be adequately explained by a seismological fault model with wave-ray bending on the adjacent shelf.  相似文献   

13.
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   

14.
In the year 2007, enhanced rockfall activity was observed within the scarp of a 500 BP rockslide in the Reintal catchment (Northern Calcareous Alps, Germany); the largest of a series of events took place in August, when almost 50000 m³ of rock were detached from the subvertical rock face and deposited on a talus cone. In this case study, we focus on three aspects of rockfall research: first, we compile detailed geomorphological and geotechnical findings to explain the causes of the recent events. The results of laboratory tests and stability estimations suggest that rockfall activity will persist in the future as the old rockslide scarp still contains unstable rock masses. Second, we use digital elevation data from a pre‐event airborne LiDAR survey (ALS) and post‐event terrestrial laserscanning (TLS) to quantify landform changes and the mass balance of the rockfall event(s). The widespread availability of ALS elevation data provides a good opportunity to quantify fresh events using a comparatively inexpensive TLS survey; this approach is complicated by uncertainties resulting from the difficult coregistration of ALS and TLS data and the specific geometric problems in steep (ALS) and flat (TLS) terrain; it is therefore limited to at least medium‐sized events. Third, the event(s) is simulated using the results of the LiDAR surveys and a modified GIS‐based rockfall model in order to test its capability of predicting the extent and the spatial distribution of deposition on the talus cone. Results show that the model generally reproduces the process domain and the spatial distribution of topographic changes but frequently under‐ and over‐estimates deposition heights. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

15.
Over the last 25 years mining-induced seismicity in the Ruhr area has continuously been monitored by the Ruhr-University Bochum. About 1,000 seismic events with local magnitudes between 0.7 ≤ M L ≤ 3.3 are located every year. For example, 1,336 events were located in 2006. General characteristics of induced seismicity in the entire Ruhr area are spatial and temporal correlation with mining activity and a nearly constant energy release per unit time. This suggests that induced stresses are released rapidly by many small events. The magnitude–frequency distribution follows a Gutenberg–Richter relation which is a result from combining distributions of single longwalls that themselves show large variability. A high b-value of about 2 was found indicating a lack of large magnitude events. Local analyses of single longwalls indicate that various factors such as local geology and mine layout lead to significant differences in seismicity. Stress redistribution acts very locally since differences on a small scale of some hundreds of meters are observed. A regional relation between seismic moment M 0 and local magnitude M L was derived. The magnitude–frequency distribution of a single longwall in Hamm was studied in detail and shows a maximum at M L = 1.4 corresponding to an estimated characteristic source area of about 2,200 m2. Sandstone layers in the hanging or foot wall of the active longwall might fail in these characteristic events. Source mechanisms can mostly be explained by shear failure of two different types above and below the longwall. Fault plane solutions of typical events are consistent with steeply dipping fracture planes parallel to the longwall face and nearly vertical dislocation in direction towards the goaf. We also derive an empirical relation for the decay of ground velocity with epicenter distance and compare maximum observed ground velocity to local magnitude. This is of considerable public interest because about 30 events larger than M L ≥ 1.2 are felt each month by people living in the mining regions. Our relations, for example, indicate that an event in Hamm with a peak ground velocity of 6 mm/s which corresponds to a local magnitude M L between 1.7 and 2.3 is likely to be felt within about 2.3 km radius from the event.  相似文献   

16.
For faster and more robust ray tracing in 1-D velocity models and also due to the lack of reliable 3-D models, most seismological centers use 1-D models for routine earthquake locations. In this study, as solution to the coupled hypocenter-velocity problem, we compute a regional P-wave velocity model for southern Iran that can be used for routine earthquake location and also a reference initial model for 3-D seismic tomography. The inversion process was based on travel time data from local earthquakes paired reports obtained by merging the catalogues of Iranian Seismic Center (IRSC, 6422 events) and by the Broadband Iranian National Seismic Network (BIN, 4333 events) for southern Iran in the period 2006 through July 2017. After cleaning the data set from large individual reading errors and by identifying event reports from both networks belonging to same earthquake (a process called event pairing), we obtained a data set of 1115 well-locatable events with a total number of 24,606 P-wave observations. This data set was used to calculate a regional minimum 1-D model for southern Iran as result of an extensive model search by trial-and-error process including several dozens of inversions. Significantly different from previous models, we find a smoothly increasing P-velocity by depth with velocities of 5.8 km/s at shallow and velocities of 6.4 km/s at deepest crustal levels. For well-locatable events, location uncertainties are estimated in the order of ±?3 km for epicenter and double this uncertainty for hypocentral depth. The use of the minimum 1-D model with appropriate station delays in routine hypocenter location processing will yield a high-quality seismic catalogue with consistent uncertainty estimates across the region and it will also allow detection of outlier observations. Based on the two catalogues by IRSC and BIN and using the minimum 1-D model and station delays for all stations in the region, we established a new combined earthquake catalogue for southern Iran. While the general distribution of the seismicity corresponds well with that of the two individual catalogues by IRSC and BIN, the new catalogue significantly enhances the correlation of seismicity with the regional fault systems within and between the major crustal blocks that as an assembly build this continental region. Furthermore, the unified seismic catalogue and the minimum 1-D model resulting from this study provide important ingredients for seismic hazard studies.  相似文献   

17.
Sources of Tsunami and Tsunamigenic Earthquakes in Subduction Zones   总被引：1，自引：0，他引：1  
—We classified tsunamigenic earthquakes in subduction zones into three types earth quakes at the plate interface (typical interplate events), earthquakes at the outer rise, within the subducting slab or overlying crust (intraplate events), and "tsunami earthquakes" that generate considerably larger tsunamis than expected from seismic waves. The depth range of a typical interplate earthquake source is 10–40km, controlled by temperature and other geological parameters. The slip distribution varies both with depth and along-strike. Recent examples show very different temporal change of slip distribution in the Aleutians and the Japan trench. The tsunamigenic coseismic slip of the 1957 Aleutian earthquake was concentrated on an asperity located in the western half of an aftershock zone 1200km long. This asperity ruptured again in the 1986 Andreanof Islands and 1996 Delarof Islands earthquakes. By contrast, the source of the 1994 Sanriku-oki earthquake corresponds to the low slip region of the previous interplate event, the 1968 Tokachi-oki earthquake. Tsunamis from intraplate earthquakes within the subducting slab can be at least as large as those from interplate earthquakes; tsunami hazard assessments must include such events. Similarity in macroseismic data from two southern Kuril earthquakes illustrates difficulty in distinguishing interplate and slab events on the basis of historical data such as felt reports and tsunami heights. Most moment release of tsunami earthquakes occurs in a narrow region near the trench, and the concentrated slip is responsible for the large tsunami. Numerical modeling of the 1996 Peru earthquake confirms this model, which has been proposed for other tsunami earthquakes, including 1896 Sanriku, 1946 Aleutian and 1992 Nicaragua.  相似文献   

18.
On March 11, 2011 at 5:46:23 UTC (March 10 11:46:23 PM Galapagos Local Time), the Mw 9.0 Great East Japan Earthquake occurred near the Tohoku region off the east coast of Japan, spawning a Pacific-wide tsunami. Approximately 12,000 km away, the Galapagos Islands experienced moderate tsunami impacts, including flooding, structural damage, and strong currents. In this paper, we present observations and measurements of the tsunami effects in the Galapagos, focusing on the four largest islands in the archipelago; (from west to east) Isabela, Santiagio, Santa Cruz, and San Cristobal. Access to the tsunami affected areas was one of the largest challenges of the field survey. Aside from approximately ten sandy beaches open to tourists, all other shoreline locations are restricted to anyone without a research permit; open cooperation with the Galapagos National Park provided the survey team complete access to the Islands coastlines. Survey locations were guided by numerical simulations of the tsunami performed prior to the field work. This numerical guidance accurately predicted the regions of highest impact, as well as regions of relatively low impact. Tide-corrected maximum tsunami heights were generally in the range of 3–4 m with the highest runup of 6 m measured in a small pocket beach on Isla Isabela. Puerto Ayora, on Santa Cruz Island, the largest harbor in the Galapagos experienced significant flooding and damage to structures located at the shoreline. A current meter moored inside the harbor recorded relatively weak tsunami currents of less than 0.3 m/s (0.6 knot) during the event. Comparisons with detailed numerical simulations suggest that these low current speed observations are most likely the result of data averaging at 20-min intervals and that maximum instantaneous current speeds were considerably larger. Currents in the Canal de Itabaca, a natural waterway between Santa Cruz Island and a smaller island offshore, were strong enough to displace multiple 5.5-ton navigation buoys. Numerical simulations indicate that currents in the Canal de Itabaca exceeded 4 m/s (~8 knots), a very large flow speed for a navigational waterway.  相似文献   

19.
Regional source tsunamis pose a potentially devastating hazard to communities and infrastructure on the New Zealand coast. But major events are very uncommon. This dichotomy of infrequent but potentially devastating hazards makes realistic assessment of the risk challenging. Here, we describe a method to determine a probabilistic assessment of the tsunami hazard by regional source tsunamis with an “Average Recurrence Interval” of 2,500-years. The method is applied to the east Auckland region of New Zealand. From an assessment of potential regional tsunamigenic events over 100,000 years, the inundation of the Auckland region from the worst 100 events is modelled using a hydrodynamic model and probabilistic inundation depths on a 2,500-year time scale were determined. Tidal effects on the potential inundation were included by coupling the predicted wave heights with the probability density function of tidal heights at the inundation site. Results show that the more exposed northern section of the east coast and outer islands in the Hauraki Gulf face the greatest hazard from regional tsunamis in the Auckland region. Incorporating tidal effects into predictions of inundation reduced the predicted hazard compared to modelling all the tsunamis arriving at high tide giving a more accurate hazard assessment on the specified time scale. This study presents the first probabilistic analysis of dynamic modelling of tsunami inundation for the New Zealand coast and as such provides the most comprehensive assessment of tsunami inundation of the Auckland region from regional source tsunamis available to date.  相似文献   

20.
Contamination of the marine environment following the accident at the Fukushima Daiichi nuclear power plant (FDNPP) represents the most important influx of artificial radioactivity released into the sea ever recorded. The evaluation, in near real time, of the total amount of radionuclide released at sea and of the residence time in coastal waters were ones of challenges for nuclear authorities during this event. In the framework of a crisis situation, a numerical hydrodynamical model has been built and used ‘as is’. The concomitant use of this numerical model and in situ data allows the comparison of the simulated and measured environmental half-times. A tuning of the wind drag coefficient has been nevertheless necessary to reproduce the evolution of measured inventories of 137Cs and 134Cs between April and June 2011. After tuning, the relative mean absolute error between measured and simulated concentrations for the 849 measurements in the dataset is 69 %, while the relative bias indicates a model underestimation of 4 %. These results confirm the estimates of the source term, i.e. 27 PBq (12–41 PBq) for direct releases and 3 PBq for atmospheric deposition onto the sea. The parameters applied here to simulate atmospheric deposition onto the sea are within the correct order of magnitude for reproducing seawater concentrations. Quantitative inventories of tracers which integrate dispersion and transport processes are useful to test model reliability. It exhausts the model sensibility to meteorological forcing, which remains difficult to appraise to reproduce mid- to long-term transport.  相似文献   

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