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1.
We designed a new seismic source model for Italy to be used as an input for country-wide probabilistic seismic hazard assessment (PSHA) in the frame of the compilation of a new national reference map. We started off by reviewing existing models available for Italy and for other European countries, then discussed the main open issues in the current practice of seismogenic zoning. The new model, termed ZS9, is largely based on data collected in the past 10 years, including historical earthquakes and instrumental seismicity, active faults and their seismogenic potential, and seismotectonic evidence from recent earthquakes. This information allowed us to propose new interpretations for poorly understood areas where the new data are in conflict with assumptions made in designing the previous and widely used model ZS4. ZS9 is made out of 36 zones where earthquakes with Mw > = 5 are expected. It also assumes that earthquakes with Mw up to 5 may occur anywhere outside the seismogenic zones, although the associated probability is rather low. Special care was taken to ensure that each zone sampled a large enough number of earthquakes so that we could compute reliable earthquake production rates. Although it was drawn following criteria that are standard practice in PSHA, ZS9 is also innovative in that every zone is characterised also by its mean seismogenic depth (the depth of the crustal volume that will presumably release future earthquakes) and predominant focal mechanism (their most likely rupture mechanism). These properties were determined using instrumental data, and only in a limited number of cases we resorted to geologic constraints and expert judgment to cope with lack of data or conflicting indications. These attributes allow ZS9 to be used with more accurate regionalized depth-dependent attenuation relations, and are ultimately expected to increase significantly the reliability of seismic hazard estimates. 相似文献
2.
This note discusses three interconnected statistical problems concerning the Parkfield sequence of moderate earthquakes and the Parkfield prediction experiment: (a) Is it possible that the quasi-periodic Parkfield sequence of characteristic earthquakes is no uncommon, specific phenomenon (the research hypothesis), but can be explained by a preferential selection from available earthquake catalogs? To this end we formulate the null hypothesis (earthquakes occur according to the Poisson process in time and their size follows the Gutenberg-Richter relation). We test whether the null hypothesis can be rejected as an explanation for the Parkfield sequence. (b) If the null hypothesis cannot be refuted, what is the probability of magnitude m ≥ 6 earthquake occurrence in the Parkfield region? (c) The direct goal of the Parkfield experiment is the registration of precursory phenomena prior to a m6 earthquake. However, in the absence of the characteristic earthquake, can the experiment resolve which of the two competing hypotheses is true in a reasonable time? Statistical analysis is hindered by an insufficiently rigorous definition of the research model and inadequate or ambiguous data. However, we show that the null hypothesis cannot be decisively rejected. The quasi-periodic pattern of intermediate size earthquakes in the Parkfield area is a statistical event likely to occur by chance if it has been preferentially selected from available earthquake catalogs. The observed magnitude-frequency curves for small and intermediate earthquakes in the Parkfield area agree with the theoretical distribution computed on the basis of a modified Gutenberg-Richter law (gamma distribution), using deformation rates for the San Andreas fault. We show that the size distribution of the Parkfield characteristic earthquakes can also be attributed to selection bias. According to the null hypothesis, the yearly probability of a m ≥ 6 earthquake originating in the Parkfield area is less than 1%, signifying that several more decades of observation may be needed before the expected event occurs. By its design, the Parkfield experiment cannot be expected to yield statistically significant conclusions on the validity of the research hypothesis for many decades. 相似文献
3.
The Sannio-Matese region is one of the most seismically active regions of Italy and has been struck by large historical earthquakes. At present, the area is characterized by low magnitude background seismicity and small seismic sequences following M4 main events. In this paper, we show Vp and Vp/Vs models and 3D locations for a complete set of earthquakes occurring in the period 1991–2001. We observe a significant crustal heterogeneity, with large scale east-verging high Vp fault-related-folds, stacked by the Pliocene compression. The relocated earthquakes cluster along a 70° east-dipping, NW-striking plane located at the border of the high Vp thrust units. Normal fault earthquakes related to the young and active extension occur within these high Vp zones, interpreted as high strength material. We expect large future earthquakes to occur within these high Vp zones actually characterized by low magnitude seismicity at their borders. 相似文献
4.
The study computes time-dependant earthquake probabilities on the basis of seismicity data mainly deriving from historic records.
It provides a methodological approach useful for those countries where the scarcity of instrumental data and/or paleoseismological
evidences requires that historical information shall be stressed. Thus, the conditional probability that damaging earthquakes
( M ≥ 6) may occur in Italy in the next 30 years is shown, and the potential for the main worldwide known Italian cities with
a cultural heritage is outlined. Earthquake probabilities are computed referring to the application of renewal processes,
where the periodicity is analytically modelled by means of the Brownian Passage Time function; an estimate of the dispersion
(i.e., uncertainty) introduced on probabilities is provided making use of Monte Carlo simulations. The computed probabilities
refer to seismic source zones deriving from the spatial clustering of the historically documented seismicity. The computation
of probabilities based on the interaction of earthquakes occurring in nearby zones, has been also attempted for a test area
to explore the influence exerted by the stress transfer effect. The main findings of this study are that (1) seismic source
zones in Southern Italy are the most prone to experience damaging earthquakes in the next 30-years, with conditional probabilities
a large as 10%; and (2) the influence exerted by the earthquake interaction in increasing such probabilities, doesn’t seem
to be relevant, because the mean recurrence times of large earthquakes (above the threshold magnitude of six chosen in this
study) are in general much longer than the time shortening produced by the stress transfer. 相似文献
5.
The border area between Italy and Slovenia has been chosen for a proposed project on border earthquake's assessment (BEA). Attempts at the unification of macroseismic practice among the countries have been rare and not very successful, due to the different and often incompatible local traditions for the derivation of intensity data. With the publication of the new EMS-92 scale, the idea was born to try to unify the procedures in data collection on both sides of the border. The pilot project was proposed, consisting mainly of the preparation for eventual strong earthquakes in the future. A special civil engineering form for damage assessment was designed to be used in the damaged area. The path of this idea is presented. 相似文献
6.
A previous analysis [Improta, L., G. Di Giulio, and A. Rovelli (2005). Variations of local seismic response in Benevento (Southern Italy) using earthquakes and ambient noise recordings, J. Seism. 9, 191–210.] of small magnitude earthquakes recorded at 12 sites within the city of Benevento has stressed the significant role played by near-surface geology in causing variability of the ground motion. In this paper, we extend the study of the seismic response from 12 sites to the entire urban area. Based on inferences from the comparison at the 12 sites between earthquake and ambient vibration results, we have collected ambient noise at about 100 sites within the city, intensifying measurements across the main shallow geological variations. We use borehole data to interpret ambient noise H/V spectral ratios in terms of near-surface geology comparing H/V curves to theoretical transfer functions of 1D models along five well-constrained profiles. On the basis of geological, geotechnical, and seismic data, we identify three main typologies of seismic response in the city. Each type of response is associated to zones sharing common soil conditions and similar soil classes according to building codes for seismic design. Moreover, we find that the spatial variation of the seismic response in the ancient town area is consistent with the damage pattern produced by a very destructive, well-documented historical earthquake that struck the city in 1688, causing MCS intensity of IX–X in Benevento. Finally, we use ground motions recorded during the experiment by Improta et al. [Improta, L., G. Di Giulio, and A. Rovelli (2005). Variations of local seismic response in Benevento (Southern Italy) using earthquakes and ambient noise recordings, J. Seism. 9, 191–210.] to generate synthetic seismograms of moderate to strong (Mw 5.7, Molise 2002 and Ms 6.9, 1980 Irpinia) earthquakes. We calibrate the random summation technique by Ordaz et al. [Ordaz, M., J. Arboleda, and S.K. Singh (1995). A scheme of random summation of an Empirical Green's Function to estimate ground motions for future large earthquakes, Bull. Seism. Soc. Am. 85, 1635–1647.] using recordings of these earthquakes available in Benevento. After a satisfactory fit between observed and synthetic seismograms, we compute response spectra at different sites and speculate on effects of the geology class at large level of shaking, including soil nonlinearity. We find that large discrepancies from design spectra prescribed by seismic codes can occur for a wide sector of Benevento, especially for periods < 0.5 s. 相似文献
7.
A series of long karst spring discharges have been analysed to determine trends, fluctuations and relationship to rainfall.
Data come from aquifers in southern Italy, and in some cases cover more than one hundred years of records. Based on yearly
discharge data, hydrological series show the drop of the discharge after 1986, which has been interrupted by the recent wet
years of 2009 and 2010. This drop is connected to the decrease in annual rainfall, but other factors also seem to contribute
to this phenomenon. Based on monthly scale data series, the relationship between meteorological and hydrological droughts
has been analyzed, using the standard precipitation index (SPI). As karst systems are large reservoirs, only longer meteorological
droughts induce groundwater droughts, and the start, duration and time-lag of the hydrological droughts have been evaluated. 相似文献
8.
The relevant results of the study of more than 1700 Italian historical earthquakes from the year 1000 to 1982 are presented here. The research was carried out from 1983 to 1987 as part of a study promoted by ENEL (the National Electricity Board) for the seismic siting of nuclear power plants. A single coherent project has been developed, that involved 111 historical researchers who operated in 813 research centres in Italy and abroad. Problems such as the methods, research, analysis and interpretation of the numerous and various effects caused both by destructive and non-destructive earthquakes recorded in the historical sources, have been considered on a large scale for the first time. The earthquake records, collected in a data bank and interpreted according to a multi-disciplinary historical and seismological approach, have allowed the detailed reconstruction of the location and chronology of both individual and repeated events. This major research study has allowed us to evaluate the inexactness of the present Catalogue of Italian earthquakes in relation to the parameters of intensity, location and dating. From the synthesis of the results of the revision emerged sufficient information to value the reliability of the present Catalogue. TERRA Nova (1989) 1 , 151–162. 相似文献
9.
Sand- and gravel-filled clastic dikes of seismic liquefaction origin occur throughout much of southern Indiana and Illinois. Nearly all of these dikes originated from prehistoric earthquakes centered in the study area. In this area at least seven and probably eight strong prehistoric earthquakes have been documented as occurring during the Holocene, and at least one during the latest Pleistocene. The recognition of different earthquakes has been based mainly on timing of liquefaction in combination with the regional pattern of liquefaction effects, but some have been recognized only by geotechnical testing at sites of liquefaction. Most paleo-earthquakes presently recognized lie in Indiana, but equally as many may have occurred in Illinois. Studies in Illinois have not yet narrowly bracketed the age of clastic dikes at many sites, which sometimes causes uncertainty in defining the causative earthquake, but even in Illinois the largest paleo-earthquakes probably have been identified. Prehistoric magnitudes were probably as high as about moment magnitude M 7.5. This greatly exceeds the largest historic earthquake of M 5.5 centered in Indiana or Illinois. The strongest paleo-earthquakes struck in the vicinity of the concentration of strongest historic seismicity. Elsewhere, paleo-earthquakes on the order of M 6–7 have occurred even where there has been little or no historic seismicity. Both geologic and geotechnical methods of analysis have been essential for verification of seismic origin for the dikes and for back-calculating prehistoric magnitudes. Methods developed largely as part of this study should be of great value in unraveling the paleoseismic record elsewhere. 相似文献
10.
We tested a new hybrid method for the evaluation of seismic hazard. A recently proposed fault segmentation and earthquake recurrence model of peninsular Italy suggests that the interval for which the local historical catalogue is complete is shorter than the mean recurrence time of individual large faults (1000 years), or at the most comparable. These new findings violate the fundamental assumption of historical probabilistic seismic hazard methods that the historical record is representative of the activity of all the seismogenic sources. The hybrid method we propose uses time-dependent modelling of the major earthquakes and catalogue-based historical probabilistic estimates for all minor events. We assume that the largest earthquakes are characteristic for individual discrete fault segments, model their probability of occurrence by a renewal process and compute the shaking associated with each of them with a simplified procedure. Then we calculate the probability of exceeding a given threshold of peak ground acceleration for specific sites as the aggregate probability of occurrence of large characteristic earthquakes and minor shocks. We apply the method to the Calabrian Arc (Southern Italy) performing the calculations for five major towns. The exposure to seismic hazard of Reggio Calabria, Catanzaro and Vibo Valentia, which locate close to recently activated large faults, decreases with respect to traditional time-independent estimates. On the contrary, an increase of seismic hazard is obtained for Castrovillari, which locates in an area where large faults displaying Holocene activity have been recently recognized but no significant earthquake is reported in the historical catalogue. Cosenza has the highest probability to experience a significant peak ground acceleration with both the new hybrid and the traditional approaches. We wish to stress that the present results should be interpreted only in terms of the differences between the new hybrid and the traditional approaches, not for their absolute values, and that they are not intended to be used for updating or modifying the current national seismic zonation. 相似文献
11.
Frequency-size relation of earthquakes in a region can be approximated by the Gutenberg-Richter law(GR). This power-law model involves two parameters: a-value measuring seismic activity or earthquake productivity, and b-value describing the relation between frequencies of small and large earthquakes.The spatial and temporal variations of these two parameters, especially the b-value, have been substantially investigated. For example, it has been shown that b-value depends inversely on differential stress. The b-value has also been utilized as earthquake precursor in large earthquake prediction.However, the physical meaning and properties of b-value including its value range still remain as an open fundamental question. We explore the property of b-value from frequency-size GR model in a new form which relates average energy release and probability of large earthquakes. Based on this new form of GR relation the b-value can be related to the singularity index(1-2/3 b) of fractal energy-probability power-law model. This model as applied to the global database of earthquakes with size M ≥ 5 from 1964 to 2015 indicates a systematic increase of singularity from earthquakes occurring on mid-ocean ridges, to those in subduction zones and in collision zones. 相似文献
12.
The case history and the research work in regard to the water-induced earthquakes at Hsinfengkiang reservoir, 160 km. northeast of Canton, have been reported elsewhere. [1] The installation of strong-motion seismograph system at the dam site is a component part of the comprehensive scientific program for studying the water-induced earthquakes at this place. The system was in operation after the occurrence of the main shock ( Ms= 6.1) in 1962. Since 1966, a number of accelerograms have been obtained, for the aftershocks, on exposed bedrock in the dam site and at different positions on the dam proper, providing useful data for studying the characteristics and the effects of water-induced earthquakes. This paper, as a supplement to the previous report, gives a presentation of such data with preliminary analysis. 相似文献
13.
In order to enhance the detection of prospective rock falls in calcareous cliffs, 25 rock falls have been described in a more detailed way than for an inventory. They are representative of middle size rock falls (10 to 100,000 m 3) occurring in the French Subalpine Ranges, at an elevation between 200 m and 2000 m. Structural conditions of the rock masses, morphology of the initial cliff surface and the scar, possible failure mechanisms and processes have been studied. Typical failure configurations have been identified, based on the attitude of the failure surface, in relation to the bedding planes and the cliff surface. Irregular cliff morphology appears to be another important susceptibility factor. In most cases, the classical comparison of the average planes of the main joint sets with the average plane of the slope could not define the potentially unstable masses. Rather, those ones are due to joint planes that deviate from their mean set plane or to irregularities of the cliff surface. The proposed investigation method to detect prospective rock falls mainly consists in observing stereoscopic aerial photographs in order to look for critical configurations. Once a critical mass has been detected, its failure probability for a period of the order of one century must be evaluated (or its life expectancy). The main factor to consider for this purpose appears to be the proportion of rock bridges in the potential failure surface. The triggering factors of rock falls in our study area have been investigated, by analysing an inventory of 46 rock falls. Statistical tests have been carried out to study the relation between rock falls and daily rainfall, freeze–thaw cycles or earthquakes. A good correlation has been obtained with freeze–thaw cycles, a slight correlation with rainfall and no correlation with earthquakes. This suggests that ice jacking could the main physical process leading to failure by causing microcrack propagation. 相似文献
14.
The earthquake is known to be an unpredictable geophysical phenomenon. Only few seismic indicators and assumptions of earthquakes can be predicted with probable certainty. This study attempts to analyze the earthquakes over the Indo-Himalayan Border region including Bhutan, Bangladesh, Nepal, China and India during the period from 1995 to 2015. Bangladesh, Bhutan and China borders experience fewer earthquakes than Nepal and India border regions. However, Indo-China rim has inconsistency and vast range in its magnitude. Bangladesh though is a small country with respect to others, but it experiences earthquakes comparable to Bhutan. Nepal experiences highest number of earthquakes. In the last 20 years around 800 records have been observed with moment magnitude > 4.0 Richter scale, while very few records (around 10–12) have been observed for large earthquakes having moment magnitude > 6.0 Richter scale over the region. In this study adaptive neuro-fuzzy inference system has been implemented to assess the predictability of seismic moment associated with large earthquakes having the moment magnitude between 6.0 and 8.0 Richter scales using different combination of epochs, technique and membership functions. The Gaussian membership function with hybrid technique and 40 epochs is observed to be the reasonable model on the basis of the selected spatial and temporal scale. The forecast error in terms of root-mean-square error with the stopping criterion 0.001 has been observed to be 0.006 in case of large earthquakes (> 6.5 Richter scale), that is, forecast accuracy of 99.4%. The model bias of 0.6% may be due to inadequate number of large earthquakes having moment magnitude > 6.5 Richter scale over the region. 相似文献
15.
Summary. Experimental results clearly indicate that large faults involved in earthquakes possess low strength, low friction coefficient
and high fracture energy, in comparison with data obtained from small scale laboratory tests on rock samples. The reasons
for such an unexpected anomalous behaviour have been the subject of several studies in the past and are still under debate
in the Scientific Community. In this paper we propose a unifying interpretation of these size-scale effects on the basis of
fractal geometry, which represents the proper mathematical framework for the analysis of multi-scale properties of rough surfaces
in contact. A rather good agreement between the proposed scaling laws and the experimental data ranging from the laboratory
scale up to the planetary scale typical of natural faults is achieved.
Author’s address: Marco Paggi, Politecnico di Torino, Department of Structural and Geotechnical Engineering, C.so Duca degli
Abruzzi 24, 10129 Torino, Italy 相似文献
16.
CO 2 capture and storage projects must consider the potential possibility ofinjection induced seismicity. Moderate earthquakes and strong earthquakes may endanger human life and property, and even felt earthquakes and microquakes also pose a threat to seal integrity of CO 2 reservoir and increase the risk of leakage. Underground fluid injection induced seismicity usually happens in some geoengineering projects such as waste fluid disposal, EOR and EGS, and it occurs when fluid is injected along the fault. Therefore, it can be studied through stress analysis. The density of supercritical CO 2 is smaller than water, which may develop density flow in the deep strata or water-rock interactions in pre-existing structures, and cause the variation in permeability and pressure to induce a seismic activity. In this paper, we reviewed the mechanism of underground fluid injection induced seismicity with the focus of CCS, combined with fluid injection projects and seismic monitoring analysis in both commercial scale and experimental scale, to investigate its impact on the integrity of the cap rock of the reservoir. Finally, we summarized the appropriate site selection, injection methods and monitoring programs to prevent the occurrence of induced seismicity. 相似文献
17.
Mathematical models for forecasting landslides and mudflow movements triggered by heavy rainfalls are useful tools to develop warning systems and hazard mitigation strategy for loss reduction. In the present paper, an application of Forecasting of Landslides Induced by Rainfalls (FLaIR) hydrological model, correlating the rainfall amount and landslide or mudflow movement occurrences, will be performed. Model application presented here refers to the mudflows of Sarno, Southern Italy, and is based on hourly precipitation data available from a real-time rain gauge installed immediately after the catastrophic event that occurred on May 1998. The application is extended from October 1998 to May 2002. The main objective is to perform a backanalysis in order to verify the reliability of the proposed scheme for use in a warning system. Among the most interesting results of the application, the relatively few false alarms for populations given by the model may be highlighted. The FLaIR model is more useful when it is integrated with a probabilistic model for forecasting precipitation depths during a storm event at an hourly scale. By stochastic modelling of hourly precipitation, it is possible to estimate the probability of reaching the alarm threshold before allowing civil protection actions. 相似文献
18.
以粒度分析结果为依据,结合地层的序列、结构、构造及岩性等方面的特征,在辽西兴城地区的上古生界中识别出四种沉积环境,每种环境均有独特的粒度特征:①曲流河环境:所在层位为本溪组与石盒子组中下部,沉积物平均粒径多集中在3 φ附近,分选度较好,频率曲线多为微正偏的正态分布,概率累积曲线存在差异,河道为典型两段式,决口扇为低悬两段式;②三角洲平原环境,所在层位为太原组与山西组,其中平原沼泽沉积物粒度较细,集中在3.2 φ之间,但分支河道粒度相对较粗,与曲流河类似,三角洲平原沉积物分选好,频率曲线正偏、负偏均存在,概率累积曲线存在差异,分支河道为低悬两段式而平原沼泽则为一段式,反映垂向加积特征;③辫状河环境,对应石盒子组上部层位,沉积物平均粒度2.5 φ左右,分选中等至较好,频率曲线多为微正偏态,概率累积曲线介于典型两段式与高悬两段式之间;④冲积扇环境,所在层位为蛤蟆山组,平均粒径集中在2 φ左右,分选中等,频率曲线为正偏态至很正偏态,表明沉积物以粗组分为主,概率累积曲线均为高悬两段式,代表很高的水动力条件。从水动力条件及沉积环境的演化趋势来看,本地区晚石炭世至中二叠世中期处于温暖湿润的濒海盆地环境,中二叠世后期开始,随着地壳抬升,本地区不断向内陆环境变化,至晚二叠世末期,已经进入干旱炎热的内陆盆地环境。 相似文献
19.
Earthquakes cause massive road damage which in turn causes adverse effects on the society. Previous studies have quantified
the damage caused to residential and commercial buildings; however, not many studies have been conducted to quantify road
damage caused by earthquakes. In this study, an attempt has been made to propose a new scale to classify and quantify the
road damage due to earthquakes based on the data collected from major earthquakes in the past. The proposed classification
for road damage due to earthquake is called as road damage scale (RDS). Earthquake details such as magnitude, distance of
road damage from the epicenter, focal depth, and photographs of damaged roads have been collected from various sources with
reported modified Mercalli intensity (MMI). The widely used MMI scale is found to be inadequate to clearly define the road
damage. The proposed RDS is applied to various reported road damage and reclassified as per RDS. The correlation between RDS
and earthquake parameters of magnitude, epicenter distance, hypocenter distance, and combination of magnitude with epicenter
and hypocenter distance has been studied using available data. It is observed that the proposed RDS correlates well with the
available earthquake data when compared with the MMI scale. Among several correlations, correlation between RDS and combination
of magnitude and epicenter distance is appropriate. Summary of these correlations, their limitations, and the applicability
of the proposed scale to forecast road damages and to carry out vulnerability analysis in urban areas is presented in the
paper. 相似文献
20.
We determine seismic strain rate of tectonic earthquakes along the Central America Volcanic Arc. We then compare this result to those obtained from earthquakes related to the convergence of the Cocos and Caribbean plates and to earthquakes in the back-arc region of northern Central America. The seismic strain-rate tensor for shallow-focus earthquakes along the Central America volcanic arc since 1700, has a compressive eigenvector with a magnitude of 0.7 × 10−8 year−1, and oriented in a 357° azimuth. The extensive eigenvector is oriented in a 86° azimuth, with a magnitude of 0.82 × 10−8 year−1. When only Centroid Moment-tensor solutions (CMT) are considered, the respective eigenvectors are 1.2 × 10−8 year−1 and 1.0 × 10−8 year−1. The compressive eigenvector from the seismic strain-rate tensor for earthquakes along the Cocos-Caribbean convergent margin is 2.0 × 10−8 year−1, plunging at 25°, and oriented in a 29° azimuth. Its magnitude and direction are similar to those of the compressive eigenvector for earthquakes along the volcanic arc. The extensive eigenvector along the convergent margin, on the other hand, has a large vertical component. The compressive and extensive eigevenvectors are 4.9 × 10−8 year−1 and 4.6 × 10−8 year−1, using only CMTs as the database. Earthquakes along the grabens of northern Central America yield a seismic strain-rate tensor whose extensive eigenvector has a magnitude of 2.4 × 10−8 year−1, oriented in a 109° azimuth. Magnitude and direction are similar to those of the extensive eigenvector for earthquakes along the volcanic arc. The compressive eigenvector along the grabens is practically vertical. Similarities in magnitudes and directions for compressive and extensive eigenvectors suggest to us that the strain field along the Central America volcanic arc is the result of compression along the convergent Cocos-Caribbean margin, and extension in the back-arc region, along the grabens of northern Central America. This field is resolved as strike-slip faulting along the arc. 相似文献
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