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1.
Ground motion for the 6 April 2009 (Mw 6.3) earthquake is computed along 2-D cross-sections at L’Aquila by a hybrid method (modal summation plus finite differences) and validated with recordings at AQU, AQK, AQG, AQA and AQV stations. Parametric studies of S-wave velocities of the shallowest lithotypes allow to get a general agreement between synthetic and observed response spectra, despite the scaled point-source approach and the lack of detailed geological and seismic studies. It results that the megabreccia covering on lacustrine soils, characterizing the historical center of L’Aquila, is responsible of spectral amplifications along the vertical (2–7) and horizontal components (2–3) at a wide frequency range (0.6–7 Hz). The covering of alluvial soils in the middle Aterno river valley is responsible of amplifications at 2–7 Hz both in the horizontal and vertical planes of the motion. Such amplifications evidence that site effects might have been responsible of structural damages. 相似文献
2.
On 6 April 2009 a Mw=6.1 earthquake produced severe destruction and damage over the historic center of L’Aquila City (central Italy), in which the accelerometer stations AQK and AQU recorded a large amount of near-fault ground motion data. This paper analyzes the recorded ground motions and compares the observed peak accelerations and the horizontal to vertical response spectral ratios with those revealed from numerical simulations. The finite element method is considered herein to perform dynamic modeling on the soil profile underlying the seismic station AQU. The subsurface model, which is based on the reviewed surveys that were carried out in previous studies, consists of 200–400 m of Quaternary sediments overlying a Meso-Cenozoic carbonate bedrock. The Martin-Finn-Seed's pore-water pressure model is used in the simulations. The horizontal to vertical response spectral ratio that is observed during the weak seismic events shows three predominant frequencies at about 14 Hz, 3 Hz and 0.6 Hz, which may be related to the computed seismic motion amplification occurring at the shallow colluvium, at the top and base of the fluvial-lacustrine sequence, respectively. During the 2009 L’Aquila main shock the predominant frequency of 14 Hz shifts to lower values probably due to a peculiar wave-field incidence angle. The predominant frequency of 3 Hz shifts to lower values when the earthquake magnitude increases, which may be associated to the progressive softening of soil due to the excess pore-water pressure generation that reaches a maximum value of about 350 kPa in the top of fluvial-lacustrine sequence. The computed vertical peak acceleration underestimates the experimental value and the horizontal to vertical peak acceleration ratio that is observed at station AQU decreases when the earthquake magnitude increases, which reveals amplification of the vertical component of ground motion probably due to near-source effects. 相似文献
3.
Aybige Akinci Luca Malagnini Fabio Sabetta 《Soil Dynamics and Earthquake Engineering》2010,30(5):320-335
An Mw 6.25 earthquake occurred on April 6, 2009 at 03:33 a.m. local time, in the Abruzzo region (Central Italy), close to the city of L’Aquila. The earthquake ruptured a North-West (NW)–South-East (SE) oriented normal fault dipping toward the South-West (SW), with the city of L’Aquila lying a few kilometers away on the hanging wall.The main shock has been recorded by fifty-eight accelerometric stations: the highest number of digital recordings ever obtained in Italy for a single earthquake, one of the best-recorded earthquakes with a normal fault mechanism. Very high values of peak ground acceleration (0.3–0.65 g) were observed close to the center of L’Aquila (6 stations at zero JB distance from the fault). The earthquake caused severe loss of lives (299 victims and 1500 injured) and damage (about 18000 unusable buildings) in the epicentral area.In this study we analyze the ground motion characteristics of both the main shock in terms of peak ground acceleration (PGA), peak ground velocity (PGV), and pseudo-acceleration response spectra (5% of damping ratio). In particular, we compare the pseudo-acceleration response spectra for horizontal directions with the EC8 design spectrum and the new Italian building code (NTC08). In order to understand the characteristics of the ground motions induced by L’Aquila earthquake, we also study the source-related effects and site response of the strong motion stations that recorded the seismic sequence. A novel method is used for the analysis of inter-station and site-specific H/V spectral ratios for the main event and for 12 aftershocks. 相似文献
4.
本文选择2011年3月11日M9.0日本东北大地震震中附近三个地磁台站16个月(2010/01/01—2011/04/30)的特低频地磁观测资料,采用去倾扰动分析方法,得到了这三个台站地磁记录的非均匀标度特征随时间的变化,提出了一种能反映地磁三分量非均匀标度特征同步变化的指标,并据此探讨了特低频地磁信号分形标度特征变化与日本东北大地震之间的可能关联性,初步结果表明,这三个台站的特低频地磁信号分形标度特征指标在日本东北大地震前25~50天左右呈现出同步的异常增加,基于磁静日观测资料的随机合成地磁数据的统计检验结果可知前述异常并非随机异常,而是一种具有统计显著性的异常,可能反映了日本东北大地震对周边地磁信号内在的非线性系统特征产生了有统计意义的影响. 相似文献
5.
Sara Amoroso Iolanda Gaudiosi Marco Tallini Giuseppe Di Giulio Giuliano Milana 《Bulletin of Earthquake Engineering》2018,16(10):4443-4466
The Santa Maria di Collemaggio Basilica is an important cultural heritage site and exemplifies Romanesque-Gothic art in the Abruzzo region (central Italy). Erected in the second half of the XII century, the Basilica was severely damaged during the April 6, 2009 L’Aquila earthquake (MW 6.1). In particular, the area of the transept collapsed causing the dome to fall. A refined two-dimensional (2D) geotechnical model was built representing a section that includes the Basilica, in order to better understand the soil response of the Basilica site. The subsoil model was constrained using the geophysical and geotechnical data collected from the seismic microzonation studies, the reconstruction of private damaged buildings and other technical and scientific studies realized in the L’Aquila basin and in the area of the Basilica before and after L’Aquila earthquake. 2D site response analyses were performed to verify the presence of local site effects by comparing simulated versus experimental transfer functions. Moreover, a frequency–wavenumber (f–k) analysis was executed with the aim of evaluating the occurrence of surface waves generated within the basin. 2D seismic effects involve significant amplification in the period range of engineering interest, therein providing an appropriate elastic response spectrum for the restoration of the Basilica. 相似文献
6.
On 6 April 2009, 01:32 GMT, an Mw 6.3 earthquake hit the Abruzzi region of central Italy causing widespread damage in the City of L’Aquila and its nearby villages. The mainshock of this earthquake was recorded by 57 digital strong-motion instruments, four of which are located on the hanging wall of the Paganica Fault near L’Aquila. These stations are no more than 6 km from the epicentre. We use accelerometric data from these four stations to estimate permanent ground displacements caused by the mainshock. Our numerical results reveal south-east and downwards directed permanent co-seismic displacements which are in fair agreement with the outcomes of GPS and InSAR measurements reported in preliminary Istituto Nazionale di Geofisica e Vulcanologia (INGV) reports. 相似文献
7.
The 11-year solar cycle effect in the geomagnetic components H and Z is made clear for Surlari Observatory and 19 repeat stations for the interval 1952–1974. The correlation with Wolf number and its time derivative is discussed in terms of the effects of the external and induced current systems.The data available for solar cycle 20 (1964–1976) were processed to give the geographical distribution of the secular variation impulse for epoch 1969.5 in Romania. It is suggested that this distribution might reflect the deep internal structure of the area considered.A qualitative correlation is noted between long-period solar activity and variation of the horizontal component of the geomagnetic field at some repeat stations. 相似文献
8.
Stress drop estimates of moderate-magnitude earthquakes in the Umbria–Marche region, in the northern Apennines, exhibit a large scatter. For the two M w 5.7 and 6.0 main shocks of 26 September 1997 near Colfiorito, several papers resulted in stress drop estimates of 20 MPa, but values as low as 2–3 MPa were proposed as well. Also for the largest aftershocks (M w > 4), estimates spread from < 1 MPa up to values ten times larger. We have critically revisited methods and data used in the literature. We have specifically faced the trade-off between source and propagation effects, as we believe that it is responsible for a part of the large scatter. To keep this trade-off under control, we have applied a methodology that combines the best fit of both source spectra after Empirical Green’s Function (EGF) deconvolution and observed ground motion spectra, finding that the results of the two different data sets converge independently at the same solution. We have used ground motions observed in the Colfiorito basin, where an accelerograph and a co-located seismological broad-band station recorded three clusters of earthquakes in a broad magnitude interval (1.7 ≤ M w ≤ 6.0). We have found that the mainshock–aftershock sequences result in stress drops of 2–5 MPa at M w ≥ 5.6, with an average tendency to decrease at smaller magnitudes where stress drop variability increases. These findings confirm the source scaling recently assessed through Empirical Green’s Function deconvolution for another well-monitored seismic sequence of normal-faulting earthquakes, which struck the city of L’Aquila in the central Apennines in April 2009. The similar scaling law of the two areas suggests common mechanisms of stress release for the shallow normal faults in the Apennines. The propensity of smaller earthquakes to increase in variability, with a tendency toward smaller stress drops, may reflect an effect of fault strength heterogeneities for smaller size ruptures. 相似文献
9.
The present study revisits the Carrington’s storm using the observations of geomagnetic declination (D) made in the meteorological observatory of Guatemala approximately during the 2 years preceding the storm. The available monthly data for absolute values (diurnal variation) cover the period that spans between May (April) 1857 and December 1859. The analysis of the temporal evolution of monthly means confirmed its overall good quality. Additionally, highly relevant quasi-hourly declination data was analysed for the 2 stormy days of 28 August and 2 September 1859, including complementary information on the auroral sightings on those days. The quasi-hourly data shows that an extremely large deviation (18′) of the geomagnetic declination occurred at 12–13 h (UT) on the 2 September 1859. The comparison of this disturbance with the maximum hourly variations of D recorded at other low-latitude stations during more recent major geomagnetic storms shows the reliability of the Guatemala data. Furthermore, it provides an additional confirmation of the global scale of the great Carrington’s storm. 相似文献
10.
利用空间相关法对2013年岷县—漳县6.6级地震前后151个台站地磁垂直分量日变化进行分析,结果显示:(1)2013年7月3日、4日在震中附近分别出现16和17个台站的地磁Z分量日变化明显反相位异常,具有明显的分界线。(2)利用S变换方法对分界线两侧的天水和兰州台的Z分量日变化进行分频率相关系数计算,发现7月3日、4日的地磁Z分量的日变化均在6 h左右的周期出现负相关变化。其他时段未出现类似变化,认为岷县—漳县6.6级地震前地磁Z分量日变化异常产生的反相位异常主要在6 h左右。此外,还对异常产生的机理进行了解释。 相似文献
11.
A MW6.4 earthquake occurred in L'Aquila, central Italy at 1:32:42 (UTC), April 6, 2009. We quickly obtained the moment tensor solution of the earthquake by inverting the P waveforms of broadband recordings from the global seismographic network (GSN) stations using the quick technique of moment tensor inversion, and further inferred that the nodal plane of strike 132°, dip 53° and rake ?103° is the seismogenic fault. 相似文献
12.
The modifications of some atmospheric physical properties prior to a high magnitude earthquake were debated in the frame of the Lithosphere Atmosphere Ionosphere Coupling (LAIC) model. In this work, among the variety of involved phenomena, the ionisation of air at the ionospheric levels triggered by the leaking of gases from the Earth’s crust was investigated through the analysis of GNSS (Global Navigation Satellite System) signals. In particular, the authors analysed a 5 year (2008–2012) long series of GNSS based ionospheric TEC to produce maps over an area surrounding the epicentre of the L’Aquila (Italy, Mw = 6.3) earthquake of April 6th, 2009. The series was used to detect and quantify amplitude and duration of episodes of ionospheric disturbances by a statistical approach and to discriminate local and global effects on the ionosphere comparing these series with TEC values provided by the analysis of GNSS data from international permanent trackers distributed over a wider region. The study found that during this time interval only three statistically meaningful episodes of ionospheric disturbances were observed. One of them, occurring during the night of 16th of March 2009, anticipated the main shock by 3 weeks and could be connected with the strong earthquake of 6th of April. The other two significant episodes were detected within periods that were not close to the main seismic events and are more likely due to various and global reasons. 相似文献
13.
We investigate the features of the planetary distribution of wave phenomena (geomagnetic pulsations) in the Earth’s magnetic shell (the magnetosphere) during a strong geomagnetic storm on December 14–15, 2006, which is untypical of the minimum phase of solar activity. The storm was caused by the approach of the interplanetary magnetic cloud towards the Earth’s magnetosphere. The study is based on the analysis of 1-min data of global digital geomagnetic observations at a few latitudinal profiles of the global network of ground-based magnetic stations. The analysis is focused on the Pc5 geomagnetic pulsations, whose frequencies fall in the band of 1.5–7 mHz (T ～ 2–10 min), on the fluctuations in the interplanetary magnetic field (IMF) and in the solar wind density in this frequency band. It is shown that during the initial phase of the storm with positive IMF Bz, most intense geomagnetic pulsations were recorded in the dayside polar regions. It was supposed that these pulsations could probably be caused by the injection of the fluctuating streams of solar wind into the Earth’s ionosphere in the dayside polar cusp region. The fluctuations arising in the ionospheric electric currents due to this process are recorded as the geomagnetic pulsations by the ground-based magnetometers. Under negative IMF Bz, substorms develop in the nightside magnetosphere, and the enhancement of geomagnetic pulsations was observed in this latitudinal region on the Earth’s surface. The generation of these pulsations is probably caused by the fluctuations in the field-aligned magnetospheric electric currents flowing along the geomagnetic field lines from the substorm source region. These geomagnetic pulsations are not related to the fluctuations in the interplanetary medium. During the main phase of the magnetic storm, when fluctuations in the interplanetary medium are almost absent, the most intense geomagnetic pulsations were observed in the dawn sector in the region corresponding to the closed magnetosphere. The generation of these pulsations is likely to be associated with the resonance of the geomagnetic field lines. Thus, it is shown that the Pc5 pulsations observed on the ground during the magnetic storm have a different origin and a different planetary distribution. 相似文献
14.
S. Lepidi P. Francia U. Villante A. Meloni A. J. Lazarus R. P. Lepping 《Annales Geophysicae》1999,17(10):1245-1250
An analysis of the low frequency geomagnetic field fluctuations at an Antarctic (Terra Nova Bay) and a low latitude (L’Aquila, Italy) station during the Earth’s passage of a coronal ejecta on April 11, 1997 shows that major solar wind pressure variations were followed at both stations by a high fluctuation level. During northward interplanetary magnetic field conditions and when Terra Nova Bay is close to the local geomagnetic noon, coherent fluctuations, at the same frequency (3.6 mHz) and with polarization characteristics indicating an antisunward propagation, were observed simultaneously at the two stations. An analysis of simultaneous measurements from geosynchronous satellites shows evidence for pulsations at approximately the same frequencies also in the magnetospheric field. The observed waves might then be interpreted as oscillation modes, triggered by an external stimulation, extending to a major portion of the Earth’s magnetosphere. 相似文献
15.
F. Bergamaschi G. Cultrera L. Luzi R. M. Azzara G. Ameri P. Augliera P. Bordoni F. Cara R. Cogliano E. D��Alema D. Di Giacomo G. Di Giulio A. Fodarella G. Franceschina F. Galadini M. R. Gallipoli S. Gori P. Harabaglia C. Ladina S. Lovati S. Marzorati M. Massa G. Milana M. Mucciarelli F. Pacor S. Parolai M. Picozzi M. Pilz S. Pucillo R. Puglia G. Riccio M. Sobiesiak 《Bulletin of Earthquake Engineering》2011,9(3):697-715
A temporary network of 33 seismic stations was deployed in the area struck by the 6th April 2009, Mw 6.1 (Scognamiglio et?al. in Seism Res Lett 6/81, 2010), L??Aquila earthquake (central Italy), with the aim to investigate the site amplification within the Aterno river Valley. The seismograms of 18 earthquakes recorded by 14 of the 33 stations were used to evaluate the average horizontal to vertical spectral ratio (HVSR) for each site and the standard horizontal spectral ratio (SSR) between a site and a reference station. The obtained results have been compared to the geological and geophysical information in order to explain the resonance frequencies and the amplification levels with respect to surface geology of the valley. The results indicate that there is no uniform pattern of amplification, because of the complex geologic setting, as the thickness and degree of cementation of the deposits is highly variable. 相似文献
16.
O. V. Kozyreva N. G. Kleimenova A. E. Levitin J. Watermann 《Geomagnetism and Aeronomy》2006,46(5):622-634
Based on the observations in six pairs of almost conjugate high-latitude stations in the Arctic and Antarctic regions, the spectral and spatial-temporal structures of long-period geomagnetic pulsations (f = 2–5 mHz) during the magnetic storm of April 16–17, 1999, which is characterized by a high (up to 20 nPa) solar wind dynamic pressure, have been studied. It has been indicated that the magnetic storm sudden commencement is accompanied by a symmetrical excitation of np pulsations near the dayside polar cusps with close amplitudes. Under the conditions when IMF B z > 0 and B y < 0, strong magnetic field variations with the periods longer than 15–20 min were observed only in the northern polar cap. When IMF B z and B y became close to zero, geomagnetic pulsation bursts in both hemispheres were registered simultaneously but differed in the spectral composition and spatial distribution. In the Northern Hemisphere, pulsations were as a rule observed in a more extensive latitude region than in the Southern Hemisphere. In the Northern Hemisphere, the oscillation amplitude maximum was observed at higher latitudes than in the Southern Hemisphere. The pulsation amplitude at geomagnetic latitude lower than 74° was larger in the Arctic Regions than in the Antarctic Regions. This can be explained by sharply different geographic longitudes in the polar cap and latitudes in the auroral zone, which results in a different ionospheric conductivity affecting the amplitude of geomagnetic pulsations. 相似文献
17.
18.
Eugen Vujić Giuliana Verbanac Vladis Vujnović Antun Marki 《Studia Geophysica et Geodaetica》2009,53(4):497-517
During the time interval 2003–2005 a ground survey of the total magnetic field intensity in the middle-northern part of Croatia
was performed, in order to get a detailed insight of the field distribution over the region. A special effort was done to
understand the uncertainty and errors in data reduction, namely different amplitudes of the diurnal variations and different
secular variations at the ground stations with respect to the observatories. For data reduction to epoch 2004.5 the total
field recordings from AQU, FUR, NCK and THY geomagnetic observatories have been used. We estimate the mean determination error
to be one order of magnitude smaller than the maximal reduction error. Multiple linear regression and the method of empirical
orthogonal functions were applied on the ground survey and observatory time series. This allowed us to explain the correlations
among them and the variance of the total field. Furthermore, we identified two sources of serious artificial disturbances
caused by DC leakage: the tramway system of the capital and one railway station in neighbouring Slovenia. Also, we estimate
the region free of these disturbances. The magnitude of one of them is estimated to be more than five nT at the distance of
about 10 km. 相似文献
19.
Carlo Del Gaudio Paolo Ricci Gerardo M. Verderame Gaetano Manfredi 《Bulletin of Earthquake Engineering》2016,14(10):2643-2678
A damage scenario based on observational data collected in L’Aquila Municipality after the 6th April 2009 earthquake is compared with a predicted damage scenario derived from the application of a simplified analytical method for seismic vulnerability assessment of Reinforced Concrete (RC) buildings at large scale. The observational damage scenario is derived from a database of 131 RC buildings located in the Municipality of L’Aquila, which after the 2009 earthquake were subjected to post-earthquake usability assessment procedure. The simplified analytical approach adopted is based on the Capacity Spectrum Method to evaluate seismic capacity at different Damage States (DSs) based on the displacement capacity of structural and non-structural elements. DSs and the corresponding displacement capacity are defined through the interpretation of the observational-based DSs provided by the European Macroseismic Scale EMS-98. Data predicted by the adopted methodology are in good agreement with the observed damage distribution. The observed damage scenario is also compared with predicted scenarios derived from other methodologies from literature. 相似文献
20.
《Journal of Atmospheric and Solar》2000,62(9):737-749
During an interaction of the Earth’s magnetosphere with the interplanetary magnetic cloud on October 18–19, 1995, a great magnetic storm took place. Extremely intense disturbances of the geomagnetic field and ionosphere were recorded at the midlatitude observatory at Irkutsk (Φ′≈45°, Λ′≈177°, L≈2) in the course of the storm. The most important storm features in the ionosphere and magnetic field are: a significant decrease in the geomagnetic field Z component during the storm main phase; unusually large amplitudes of geomagnetic pulsations in the Pi1 frequency band; extremely low values of critical frequencies of the ionospheric F2-layer; an appearance of intense Es-layers similar to auroral sporadic layers at the end of the recovery phase. These magnetic storm manifestations are typical for auroral and subauroral latitudes but are extremely rare in middle latitudes. We analyze the storm-time midlatitude phenomena and attempt to explore the magnetospheric storm processes using the data of ground observations of geomagnetic pulsations. It is concluded that the dominant mechanism responsible for the development of the October 18–19, 1995 storm is the quasi-stationary transport of plasma sheet particles up to L≈2 shells rather than multiple substorm injections of plasma clouds into the inner magnetosphere. 相似文献