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1.
High frequency sea level oscillations at Wells Harbor (Maine, Northeastern US), with periods in the range of several tens of minutes, display a tidally modulated response. During low tides, these sea level oscillations reach amplitudes of 10–20 cm, while during high tides they are significantly smaller. Wells Harbor is located in a low lying area with a tidal range of about 2 m and is connected to the open ocean through a narrow channel. Thus, the extent and depth of the bay significantly vary over a tidal cycle. This changing geometry determines both the resonant periods and the amplification factor of the bay. Numerical results confirm the link between observed variability and these specific topographic features. Results imply that when exceptionally energetic long waves reach the Wells Harbor entrance (as in the case of a tsunami or meteotsunami) the expected response will be significantly stronger during low tide than during high tide. Although mean sea level would be lower in the former case, the currents inside the bay would be stronger and potentially more dangerous. This tidally modulated response could be extrapolated to other sites with similar topographic characteristics. 相似文献
2.
Space spectral analysis of zonal (u) and meridional (v) components of wind and time spectral analysis of kinetic energy of zonal waves at 850 hPa during monsoon 1991 (1st June
1991 to 31st August 1991) for the global belt between equator and 40°N are investigated. Space spectral analysis shows that
long waves (wavenumbers 1 and 2) dominate the energetics of Region 1 (equator to 20°N) while over Region 2 (20°N to 40°N)
the kinetic energy of short waves (wavenumbers 3 to 10) is more than kinetic energy of long waves. It has been found that
kinetic energy of long waves is dominated by zonal component while both (zonal and meridional) the components of wind have
almost equal contribution in the kinetic energy of short waves.
Temporal variations of kinetic energy of wavenumber 2 over Region 1 and Region 2 are almost identical. The correlation matrix
of different time series shows that (i) wavenumber 2 over Regions 1 and 2 might have the same energy source and (ii) there
is a possibility of an exchange of kinetic energy between wavenumber 1 over Region 1 and short waves over Region 2. Wave to
wave interactions indicate that short waves over Region 2 are the common source of kinetic energy to wavenumber 2 over Regions
1 and 2 and wavenumber 1 over Region 1. Time spectral analysis of kinetic energy of zonal waves indicates that wavenumber
1 is dominated by 30–45 day and bi-weekly oscillations while short waves are dominated by weekly and bi-weekly oscillations.
The correlation matrix, wave to wave interaction and time spectral analysis together suggest that short period oscillations
of kinetic energy of wavenumber 1 might be one of the factors causing dominant weekly (5–9 day) and bi-weekly (10–18 day)
oscillations in the kinetic energy of short waves. 相似文献
3.
Osmar O. Möller Patrice Castaing Elisa Helena Leão Fernandes Pascal Lazure 《Estuaries and Coasts》2007,30(2):311-320
The Patos Lagoon is a choked, microtidal coastal laggon situated in southern Brazil between 30°S and 32°S. The response of
the lagoon to tidal oscillations is studied through data analysis and numerical modeling experiments. Two types of high frequency
oscillations are observed in the tidal frequency band: mixed tides, predominantly diurnal; and forced oscillations having
a period of 24 h occurring in the inner lagoon. In the southern portion of the lagoon, tides are selectively filtered by the
entrance channel. The main diurnal constituent O1 is linearly attenuated as it progresses landwards. In the inner parts of the lagoon, 24-h oscillations are mainly forced
by the combined effect of diurnal tides and sea breeze action. They are tied with a natural period of oscillation of 24 h.
Results also indicate that these are not inertial frequency oscillations, despite the lagoon being placed in a critical 30°S
area. The interaction between astronomical tides and meteorological effects produces a complicated picture for tidal forecasting
derived from data collected inside the lagoon. 相似文献
4.
Measurements of intensities at two fixed wavelengths in the OH (7-2) band were carried out at Mt Abu (24.6° N, 76.7° E) from
1973–76 to estimate neutral temperature in the region of 80–90 km altitude. It was observed that on some nights the temperature
in this region shows periodic oscillations throughout the night. It was found from statistical analysis that the periods of
these fluctuations are comparable to the theoretically predicted periods of internal gravity waves.
If the periodic temperature variations observed in this region are attributed to the influence of gravity waves, according
to the Hines theory only the magnitude of the horizontal component of wave-induced wind velocity can be computed. Using the
measured relative temperature fluctuations it is found that the magnitude is 15–30 m/sec. 相似文献
5.
R. Raghavarao R. Suhasini R. Sridharan B. V. Krishnamurthy O. P. Nagpal 《Journal of Earth System Science》1990,99(3):413-423
The equatorial wave campaign-II which formed a part of the Indian Middle Atmosphere Programme (IMAP), was conducted from SHAR
(13.7°N, 80.2°E) from 15 January to 28 February 1986. Winds were measured from ground to 60 km by means of high altitude balloon
and a meteorological rocket (RH-200), once everyday, for 45 days. The frequencies of the oscillations in the deviations of
the east-west component of the winds from its mean at each height with one kilometer interval were obtained by the maximum
entropy (ME) method and phases/amplitudes of these frequencies were determined by the least squares technique on the wind
variation time series. The ME method has the inherent advantage of providing periodicities up to 1.5 times the data length.
The height structure of the long period waves of > 23 day periodicities that have larger amplitudes nearly by a factor of
2 as compared to the medium (9 to 22 day) or shorter period (4 to 8 day) ones, reveal two height regions of enhanced amplitudes,
one in the troposphere and another in the upper stratosphere/lower mesosphere, that too, mostly in the regions of positive
(westerly increasing or easterly decreasing with height) wind shears. The waves are seen to be inhibited in the negative wind
shear regions. From the abrupt changes in the altitude variation of phase, the possible source region has been identified.
The vertical wavelengths have been estimated to be 34 km and 19 km in the troposphere and lower stratosphere respectively
and 8 km in the upper stratosphere and lower mesosphere. Around 56 km the wave amplitude is reduced to 1/4 of its value below,
while the vertical shear strength in the mean wind doubled up. The tropospheric waves are suggested to be Rossby waves of
extratropical origin penetrating to tropical latitudes. The stratospheric/mesospheric waves however appear to emanate from
a source around the stratopause. 相似文献
6.
Hilkka Pellikka Jenni Rauhala Kimmo K. Kahma Tapani Stipa Hanna Boman Antti Kangas 《Natural Hazards》2014,74(1):197-215
We present four case studies of exceptional wave events of meteorological origin, observed on the Finnish coast in the summers of 2010 and 2011. Eyewitnesses report unusually rapid and strong sea-level variations (up to 1 m in 5–15 min) and strong oscillating currents during these events. High-resolution sea-level measurements confirm the eyewitness observations, but the oscillations recorded by tide gauges mostly have a considerably smaller amplitude. The oscillations coincide with sudden jumps in surface air pressure at coastal observation stations, related to the passage of squall lines or gust fronts. These fronts propagate above the sea at a resonant speed, allowing efficient energy transfer between the atmospheric disturbance and the sea wave that it generates. Thus, we interpret the observed sea-level oscillations as small meteotsunamis, long tsunami-like waves generated by meteorological processes and resonance effects. 相似文献
7.
Trapped waves of the 27 November 1945 Makran tsunami: observations and numerical modeling 总被引:1,自引:1,他引:0
S. Neetu I. Suresh R. Shankar B. Nagarajan R. Sharma S. S. C. Shenoi A. S. Unnikrishnan D. Sundar 《Natural Hazards》2011,59(3):1609-1618
The 27 November 1945 earthquake in the Makran Subduction Zone triggered a destructive tsunami that has left important problems
unresolved. According to the available reports, high waves persisted along the Makran coast and at Karachi for several hours
after the arrival of the first wave. Long-duration sea-level oscillations were also reported from Port Victoria, Seychelles.
On the other hand, only one high wave was reported from Mumbai. Tide-gauge records of the tsunami from Karachi and Mumbai
confirm these reports. While the data from Mumbai shows a single high wave, Karachi data shows that high waves persisted for
more than 7 h, with maximum wave height occurring 2.8 h after the arrival of the first wave. In this paper, we analyze the
cause of these persistent high waves using a numerical model. The simulation reproduces the observed features reasonably well,
particularly the persistent high waves at Karachi and the single high wave at Mumbai. It further reveals that the persistent
high waves along the Makran coast and at Karachi were the result of trapping of the tsunami-wave energy on the continental
shelf off the Makran coast and that these coastally-trapped edge waves were trapped in the along-shore direction within a
∼300-km stretch of the continental shelf. Sensitivity experiments establish that this along-shore trapping of the tsunami
energy is due to variations in the shelf width. In addition, the model simulation indicates that the reported long duration
of sea-level oscillations at Port Victoria were mainly due to trapping of the tsunami energy over the large shallow region
surrounding the Seychelles archipelago. 相似文献
8.
G. A. Sobolev 《Doklady Earth Sciences》2017,472(1):87-90
The records of strong earthquakes (December 26, 2004, Sumatra; February 27, 2010, Chile; and March 11, 2011, Tohoku) from broadband IRIS seismic stations are analyzed. Several days after the events, oscillations of 128–130 minutes in period start and last for about a month. The period of oscillations exceeds that of the Earth’s spheroidal eigen oscillation with the lowest frequency (53.9 min) by a factor of about two. Oscillations are of opposite polarity at stations located near the epicenters and at the symmetric point in the other hemisphere of the Earth. They manifest as trains of fluctuations migrating westward at 2.5° per hour. The amplitude of oscillations is up to few μGal. 相似文献
9.
Laurence C. Breaker William W. Broenkow William E. Watson Young-Heon Jo 《Estuaries and Coasts》2008,31(2):239-257
Elkhorn Slough is a shallow, tidally forced estuary that is directly connected to Monterey Bay. It is ebb-dominated and, due
to continued erosion, the tidal prism has tripled over the past 40 years. Water level measurements at four locations are used
to examine tidal and nontidal oscillations in Elkhorn Slough. The tidal response of Elkhorn Slough differs from that of Monterey
Bay primarily due to the generation of a relatively large number of shallow-water tidal constituents that are due to tidal
distortion caused by friction along the bottom and lateral boundaries, intertidal storage, and nonlinear advection. The shallow-water
constituents range from 3 to almost 15 cycles per day (cpd) and include a rich variety of overtides and compound tides, whose
amplitudes generally increase toward the head of the slough. The tidal harmonics are seasonally dependent, with lower amplitudes
during the fall and winter and higher amplitudes in summer. The tidal constituents were examined using two types of spectral
decomposition, the conventional power spectrum and the more recent Hilbert spectrum. Unlike the power spectrum, the Hilbert
spectrum does not reveal any harmonic structure in the data. Energy associated with tidal distortion in this case appears
to be broadly distributed across the spectral continuum. At least four nontidal oscillations occur in Elkhorn Slough with
frequencies of 26.0, 39.7, 52.7, and 66.9 cpd. The Hilbert spectrum reveals maxima at 26, 39.7, and 66.9 cpd, but not at 52.7 cpd,
suggesting that it is harmonically related to the oscillation at 26.0 cpd. The nontidal oscillations fall into the range of
frequencies associated with the natural oscillations of Monterey Bay. However, evolutionary power spectra indicate that they
appear to be permanent features of the system and thus are not necessarily consistent with seiche-like oscillations that are
often transient and subject to damping. These oscillations could be caused by several factors including edge waves along the
coast of Monterey Bay, long-period surface waves of atmospheric origin that enter the bay from offshore, or breaking internal
waves in and around the Monterey Submarine Canyon. In conclusion, detailed hydrodynamic models are needed to provide a better
understanding of how tidal harmonics are generated and preserved in Elkhorn Slough, and to determine the origin of the natural
oscillations in Monterey Bay. 相似文献
10.
Tide gauge data were used to identify the occurrence, characteristics, and cause of tsunamis of meteorological origin (termed ‘meteotsunamis’) along the Western Australian coast. This is the first study to identify meteotsunamis in this region, and the results indicated that they occur frequently. Although meteotsunamis are not catastrophic to the extent of major seismically induced basin-scale events, the wave heights of meteotsunamis examined at some local stations in this study were higher than those recorded through seismic tsunamis. In June 2012, a meteotsunami contributed to an extreme water-level event at Fremantle, which recorded the highest water level in over 115 years. Meteotsunamis (wave heights >0.4 m, when the mean tidal range in the region is ~0.5 m) were found to coincide with thunderstorms in summer and the passage of low-pressure systems during winter. Spectral analysis of tide gauge time series records showed that existing continental seiche oscillations (periods between 30 min and 5 h) were enhanced during the meteotsunamis, with a high proportion of energy transferred to the continental shelf oscillation period. Three recent meteotsunami events (22 March 2010, 10 June 2012, and 7 January 2013) two due to summer thunderstorms and one due to a winter frontal system were chosen for detailed analysis. The meteotsunami amplitudes were up to a factor 2 larger than the local tidal range and sometimes contributed up to 85 % of the non-tidal water signal. A single meteorological event was found to generate several meteotsunamis along the coast, up to 500 km apart, as the air pressure disturbance propagated over the continental shelf; however, the topography and local bathymetry of the continental shelf defined the local sea-level resonance characteristics at each location. With the available data (sea level and meteorological), the exact mechanisms for the generation of the meteotsunamis could not be isolated. 相似文献
11.
Spectral observations of the 639.361-nm FeI line at the center of the quiet solar disk with high spatial (0.4″) and temporal (10 s) resolution are used to investigate the behavior of local 5-min oscillations over granules and intergranular lanes. The power of the 5-min oscillations in the upper photosphere (at heights of H ≈ 490 km) is higher the faster the convective motions in the lower photosphere (H ≈ 10 km). This suggests that turbulent convection is responsible for the excitation of local solar oscillations. A statistical analysis of the oscillations shows that, on average, both the intensity and velocity of the oscillation amplitudes are greater over intergranular lanes. This difference in amplitudes is present throughout the studied heights in the photosphere (H = 0?490 km). The period at which the power spectrum of velocity oscillations reaches its maximum is longer over intergranules than over granules. Simulations of the propagation of acoustic-gravity waves in an atmosphere taking into account the convection pattern give a satisfactory explanation for the above observed effects. It is concluded that the atmospheric modulation of the 5-min oscillations is an additional or alternative mechanism responsible for differences between these oscillations over granules and intergranules. 相似文献
12.
Assessment of the wave climate at near coast is vital for estimation of morphological changes, such as growth of sand spit
and associated siltation of tidal inlets. Vellar (bar-built) estuary is one of the prominent estuaries along the southeast
coast of India, located at 11°30′N and 79°46′E, less studied in terms of its morphological features. The inlet of Vellar is
exposed to high energetic waves, inducing large sediment transport rates and shoreline changes. Local wave characteristics
are not accurately defined and the available wave information at near coast is limited (point based observations). In the
present study, three decoupled numerical models are employed to derive the monthly nearshore wave climate at Vellar by transforming
waves from deep water to nearshore. These models are independently validated with buoy observations in deep water and wave
gauge data at nearshore. Based on the nearshore wave data, littoral drift along the coast was estimated and compared with
the spit growth at Vellar inlet. The estimated average littoral drift along this coast from February to October is 1.93 × 106 m3 toward north and from November to January it is 1.52 × 106 m3 toward south, resulting in a net northerly drift. Results indicated that increase in the wave energy during the period of
July to September is responsible for the maximum growth of the sand spit observed in the field. 相似文献
13.
Walter C. Dragani Enrique E. D’Onofrio Fernando Oreiro Guadalupe Alonso Mónica Fiore Walter Grismeyer 《Natural Hazards》2014,74(1):269-280
Meteorological tsunamis are frequently observed in different tide stations at the southeastern coast of South America. They are associated with the occurrence of atmospheric gravity waves during the passages of cold fronts over the Buenos Aires Province continental shelf. On the other hand, storm surges are also frequent in the region, and they are associated with strong and persistent southerlies, which are also frequent during cold front passages. The impact of meteorological tsunamis in coastal erosion and in the statistics of storm surge trends is discussed in this paper. For this study, fifteen meteorological tsunamis (with maximum wave heights higher than 0.20 m), seven of them simultaneous to the occurrence of storm surge events (with extreme levels higher than |±0.60 m|), are selected from April 2010 to January 2013. The impact of meteorological tsunamis in the storm erosion potential index (SEPI) is evaluated. Not significant differences are obtained between SEPI calculated with and without filtering the meteorological tsunami signal from the storm surge data series. Moreover, several experiments are carried out computing SEPI from synthetic sea level data series, but very low changes (lower than 4 %) are also obtained. It is concluded that the presence of moderate meteorological tsunamis on sea level records would not enhance this index at the Buenos Aires Province coast. On the other hand, taking into account that meteorological tsunamis can reach up the 20–30 % of the storm surge height, it was concluded that the statistics of storm surge trends (and their uncertainties) should be revised for Mar del Plata data series. 相似文献
14.
P Amol D Shankar V Fernando A Mukherjee S G Aparna R Fernandes G S Michael S T Khalap N P Satelkar Y Agarvadekar M G Gaonkar A P Tari A Kankonkar S P Vernekar 《Journal of Earth System Science》2014,123(5):1045-1074
We present current data from acoustic Doppler current profilers (ADCPs) moored on the continental slope off the west coast of India. The data were collected at four locations (roughly at Kanyakumari, Kollam, Goa, and Mumbai) extending from ~ 7° to ~ 20°N during 2008–2012. The observations show that a seasonal cycle, including an annual cycle, is present in the West India Coastal Current (WICC); this seasonal cycle, which strengthens northward, shows considerable interannual variability and is not as strongly correlated along the coast as in climatologies based on ship drifts or the altimeter. The alongshore decorrelation of the WICC is much stronger at intraseasonal periods, which are evident during the winter monsoon all along the coast. This intraseasonal variability is stronger in the south. A striking feature of the WICC is upward phase propagation, which implies an undercurrent whose depth becomes shallower as the season progresses. There are also instances when the phase propagates downward. At the two southern mooring locations off Kollam and Kanyakumari, the cross-shore current, which is usually associated with eddy-like circulations, is comparable to the alongshore current on occasions. A comparison with data from the OSCAR (Ocean Surface Currents Analyses Real-time) data product shows not only similarities, but also significant differences, particularly in the phase. One possible reason for this phase mismatch between the ADCP current at 48 m and the OSCAR current, which represents the current in the 0–30 m depth range, is the vertical phase propagation. Current products based on Ocean General Circulation Models like ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II) and GODAS (Global Ocean Data Assimilation System) show a weaker correlation with the ADCP current, and ECCO2 does capture some of the observed variability. 相似文献
15.
Antony Joseph R. G. Prabhudesai Prakash Mehra V. Sanil Kumar K. V. Radhakrishnan Vijay Kumar K. Ashok Kumar Yogesh Agarwadekar U. G. Bhat Ryan Luis Pradhan Rivankar Blossom Viegas 《Natural Hazards》2011,57(2):293-312
Response of the coastal regions of eastern Arabian Sea (AS) and Kavaratti Island lagoon in the AS to the tropical cyclonic storm `Phyan??, which developed in winter in the south-eastern AS and swept northward along the eastern AS during 9?C12 November 2009 until its landfall at the northwest coast of India, is examined based on in situ and satellite-derived measurements. Wind was predominantly south/south-westerly and the maximum wind speed (U10) of ~16 m/s occurred at Kavaratti Island region followed by ~8 m/s at Dwarka (Gujarat) and ~7 m/s at Diu (located south of Dwarka) as well as two southwest Indian coastal locations (Mangalore and Malpe). All other west Indian coastal sites recorded maximum wind speed of ~5?C6 m/s. Gust factor (i.e., gust-to-speed ratio) during peak storm event was highly variable with respect to topography, with steep hilly stations (Karwar and Ratnagiri) and proximate thick and tall vegetation-rich site (Kochi) exhibiting large values (~6), whereas Island station (Kavaratti) exhibiting ~1 (indicating consistently steady wind). Rainfall in association with Phyan was temporally scattered, with the highest 24-h accumulated precipitation (~60 mm) at Karwar and ~45 mm at several other west Indian coastal sites. Impact of Phyan on the west Indian coastal regions was manifested in terms of intensified significant waves (~2.2 m at Karwar and Panaji), sea surface cooling (~5°C at Calicut), and moderate surge (~50 cm at Verem, Goa). The surface waves were south-westerly and the peak wave period (T p) shortened from ~10?C17 s to ~5?C10 s during Phyan, indicating their transition from the long-period `swell?? to the short-period `sea??. Reduction in the spread of the mean wave period (T z) from ~5?C10 s to a steady period of ~6 s was another manifestation of the influence of the cyclone on the surface wave field. Several factors such as (1) water piling-up at the coast supported by south/south-westerly wind and seaward flow of the excess water in the rivers due to heavy rains, (2) reduction of piling-up at the coast, supported by the upstream penetration of seawater into the rivers, and (3) possible interaction of upstream flow with river run-off, together resulted in the observed moderate surge at the west Indian coast. Despite the intense wind forcing, Kavaratti Island lagoon experienced insignificantly weak surge (~7 cm) because of lack of river influx and absence of a sufficiently large land boundary required for the generation and sustenance of wave/wind-driven water mass piling-up at the land?Csea interface. 相似文献
16.
Natural Hazards - A weak tsunami was induced by the 2016 Mw?=?7.8 Sumatra earthquake, which occurred at 12:49 on March 2, 2016 (UTC). The epicenter was at 5.060°S, 94.170°E at... 相似文献
17.
JOHN H. HOYT 《Sedimentology》1967,8(3):229-238
High-angle stratification (greater than 20°) is produced in several areas of shallow marine sedimentation along the barrier islands of the central Georgia coast. The maximum angle of inclination is 30° which is the angle of repose for the saturated, fine-grained, angular sand of this area. High-angle stratification forms in the following locations: (1) The depositional margin of tidal channel inlets. Under some wave and current conditions, sand accumulates near low tide level and steepens the depositional interface to the angle of repose. (2) The steep face of asymmetrical megaripples developed by tidal currents. Ripples with amplitudes as much as 3 ft. and wave lengths of 20–40 ft. commonly develop in channel inlets and other areas of sand sediments. (3) The steep face of sand waves formed in channel inlets. These large asymmetrical ripples have amplitudes as great as 12 ft. and wave lengths of ca. 300 ft. Lengths along the crests are over 600 ft. (4) The landward side of low bars developed on the beach. Bars and troughs (ridges and runnels) are common on the beaches of this area. The bars, which are as much as 5 ft. high, shift landward by deposition on the steep landward face. (5) The oceanward side of large sand waves at the mouth of offshore tidal channels. Large sand waves are located 6 miles offshore from Doboy Sound inlet in 20–25 ft. of water. The steep face of these asymmetrical sand waves is orientated toward the ocean. Amplitude of these large ripples is as much as 17 ft. and length along the crests is over 1/2 mile. 相似文献
18.
Tsunami-like intense sea-level oscillations, associated with atmospheric activity (meteorological tsunamis), are common in the Great Lakes and on the East Coast of the United States. They are generated by various types of atmospheric disturbances including hurricanes, frontal passages, tornados, trains of atmospheric gravity waves, and derechos. “Derecho” is a rapidly moving line of convectively induced intense thunder storm fronts producing widespread damaging winds and squalls. The derecho of June 29–30, 2012 devastatingly propagated from western Iowa to the Atlantic coast, passing more than 1,000 km and producing wind gusts up to 35 m/s. This derecho induced pronounced seiche oscillations in Lake Michigan, Chesapeake Bay, and along the US Atlantic coast. Sea-level records from the updated National Oceanic and Atmospheric Administration (NOAA) tide gauge network, together with the NOAA and automated surface-observing system air pressure and wind records, enabled us to examine physical properties and temporal/spatial variations of the generated waves. Our findings indicate that the generation mechanisms of extreme seiches in the basins under study are significantly different: energetic winds play the main role in seiche formation in Chesapeake Bay; atmospheric pressure disturbances are most important for the Atlantic coast; and the combined effect of pressure oscillations and wind is responsible for pronounced events in the Great Lakes. The “generation coefficient,” which is the ratio of the maximum observed sea-level height and the height of air pressure disturbance, was used to map the sea-level response and to identify “hot spots” for this particular event, i.e., harbors and bays with amplified seiche oscillations. The Froude number, Fr = U/c, where U is the speed of the atmospheric disturbance and c is the long-wave speed, is the key parameter influencing the water response to specific atmospheric disturbances; the maximum response was found for those regions and disturbance parameters for which Fr ~1.0. 相似文献
19.
The Sultanate of Oman is among the Indian Ocean countries that were subjected to at least two confirmed tsunamis during the twentieth and twenty-first centuries: the 1945 tsunami due to an earthquake in the Makran subduction zone in the Sea of Oman (near-regional field tsunami) and the Indian Ocean tsunami in 2004, caused by an earthquake from the Andaman Sumatra subduction zone (far - field tsunami). In this paper, we present a probabilistic tsunami hazard assessment for the entire coast of Oman from tectonic sources generated along the Makran subduction zone. The tsunami hazard is assessed taking into account the contribution of small- and large-event magnitudes. Results of the earthquake recurrence rate studies and the tsunami numerical modeling for different magnitudes were used through a logic-tree to estimate the tsunami hazard probabilities. We derive probability hazard exceedance maps for the Omani coast considering the exposure times of 100, 250, 500, and 1000 years. The hazard maps consist of computing the likelihood that tsunami waves exceed a specific amplitude. We find that the probability that a maximum wave amplitude exceeds 1 m somewhere along the coast of Oman reaches, respectively, 0.7 and 0.85 for 100 and 250 exposure times, and it is up to 1 for 500 and 1000 years of exposure times. These probability values decrease significantly toward the southern coast of Oman where the tsunami impact, from the earthquakes generated at Makran subduction zone, is low. 相似文献
20.
A. K. Abdel-Fattah A. M. Al-Amri M. S. Fnais kamal Abdelrahman 《Arabian Journal of Geosciences》2014,7(8):3325-3337
On 19 May 2009, an earthquake sequence of M w?=?4.8 occurred at 25.20°N 37.76°E about 60 km onshore of the Red Sea coastline, Saudi Arabia. In the present study, the digital waveform data from the largest four events were used to estimate the source parameters and attenuation characteristics along the source-to-station path in the Arabian Shield. A grid search technique, combined with an assumption of circular source model, was applied to find the best-fit spectral amplitude over the space parameters: long period spectral level (Ω 0), corner frequency (f 0) and asymptotic high-frequency fall-off (γ). Consequently, the spectral parameters were used to estimate source parameters: seismic moment, fault radius (assumed circular rupture model) and stress drop. Seismic moments are founded to be within the range of 2.34E+14 to 2.83E+16 Nm and their corresponding moment magnitudes range from 3.5 to 4.8; the fault radius ranges from 369 to 1,498 m, and stress drops are observed in the range of 8.7 to 32.0 b. The spectral slopes beyond the corner frequency displayed ω ?2.4 to ω ?2.6 behaviours in contrast with Brune's source model of ω ?2. This finding requires more detailed investigations on large data sets to distinguish the behaviour mechanism of the spectral slopes at high frequencies. By taking the ratio between observed and calculated spectra, the attenuation curves for P and S waves were derived along the source-to-station paths. The preliminarily results exhibited high quality factors of Q α?=?3,883 and Q β?=?3,530 for P and S waves, respectively. To this end, the ratio Q β/Q α is founded to be slightly less than unity indicating that the body waves from source-to-station paths crossed a crustal volume that is partially saturated with fluids causing lower attenuation effect on P waves than on S waves in the Arabian Shield. 相似文献