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91.
Starting from the classical empirical magnitude-energy relationships, in this article, the derivation of the modern scales
for moment magnitude M
w and energy magnitude M
e is outlined and critically discussed. The formulas for M
w and M
e calculation are presented in a way that reveals, besides the contributions of the physically defined measurement parameters
seismic moment M
0 and radiated seismic energy E
S, the role of the constants in the classical Gutenberg–Richter magnitude–energy relationship. Further, it is shown that M
w and M
e are linked via the parameter Θ = log(E
S/M
0), and the formula for M
e can be written as M
e = M
w + (Θ + 4.7)/1.5. This relationship directly links M
e with M
w via their common scaling to classical magnitudes and, at the same time, highlights the reason why M
w and M
e can significantly differ. In fact, Θ is assumed to be constant when calculating M
w. However, variations over three to four orders of magnitude in stress drop Δσ (as well as related variations in rupture velocity V
R and seismic wave radiation efficiency η
R) are responsible for the large variability of actual Θ values of earthquakes. As a result, for the same earthquake, M
e may sometimes differ by more than one magnitude unit from M
w. Such a difference is highly relevant when assessing the actual damage potential associated with a given earthquake, because
it expresses rather different static and dynamic source properties. While M
w is most appropriate for estimating the earthquake size (i.e., the product of rupture area times average displacement) and
thus the potential tsunami hazard posed by strong and great earthquakes in marine environs, M
e is more suitable than M
w for assessing the potential hazard of damage due to strong ground shaking, i.e., the earthquake strength. Therefore, whenever
possible, these two magnitudes should be both independently determined and jointly considered. Usually, only M
w is taken as a unified magnitude in many seismological applications (ShakeMap, seismic hazard studies, etc.) since procedures
to calculate it are well developed and accepted to be stable with small uncertainty. For many reasons, procedures for E
S and M
e calculation are affected by a larger uncertainty and are currently not yet available for all global earthquakes. Thus, despite
the physical importance of E
S in characterizing the seismic source, the use of M
e has been limited so far to the detriment of quicker and more complete rough estimates of both earthquake size and strength
and their causal relationships. Further studies are needed to improve E
S estimations in order to allow M
e to be extensively used as an important complement to M
w in common seismological practice and its applications. 相似文献
92.
D. Bindi L. Luzi S. Parolai D. Di Giacomo G. Monachesi 《Bulletin of Earthquake Engineering》2011,9(6):1941-1959
In this work, we investigate the site amplification effects observed in the Norcia plain, Central Italy. Data from 30 selected
local earthquakes (2 ≤ Ml ≤ 4.1) recorded by a temporary seismic network composed by 15 stations, are analyzed to determine
the spatial variability of site effects. Both the Horizontal-to-Vertical spectral ratio and the Standard Spectral Ratio techniques
are applied to estimate the site amplification effects. The results show that most of the sites in the valley are affected
by strong amplifications (up to a factor of 20) in the frequency range 0.5–5 Hz. The value of the fundamental frequency of
resonance is strictly dependent on the location within the basin and on the sediment thickness. Strong amplifications also
affect the vertical components. The time-frequency analysis performed on a station located inside the basin shows the presence
of a large spectral amplitudes after the S-wave phase, not observed on a station located on the bedrock, suggesting the presence
of locally generated wave trains. Then, in agreement with earlier observations for other alluvial basins in Central Italy,
2D–3D effects play an important role in determining the site amplification effects in Norcia. 相似文献
93.
Mario Boccaletti Giacomo Corti Luca Martelli 《International Journal of Earth Sciences》2011,100(6):1331-1348
We present a comprehensive study of the recent and active tectonics of the external part of the Northern Apennines (Italy)
by using morphotectonic, geological–structural, and stratigraphic analysis, compared with the current seismicity of the region.
This analysis suggests that the external part of the Northern Apennines is characterised by presence of three major systems
of Quaternary compressive structures corresponding to (1) the Apenninic watershed, (2) the Apennines–Po Plain margin (pede-Apenninic
thrust front), and (3) the Emilia, Ferrara, and Adriatic Fold systems buried below the Po Plain. Geological data and interpreted
seismic sections indicate a roughly N–S Quaternary deformation direction, with rates <2.5 mm/year. The shortening decreased
since the Pliocene, when our data indicate compression in a NNW–SSE direction and rates up to 7 mm/year. The trend and kinematics
of the structures affecting the Apennines–Po Plain margin and the Po Plain subsoil fit well the pattern of the current seismicity
of the area, as well as recent GPS and geodetic levelling data, pointing to a current activity of these thrust systems controlled
by an overall compressive stress field. Close to the Apenninic watershed, earthquake focal mechanisms indicate that shallow
extension is associated to deep compression. The extensional events may be related to a secondary extensional stress field
developing on the hangingwall of the thrust system affecting the Apenninic watershed; alternatively, this thrust system may
have been recently deactivated and overprinted by active normal faulting. Deeper compressive events are related to the activity
of both a major basement thrust that connects at surface with the pede-Apenninic thrust front and a major Moho structure. 相似文献
94.
95.
96.
97.
Mapping Mercury's internal magnetic field with a magnetometer in closed orbit around the planet will provide valuable information about its internal structure. By measuring magnetic field multipoles of order higher than the dipole we could, in principle, determine some properties, such as size and location, of the internal source. Here we try to quantify these expectations. Using conceptual models, we simulate the actual measurement during the BepiColombo mission, and then we analyze the simulated data in order to estimate the measurement errors due to the limited spatial sampling. We also investigate our ability to locate the field generating current system within the planet. Finally, we address the main limitation of our model, due to the presence of time-varying external magnetospheric currents. 相似文献
98.
Giacomo Corti Marco Bonini Francesco Mazzarini Mario Boccaletti Fabrizio Innocenti Piero Manetti Genene Mulugeta Dimitrios Sokoutis 《Tectonophysics》2002,348(4)
Scaled centrifuge experiments have been used to investigate the dynamic relations between deformation and magma distribution in rift-related transfer zones. The physical models were built using suitable analogue materials, such as sand to represent the brittle upper crust, various kinds of silicone mixtures to simulate the lower crust and upper mantle and glycerol to reproduce magma. Models simulated the development of transfer zones across pre-existing glycerol reservoirs placed at the base of the analogue continental crust. In plan view, different geometries, dimensions and positions of subcrustal reservoirs were reproduced in three different sets of experiments; to compare results, models were also performed without magma-simulating glycerol.Set 1 experiments, incorporating a narrow rectangular glycerol reservoir, show that the low-viscosity material is able to localise deformation into the overlying crust, giving rise to discrete transfer zones. This concentrated surface deformation corresponds at depth to major magma accumulation. Set 2 experiments, with an initial wide squared glycerol reservoir, show instead that deformation is distributed across the whole model surface, corresponding at depth to relatively minor magma accumulation. Set 3 experiments explored various positions of a small squared reservoir that invariably localised faulting in the overlying analogue brittle crust at the onset of model deformation.The overall model behaviour suggests that magma distribution at depth can effectively control the strain distribution in the overlying crust and the deformative pattern of transfer zones. Strain distribution, in turn, may control magma emplacement as localized deformation would favour major accumulation of magma at transfer zones. Coupled to a strong thermal weakening of the country rocks, this process may ultimately lead to a positive feedback interaction between magma and deformation. 相似文献
99.
Giacomo D''Amato Avanzi Roberto Giannecchini Alberto Puccinelli 《Engineering Geology》2004,73(3-4):215-228
On June 19, 1996, an extremely heavy rainstorm hit a restricted area in the Apuan Alps (northwestern Tuscany, Italy). Its max intensity concentrated over an area of about 150 km2 astride the Apuan chain, where 474 mm was recorded in about 12 h (21% of the mean annual precipitation, with an intensity up to 158 mm/h). The storm caused floods and hundreds of landslides and debris flows, which produced huge damage (hundreds of millions of Euros), partially destroyed villages and killed 14 people. This paper reports the results obtained from a detailed field survey and aerial view interpretation. In the most severely involved area, 647 main landslides were investigated, mapped and related to the geologic, geomorphic and vegetational factors of the source areas. This was in order to define the influence of these factors and contribute to an evaluation of the landslide hazard in the study area. An assessment was also made of the total area and volume of material mobilised by landsliding. The study area, about 46 km2 wide, includes three typically mountainous basins, characterised by narrow, deep cut valleys and steep slopes, where many rock types outcrop. Most of the landslides were shallow and linear, referable to complex, earth and debris translational slide, which quickly developed into flow (soil slip–debris flow). Usually, they involved colluvium and started in hollows underlain by metamorphic rock (metasandstone and phyllite), often dipping downslope. Therefore, bedrock lithology and impermeability appeared to be important factors in the localisation of the landslide phenomena. The investigation of the geomorphic and land use features in the source areas also frequently highlighted a rectilinear profile of the slope, a high slope gradient (31–45°) and dense chestnut wood cover. In the area, about 985,000 m2 (2.1% of 46 km2) was affected by landsliding and about 700,000 m2 of this area was covered by chestnut forest. The landslides removed about 7000 trees. The volume of mobilised material was about 1,360,000 m3; about 220,000 m3 remained on the slopes, while the rest poured into the streams. In addition, about 945,000 m3 was mobilised by the torrential erosion in the riverbeds. 相似文献
100.
The main problem in the orbit determination of the space debris population orbiting our planet is identifying which separate
sets of data belong to the same physical object. The observations of a given object during a passage above an observing station
are collectively called a Too Short Arc (TSA): data from a TSA cannot allow for a complete determination of an orbit. Therefore, we have to solve first the identification
problem, finding two or more TSAs belonging to the same physical object and an orbit fitting all the observations. This problem
is well known for the determination of orbits of asteroids: we shall show how to apply the methods developed for preliminary
orbit determination of heliocentric objects to geocentric objects. We shall focus on the definition of an admissible region for space debris, both in the case of optical observations and radar observations; then we shall outline a strategy to perform
a full orbit determination. 相似文献