Comparison of damage data from questionnaires and field survey: the case of the June 20, 1978 Thessaloniki (northern Greece) M6.5 earthquake

The earthquake of June 20, 1978 (M6.5) near Thessaloniki, Greece, and the abundant information on damage distribution provided researchers with an opportunity for a more detailed study of earthquake effects. The damage on buildings caused by that earthquake was recorded in several ways. In this paper two of them will be presented and discussed: First, the use of questionnaires filled in by citizens and second, the in situ inspection of the buildings by a team of expert engineers, enriched by data of retrofitting costs, where available. In the current study, the damage data derived from the questionnaires are compared against the ones given by the engineers after they have been both converted to the European Macroseismic Scale 1998 (EMS-98) Damage Grades. It is observed that for EMS-98 damage grades equal and larger than 2 the questionnaire method overestimates damage while for lower grades both approaches provide comparable results.     

Retrospective Prediction of Macroseismic Intensities Using Strong Ground Motion Simulation: The Case of the 1978 Thessaloniki (Greece) Earthquake (M6.5)

The densely populated city of Thessaloniki (Northern Greece) is situated in~the vicinity of active seismic faults, capable of producing moderate to strong earthquakes. The city has been severely affected by such events several times during the last 15 centuries. The most recent event occurred on 20 June 1978 (M6.5) in the Mygdonian graben, with an epicentral distance of about 30 km, causing extended damage in the city, with macroseismic intensities between MSK V+ and VIII+. The majority of buildings affected by the earthquake were of reinforced-concrete typology, typical to many southern European metropolitan areas. The source properties of the normal-faulting causative event and the source-to-city propagation path are well known from previous studies. The soil structure under the metropolitan area of Thessaloniki is assigned NEHRP categories B, C, D on the basis of geotechnical and geologic information and single-station ambient-noise measurements. A finite source model and various rupture scenarios of the June 1978 earthquake are used to perform forward stochastic modeling of strong ground motion in terms of peak ground and spectral acceleration. Rock motion is assessed under the city and it is transferred to the surface in accordance with the respective soil category. A GIS tool is employed to compare the estimated strong-motion parameters with the observed detailed damage pattern induced by the 1978 earthquake. For selected natural periods, a satisfactory correlation is established between macroseismic intensity and peak ground and spectral acceleration, thus encouraging the application of stochastic modeling for generating realistic ground-shaking scenarios in metropolitan areas.     

A geophysical study of the granites and the sedimentary basins of the Xanthi area (N. Greece)

Intrusive features of varying size can be interpreted from the aeromagnetic map of the Xanthi area in N. Greece.The Xanthi pluton, which outcrops north of the city of Xanthi, seems to have the shape of a truncated pyramid. This feature has relatively large areal extent and reaches an approximate depth of 7 km. Another, relatively large magnetic body is buried under the sediments at the estuary of the Nestos River.3-D models of several smaller intrusions were constructed and the produced effect was compared to the observed. Some of these intrusions seem to be detached branches of the large Xanthi pluton.The basement in the outer part of the basin of the Nestos River seems to be buried at about 4 km depth. This figure is obtained by the Multiple Source Werner Deconvolution estimates and it is in agreement with the results of former geophysical studies and deep industrial boreholes.A 3-D model of the Xanthi-Komotini basin suggests that this basin is about 0.4 km deep at its southern part. The depth at its northern boundary is about 1.8 km while the boundary itself is formed by the large Kavala-Xanthi-Komotini fault.The Tertiary basin of the Nestos River and the observed magmatism are consistent with the idea of an older extensional tectonic regime in the area.     

Attenuation of P and pP waves in Vrancea area – Romania

The seismic attenuation in the Vrancea region (Romania) is investigated from teleseismic recordings of P and pP waves during the four major, intermediate-depth Romanian events that occurred since the onset of digital instrumentation. Most stations are located in Canada and in the United States, being equipped with a variety of sensors, especially short-period ones. The amplitude spectral ratio method is used, assuming no frequency dependence of the Q _P factor in the range 0.2–2 Hz. No apparent correlation between the derived attenuation value and the type of recording sensor is observed. Lateral variations of the attenuation are obtained, with a very low Q _P area (values down to 33) located in the northwestern part of the Vrancea seismogenic volume. For the stations with different azimuth angles in relation to the epicentral area, Q _P values routinely exceed 200. Most likely, the low attenuation values are related to an upwelling mantle material located immediately beneath the crust, but limited in depth to at least 100 km.     

A Geophysical Study Of The Ophiolite Complex And The Sedimentary Basins In The Northwest Part Of The Chalkidiki Peninsula (N. Greece)

The present work focuses on the study of the main ophiolite complex ofNorthern Greece, which is one of the dominant geological features in thebroader Aegean area, by the use of geophysical (gravity and magnetic)data. This ophiolite complex, which trends in a NW-SE direction, startsat the eastern part of the borders of Greece with F.Y.R.O.M. and continuesup to the southern part of the Chalkidiki Peninsula. The ophiolites mainlyconsist of dense, high-susceptibility peridotitic and gabbroic rocks. As aresult, the southwestern part of the ophiolitic complex, which crosses thenorthwestern part of the Chalkidiki-Peninsula, gives rise to both highamplitude aeromagnetic and Bouguer anomaly values. On the other hand,the Axios-Thermaikos basin, which is situated at the western border of theophiolitic complex, exhibits a deep sedimentary cover that results in lowBouguer anomaly values. The corresponding Bouguer anomaly decreasesto the southwest, indicating an increase of the sedimentary layer thicknessin that direction.2.5-D inversion was applied to both the aeromagnetic and the Bouguergravity data along several profiles. All the profiles were oriented normalto the main trend of the ophiolitic complex. Information from two deepboreholes, as well as the surface occurrence of the ophiolites was used asconstrains to the inversion scheme. The produced model shows an averagesedimentary thickness of 2.5 km along the coastline. From the joint inversionof the Bouguer and aeromagnetic anomaly data the existence of two ophioliticstripes is revealed. The first ``external' one is located in the southwest part, while the other ``internal' one to the northeast part of the belt. In the internal one, the depth extent of the ophiolites was estimated to range between 1 to 4 km. Moreover, the ophiolites were found to dip towards the northeast, but their dip varies from 20–45° in the northern part to 10–15° in the southern part of the stripe. For the ``external' stripe the extent of the ophiolitic bodies varies from northwest to southeast, reaching its highest depth of 5 km to the south. This stripe is also dipping towards the northeast with a dip of 10–15°.     

Am improved source mechanism for the 1935 Timiskaming,Quebec earthquake from regional waveforms

The Timiskaming earthquake, which occurred near the Quebec-Ontario border at the northwest end of the Western Quebec seismic zone in 1935, is one of the five largest instrumentally recorded southeastern Canadian earthquakes. Previous studies of this earthquake concentrated on modeling teismograms recorded at regional distances, a better constrained focal mechanism is obtained. The waveforms indicate thrust faulting on a moderately dipping northwest striking plane at a depth of 10 km. TheM _w of 6.1 determined in this study is in good agreement with previous magnitude estimates (m _b 6.1,M _s 6.0, andm _bLg 6.2–6.3). The focal mechanism is similar to those of many recent small to moderate earthquakes in the region, and the inferred (from theP axis) acting stress of northeast compression is consistent with the overall eastern North American stress field. The Lake Timiskaming Rift Valley in which the earthquake occurred, comprises several northwest striking faults consistent with the strike of the 1935 event. Thus, the 1935 earthquake appears to be a result of faulting on the reactivated Timiskaming graben.     

Reconstruction of summer temperature (June—August) at Mt. Helan, China, from tree-ring stable carbon isotope values since AD 1890

From stable carbon isotope analysis of tree-rings of Chinese pine (Pinus tabulaeformis) from Mt. Helan, China, we found that high-δ¹³C values were related to high mean temperatures from June to August (T ₆₈), and Iow-δ¹³C values corresponded to low T ₆₈. From these data, a transfer function has been used to reconstruct summer temperatures (T ₆₈) for the Mt. Helan region. The explained variance of reconstruction is 34.9% (F=15.01, p<0.001). The time period containing the highest summer temperatures in northern China (late 1920-1930s) was confirmed by our reconstruction. The data indicate that there is a tele-connection between summer temperatures in Mt. Helan area and sea-surface-temperatures in the tropical Pacific. The extreme low temperature periods around the years of 1920 and 1947 for Mt. Helan region correspond well to the cold climate in the tropical Pacific. Along with other analyses, this suggests that climate variations in the Mt. Helan region are driven not only by local events, but also by the global climate. Significant periodicities appearing in the reconstruction are 2.56 and 2.63 years.     

Biometric analysis of lacustrine and riverine populations of Palemonetes antennarius (H. Milne-Edwards, 1837) (Crustacea, Decapoda, Palaemonidae) from north-western Greece

Comparative study of morphometric measurements was undertaken on populations of Palaemonetes antennarius from two freshwater habitat zones (lacustrine pelagic and lacustrine littoral) and from the fluvial littoral habitat zone of three estuaries of north-western Greece. Multivariate statistical analyses (principal component analysis and discriminant function analysis) revealed clear morphometric differences between sexes and sampling sites. The observed differences are expressed mainly thought the measurements related to the body heights (carapace height and second pleon height), as a result of sexual dimorphism, High values for the female body heights seem to be correlated to specific fecundity profile and reproductive strategy. On the other hand, morphometrical variables related mainly to body lengths, such as rostral, telson and pleon lengths, were observed to be correlated to the study sites. Characters related to the summing capacity (telson length, telson width and pleon lengths) were generally found to have higher values in the specimens from habitats with high reophilic profile.     

Harmonization check of M w within the central, northern, and northwestern European earthquake catalogue (CENEC)

Large data sets covering large areas and time spans and composed of many different independent sources raise the question of the obtained degree of harmonization. The present study is an analysis of the harmonization with respect to the moment magnitude M _w within the earthquake catalogue for central, northern, and northwestern Europe (CENEC). The CENEC earthquake catalogue (Grünthal et al., J Seismol, 2009) contains parameters for over 8,000 events in the time period 1000–2004 with magnitude M _w ≥ 3.5. Only about 2% of the data used for CENEC have original M _w magnitudes derived directly from digital data. Some of the local catalogues and data files providing data give M _w, but calculated by the respective agency from other magnitude measures or intensity. About 60% of the local data give strength measures other than M _w, and these have to be transformed by us using available formulae or new regressions based on original M _w data. Although all events are thus unified to M _w magnitude, inhomogeneity in the M _w obtained from over 40 local catalogues and data files and 50 special studies is inevitable. Two different approaches have been followed to investigate the compatibility of the different M _w sets throughout CENEC. The first harmonization check is performed using M _w from moment tensor solutions from SMTS and Pondrelli et al. (Phys Earth Planet Inter 130:71–101, 2002; Phys Earth Planet Inter 164:90–112, 2007). The method to derive the SMTS is described, e.g., by Braunmiller et al. (Tectonophysics 356:5–22, 2002) and Bernardi et al. (Geophys J Int 157:703–716, 2004), and the data are available in greater extent since 1997. One check is made against the M _w given in national catalogues and another against the M _w derived by applying different empirical relations developed for CENEC. The second harmonization check concerns the vast majority of data in CENEC related to earthquakes prior to 1997 or where no moment tensor based M _w exists. In this case, an empirical relation for the M _w dependence on epicentral intensity (I ₀) and focal depth (h) was derived for 41 master events, i.e., earthquakes, located all over central Europe, with high-quality data. To include also the data lacking h, the corresponding depth-independent relation for these 41 events was also derived. These equations are compared with the different sets of data from which CENEC has been composed, and the goodness of fit is demonstrated for each set. The vast majority of the events are very well or reasonably consistent with the respective relation so that the data can be said to be harmonized with respect to M _w, but there are exceptions, which are discussed in detail.     

Variation of Q value before and after the 1999 Xiuyan, Liaoning Province, M =5.4 earthquake on the basis of analysis on attenuation dispersion of P waves

A method for determining medium quality factor is developed on the basis of analyzing the attenuation dispersion of the arrived first period P wave. In order to enhance signal to noise ratio, improve the resolution in measurement and reduce systematic error we applied the data resampling technique. The group velocity delay of P wave was derived by using an improved multi-filtering method. Based on a linear viscoelastic relaxation model we deduced the medium quality factor Q _m, and associated error with 95% confidence level. Applying the method to the seismic record of the Xiuyan M=5.4 earthquake sequences we obtained the following result: (1) High Q _m started to appear from Nov. 9, 1999. The events giving the deduced high Q _m value clustered in a region with their epicenter distances being between 32 and 46 km to the Yingkou station. This Q _m versus distance observation obviously deviates from the normal trend of Q _m linearly increasing with distance. (2) The average Q _m before the 29 Dec. 1999 M=5.4 earthquake is 460, while the average Q _m between the M=5.4 event and the 12 Jan. 2000 M=5.1 earthquake is 391, and the average Q _m after the M=5.1 event is 204. Foundation item: State Key Project of Science and Technology during the Tenth Five-year Plan (2004BA601B01-03-01).     

Source time functions of the 1999, Jiji (Chi-Chi) earthquake from GDSN long period waveform data using aftershocks as empirical Green''''s functions

IntroductionA large earthquake occurred in Jiji (Chi-Chi) town of Nantou County, Taiwan, China at 17h47min on September 20, 1999 (UTC). The origin time was determined to be 17h47min19s of September 20 UTC (1h47min19s of September 21, Beijing Time). The epicenter was determined to be longitude 120.80°E and latitude 23.86°N. It was reported that 2 333 people were killed, 10 002 people were injured, and thousands of houses collapsed which made more than 100 000 people homeless (Shin, e…     

苏北溱湖芦苇和芦苇+香蒲群落中植物对湿地土壤N、P的固持效果

湿地土壤是湿地生态系统固持氮(N)、磷(P)的重要库,水生高等植物在湿地土壤固持N、P过程中起到了非常重要的作用.本研究采用室外取样与室内实验结合的方法,对溱湖湿地两种主要湿地类型(芦苇(Phragmites australis)群落和芦苇+香蒲(Typha latifolia)群落)影响湿地土壤N、P固持过程的规律展开研究.分析了芦苇、香蒲各器官生物量和总氮(TN)、总磷(TP)含量及储量对于土壤各土层TN和TP含量的影响.结果显示:(1)溱湖湿地对于水体TN和TP有一定的削减作用,且对TN的削减作用更大;(2)芦苇可以增强湿地土壤(30 cm以下的土层)富集N的效率,并且芦苇+香蒲群落中土壤固N效率更高,芦苇植株内TN和TP储量都是根茎叶穗,而香蒲则是根穗茎叶;(3)芦苇和香蒲茎、叶器官的TN和TP含量在夏季均显著高于其他几个季节,尤其是芦苇茎的TN含量在夏季高出其他几个季节70%~84%,而TP含量甚至高出其他几个季节81%~92%;(4)芦苇、香蒲对于P贫瘠的响应机制不同,导致芦苇会消耗土壤P,而香蒲的介入可以抵消这一消耗过程.因此,芦苇+香蒲的植物配置模式可以提高湿地土壤固持N、P的综合效率.     

The December 26, 2004, off the west coast of northern Sumatra, Indonesia, M W=9.0, earthquake and the critical-point-like model of earthquake preparation

Long-term seismic activity prior to the December 26, 2004, off the west coast of northern Sumatra, Indonesia, M _W=9.0 earthquake was investigated using the Harvard CMT catalogue. It is observed that before this great earthquake, there exists an accelerating moment release (AMR) process with the temporal scale of a quarter century and the spatial scale of 1 500 km. Within this spatial range, the M _W=9.0 event falls into the piece-wise power-law-like frequency-magnitude distribution. Therefore, in the perspective of the critical-point-like model of earthquake preparation, the failure to forecast/predict the approaching and/or the size of this earthquake is not due to the physically intrinsic unpredictability of earthquakes. Foundation item: Ministry of Science and Technology Project (2004CB418406). Contribution No. 05FE3010, Institute of Geophysics, China Earthquake Administration.     

Seasonal variation of space–time parameters of internal gravity waves at Kharkiv (49°30′N, 36°51′E)

Internal gravity waves (IGWs) over Kharkiv (49°30′N, 36°51′E) have been studied by using an automatic goniometer of a meteor radar (AG MR), with its antenna directed to the East. The AG MR carries out Doppler measurements of the radial drift velocity and the position of the reflecting area of meteor trails. In order to obtain information about IGW parameters, an algorithm was used that processes the AG MR wind data by dividing the measured volume into several sub-volumes, and by carrying out wavelet analysis of wind variations in these areas. Results of 1 year (1987) of AG MR data show a good qualitative correspondence with literature results. There is an increase of IGW activity during the change of the zonal background wind in spring and autumn. It was found that the mean IGW horizontal phase velocity and predominating horizontal propagation direction change with season. However, the mean period (1.5 h), the dominant amplitude (30 m/s) and the vertical phase velocity do not strongly vary in the course of the year. The mean vertical and horizontal wavelengths were found to be 40 and 250 km, respectively.     

Life history and temporal distribution of Orchestia sp. cf. cavimana (Amphipoda, Talitridae) on a lake shore in central Italy

The life history of the amphipod Orchestia sp. cf. cavimana (Heller, 1865) was studied throughout the course of a year with monthly samplings and the use of pitfall traps along the shores of Lake Albano in central Italy. The data thus obtained showed two peaks in abundance (the first in June and the second in October) and a minimum capture frequency in February. Egg-bearing females were recorded in spring and late summer, whilst recruitment occurred from spring to autumn, with maximum in June and October. The data collected also indicated the presence of a positive correlation between the abundance of talitrids and both temperature and sediment moisture. Morphological analysis enabled the identification of four different cohorts (with a lifespan of the species of approximately 12–15 months) all four of which remained distinguishable throughout the course of the year. It, moreover, enabled sex determination in individuals of 5 or more millimetres. The subsequent distribution indicated that, when significant, the sex ratio was female biased and that maximum size was greater in males. In particular, maximum sizes were recorded in spring for both males and females and were of 17.5 and 13.0 mm, respectively. Furthermore, the total body length recorded for egg-bearing females was positively correlated with the number of eggs in their brood pouch.     

Source time functions of the 1999, Jiji (Chi-Chi) earthquake from GDSN long period waveform data using aftershocks as empirical Green’s functions

A large earthquake (M _W=7.6) occurred in Jiji (Chi-Chi), Taiwan, China on September 20, 1999, and was followed by many moderate-size shocks in the following days. Two of the largest aftershocks with the magnitudes of M _W=6.1 and M _W=6.2, respectively, were used as empirical Green’s functions (EGFs) to obtain the source time functions (STFs) of the main shock from long-period waveform data of the Global Digital Seismograph Network (GDSN) including IRIS, GEOSCOPE and CDSN. For the M _W=6.1 aftershock of September 22, there were 97 pairs of phases clear enough from 78 recordings of 26 stations; for the M _W=6.2 aftershock of September 25, there were 81 pairs of phases clear enough from 72 recordings of 24 stations. For each station, 2 types of STFs were retrieved, which are called P-STF and S-STF due to being from P and S phases, respectively. Totally, 178 STF individuals were obtained for source-process analysis of the main shock. It was noticed that, in general, STFs from most of the stations had similarities except that those in special azimuths looked different or odd due to the mechanism difference between the main shock and the aftershocks; and in detail, the shapes of the STFs varied with azimuth. Both of them reflected the stability and reliability of the retrieved STFs. The comprehensive analysis of those STFs suggested that this event consisted of two sub-events, the total duration time was about 26 s, and on the average, the second event was about 7 s later than the first one, and the moment-rate amplitude of the first event was about 15% larger than that of the second one. Foundation item: State Natural Science Foundation of China (49904004) and IPGP of France. Contribution No. 02FE2007, Institute of Geophysics, China Seismological Bureau.     

Source process of the 1990 Gonghe,China, earthquake and tectonic stress field in the northeastern Qinghai-Xizang (Tibetan) plateau

TheM _s =6.9 Gonghe, China, earthquake of April 26, 1990 is the largest earthquake to have been documented historically as well as recorded instrumentally in the northeastern Qinghai-Xizang (Tibetan) plateau. The source process of this earthquake and the tectonic stress field in the northeastern Qinghai-Xizang plateau are investigated using geodetic and seismic data. The leveling data are used to invert the focal mechanism, the shape of the slipped region and the slip distribution on the fault plane. It is obtained through inversion of the leveling data that this earthquake was caused by a mainly reverse dip-slipping buried fault with strike 102°, dip 46° to SSW, rake 86° and a seismic moment of 9,4×10¹⁸ Nm. The stress drop, strain and energy released for this earthquake are estimated to be 4.9 MPa, 7.4×10^–5 and 7.0×10¹⁴ J, respectively. The slip distributes in a region slightly deep from NWW to SEE, with two nuclei, i.e., knots with highly concentrated slip, located in a shallower depth in the NWW and a deeper depth in the SEE, respectively.Broadband body waves data recorded by the China Digital Seismograph Network (CDSN) for the Gonghe earthquake are used to retrieve the source process of the earthquakes. It is found through moment-tensor inversion that theM _s =6.9 main shock is a complex rupture process dominated by shear faulting with scalar seismic moment of the best double-couple of 9.4×10¹⁸ Nm, which is identical to the seismic moment determined from leveling data. The moment rate tensor functions reveal that this earthquake consists of three consecutive events. The first event, with a scalar seismic moment of 4.7×10¹⁸ Nm, occurred between 0–12 s, and has a focal mechanism similar to that inverted from leveling data. The second event, with a smaller seismic moment of 2.1×10¹⁸ Nm, occurred between 12–31 s, and has a variable focal mechanism. The third event, with a sealar seismic moment of 2.5×10¹⁸ Nm, occurred between 31–41 s, and has a focal mechanism similar to that inverted from leveling data. The strike of the 1990 Gonghe earthquake, and the significantly reverse dip-slip with minor left-lateral strike-slip motion suggest that the pressure axis of the tectonic stress field in the northeastern Qinghai-Xizang plateau is close to horizontal and oriented NNE to SSW, consistent with the relative collision motion between the Indian and Eurasian plates. The predominant thrust mechanism and the complexity in the tempo-spatial rupture process of the Gonghe earthquake, as revealed by the geodetic and seismic data, is generally consistent with the overall distribution of isoseismals, aftershock seismicity and the geometry of intersecting faults structure in the Gonghe basin of the northeastern Qinghai-Xizang plateau.Contribution No. 96 B0006 Institute of Geophysics, State Seismological Bureau, Beijing, China.     

Reconstruction of summer temperature (June-August) at Mt. Helan, China, from tree-ring stable carbon isotope values since AD 1890

From stable carbon isotope analysis of tree-rings of Chinese pine (Pinus tabulaeformis) from Mt. Helan, China, we found that high-δ13C values were related to high mean temperatures from June to August (T68), and low-δ 13C values corresponded to low T68. From these data, a transfer function has been used to reconstruct summer temperatures (T68) for the Mt. Helan region. The explained variance of reconstruction is 34.9% (F=15.01, p<0.001). The time period containing the highest summer temperatures in northern China (late 1920-1930s) was confirmed by our reconstruction. The data indicate that there is a tele-connection between summer temperatures in Mt. Helan area and sea-surface-temperatures in the tropical Pacific. The extreme low temperature periods around the years of 1920 and 1947 for Mt. Helan region correspond well to the cold climate in the tropical Pacific. Along with other analyses, this suggests that climate variations in the Mt. Helan region are driven not only by local events, but also by the global climate. Significant periodicities appearing in the reconstruction are 2.56 and 2.63 years.