Seismicity patterns before the M=5.8 2002, Palermo (Italy) earthquake: seismic quiescence and accelerating seismicity

Seismic quiescence and accelerating seismic energy release are considered as possible spatio-temporal patterns of the preparation process of the 6 September 2002 Palermo, Italy, earthquake (M 5.8). The detailed properties of the quiescence are analyzed applying the RTL algorithm. The RTL algorithm is based on the analysis of the RTL prognostic parameter, which is designed in such a way that it has a negative value if, in comparison with long-term background, there is a deficiency of events in the time–space vicinity of the tested point. The RTL parameter increases if activation of seismicity takes place. The RTL algorithm identified that a seismic quiescence started from the beginning of November 2001 and reached its minimum at the end of May 2002. The Palermo 2002 earthquake occurred 2 months after the RTL parameter restored its long-term background level. The application of a log-periodic time-to-failure model gives a “predicted” (in retrospect) magnitude M=6.2 main shock on 5 May 2002.     

Assessing the Vibrational Frequencies of the Cathedral of Cologne (Germany) by Means of Ambient Seismic Noise Analysis

Ambient seismic noise measurements were conducted inside the Cathedral of Cologne (Germany) for assessing its frequencies of vibration and for checking whether these occur in the range where soil amplification is expected. If this is the case, damages may increase in case of an earthquake due to an increased structural response of the building. Analysis of the ratio between the horizontal and vertical components of the spectra recorded at stations located inside the building as well as the ratio between the corresponding components of the spectra recorded simultaneously inside the building and at a reference station placed in the basement of the cathedral indicated several modes of vibration. Facilitated by these results an assessment of the seismic vulnerability was attempted for a 2D ground motion scenario using the finite element method.     

基于ASTER光谱特征的科技廊带岩性填图:以新疆塔什库尔干地区为例

科技廊带填图是以解决关键地质问题为目的填图方式,但部分地区海拔高差大,交通不便,给填图工作造成巨大困难。遥感岩性解译可为填图工作提供重要参考。然而,当前主流的遥感岩性解译方法仍是基于地貌纹理等间接解译标志开展的。相对而言,矿物岩石光谱特征作为最为直接和准确的遥感岩性解译标志却少有实例报道。本文基于ASTER遥感影像和岩石光谱特征分析,对部分地区海拔高差较大的新疆塔什库尔干地区进行岩性解译工作,以检验其适用性。在野外工作对研究区岩性类型进行识别和鉴定的基础上,ASTER光谱分析成果影像可较准确显示区内主要岩性类型的地表出露。其中,ASTER热红外波段比可反映区内中高级变质岩、花岗岩类及碳酸盐岩的整体分布特征;在此基础上,ASTER可见光-近红外及短波红外波段比可准确鉴定与Fe~(3+)、Fe~(2+)-硅酸盐、Al-OH、Mg-OH等成分相关的矿物组成(如绿泥石、白云母及石榴子石等),从而对地表岩性出露进行更为细致的识别和分类。研究结果表明基于ASTER光谱特征的岩性填图方法在新疆、西藏等地区有天然的实用性,既可克服区内海拔高、交通不便等困难,又可准确指示地表关键岩性类型的出露情况,可作为科技廊带填图及地质研究工作的重要手段。     

Assessing the Vibrational Frequencies of the Holweide Hospital in the City of Cologne (Germany) by Means of Ambient Seismic Noise Analysis and FE modelling

Ambient seismic noise measurements were conducted inside the Holweide Hospital (Cologne) for checking whether its frequencies of vibration fall into the range where soil amplification is expected. If this is the case, damage might increase in case of an earthquake due to an amplified structural response of the building. Two different techniques were used: the ratio between the horizontal and vertical components of the spectra recorded at stations located inside the building and the ratio between the corresponding components of the spectra recorded simultaneously inside the building and at a reference station placed outside. While the former method might be preferred because of less equipment involved, the latter has the advantage of producing more stable results and deleting automatically the influence of the sedimentary cover, which might obscure some eigenfrequencies of vibration of the building. An independently performed finite-element analysis of the hospital showed a good correlation between measured and calculated eigenmodes.     

Co-seismic displacements associated to the Molise (Southern Italy) earthquake sequence of October–November 2002 inferred from GPS measurements

The 2002 earthquake sequence of October 31 and November 1 (main shocks Mw = 5.7) struck an area of the Molise region in Southern Italy. In this paper we analyzed the co-seismic deformation related to the Molise seismic sequence, inferred from GPS data collected before and after the earthquake, that ruptured a rather deep portion of crust releasing a moderate amount of seismic energy with no surface rupture. The GPS data have been reduced using two different processing strategies and softwares (Bernese and GIPSY) to have an increased control over the result accuracy, since the expected surface displacements induced by the Molise earthquake are in the order of the GPS reliability. The surface deformations obtained from the two approaches are statistically equivalent and show a displacement field consistent with the expected deformation mechanism and with no rupture at the surface. In order to relate this observation with the seismic source, an elastic modeling of fault dislocation rupture has been performed using seismological parameters as constraints to the model input and comparing calculated surface displacements with the observed ones. The sum of the seismic moments (8.9 × 10¹⁷ Nm) of the two main events have been used as a constraint for the size and amount of slip on the model fault while its geometry has been constrained using the focal mechanisms and aftershocks locations. Since the two main shocks exhibit the same fault parameters (strike of the plane, dip and co-seismic slip), we modelled a single square fault, size of 15 km × 15 km, assumed to accommodate the whole rupture of both events of the seismic sequence. A vertical E–W trending fault (strike = 266°) has been modeled, with a horizontal slip of 120 mm. Sensitivity tests have been performed to infer the slip distribution at depth. The comparison between GPS observations and displacement vectors predicted by the dislocation model is consistent with a source fault placed between 5 and 20 km of depth with a constant pure right-lateral strike-slip in agreement with fault slip distribution analyses using seismological information. The GPS strain field obtained doesn't require a geodetic moment release larger than the one inferred from the seismological information ruling out significant post-seismic deformation or geodetic deformation released at frequencies not detectable by seismic instruments. The Molise sequence has a critical seismotectonic significance because it occurred in an area where no historical seismicity or seismogenic faults are reported. The focal location of the sequence and the strike-slip kinematics of main shocks allow to distinguish it from the shallower and extensional seismicity of the southern Apennines being more likely related to the decoupling of the southern Adriatic block from the northern one.     

Site response evolution and sediment mapping using horizontal to vertical spectral ratios (HVSR) of ground ambient noise in Jammu city,NW India

The technique of ground ambient noise (micro tremor) measurement and analysis has been successful for site characterization in many places around the world. This technique has the advantage of being a fast and easy way to estimate the effect of ground motion characteristics due to an earthquake. Single station ground ambient noise (micro tremor) measurements were carried out at 136 sites in the municipal limit of Jammu city, NW Himalaya. This extensive survey allows the estimation of fundamental resonance frequencies (0.432 to 7 Hz) of the region and identifies the areas prone to site amplification. The thickness of the soft sediments has been derived using empirical relationship that comes out to be 14 to 295 mts above the bedrock. The results are in good agreement with the 1-D profile derived using MASW measurements from representative sites. The resonance frequency and sediment thickness is in good agreement with the geological distribution of sedimentary units, indicating a progressive decrease of the fundamental resonance frequencies from the northeastern part (where the bedrock outcrops is exposed) to the southwestern and southern side where a thick sedimentary cover is estimated.     

新疆喀拉通克铜镍矿地震资料噪声分析与压制

金属矿地震勘探中原始数据的信噪比较低,多种干扰波混杂在地震记录中,严重影响了金属矿地震资料的成像质量。因此,选择有效的去噪方法是提高资料品质的关键。以新疆喀拉通克铜镍金属矿区地震资料处理为基础,在FOCUS5.4处理软件平台下采用多方法联合去噪技术压制单频波、声波、面波以及机械振动等干扰。通过模块测试和参数调试,找到适合该金属矿区的去噪方法技术。经过去噪处理,大幅提高了金属矿地震资料的信噪比。     

3-D velocity structure of the 2003 Bam earthquake area (SE Iran): Existence of a low-Poisson's ratio layer and its relation to heavy damage

To understand the generation mechanism of the Bam earthquake (Mw 6.6), we studied three-dimensional V_P, V_S and Poisson's ratio (σ) structures in the Bam area by using the seismic tomography method. We inverted accurate arrival times of 19490 P waves and 19015 S waves from 2396 aftershocks recorded by a temporal high-sensitivity seismic network. The 3-D velocity structure of the seismogenic region was well resolved to a depth of 14 km with significant velocity variations of up to 5%. The general pattern of aftershock distribution was relocated by using the 3-D structure to delineate a source fault for a length of approximately 20 km along a line 4.5 km west of the known geological Bam fault; this source fault dips steeply westward and strikes a nearly north–south line. The main shallow cluster of aftershocks south of the city of Bam is distributed just under the minor surface ruptures in the desert. The 3-D velocity structure shows a thick layer of high V_S and low σ (minimum: 0.20) at a depth range of 2–6 km. The deeper layer, with a thickness of about 2 km, appears to have a low V_S and high σ (maximum: 0.28) from 6 km depth beneath Bam to a depth of 9 km south of the city. The inferred increase of Poisson's ratio from 2 to 10 km in depth may be associated with a change from rigid and SiO₂-rich rock to more mafic rock, including the probable existence of fluids. The main seismic gap of aftershock distribution at the depth range of 2 to 7 km coincides well with the large slip zone in the shallow thick layer of high V_S and low σ. The large slip propagating mainly in the shallow rigid layer may be one of the main reasons why the Bam area suffered heavy damage.     

Analysis of soil effects and distribution of damage from the Pyrgos 1993 (Greece) earthquake

Summary On 26 March, 1993, a moderate magnitude earthquake (M _s=5.5) occurred at 3 km epicentral distance from the town of Pyrgos, in Southern Greece, causing extensive damage to masonry houses. To explain the variability of seismic intensity over the town and to propose measures against future seismic activity, a microzonation study was undertaken which combined geological, geophysical and geotechnical investigations, site specific analyses of seismic ground response and detailed recording of structural damage. The analytical predictions of ground response are correlated to soil conditions and then used to identify (micro-)zones of sites with similar seismic response. Furthermore, they are compared to quantitative estimates of damage distribution over the town. It is concluded that the peak ground acceleration, normalized against the input peak seismic acceleration, is a function of the local soil conditions as well as the seismic excitation characteristics. Hence, it cannot be defined uniquely at a site, without reference to the seismic excitation. However, the normalized peak ground velocity and the acceleration response spectra are mainly functions of the soil conditions and can be used as criteria for the practical definition of (micro-)zones. The distribution of damage in various parts of the town is at least partially attributable to local soil effects. The small epicentral distance of the earthquake, connected with the direction of the fault rupture, as well as the quality and techniques of construction, are additional factors that may have influenced the extent and distribution of damage.     

An integrated geophysical investigation of the upper crust in the epicentral area of the 1980, Ms=6.9, Irpinia earthquake (Southern Italy)

In this paper, we investigate the upper crustal structure of the Irpinia region, Southern Apennines thrust belt, Italy, through analysis and joint interpretation of gravity data, seismic reflection lines and subsurface information from many deep wells. The investigated region includes the epicentral area of the 1980 (M_s=6.9) Irpinia earthquake and is one of the Italian regions with the highest seismic hazard. The upper crustal structure is imaged by modeling a series of 15 SW-trending gravity profiles, spaced about 5 km apart, plentifully constrained by seismic reflection lines and wells, thus reducing the inherent ambiguity of the gravity modeling. Despite of the complexity of the modeled Bouguer anomalies, the application of a calibrating procedure to constrain the range of variability of the density values, as well as the use of geometric constraints, results in a good level of stability in the final density cross-sections, which in fact appear coherent both in the density values and in the geometrical features. The inferred model shows important lateral density variations that can be mostly related to NW-trending geologic structures. High-density bodies delineate carbonate platform thrust sheets and broad antiforms involving Mesozoic basinal rocks, while low-density shallow bodies are associated with Pliocene basins. In addition, important density (i.e. lithological) variations are evident along the strike of the range, the most relevant being an abrupt deepening of the Apulia Carbonate Platform in the southeastern part of the investigated region. In the epicentral region of the 1980 event, we find that the geometry of the high-density, high-velocity carbonates of the Apulia Platform appears correlated with the distribution of the aftershocks and with the P-wave velocity anomaly pattern as inferred from a previous local earthquake tomography. The structural highs of the Apulia Platform correspond to high-velocity regions, where aftershocks and coseismic slip of the mainshock are concentrated. This correlation suggests that the Apulia Carbonate Platform geometry played an important role in the rupture propagation and in the aftershock distribution.     

Chemical forms of some heavy metals in Huanghe River sediments (China) and comparison with data from Rhine River sediments (West Germany)

The chemical forms of Fe, Mn, Zn, Cu, Cr, Pb and Cd in the Huanghe River sediments have been studied by sequential extraction techniques and the comparison with data from the Rhine River sediments has been made. In the Huanghe River sediments the average contents of metals, without exception, are below their respective contents in average shales and very close to their levels in Ca-poor granites. The major portion of metals is combined with the detrital and moderately reducible phases. Both in the Huanghe River and in the Rhine River sediments the distribution ratios of metals between the moderately reducible and the easily reducible phases are generally more than unity. However, the distribution ratios of Mn, Zn and Cd are obviously lower than those of Fe, Cr, Cu and Pb. As a result of contamination, the ratios of Fe, Cr, Cu and Pb show an apparent increase, but no remarkable ratio variation is observed for Mn, Zn and Cd. Metals in the Huanghe River sediments, especially Cu and Zn, show a tendency to be associated with the organic phase. The effect of carbonate on metal association preference seems to be less important than that in the Rhine River although there is higher content of carbonate in the Huanghe River sediments. Cd has a greater percentage of the exchangeable phase, which is similar to the result from the Rhine River sediments.     

Mechanism of the 2011 Tohoku-oki earthquake (Mw 9.0) and tsunami: Insight from seismic tomography

To clarify the generating mechanism of the 2011 Tohoku-oki earthquake (Mw 9.0) and the induced tsunami, we determined high-resolution tomographic images of the Northeast Japan forearc. Significant lateral variations of seismic velocity are visible in the megathrust zone, and most large interplate thrust earthquakes are found to occur in high-velocity (high-V) areas. These high-V zones may represent high-strength asperities at the plate interface where the subducting Pacific plate and the overriding Okhotsk plate are coupled strongly. A shallow high-V zone with large coseismic slip near the Japan Trench may account for the mainshock asperity of the 2011 Tohoku-oki earthquake. Because it is an isolated asperity surrounded by low-velocity patches, most stress on it was released in a short time and the plate interface became decoupled after the Mw 9.0 earthquake. Thus the overriding Okhotsk plate there was shot out toward the Japan Trench and caused the huge tsunami.     

Seismic properties of the upper crust in the central Friuli area (northeastern Italy) based on petrophysical data

The compressional and shear wave velocities have been measured at room temperature and pressure up to 450 MPa on 5 sedimentary rock samples, representative of the most common lithologies of the upper crust in the central Friuli area (northeastern Italy). At 400 MPa confining pressure the Triassic dolomitic rock shows the highest velocities (Vp  7 km/s, Vs  3.6 km/s), the Jurassic and Triassic limestones samples intermediate velocities (Vp  6.3 /s, Vs  3.5 km/s) and the Cenozoic and Paleozoic sandstones the lowest velocities (Vp  6.15 km/s, Vs  3.35 km/s). The Paleozoic sandstone sample is characterized by the strongest anisotropy (10%) and significant birefringence (0.2 km/s) is found only on the Cenozoic sandstone sample. We elaborated the synthetic profiles of seismic velocities, density, elastic parameters and reflection coefficient, related to 4 one-dimensional geological models extended up to 22 km depth. The synthetic profiles evidence high rheological contrasts between Triassic dolomitic rocks and the soft sandstones and the Jurassic limestones. The Vp profiles obtained from laboratory measurements match very well the in-situ Vp profile measured by sonic log for the limestones and dolomitic rocks, supporting our one-dimensional modelling of the calcareous-carbonatic stratigraphic series. The Vp and Vs values of the synthetic profiles are compared with the corresponding ones obtained from the 3-D tomographic inversion of local earthquakes. The laboratory Vp are generally higher than the tomographic ones with major discrepancies for the dolomitic lithology. The comparison with the depth location of seismicity reveals that the seismic energy is mainly released in correspondence of high-contrast rheological boundaries.     

Geo-Characterization at selected accelerometric stations in Crete (Greece) and comparison of earthquake data recordings with EC8 elastic spectra

To estimate the seismic response according to Eurocode (EC8) and almost all other national codes, site conditions have to be properly characterized so that soil amplification and the corresponding peak ground motion can be calculated. In this work, different geophysical and geotechnical methods are combined in order to define the detailed ground conditions in selected sites of the Hellenic Accelerometric Network (HAN) in Crete. For this purpose, the geological information of the sites and shear wave velocity, calculated from surface wave measurements, is used. Additionally, ground acceleration data recorded through HAN have been utilized from intermediate depth earthquakes in the broader area of South Aegean Sea. Using the recorded ground motion data and the procedure defined in EC8, the corresponding elastic response spectrum is calculated for the selected sites. The resulting information is compared to the values defined in the corresponding EC8 spectrum for the seismic zone that includes the island of Crete. The comparison shows that accurate definition of ground type through geological, geotechnical and geophysical investigations is important. However, our current comparison focuses on the distribution of values rather than the absolute values of EC8-prescribed spectra, and the results should be considered in this context.     

Zircon and whole-rock Zr/Hf ratios as markers of the evolution of granitic magmas: Examples from the Teplice caldera (Czech Republic/Germany)

Mineralogy and Petrology - Hafnium contents and Zr/Hf ratios were studied in zircons and their parent rocks from three magmatic suites associated with the Teplice caldera, Eastern Erzgebirge:...     

Geological mapping of the Francistown area in northeastern Botswana by surface temperature and spectral emissivity information derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) thermal infrared data

We identified geological units in the Francistown area in northeastern Botswana by using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) thermal infrared (TIR) data, which contains both surface temperature and spectral emissivity information. A scatter plot of ASTER L1B daytime TIR digital values and L2 daytime temperature indicates that in the ASTER L1B daytime TIR data, bands 10, 11, and 12 contain spectral emissivity and temperature information, whereas surface temperature dominates the spectral emissivity information in bands 13 and 14. Visual interpretation of the ASTER TIR false color composite (FCC) images generated by assigning red, green, and blue to band 14:band 12:band 10 using L1B daytime data allowed us to identify mafic-to-ultramafic units and quartz-rich felsic units. Mafic-to-ultramafic units such as gabbro, dolerite, and dunite appear white in ASTER L1B daytime TIR FCC images due to their high spectral emissivities in the 8–9 μm region (bands 10 and 12) and high surface temperatures. Mafic-to-ultramafic units have higher surface temperatures than other geological units because they absorb more solar radiation due to their lower albedos and they have a lower thermal inertia. Quartz-rich felsic units such as granite and dry river sand appear reddish in the ASTER L1B daytime TIR FCC image because the spectral emissivity of quartz is lower in the 8–9 μm region (bands 10 and 12) than in the 10–12 μm region (band 14). Mafic-to-ultramafic and granitic units are important targets for mineral exploration because they are potential geological units to host or accompany mineralization. The proposed ASTER L1B daytime TIR FCC images can be prepared very simply and they provide valuable information for geological mapping and mineral exploration.     

Inferring protoliths of high-grade metamorphic gneisses of the Erzgebirge using zirconology,geochemistry and comparison with lower-grade rocks from Lusatia (Saxothuringia,Germany)

Protoliths of highly metamorphosed gneisses from the Erzgebirge are deduced from the morphology, age and chemistry of zircons as well as from whole rock geochemistry and are compared with lower-grade rocks of Lusatia. Gneisses with similar structural appearance and/or geochemical pattern may have quite different protoliths. The oldest rocks in the Erzgebirge are paragneisses representing meta-greywackes and meta-conglomerates. The youngest group of zircon of meta-greywackes that did not undergo Pb loss represents the youngest igneous component for source rocks (about 575 Ma). Similar ages and zircon morphology reflect the subordinate formation of new zircon grains or only zircon rims in the augengneiss from Bärenstein and Wolkenstein, which probably represent metamorphic equivalents to Lower Cambrian two-mica granodiorites from Lusatia. Bulk rock chemistry, intense fracturing and high U and Th concentrations of zircons suggest deformation-induced and fluid-enhanced recrystallisation of zircon grains. Temperatures during tectonic overprinting—too low to reset zircon ages—indicate mid- or upper crustal levels for shearing recorded in these augengneisses. Lower Cambrian (~540 Ma) granodiorites are widespread in Lusatia but are exclusively represented by the Freiberg gneiss dome in the Eastern Erzgebirge. Ordovician protolith ages were recorded by zircons from the augengneisses of the Reitzenhain–Catherine dome and the Schwarzenberg dome (Western Erzgebirge) documenting significant regional differences between the eastern and the western Erzgebirge (~540 vs. ~490 Ma). In the Western Erzgebirge, most meta-volcanic rocks (muscovite gneisses) and meta-granites (mainly red augengneisses) yield Ordovician zircon ages, whereas in the Eastern part, similar rocks mainly recorded Lower Cambrian protolith ages. Zircon overprinting was highest within discrete tectonic zones where the combination of fluid infiltration and deformation induced variable degrees of recrystallisation and formation of a new augengneiss structure. Variable degrees of Pb loss caused age shifts that do not correspond to changes in zircon morphology but may be associated with U and Th enrichments. Major changes in bulk rock composition appear to be restricted to discrete zones and to (U)HP nappes, whereas gneisses with a MP–MT metamorphic overprint basically show no geochemical modifications.     

Fault structures and their geoelectric parameters in the epicentral zone of the 27 September 2003 Chuya earthquake (Gorny Altai) from resistivity data

This paper presents an integrated measurement technique based on DC methods (vertical electrical sounding, electrical resistivity tomography) which was used to identify faults and determine their geoelectric parameters in the western part of the Chuya basin. New information on the structure of the Chagan River valley located in the zone of the disastrous 27 September 2003 Chuya earthquake has been obtained from the results of these methods. Geoelectric cross-sections of the sedimentary sequence and the upper part of the basement were obtained from VES data, showing the block structure of the study area. Electrical resistivity tomography sections confirm the presence of a major fault between basement blocks of different heights and indicate the presence of faults bounding the valley on its right side and in the southwestern part.