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1.
The paper presents the results of Croatian earthquake catalogue revision for the period 1908–1992. The revised catalogue lists a total of 4853 events (4486 after 1908), of which 3700 are mainshocks. All primary data sources available to us (seismograms, phase onset time readings, macroseismic questionnaires…) were consulted in order to improve the quality and reliability of magnitude, intensity and location. Along with the most important earthquake parameters the catalogue contains entries that enable assessment of the reliability of location and bibliographic references. Using the temporal analysis of the maximum-likelihood estimate of the b -value in the frequency-magnitude relation, the catalogue is estimated to be complete for events with M ≥ 4.0 throughout the investigated period. The magnitude completeness threshold decreases to 3.8 after the middle of the century, and to about 3.6 in the last three decades. It is noted that the b-value variation with time is closely tied to the seismic activity, as well as that at present there seems to be a lack of seismic energy release corresponding to the M = 6.0–6.5 earthquake. 相似文献
2.
Herak Marijan Herak Davorka Markušić Snježana Ivančić Ines 《Studia Geophysica et Geodaetica》2001,45(3):251-266
The rate of aftershock occurrence after the M6 Ston-Slano (Croatia) earthquake is modeled as the Epidemic Type Aftershock Sequence (ETAS). Increase of the modeled cumulative number of aftershocks with time was fitted to observations by the least-squares criterion using the combined grid-search and Monte-Carlo approach. This enabled not only the estimation of the most probable ETAS parameters, but also the determination of their confidence limits, as well as the estimation of the bias between them. It has been found that the bias is significant for some of the parameter pairs, regardless of the threshold magnitude assumed. Residual analyses revealed that all strong aftershocks (M
L
4.5) occurred during the periods of normal to high aftershock activity. There were two periods of quiescence in the sequence, both of which were followed by a strong aftershock. 相似文献
3.
Based on a large set of arrival times of the Pg phase reported by local and regional stations, we estimate azimuthal anisotropy of the Pg-wave velocity in focal volumes of the upper crust in NW Croatia. The method is based on analyses of the azimuthal dependence
of ratios of cumulative differences of arrival times and travel paths between foci of earthquake pairs, computed for rays
propagating within narrow azimuthal windows. The results clearly indicate the presence of anisotropy of 3.3% with the direction
of fast velocity (approximately NNE-SSW) coinciding with the direction of the maximum tectonic pressure as revealed by 23
available focal mechanisms and previous geological investigations. Although a large part of observed anisotropy can be explained
assuming that focal volumes are pervaded by a system of vertical extensive-dilatancy anisotropy (EDA) cracks aligned under
the influence of local tectonic stress field, there is indication that — to a smaller extent — some role was also played by
alignment of structural features in the region. 相似文献
4.
Ivo Allegretti Davorka Herak Marijan Herak Seweryn J. Duda 《Studia Geophysica et Geodaetica》2000,44(1):13-25
The magnitudes (M
S
, m
bP
, m
bS
) of the largest historical earthquakes which occurred in the first half of the 20
th
century, calculated on the basis of records of Wiechert horizontal seismographs in Göttingen (Germany) and Zagreb (Croatia), are compared with one another, as well as with the magnitudes reported in worldwide catalogues. Systematic trends are observed in the data regarding the temporal stability of magnitude estimations in Göttingen, as well as the apparent non-linearity of the instrument responsle in the case of the Wiechert seismograph in Zagreb. We were unable to clearly identify their causes – possible explanations include effects caused by the interaction of the seismometer's frame and mass, as well as local soil conditions, but nonhomogeneity of the reference catalogues cannot be ruled out. The results indicate that a careful re-examination and cross-checking of the reported magnitude figures for the earthquakes from the first half of the 20th century is required. 相似文献
5.
Davorka Herak Marijan Herak Eduard Prelogovi&#x; Snjeana Marku&#x;i&#x;
eljko Markulin 《Tectonophysics》2005,398(3-4):167-180
We present analyses of one of the strongest earthquake sequences ever recorded within the Adriatic microplate, which occurred near the Jabuka island in the very centre of the Adriatic Sea. The mainshock (29 March 2003, 17:42, ML=5.5) was preceded by over 150 foreshocks, and followed by many aftershocks, over 4600 of which were recorded on the closest station HVAR (about 90 km to the east). As the epicentre was in the open sea and due to the absence of nearby stations, we were able to confidently locate only 597 events. Hypocentral locations were computed by a grid-search algorithm after seven iterations of refining hypocentres and adjusting station corrections. Epicentres lie in a well-defined area of about 300 km2, just to the W and NW of the Jabuka island. The vertical cross-sections reveal that hypocentres dip to the NE, closely matching faults from the Jabuka-Andrija fault system, as identified on the available reflection profiles in the area. The fault-plane solution of the main shock based on the first-motion polarity readings agrees well with the CMT solutions and indicates faulting caused by a S–N directed tectonic pressure, on a reverse, dip-slip fault. This is in very good agreement with the seismotectonic framework of the area. These earthquakes are important as they identify the Jabuka-Andrija fault system as an active one, which can significantly influence seismic hazard on the islands in the central Adriatic archipelago and on the Croatian coast between Zadar and Split. Along with several other sequences which occurred in the last two decades, they force us to change our notion of Adria as nearly aseismic, compact and rigid block. In fact, it turns out that recent seismicity of the Central Adriatic Sea is comparable to the seismicity of several well known earthquake-prone areas in the circum-Adriatic region. 相似文献
6.
The attenuation of coda waves is analysed for nine seismic stations in the area of convergent motion of the Adriatic microplate
and the Dinarides. The frequency dependent coda quality factor of the form Qc = Q0 fn is estimated for up to seven central frequencies (1.5, 3, 6, 9, 12, 18 and 24 Hz) and for 21 successive 30 s long time windows.
Q0 was found to increase from 68–353 for short lapse times of 20–50 s, to 158–373 for lapse times of 90–100 s. Parameter n is
observed to vary between 0.46 and 0.89, with a pronounced tendency to decrease with increasing Q0, and vice versa. Both Q0 and n seem to stabilize for lapse times larger than 50–80 s, indicating that a change in rock properties controlling coda
attenuation occurs at depths of about 100–160 km. The spatial distribution of observed Q0 is well correlated with observed seismicity and inferred tectonic activity. In particular, we observe significant negative
correlation of Q0 with the peak ground acceleration (PGA) estimate for the return period of 475 years. The degree of frequency dependence n,
is the smallest for stations on the islands, where the crust is the thinnest. The largest n is observed over the thickest
crust in the region, where the Moho lies at depths of over 55 km. 相似文献
7.
Marijan Herak Ivo Allegretti Davorka Herak Krešimir Kuk Vlado Kuk Krešimir Marić Snježana Markušić Josip Stipčević 《Bulletin of Earthquake Engineering》2010,8(3):483-499
Horizontal-to-vertical spectral ratios (HVSR) of ambient vibrations measured in the ancient town of Ston (Croatia) on 99 locations, are shown to be well matched to the theoretical ones computed for body-waves as well as for the surface waves. This match is poorer for sites on the slopes of nearby hills. The ratios of measured peak horizontal ground acceleration during the damaging earthquake in 1996 (M L = 6.0) and the ones obtained using empirical attenuation laws is approximately equal to the mapped value of the dynamic amplification factor determined on the basis of observed HVSR in the vicinity of the accelerometric station. The HVSR of the accelerogram is very similar to the HVSR of the ambient noise. The damage to the building stock in the old town centre caused by the earthquake series of 1996 is closely related to the estimated soil amplification and its fundamental frequency. More measurements in buildings are needed to arrive at confident conclusions about possible soil-structure resonance. 相似文献
8.
编者按:克罗地亚地球物理学家莫霍洛维奇在研究1909年10月8日克罗地亚地震的地震波走时特征时,首次发现了该地区的地壳与地幔的分界面,后被命名"莫霍界面",简称Moho界面.1927年,莫霍洛维奇又在地震记录中识别出了s*震相,证实了在地壳内部还会存在另一个康拉德(Conrad)间断面.地震层析成像是研究地球内部结构的重要方法之一.为纪念莫霍洛维奇诞生150周年,莫霍界面发现100周年,特发此文,以兹纪念. 相似文献
9.
Continuous broad-band measurements of vibrations on the 3rd floor of the building of the Department of Geophysics, Faculty
of Sciences and Mathematics (DGFSM) in Zagreb provided high quality data that enabled monitoring of fluctuations of the building’s
basic dynamic parameters (fundamental frequencies and the corresponding damping). It was found that nonlinear behaviour is
present even for the small strains induced by ambient vibrations, which was manifested in measurable reduction of fundamental
frequency and increase of damping for larger excitation levels. Notable correspondence of the long-term wander of the fundamental
frequency with the relative air humidity and the annual precipitation cycle indicate that variation of soil saturation may
have caused variability in the soil-structure interaction. The damping was found to vary synchronously with the air temperature.
The results point to the importance of considering all aspects of nonlinearity of building response even for small strains. 相似文献
10.