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1.
A petrographical and chemical research carried out mainly for the rocks belonging to the 2nd cycle of volcanic activity of Boseti Mts., shows the predominance of the salic over the mafic and the intermediate products. The magmatic evolution, which chiefly took place in a thermodynamic environment with initial low \(P_{H_2 O} \) and \(f_{O_2 } \) , has brought about subaluminiferous mugearitic types, also with trachytic affinity. Among peralkali-rhyolites, an anorthoclase fractionation can explain both their chemical variation and the production of pantelleritic liquids.  相似文献   

2.
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3.
Fragility curves for risk-targeted seismic design maps   总被引：1，自引：0，他引：1  
Seismic design using maps based on “risk-targeting” would lead to an annual probability of attaining or exceeding a certain damage state that is uniform over an entire territory. These maps are based on convolving seismic hazard curves from a standard probabilistic analysis with the derivative of fragility curves expressing the chance for a code-designed structure to attain or exceed a certain damage state given a level of input motion, e.g. peak ground acceleration (PGA). There are few published fragility curves for structures respecting the Eurocodes (ECs, principally EC8 for seismic design) that can be used for the development of risk-targeted design maps for Europe. In this article a set of fragility curves for a regular three-storey reinforced-concrete building designed using EC2 and EC8 for medium ductility and increasing levels of design acceleration \((\hbox {a}_\mathrm{g})\) is developed. These curves show that structures designed using EC8 against PGAs up to about 1 m/s \(^{2}\) have similar fragilities to those that respect only EC2 (although this conclusion may not hold for irregular buildings, other geometries or materials). From these curves, the probability of yielding for a structure subjected to a PGA equal to \(\hbox {a}_\mathrm{g}\) varies between 0.14 ( \(\hbox {a}_\mathrm{g}=0.7\) m/s \(^{2})\) and 0.85 ( \(\hbox {a}_\mathrm{g}=3\) m/s \(^{2})\) whereas the probability of collapse for a structure subjected to a PGA equal to \(\hbox {a}_\mathrm{g}\) varies between 1.7 \(\times 10^{-7}\) ( \(\hbox {a}_\mathrm{g}=0.7\) m/s \(^{2})\) and 1.0 \(\times 10^{-5}\) ( \(\hbox {a}_\mathrm{g}=3\) m/s \(^{2})\) .  相似文献   

4.
This paper estimates fundamental translational period and damping ratio parameters and examines the changes in dynamic characteristics of a set of low-to-medium rise buildings in Lorca town (SE of Spain) affected by the May 11th, 2011 earthquake. These building parameters have been calculated analysing structural dynamic response from ambient vibration measurements recorded at top RC buildings pre- and post earthquake, using the Fast Fourier Transform and the Randomdec technique. The empirical expression relating period \((T)\) and number of floor \((N)\) here obtained analysing ambient noise recorded on 59 healthy buildings before the earthquake is \(T= (0.054\pm 0.002)\, N\) , very similar to others empirical period–height relationships obtained for RC structures in the European built environment but quite different from code provisions. Measurements performed in 34 damaged buildings show a period elongation after the quake according to \(T^{*} =(0.075\pm 0.002)\,N\) expression. Moreover, we found a rise of the fundamental period with the EMS’s grade of damage of buildings. In contrast to natural frequency, damping ratio \((\xi )\) do not shows a significant variation with earthquake damage degree and the product \(\xi \, T\) remains near constant.  相似文献   

5.
The full moment tensor is a mathematical expression of six independent variables; however, on a routine basis, it is a common practice to reduce them to five assuming that the isotropic component is zero. This constraint is valid in most tectonic regimes where slip occurs entirely at the fault surface (e.g. subduction zones); however, we found that full moment tensors are best represented in transform fault systems. Here we present a method to analyze source complexity of earthquakes of different sizes using a simple formulation that relates the elastic constants obtained from independent studies with the angle between the slip and the fault normal vector, referred to as angle \( \theta \) ; this angle is obtained from the full moment tensors. The angle \( \theta \) , the proportion of volume change \( \left( k \right) \) and the constant volume (shear) component \( \left( T \right) \) are numerical indicators of complexity of the source; earthquakes are more complex as \( \theta \) deviates from \( \pi /2 \) or as T and k deviate from zero as well. These parameters are obtained from the eigensolution of the full moment tensor. We analyzed earthquakes in the Gulf of California that exhibit a clear isotropic component and we observed that the constant volume parameter T is independent of scalar moments, suggesting that big and small earthquakes are equally complex. In addition, simple models of one single fault are not sufficient to describe physically all the combinations of \( \theta \) in a source type plot. We also found that the principal direction of the strike of the Transform Fault System in the Gulf of California is following the first order approximation of the normal surface of the full moment tensor solution, whereas for deviatoric moment tensors the principal direction does not coincide with the strike of the Transform Fault System. Our observations that small and large earthquakes are equally complex are in agreement with recent studies of strike-slip earthquakes.  相似文献   

6.
The Karalar-Ye?iller area lies on the estern flank of the Kazda \(\bar g\) i massif in northwestern Anatolia (Asiatic Turkey), and includes about 600 square kilometers, of which approximately 80% is covered by rhyodacite-quartz latite extrusive rocks, and a comagmatic granodiorite-quartz monzonite batholith, and stocks, all of middle Miocene age. Extrusive rocks consist chiefly of rhyodacite lava flows of the Hallaçlar Formation and quartz latite-rhyodacite ash-flow tuff, lava, and mudflow deposits of the overlying Dede Tepe Formation. These volcanic rocks lie on a basement composed, in asceding stratigraphic order, of: 1) pre-Permian Kalabak sequence, 2) Upper Triassic Halilar Formation, 3) post-Upper Triassic Ba \(\bar g\) burun Formation, and 4) allochthons of middle Permian: and Upper Jurassic limestone. Intrusion of a granodiorite-quartz monzonite batholith during the middle Miocene was accompanied or shortly followed by extensive alteration and base metal mineralization of the Hallaçlar and older rocks. Intrusion of six rhyodacitequartz latite stocks followed the main phase of hydrothermal alteration. At least one of these stocks may have contributed material to the Dede Tepe Formation of middle Miocene age. Field relations, petrologic, and geochemical data as well as radiometric age dates suggest that the intrusive and extrusive rocks are comagmatic. Parent magma is probably derived from partial melting of subducted oceanic crust and accompanying oceanic sediments. Geologic relations locally indicate assimilation of sialic crust by the grandiorite-quartz monzonite batholith.  相似文献   

7.
We derived explicit expressions in the time domain for 3-D quasi-static strain and stress fields, due to a point moment tensor source in an elastic surface layer overlying viscoelastic half-space under gravity. The expressions of strain in the elastic surface layer were directly obtained from the expressions of displacement in our previous paper. The conversion of strain into stress is easy, because the stress–strain relation of elastic material is linear. In the viscoelastic substratum, the expressions of strain were obtained by applying the correspondence principle of linear viscoelasticity to the associated elastic solution. The strain–stress conversion is not straightforward, as the stress–strain relation of viscoelastic material is usually given in a differential form. To convert strain into stress, we used an integral form of the stress–strain relation instead of the usual differential form. The expressions give the responses of elastic half-space at \( t = 0 \) , and the responses of an elastic plate floating on non-viscous liquid at \( t = \infty \) . The moment tensor is rationally decomposed into the three independent force systems, corresponding to isotropic expansion, shear faulting and crack opening, and so the expressions include the strain and stress fields for these force systems as special cases. As the first numerical example, we computed the temporal changes in strain and stress fields after the sudden opening of an infinitely long vertical crack cutting the elastic surface layer. Here, we observe that the stress changes caused by the sudden crack opening gradually decay with time and vanish at \( t = \infty \) everywhere. After the completion of stress relaxation, a characteristic pattern of shear strain remains in the viscoelastic substratum. Since the strain and stress fields at \( t = \infty \) can be read as the strain- and stress-rate fields caused by steady crack opening, respectively, this numerical example demonstrates the realization of a steady stress state supported by steady viscous flow in the asthenosphere, associated with steady seafloor spreading at mid-ocean ridges. For the second numerical example, we computed the temporal changes in strain and stress fields after the 2011 Tohoku-oki mega-thrust earthquake, which occurred at the North American-Pacific plate interface. In this numerical example, the stress changes caused by coseismic fault slip vanish at \( t = \infty \) in the viscoelastic substratum, but remain in the elastic surface layer. The coseismic stress changes (and also strain changes) in the elastic surface layer diffuse away from the source region with time, due to gradual stress relaxation in the viscoelastic substratum.  相似文献   

8.
We estimate the corner frequencies of 20 crustal seismic events from mainshock–aftershock sequences in different tectonic environments (mainshocks 5.7 < M W < 7.6) using the well-established seismic coda ratio technique (Mayeda et al. in Geophys Res Lett 34:L11303, 2007; Mayeda and Malagnini in Geophys Res Lett, 2010), which provides optimal stability and does not require path or site corrections. For each sequence, we assumed the Brune source model and estimated all the events’ corner frequencies and associated apparent stresses following the MDAC spectral formulation of Walter and Taylor (A revised magnitude and distance amplitude correction (MDAC2) procedure for regional seismic discriminants, 2001), which allows for the possibility of non-self-similar source scaling. Within each sequence, we observe a systematic deviation from the self-similar \( M_{0} \propto \mathop f\nolimits_{\text{c}}^{ - 3} \) line, all data being rather compatible with \( M_{0} \propto \mathop f\nolimits_{\text{c}}^{ - (3 + \varepsilon )} \) , where ε > 0 (Kanamori and Rivera in Bull Seismol Soc Am 94:314–319, 2004). The deviation from a strict self-similar behavior within each earthquake sequence of our collection is indicated by a systematic increase in the estimated average static stress drop and apparent stress with increasing seismic moment (moment magnitude). Our favored physical interpretation for the increased apparent stress with earthquake size is a progressive frictional weakening for increasing seismic slip, in agreement with recent results obtained in laboratory experiments performed on state-of-the-art apparatuses at slip rates of the order of 1 m/s or larger. At smaller magnitudes (M W < 5.5), the overall data set is characterized by a variability in apparent stress of almost three orders of magnitude, mostly from the scatter observed in strike-slip sequences. Larger events (M W > 5.5) show much less variability: about one order of magnitude. It appears that the apparent stress (and static stress drop) does not grow indefinitely at larger magnitudes: for example, in the case of the Chi–Chi sequence (the best sampled sequence between M W 5 and 6.5), some roughly constant stress parameters characterize earthquakes larger than M W ~ 5.5. A representative fault slip for M W 5.5 is a few tens of centimeters (e.g., Ide and Takeo in J Geophys Res 102:27379–27391, 1997), which corresponds to the slip amount at which effective lubrication is observed, according to recent laboratory friction experiments performed at seismic slip velocities (V ~ 1 m/s) and normal stresses representative of crustal depths (Di Toro et al. in Nature in press, 2011, and references therein). If the observed deviation from self-similar scaling is explained in terms of an asymptotic increase in apparent stress (Malagnini et al. in Pure Appl Geophys, 2014, this volume), which is directly related to dynamic stress drop on the fault, one interpretation is that for a seismic slip of a few tens of centimeters (M W ~ 5.5) or larger, a fully lubricated frictional state may be asymptotically approached.  相似文献   

9.
Complexity–entropy causality plane (CECP) is a diagnostic diagram plotting normalized Shannon entropy \({\cal H}_S\) versus Jensen–Shannon complexity \({\cal C}_{JS}\) that has been introduced in nonlinear dynamics analysis to classify signals according to their degrees of randomness and complexity. In this study, we explore the applicability of CECP in hydrological studies by analyzing 80 daily stream flow time series recorded in the continental United States during a period of 75 years, surrogate sequences simulated by autoregressive models (with independent or long-range memory innovations), Theiler amplitude adjusted Fourier transform and Theiler phase randomization, and a set of signals drawn from nonlinear dynamic systems. The effect of seasonality, and the relationships between the CECP quantifiers and several physical and statistical properties of the observed time series are also studied. The results point out that: (1) the CECP can discriminate chaotic and stochastic signals in presence of moderate observational noise; (2) the signal classification depends on the sampling frequency and aggregation time scales; (3) both chaotic and stochastic systems can be compatible with the daily stream flow dynamics, when the focus is on the information content, thus setting these results in the context of the debate on observational equivalence; (4) the empirical relationships between \({\mathcal H}_S\) and \({\mathcal C}_{JS}\) and Hurst parameter H, base flow index, basin drainage area and stream flow quantiles highlight that the CECP quantifiers can be considered as proxies of the long-term low-frequency groundwater processes rather than proxies of the short-term high-frequency surface processes; (6) the joint application of linear and nonlinear diagnostics allows for a more comprehensive characterization of the stream flow time series.  相似文献   

10.
Presently available data on the reaction of SO2 with OH radicals (OH + SO2 + \(M\xrightarrow[{k_1 }]{}\) HSO3 +M) are critically reviewed in light of recent stratospheric sulfur budget calculations. These calculations impose that the net oxidation ratek of SO2 within the stratosphere should fall within the range 10?7≤k≤10?9, if the SO2 oxidation model for the stratospheric sulfate layer is assumed to be correct. The effective reaction rate constantk 1 * =k 1[M] at the stratospheric temperature is estimated as $$k_1^* = \frac{{(8.2 \pm 2.2) \times 10^{ - 13} \times [M]}}{{(0.79 \mp 0.34) \times 10^{ - 13} + [M]}}cm^3 /molecules sec$$ where [M] refers to the total number density (molecules/cm3). Using the above limiting values ofk 1 * , and the estimated OH density concentrations, the net oxidation rate is calculated as 3.6×10?7≤k≤1.3×10?8 at 17 km altitude. This indicates that the upper limit of thesek values exceeds the tolerable range imposed by the model by a factor of about four. Obviously the uncertainty of thek 1 * values and of the OH concentrations in the stratosphere is still too large to make definite conclusions on the validity of the SO2 model.  相似文献   

11.
We determined depth variation of the 410- and 660-km discontinuities beneath southeastern China by common-converted-point stacking of \(\rm P\) -wave receiver functions of 121 permanent Chinese seismic stations. We then combined the results with seismic velocity variation to estimate temperature and water content variations in the mantle transition zone of the region. Previous tomographic studies have shown a stagnant slab in the mantle transition zone in eastern Asia that is connected to subduction of the western Pacific. Temperature variations obtained clearly outline the shape of the stagnant slab, with its western edge at 113.5 \(^\circ\) E and the southern edge at 28.5 \(^\circ\) N. The correlation between the location of the stagnant slab and surface tectonics suggests that the Cenozoic extension in eastern China is closely associated with the subduction of the western Pacific and its eastward migration. The water content of the stagnant slab is lower than in surrounding slabs, suggesting that the water has already been released from the subducting slab into the upper mantle.  相似文献   

12.
It is shown that when the travel-time curve of a refracted wave from a surface source is known and at least one of the following conditions is satisfied, i.e. when
  1. the travel-time curve of a wave reflected from a horizontal interface lying below the deepest low velocity layer is known, or
  2. the travel-time curve of a wave from a deep source situated below the deepest low velocity layer is known, or
  3. the measureH(u)=mes {z∶z≥0,v ?1 (z)≥u} is analytical in some segment [c, d], where \(0< c< d< \infty , c< a_n , H(a_n ) = \bar z_n ,\bar z_n\) is the depth of the lower end of the deepest low velocity layer and in the interval [c, ∞) an analytical functionH(u)) exists which providesH(u)≡H(u)) ifu∈[c, d], then (1) velocityv(z) outside the low velocity layers and (2) the measureH k (u)=mes {z∶z∈L k,v ?1 (z)≥u} for each low velocity layerL k,k=1, 2, ..., n, are defined unambiguously.
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13.
It has been observed that post-critically reflected S-waves and multiples from the Moho discontinuity could play a relevant role on the ground motion due to medium to strong size earthquakes away from the source. Although some studies investigated the correlation between the Moho reflections amplitudes and the damage in the far field, little attention was given to the frequency content of these specific phases and their scaling with magnitude. The 2012 Emilia seismic sequence in northern Italy, recorded by velocimetric and accelerometric networks, is here exploited to investigate Moho reflections and multiples (SmSM). A single station method for group velocity-period estimation, based on the multiple filter technique, is applied to strong motion data to detect SmSM. Amplitude and frequency scaling with magnitude is defined for earthquakes from \(\hbox {Mw}=3.9\) to \(\hbox {Mw}=5.9\) . Finally, the ability of SmSM to affect the ground motion for a maximum credible earthquake within the Po plain is investigated by extrapolating observed engineering parameters. Data analysis shows that high amplitude SmSM can be recognized within the Po plain, and at the boundaries between the Po plain and the Alpine chain, at epicentral distances larger than 80 km, in the period range from 0.25 to 3 s and in the group velocity window from about 2.6 to 3.2 km/s. 5 % damped pseudo-spectral accelerations at different periods (0.3, 1.0 and 2.0 s), and Housner intensities, are obtained from data characterized by large amplitude SmSM. A scaling relationship for both pseudo-spectral accelerations and Housner intensities is found for the earthquakes of the 2012 Emilia seismic sequence. \(\hbox {I}_{\mathrm{MCS}}\) from VII to VIII is estimated, as a result of SmSM amplitude enhancement, at about 100 km for a maximum credible earthquake ( \(\hbox {Mw}=6.7\) ) in the Po plain, showing that moderate to high damage cloud be caused by these specific phases.  相似文献   

14.
The TKE dissipation rate in the northern South China Sea   总被引：1，自引：0，他引：1  
The microstructure measurements taken during the summer seasons of 2009 and 2010 in the northern South China Sea (between 18°N and 22.5°N, and from the Luzon Strait to the eastern shelf of China) were used to estimate the averaged dissipation rate in the upper pycnocline 〈ε p〉 of the deep basin and on the shelf. Linear correlation between 〈ε p〉 and the estimates of available potential energy of internal waves, which was found for this data set, indicates an impact of energetic internal waves on spatial structure and temporal variability of 〈ε p〉. On the shelf stations, the bottom boundary layer depth-integrated dissipation $ {\widehat{\varepsilon}}_{\mathrm{BBL}} $ reaches 17–19 mW/m2, dominating the dissipation in the water column below the surface layer. In the pycnocline, the integrated dissipation $ {\widehat{\varepsilon}}_{\mathrm{p}} $ was mostly ～10–30 % of $ {\widehat{\varepsilon}}_{\mathrm{BBL}} $ . A weak dependence of bin-averaged dissipation $ \overline{\varepsilon} $ on the Richardson number was noted, according to $ \overline{\varepsilon}={\varepsilon}_0+\frac{\varepsilon_{\mathrm{m}}}{{\left(1+ Ri/R{i}_{\mathrm{cr}}\right)}^{1/2}} $ , where ε 0 + ε m is the background value of $ \overline{\varepsilon} $ for weak stratification and Ri cr?=?0.25, pointing to the combined effects of shear instability of small-scale motions and the influence of larger-scale low frequency internal waves. The latter broadly agrees with the MacKinnon–Gregg scaling for internal-wave-induced turbulence dissipation.  相似文献   

15.
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16.
In computational geodynamics, the Finite Element (FE) method is frequently used. The method is attractive as it easily allows employment of body-fitted deformable meshes and a true free surface boundary condition. However, when a Lagrangian mesh is used, remeshing becomes necessary at large strains to avoid numerical inaccuracies (or even wrong results) due to severely distorted elements. For this reason, the FE method is oftentimes combined with the particle-in-cell (PIC) method, where particles are introduced which track history variables and store constitutive information. This implies that the respective material properties have to be interpolated from the particles to the integration points of the finite elements. In numerical geodynamics, material parameters (in particular the viscosity) usually vary over a large range. This may be due to strongly temperature-dependent rheologies (which result in large but smooth viscosity variations) or material interfaces (which result in viscosity jumps). Here, we analyze the accuracy and convergence properties of velocity and pressure of the hybrid FE-PIC method in the presence of large viscosity variations. Standard interpolation schemes (arithmetic and harmonic) are compared to a more sophisticated interpolation scheme which is based on linear least squares interpolation for two types of elements ( \(Q_1P_0\) and \(Q_2P_{-1}\) ). In the case of a smooth viscosity field, the accuracy and convergence is significantly improved by the new interpolation scheme. In the presence of viscosity jumps, the order of accuracy is strongly decreased.  相似文献   

17.
A simple biogeochemical model coupled to an offline ocean tracer transport model driven by reanalysis ocean data is used to simulate the seasonal and interannual CO $_2$ flux variability in the northern Indian Ocean. The maximum of seasonal and interannual CO $_2$ emission variances in the northern Indian Ocean are located in the coastal Arabian Sea (AS) and Southern Peninsular India (SP) with a basin-wide seasonal amplitude and standard deviation of 0.044 $\pm $ 0.04 Pg C year $^{-1}$ . The area integrated CO $_2$ emissions from these two regions in the model are significantly correlated (above a 95 % level) with the observations of Takahashi et al. (Deep-Sea Res-II, 56:554–577, 2009). The interannual anomalies of CO $_2$ emission from the AS and SP are found as 40 and 30 % of their respective seasonal amplitudes. Both the Arabian Sea (AS) and Southern Peninsular India (SP) interannual CO $_2$ emission anomalies show a 3–4-year variability. The correlations of AS and SP CO $_2$ emission anomalies with the Indian Ocean Dipole/Zonal Mode (IODZM) and Southern Oscillation (SO) indices from 1980 to 1999 are 0.35, 0.21 and 0.32, 0.01 respectively. A 5-year window moving correlation analysis shows that the relationship of AS and SP CO $_2$ emission to the SO and IODZM are complementary to each other. During the years when the correlation of air–sea CO $_2$ emission with the IODZM is stronger, the corresponding correlation with the SO is weaker or opposite. The total change in pCO $_2$ is broken down into changes induced by the individual components such as dissolved inorganic carbon (DIC), sea surface temperature (SST), alkalinity, and salinity and found that (1) the effect of SST in the AS CO $_2$ emission increases (decreases) when the correlation of CO $_2$ emission with the IODZM is positive (negative), and (2) the SP CO $_2$ emission is strongly controlled by the circulation-driven DIC changes; however, this relation is found to be weaker when the SO correlates negatively with the SP CO $_2$ emission.  相似文献   

18.
The Lorca Basin has been the object of recent research aimed at studying the phenomena of earthquake-induced landslides and its assessment in the frame of different seismic scenarios. However, it has not been until the 11th May 2011 Lorca earthquakes when it has been possible to conduct a systematic approach to the problem. In this paper we present an inventory of slope instabilities triggered by the Lorca earthquakes which comprises more than 100 cases, mainly rock and soil falls of small size (1–100  \(\hbox {m}^{3}\) ). The distribution of these instabilities is here compared to two different earthquake-triggered landslide hazard maps: one considering the occurrence of the most probable earthquake for a 475-years return period in the Lorca Basin \((\hbox {M}_{\mathrm{w}}=5.0)\) based on both low- and high-resolution digital elevation model (DEM); and a second one matching the occurrence of the \(\hbox {M}_{\mathrm{w}}=5.2\) 2011 Lorca earthquake, which was performed using the higher resolution DEM. The most frequent Newmark displacements related to the slope failures triggered by the 2011 Lorca earthquakes are lower than 2 cm in both the hazard scenarios considered. Additionally, the predicted Newmark displacements were correlated to the inventory of slope instabilities to develop a probability of failure equation. The fit seems to be very good since most of the mapped slope failures are located on the higher probability areas. The probability of slope failure in the Lorca Basin for a seismic event similar to the \(\hbox {M}_{\mathrm{w}}\) 5.2 2011 Lorca earthquake can be considered as very low (0–4 %).  相似文献   

19.
The Aegean and surrounding area (34°N–43°N, 18°E–30°E) is separated into 76 shallow and intermediate depth seismogenic sources. For 74 of these sources intervent times for strong mainshocks have been determined by the use of instrumental and historical data. These times have been used to determine the following empirical relations: $$\begin{gathered} \log T_t = 0.24M_{\min } + 0.25M_p - 0.36\log \dot M_0 + 7.36 \hfill \\ M_f = 1.04M_{\min } - 0.31M_p + 0.28\log \dot M_0 - 4.85 \hfill \\ \end{gathered} $$ whereT 1 is the interevent time, measured in years,M min the surface wave magnitude of the smallest mainshock considered,M p the magnitude of the preceding mainshock,M f the magnitude of the following mainshock, \(\dot M_0 \) the moment rate in each source per year. A multiple correlation coefficient equal to 0.74 and a standard deviation equal to 0.18 for the first of these relations were calculated. The corresponding quantities for the second of these relations are 0.91 and 0.22. On the basis of the first of these relations and taking into consideration the time of occurence and the magnitude of the last mainshock, the probabilities for the occurrence of mainshocks in each seismogenic source of this region during the decade 1993–2002 are determined. The second of these relations has been used to estimate the magnitude of the expected mainshock.  相似文献   

20.
We tested attenuation relations obtained for different regions of the world to verify their suitability to predict strong-motion data recorded by Medellín and Aburrá Valley Accelerographic Networks. We used as comparison criteria, the average of the difference between the observed and the predicted data as a function of epicenter distance and its standard deviation. We also used the approach developed by Sherbaum et al. (Bull Seism Soc Am 94:2164–2185, 2004) that provides a method to evaluate the overall goodness-of-fit of ground-motion prediction equations. The predictive models selected use a generic focal depth. We found that this parameter has an important influence in the ground-motion predictions and must be taken into account as an independent variable. We also found important to characterize the local soil amplification to improve the attenuation relations. We found empirical relations for peak horizontal acceleration PGA and velocity PGV based on the Kamiyama and Yanagisawa (Soils Found 26:16–32, 1986) approach. $$\begin{aligned} \log _{10} (PGA)=0.5886M_L -1.0902\log _{10}(R)-0.0035H+C_{st}\pm 0.\text{29} \end{aligned}$$ $$\begin{aligned} \log _{10} (PGV)=0.7255M_L -1.8812\log _{10}(R)-0.0016H+C_{st}\pm 0.36 \end{aligned}$$ where PGA is measured in cm/s $^{2}$ and PGV in cm/s, $M_{L}$ is local magnitude in the range 2.8–6.5, $R$ is epicentral distance up to 290 km, $H$ is focal depth in km and $C_{st}$ is a coefficient that accounts for the site response due to soil conditions of each recording station. The introduction of focal depth and local site conditions as independent variables, minimize the residuals and the dispersion of the predicted data. We conclude that $H$ and $C_{st}$ are sensitive parameters, having a strong influence on the strong-motion predictions. Using the same functional form, we also propose an empirical relation for the root mean square acceleration a $_\mathrm{rms}$ : $$\begin{aligned} \log _{10} \left( {a_{rms} } \right)=0.4797M_L -1.1665\log _{10} (R)-0.00201H+C_{st}\pm 0.40 \end{aligned}$$ where a $_\mathrm{rms}$ is measured in cm/s $^{2}$ , from the S-wave arrival and using a window length equal to the rupture duration. The other variables are the same as those for PGA and PGV. The site correction coefficients $C_{st}$ found for PGA, PGV and a $_\mathrm{rms}$ show a similar trend indicating a good correlation with the soil conditions of the recording sites.  相似文献   

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