Diffraction of an arbitrary wave due to a half plane     

Santi Priya Das Gupta 《Pure and Applied Geophysics》1971,85(1):140-152

Summary Diffraction problems of an arbitrary wave by a half plane is solved exactly with the help of the integral equation technic. The solution is made to depend on a simple real quadrature which readily evaluates in exact forms, for different complicated type of incident fields. The method is supposed to produce new results, some of which are placed in the paper. The problem of Sommer-feld's plane wave diffraction is also solved as a very simple special case.  相似文献   

A study of methods to estimate debris flow velocity   总被引：8，自引：2，他引：6  

Adam B. Prochaska  Paul M. Santi  Jerry D. Higgins  Susan H. Cannon 《Landslides》2008,5(4):431-444

Debris flow velocities are commonly back-calculated from superelevation events which require subjective estimates of radii of curvature of bends in the debris flow channel or predicted using flow equations that require the selection of appropriate rheological models and material property inputs. This research investigated difficulties associated with the use of these conventional velocity estimation methods. Radii of curvature estimates were found to vary with the extent of the channel investigated and with the scale of the media used, and back-calculated velocities varied among different investigated locations along a channel. Distinct populations of Bingham properties were found to exist between those measured by laboratory tests and those back-calculated from field data; thus, laboratory-obtained values would not be representative of field-scale debris flow behavior. To avoid these difficulties with conventional methods, a new preliminary velocity estimation method is presented that statistically relates flow velocity to the channel slope and the flow depth. This method presents ranges of reasonable velocity predictions based on 30 previously measured velocities.  相似文献   

Precursory seismic quiescence along the Sumatra-Andaman subduction zone: past and present     

Santawat Sukrungsri  Santi Pailoplee 《Journal of Seismology》2017,21(2):305-315

In this study, the seismic quiescence prior to hazardous earthquakes was analyzed along the Sumatra-Andaman subduction zone (SASZ). The seismicity data were screened statistically with mainshock earthquakes of M _w?≥?4.4 reported during 1980–2015 being defined as the completeness database. In order to examine the possibility of using the seismic quiescence stage as a marker of subsequent earthquakes, the seismicity data reported prior to the eight major earthquakes along the SASZ were analyzed for changes in their seismicity rate using the statistical Z test. Iterative tests revealed that Z factors of N?=?50 events and T?=?2?years were optimal for detecting sudden rate changes such as quiescence and to map these spatially. The observed quiescence periods conformed to the subsequent major earthquake occurrences both spatially and temporally. Using suitable conditions obtained from successive retrospective tests, the seismicity rate changes were then mapped from the most up-to-date seismicity data available. This revealed three areas along the SASZ that might generate a major earthquake in the future: (i) Nicobar Islands (Z?=?6.7), (ii) the western offshore side of Sumatra Island (Z?=?7.1), and (iii) western Myanmar (Z?=?6.7). The performance of a stochastic test using a number of synthetic randomized catalogues indicated these levels of anomalous Z value showed the above anomaly is unlikely due to chance or random fluctuations of the earthquake. Thus, these three areas have a high possibility of generating a strong-to-major earthquake in the future.  相似文献   

Altimetry with GNSS-R interferometry: first proof of concept experiment   总被引：1，自引：0，他引：1  

Antonio Rius  Oleguer Nogués-Correig  Serni Ribó  Estel Cardellach  Santi Oliveras  Enric Valencia  Hyuk Park  José Miguel Tarongí  Adriano Camps  Hans van der Marel  Roel van Bree  Bas Altena  Manuel Martín-Neira 《GPS Solutions》2012,16(2):231-241

The Global Navigation Satellite System Reflectometry (GNSS-R) concept was conceived as a means to densify radar altimeter measurements of the sea surface. Until now, the GNSS-R concept relied on open access to GNSS transmitted codes. Recently, it has been proposed that the ranging capability of the technique for ocean altimetric applications can be improved by using all the signals transmitted in the bandwidth allocated to GNSS, which includes open access as well as encrypted signals. The main objective of this study is to provide experimental proof of this enhancement through a 2-day experiment on the Zeeland Bridge (The Netherlands). In the experiment, we used a custom built GNSS-R system, composed of high gain GPS antennas, calibration subsystem, and an FPGA-based signal processor which implemented the new concepts, an X-band radar altimeter and a local geodetic network. The results obtained indicate that the new approach produces a significant improvement in GNSS-R altimetric performance.  相似文献   

Bias in topographic thresholds for gully heads   总被引：1，自引：0，他引：1  

Rossi  M.  Torri  D.  Santi  E. 《Natural Hazards》2015,77(1):51-63

Inter-event time series of seismic activities of Sumatra region with magnitude (m _b  ≥ 4.8) and period spanning over 1973–2012 has been analyzed using the techniques of nonlinear dynamics. The earthquake data were collected from the USGS Web catalog. The rank order statistics of inter-event time series reveal mixed response with distinct breaks in slope suggesting that earthquake dynamics in this region are unstable, but “self-organized.” Comparison of return maps of the data with random, stochastic, and chaotic time records shows quasi-deterministic behavior. We assessed the dimensionality of earthquake-generating mechanism using a nonlinear predictor technique on two-dimensional phase portrait constructed by recurrence time series. The nonlinear forecasting analysis suggests that the earthquake processes in the Sumatra region evolve on a non-random low-dimensional chaotic plane. Further, second-order Kolmogorov entropy “K2” analysis revealed a coherent time structure, indicating quasi-deterministic dynamical pattern. Our result is consistent with “self-organized” processes determined by the internal dynamics, where impulsively derived interdependencies cascade through the tectonic stress generated by plate movement. However, we do not preclude the triggering role of other external processes on the coupled underlying system.  相似文献   

Sub-volcanic infiltration and syn-eruptive quenching of liquids in cumulate wall-rocks: the example of the gabbroic nodules of Stromboli (Aeolian Islands, Italy)     

M. Mattioli  G. Serri  E. Salvioli-Mariani  A. Renzulli  P. M. Holm  P. Santi  G. Venturelli 《Mineralogy and Petrology》2003,78(3-4):201-230

Summary ¶Fine- to coarse-grained plutonic nodules within the Petrazza pyroclastics (Paleo-Stromboli I period) consist of gabbroic rocks with variable amounts of interstitial material. They are characterised by cumulate textures and low pressure modal mineralogy formed by plagioclase (An_96–87)+clinopyroxene (Mg-v 82–94)+olivine (Fo_83–74)±amphibole±opaque minerals; the interstitial material consists of newly crystallised microlites (quenching) of plagioclase (An_73–55)+amphibole+clinopyroxene±olivine±biotite±opaques and highly variable amounts of residual glasses that range in composition from shoshonite and high-K basaltic andesite to high-K andesite and latite. The interstitial material has a relatively high but variable degree of vesicularity. The whole rock incompatible element abundances are lower than – but the patterns are typical of – in subduction related magmas and the incompatible trace-elements are well correlated with the amount of the interstitial material. The Sr, Pb and Nd isotopic ratios resemble those of the extrusive rocks of Stromboli older series and the mineral chemistry of the gabbros is similar to that of the HKCA Paleo-Stromboli lavas. Modal mineralogy, mineral chemistry and chemical-isotopic whole rock compositions suggest that the cumulus portions of the gabbroic nodules crystallised from basaltic magmas compositionally compatible with those erupted by Stromboli volcano. The interstitial material does not represent the residual liquid after in situ crystallisation of the gabbros; it is also distinct from the juvenile host andesite magma. Textural evidence, Fe–Mg mineral/liquid partioning and mass balance calculations indicate that the interstitial material (quench crystals and vesicular glass) derived from infiltrated hydrous basaltic liquid undercooling and vesiculation of which occurred during the eruption of the Petrazza pyroclastics.Received April 17, 2002; revised version accepted November 14, 2002 Published online June 2, 2003  相似文献   

A new analysis of the red giant branch 'tip' distance scale and the value of the Hubble constant   总被引：1，自引：0，他引：1  

Maurizio Salaris  & Santi Cassisi 《Monthly notices of the Royal Astronomical Society》1998,298(1):166-178

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The contribution of multitemporal SAR data in assessing hydrological parameters     

Paloscia  S. Macelloni  G. Pampaloni  P. Santi  E. 《Geoscience and Remote Sensing Letters, IEEE》2004,1(3):201-205

The sensitivity of radar backscattering to the principal hydrological parameters, such as vegetation biomass, soil moisture, and surface roughness, is discussed. Results obtained by using multifrequency synthetic aperture radar (SAR) data measured by the Jet Propulsion Laboratory Airborne Synthetic Aperture Radar, Spaceborne Imaging Radar-C, and European Remote Sensing 1/2 sensors are summarized. The sensitivity of L- and C-bands to spatial variations of plant and soil parameters is masked by the presence of surface roughness, which in turn affects the radar signal. However, from the observation of data collected at different dates and averaged over a relatively wide area that includes several fields, the correlation to soil moisture and vegetation biomass is found to be significant, since the effects of spatial variations are smoothed. On the other hand, the sensitivity to surface roughness becomes appreciable when multitemporal data are averaged in time, thus reducing the effects of temporal moisture variations.  相似文献   

Manifestazioni esalativo-idrotermali dell’ Isola d’ Ischia     

B. Santi 《Bulletin of Volcanology》1955,16(1):181-223

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Sources of debris flow material in burned areas   总被引：6，自引：2，他引：4  

Paul M. Santi  Victor G. deWolfe  Jerry D. Higgins  Susan H. Cannon  Joseph E. Gartner 《Geomorphology》2008,96(3-4):310

The vulnerability of recently burned areas to debris flows has been well established. Likewise, it has been shown that many, if not most, post-fire debris flows are initiated by runoff and erosion and grow in size through erosion and scour by the moving debris flow, as opposed to landslide-initiated flows with little growth. To better understand the development and character of these flows, a study has been completed encompassing 46 debris flows in California, Utah, and Colorado, in nine different recently burned areas. For each debris flow, progressive debris production was measured at intervals along the length of the channel, and from these measurements graphs were developed showing cumulative volume of debris as a function of channel length. All 46 debris flows showed significant bulking by scour and erosion, with average yield rates for each channel ranging from 0.3 to 9.9 m³ of debris produced for every meter of channel length, with an overall average value of 2.5 m³/m. Significant increases in yield rate partway down the channel were identified in 87% of the channels, with an average of a three-fold increase in yield rate. Yield rates for short reaches of channels (up to several hundred meters) ranged as high as 22.3 m³/m. Debris was contributed from side channels into the main channels for 54% of the flows, with an average of 23% of the total debris coming from those side channels. Rill erosion was identified for 30% of the flows, with rills contributing between 0.1 and 10.5% of the total debris, with an average of 3%. Debris was deposited as levees in 87% of the flows, with most of the deposition occurring in the lower part of the basin. A median value of 10% of the total debris flow was deposited as levees for these cases, with a range from near zero to nearly 100%. These results show that channel erosion and scour are the dominant sources of debris in burned areas, with yield rates increasing significantly partway down the channel. Side channels are much more important sources of debris than rills. Levees are very common, but the size and effect on the amount of debris that reaches a canyon mouth is highly variable.  相似文献