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1.
Fractal analysis of faults network, tremor foci spatial distribution as well as the Gutenberg-Richter relationship could further explain whether the biggest seismic events are connected with recent tectonic activity. Fractality of fault systems geometry, as a first step of the analysis, was tested fro a part of the USCB embodying the main structural units. The cluster analysis and the box counting methods were employed.The calculated fractal dimension of fault network was 1.98 for the whole area yet for considered structural units it was close to 1.6. The results point to similarity of studied fault pattern to river network. Faults within selected tectonic units make separate sets which have a distinct geometry and origin. The value of 1.6 is an upper limit to the fracture geometry of rocks that can be explained on the basis of Griffith energy balance concept. 相似文献
2.
A series of stress relaxation experiments have been carried out on faulted and intact Tennessee sandstone to explore the influence of pore water on strength at different strain rates. Temperatures employed were 20, 300 and 400°C, effective confining pressure was 1.5 kb and strain rates as low as 10–10 sec–1 were achieved. Most samples were prefaulted at 2.5 kb confining pressure and room temperature. This is thought to have secured a reproducible initial microstructure.The strength of the dry rock was almost totally insensitive to strain rate in the range 10–4 to 10–10 sec–1. In contrast, the strength of the wet rock decreased rapidly with strain rate at rates less than 10–6 sec–1. Brittle fracture of the quartz grains which constitute this rock is the most characteristic mode of failure under the test conditions used.The experimental data are discussed in terms of the possible deformation rate controlling processes, and it is suggested that in the wet experiments at intermediate to high strain rates (10–7 to 10–4 sec–1) the observed deformation rate is controlled by the kinetics of water assisted stress corrosion, whilst deformation at low strain rates (ca. 10–9 sec–1) is controlled by a pressure solution process.The results have implications for the rheology of fault rocks at depths of perhaps 10 to 15 km in sialic crust. 相似文献
3.
In this paper we show evidences of the fractal nature of the 3-D inhomogeneities in the lithosphere from the study of seismic wave scattering and discuss the relation between the fractal dimension of the 3-D inhomogeneities and that of the fault surfaces. Two methods are introduced to measure the inhomogeneity spectrum of a random medium: 1. the coda excitation spectrum method, and 2. the method of measuring the frequency dependence of scattering attenuation. The fractal dimension can be obtained from the inhomogeneity spectrum of the medium. The coda excitation method is applied to the Hindu-Kush data. Based on the observed coda excitation spectra (for frequencies 1–25 Hz) and the past observations on the frequency dependence of scattering attenuation, we infer that the lithospheric inhomogeneities are multiple scaled and can be modeled as a bandlimited fractal random medium (BLFRM) with an outer scale of about 1 km. The fractal dimension of the 3-D inhomogeneities isD
3=31/2–32/3, which corresponds to a scaling exponent (Hurst number)H=1/2–1/3. The corresponding 1-D inhomogeneity spectra obey the power law with a powerp=2H+1=2–5/3. The intersection between the earth surface and the isostrength surface of the 3-D inhomogeneities will have fractal dimensionD
1=1.5–1.67. If we consider the earthquake fault surface as developed from the isosurface of the 3-D inhomogeneities and smoothed by the rupture dynamics, the fractal dimension of the fault trace on the surface must be smaller thanD
1, in agreement with recent measurements of fractal dimension along the San Andreas fault. 相似文献
4.
Regional and local characteristics of active fault patterns and elevation variation throughout Honshu, Japan are characterized in terms of their fractal dimensions; this allows variation in these complex variables to be compared directly to the scalar properties of net Quaternary vertical displacement, elevation and 10- and 110-year horizontal strains. The comparisons reveal that, throughout Honshu as a whole, there is significant correlation (r=0.75) between Quaternary vertical displacement, elevation, and its fractal properties. There is poor correlation, however, of elevation and its fractal properties to horizontal crustal strain, and also between Quaternary vertical displacement and horizontal crustal strain. A slight negative correlation is observed between the fractal properties of the active fault system and horizontal crustal strain measured over 10- and 110-year time periods (–0.43 and –0.26, respectively). The correlation between the 10-year (1985–1994) and 110-year (1883–1994) area strains, 0.48, reveals the occurrence of considerable change in the distribution of regional strain over these short time frames. Local computations of the correlation between data sets made for overlapping 160 km length windows of data spaced every 20 km along analysis lines reveal internal fluctuations in the correlation between variables. The local correlation between Quaternary vertical displacement and elevation is highest through central Japan and the Kinki Triangle. There is weak negative correlation between area strain and fractal dimensions of the active fault network. The local correlation between the fractal dimensions of active faults and horizontal area strain over the recent 10-year time period averages about –0.6 through central Japan in an area that extends across the Kinki Triangle through the northern part of central Honshu and northeast across the Itoigawa Shizuoka Tectonic Line. In general, regions of greatest complexity in the active fault network are associated with persistent negative area or compressional strain. Sparsely faulted areas in general coincide with areas of positive or roughly zero area strain. The presence of negative correlation through central Japan and the Kinki Triangle area in the recent 10-year period results from a decrease of area strain within an increasingly complex active fault system that reaches maximum negative values concentrated in the Kinki Triangle during the 1985–1994 time period. 相似文献
5.
Normal faults within the Ptolemais coal field and large seismogenic faults in the northwestern Aegean remain fractal for displacement values larger than about 1m. The kinematic parameters on reverse drag profiles such as length of rollover, footwall uplift and wavelength of footwall uplift show that all three parameters have a power law relationship, expressed by a c exponent of about 1, with the maximum displacement which take place across the fault. Footwall uplift/hanging wall subsidence ratio is about 1/2.The displacement analysis help us to propose a growth model for larger seismogenic faults in the NW Aegean, as is the ‘Hepiros fault set’ and the ‘Aliakmon fault zone’. Faults within the ‘Aliakmon fault zone’ were independently developed, at the first stages of deformation, by tip line deformation and out-of plane bifurcation, whereas later, deformation continued by segment linkage. One of these faults the ‘Sarakina fault’ was reactivated during the 1995 earthquake to produce a 25 km long surface rupture. A long term slip rate of about 0.3 mm a−1 has been estimated by taking into consideration that over the past 6 Ma a maximum displacement of 1700 m across this fault has taken place. 相似文献
6.
This study aims at quantifying the effect of rheology on plan-view shapes of lava flows using fractal geometry. Plan-view shapes of lava flows are important because they reflect the processes governing flow emplacement and may provide insight into lava-flow rheology and dynamics. In our earlier investigation (Bruno et al. 1992), we reported that flow margins of basalts are fractal, having a characteristic shape regardless of scale. We also found we could use fractal dimension (D, a parameter which quantifies flow-margin convolution) to distinguish between the two endmember types of basalts: a a (D: 1.05–1.09) and pahoehoe (D: 1.13–1.23). In this work, we confirm those earlier results for basalts based on a larger database and over a wider range of scale (0.125 m–2.4 km). Additionally, we analyze ten silicic flows (SiO2: 52–74%) over a similar scale range (10 m–4.5 km). We note that silicic flows tend to exhibit scale-dependent, or non-fractal, behavior. We attribute this breakdown of fractal behavior at increased silica contents to the suppression of small-scale features in the flow margin, due to the higher viscosities and yield strengths of silicic flows. These results suggest we can use the fractal properties of flow margins as a remote-sensing tool to distinguish flow types. Our evaluation of the nonlinear aspects of flow dynamics indicates a tendency toward fractal behavior for basaltic lavas whose flow is controlled by internal fluid dynamic processes. For silicic flows, or basaltic flows whose flow is controlled by steep slopes, our evaluation indicates non-fractal behavior, consistent with our observations. 相似文献
7.
Horizontal ground deformation measurements were made repeatedly with an electronic distance meter near the Puu Oo eruption site approximately perpendicular to Kilauea's east rift zone (ERZ) before and after eruptive episodes 22–42. Line lengths gradually extended during repose periods and rapidly contracted about the same amount following eruptions. The repeated extension and contraction of the measured lines are best explained by the elastic response of the country rock to the addition and subsequent eruption of magma from a local reservoir. The deformation patterns are modeled to constrain the geometry and location of the local reservoir near Puu Oo. The observed deformation is consistent with deformation patterns that would be produced by the expansion of a shallow, steeply dipping dike just uprift of Puu Oo striking parallel to the trend of the ERZ. The modeled dike is centered about 800 m uprift of Puu Oo. Its top is at a depth of 0.4 km, its bottom at about 2.9 km, and the length is about 1.6 km; the dike strikes N65° E and dips at about 87°SE. The model indicates that the dike expanded by 11 cm during repose periods, for an average volumetric expansion of nearly 500 000 m3. The volume of magma added to the dike during repose periods was variable but correlates positively with the volume of erupted lava of the subsequent eruption and represents about 8% of the new lava extruded. Dike geometry and expansion values are used to estimate the pressure increase near the eruption site due to the accumulation of magma during repose periods. On average, vent pressures increased by about 0.38 MPa during the repose periods, one-third of the pressure increase at the summit. The model indicates that the dikelike body below Puu Oo grew in volume from 3 million cubic meters (Mm3) to about 10–12 Mm3 during the series of eruptions. The width of this body was probably about 2.5–3.0 m. No net long-term deformation was detected along the measured deformation lines. 相似文献
8.
Fracturing and hydrothermal alteration in normal fault zones 总被引：9，自引：0，他引：9
Ronald L. Bruhn William T. Parry William A. Yonkee Troy Thompson 《Pure and Applied Geophysics》1994,142(3-4):609-644
Large normal fault zones are characterized by intense fracturing and hydrothermal alteration. Displacement is localized in a slip zone of cataclasite, breccia and phyllonite surrounding corrugated and striated fault surfaces. Slip zone rock grades into fractured, but less comminuted and hydrothermally altered rock in the transition zone, which in turn grades abruptly into the wall rock. Fracturing and fluid flow is episodic, because permeability generated during earthquakes is destroyed by hydrothermal processes during the time between earthquakes.Fracture networks are described by a fracture fabric tensor (F). The permeability tensor (k) is used to estimate fluid transport properties if the trace of F is sufficiently large. Variations in elastic moduli and seismic velocities between fault zone and wall rock are estimated as a function of fracture density (). Fracturing decreases elastic moduli in the transition zone by 50–100% relative to the country rock, and similar or even greater changes presumably occur in the slip zone.P-andS-wave velocity decrease, andV
p
/V
s
increases in the fault zone relative to the wall rock. Fracture permeability is highly variable, ranging between 10–13 m2 and 10–19 m2 at depths near 10 km. Changes in permeability arise from variations in effective stress and fracture sealing and healing.Hydrothermal alteration of quartzo-feldspathic rock atT>300°C creates mica, chlorite, epidote and alters the quartz content. Alteration changes elastic moduli, but the changes are much less than those caused by fracturing.P-andS-wave velocities also decrease in the hydrothermally altered fault rock relative to the country rock, and there is a slight decrease inV
p
/V
s
, which partially offsets the increase inV
p
/V
s
caused by fracturing.Fracturing and hydrothermal alteration affect fault mechanics. Low modulus rock surrounding fault surfaces increases the probability of exceeding the critical slip distance required for the onset of unstable slip during rupture initiation. Boundaries between low modulus fault rock and higher modulus wall rock also act as rupture guides and enhance rupture acceleration to dynamic velocity. Hydrothermal alteration at temperatures in excess of 300°C weakens the deeper parts of the fault zone by producingphyllitic mineral assemblages. Sealing of fracture in time periods between large earthquakes generates pods of abnormally pressured fluid which may play a fundamental role in the initiation of large earthquakes. 相似文献
9.
Mihnea Corneliu Oncescu 《Pure and Applied Geophysics》1986,124(4-5):931-940
The method of relative seismic moment tensor determination proposed byStrelitz (1980) is extended a) from an interactive time domain analysis to an automated frequency domain procedure, and b) from an analysis of subevents of complex deep-focus earthquakes to the study of individual source mechanism of small events recorded at few stations.The method was applied to the recovery of seismic moment tensor components of 95 intermediate depth earthquakes withM
L=2.6–4.9 from the Vrancea region, Romania. The main feature of the obtained fault plane solutions is the horizontality ofP axes and the nonhorizontal orienaation ofT axes (inverse faulting). Those events with high fracture energy per unit area of the fault can be grouped unambiguously into three depth intervals: 102–106 km, 124–135 km and 141–152 km. Moreover, their fault plane solutions are similar to ones of all strong and most moderate events from this region and the last two damaging earthquakes (November 10, 1940 withM
W=7.8 and March 4 1977 withM
W=7.5) occurred within the third and first depth interval, respectively. This suggests a possible correlation at these depths between fresh fracture of rocks and the occurrence of strong earthquakes. 相似文献
10.
P. Bernard P. Briole B. Meyer H. Lyon-Caen J.-M. Gomez C. Tiberi C. Berge R. Cattin D. Hatzfeld C. Lachet B. Lebrun A. Deschamps F. Courboulex C. Larroque A. Rigo D. Massonnet P. Papadimitriou J. Kassaras D. Diagourtas K. Makropoulos G. Veis E. Papazisi C. Mitsakaki V. Karakostas E. Papadimitriou D. Papanastassiou M. Chouliaras G. Stavrakakis 《Journal of Seismology》1997,1(2):131-150
We present the results of a multidisciplinary study of the Ms = 6.2, 1995, June 15, Aigion earthquake (Gulf of Corinth, Greece). In order to constrain the rupture geometry, we used all available data from seismology (local, regional and teleseismic records of the mainshock and of aftershocks), geodesy (GPS and SAR interferometry), and tectonics. Part of these data were obtained during a postseismic field study consisting of the surveying of 24 GPS points, the temporary installation of 20 digital seismometers, and a detailed field investigation for surface fault break. The Aigion fault was the only fault onland which showed detectable breaks (< 4 cm). We relocated the mainshock hypocenter at 10 km in depth, 38 ° 21.7 N, 22 ° 12.0 E, about 15 km NNE to the damaged city of Aigion. The modeling of teleseismic P and SH waves provides a seismic moment Mo = 3.4 1018 N.m, a well constrained focal mechanism (strike 277 °, dip 33 °, rake – 77°), at a centroidal depth of 7.2 km, consistent with the NEIC and the revised Harvard determinations. It thus involved almost pure normal faulting in agreement with the tectonics of the Gulf. The horizontal GPS displacements corrected for the opening of the gulf (1.5 cm/year) show a well-resolved 7 cm northward motion above the hypocenter, which eliminates the possibility of a steep, south-dipping fault plane. Fitting the S-wave polarization at SERG, 10 km from the epicenter, with a 33° northward dipping plane implies a hypocentral depth greater than 10 km. The north dipping fault plane provides a poor fit to the GPS data at the southern points when a homogeneous elastic half-space is considered: the best fit geodetic model is obtained for a fault shallower by 2 km, assuming the same dip. We show with a two-dimensional model that this depth difference is probably due to the distorting effect of the shallow, low-rigidity sediments of the gulf and of its edges. The best-fit fault model, with dimensions 9 km E–W and 15 km along dip, and a 0.87 m uniform slip, fits InSAR data covering the time of the earthquake. The fault is located about 10 km east-northeast to the Aigion fault, whose surface breaks thus appears as secondary features. The rupture lasted 4 to 5 s, propagating southward and upward on a fault probably outcropping offshore, near the southern edge of the gulf. In the shallowest 4 km, the slip – if any – has not exceeded about 30 cm. This geometry implies a large directivity effect in Aigion, in agreement with the accelerogram aig which shows a short duration (2 s) and a large amplitude (0.5 g) of the direct S acceleration. This unusual low-angle normal faulting may have been favoured by a low-friction, high pore pressure fault zone, or by a rotation of the stress directions due to the possible dip towards the south of the brittle-ductile transition zone. This fault cannot be responsible for the long term topography of the rift, which is controlled by larger normal faults with larger dip angles, implying either a seldom, or a more recently started activity of such low angle faults in the central part of the rift. 相似文献
11.
Rapid decompression experiments on natural volcanic rocks mimick explosive eruptions. Fragment size distributions (FSD) of such experimentally generated pyroclasts are investigated using fractal geometry. The fractal dimension of fragmentation, D, of FSD is measured for samples from Unzen (Japan) and Popocatépetl (Mexico) volcanoes.Results show that: (i) FSD are fractal and can be quantified by measuring D values; (ii) D increases linearly with potential energy for fragmentation (PEF) and, thus, with increasing applied pressure; (iii) the rate of increase of D with PEF depends on open porosity: the higher the open porosity, the lower the increase of D with PEF; (iv) at comparable open porosity, samples display a similar behavior for any rock composition.The method proposed here has the potential to become a standard routine to estimate eruptive energy of past and recent eruptions using values of D and open porosity, providing an important step towards volcanic hazard assessment. 相似文献
12.
H. Austrheim 《Earth and Planetary Science Letters》1987,81(2-3)
The granulite facies assemblages of the anorthositic rocks of the Bergen Arcs (stable at 800–900°C and 10 kbar) have been transformed to eclogite facies assemblages (stable at 700–750°C and 16–19 kbar) in the vicinity of Caledonian shear zones. This section of the root zone of the Caledonian mountain chain reveals a deep polymetamorphic crust where Precambrian granulites (mean density 3.02 g/cm3) and Caledonian eclogites (mean density 3.19 g/cm3) alternate on a scale of meters over a minimum area of 3 × 12 km. Detailed mapping of three localities shows that eclogites account for up to 30–45% of the rock volume. The stabilitization of the eclogite mineralogy is controlled by fluids penetrating these deep crustal shear zones. The eclogitization is independent of preexisting compositional variation in this anorthosite-norite complex. The Bergen Arcs example suggests that the amount of eclogite versus granulites in the lowermost crust is a function of deformation and fluid access, rather than being controlled byT, P and rock composition alone. These relationships may explain the gradual increase in seismic velocity observed in some deep crustal sections and also the complex reflection pattern obtained from the lowermost crust in many areas. 相似文献
13.
Fractal research of fault gouge 总被引：1，自引：0，他引：1
ＦｒａｃｔａｌｒｅｓｅａｒｃｈｏｆｆａｕｌｔｇｏｕｇｅＳＨＵＮ－ＭＥＩＳＨＡＯ（邵顺妹）ａｎｄＪＩＮ－ＣＨＡＮＧＺＯＵ（邹瑾敞）ＥａｒｔｈｑｕａｋｅＲｅｓｅａｒｃｈＩｎｓｔｉｔｕｔｅｏｆＬａｎｚｈｏｕ，ＳｔａｔｅＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａ... 相似文献
14.
The time clustering of earthquakes occurring in the Hellenic arc-trench system is quantitatively analyzed by means of the fractal dimension,D, of their time distribution in the time intervals of 1950–1985 (M
s
>-4.5) and 1964–1985 (M
s
4.0). The results obtained imply that scale-invariant clustering holds over very large scale lengths of time,T, with 22–28T (in min) 220–222, depending on the seismotectonic segment considered. In all segments a common feature is the relation between theD
1,D
2 andD
3-values found for shallow, intermediate-depth and all-depth shocks, respectively:D
3>D1>D2. TheD-values found for shallow shocks range between 0.137 and 0.191 with the exception of the Ionian Islands and Cretan segments where anomalously high values (D=0.221–0.251) have been determined. We discuss possible seismotectonic interpretations of the results. 相似文献
15.
Masatoshi Bando Greg Bignall Kotaro Sekine Noriyoshi Tsuchiya 《Journal of Volcanology and Geothermal Research》2003,120(3-4):215-234
The Quaternary Takidani Granodiorite (Japan Alps) is analogous to the type of deep-seated (3–5 km deep) intrusive-hosted fracture network system that might support (supercritical) hot dry/wet rock (HDR/HWR) energy extraction. The I-type Takidani Granodiorite comprises: porphyritic granodiorite, porphyritic granite, biotite-hornblende granodiorite, hornblende-biotite granodiorite, biotite-hornblende granite and biotite granite facies; the intrusion has a reverse chemical zonation, characterized by >70 wt% SiO2 at its inferred margin and <67 wt% SiO2 at the core. Fluid inclusion evidence indicates that fractured Takidani Granodiorite at one time hosted a liquid-dominated, convective hydrothermal system, with <380°C, low-salinity reservoir fluids at hydrostatic (mesothermal) pressure conditions. ‘Healed’ microfractures also trapped >600°C, hypersaline (35 wt% NaCleq) fluids of magmatic origin, with inferred minimum pressures of formation being 600–750 bar, which corresponds to fluid entrapment at 2.4–3.0 km depth. Al-in-hornblende geobarometry indicates that hornblende crystallization occurred at about 1.45 Ma (7.7–9.4 km depth) in the (marginal) eastern Takidani Granodiorite, but later (at 1.25 Ma) and shallower (6.5–7.0 km) near the core of the intrusion. The average rate of uplift across the Takidani Granodiorite from the time of hornblende crystallization has been 5.1–5.9 mm/yr (although uplift was about 7.5 mm/yr prior to 1.2 Ma), which is faster than average uplift rates in the Japan Alps (3 mm/yr during the last 2 million years). A temperature–depth–time window, when the Takidani Granodiorite had potential to host an HDR system, would have been when the internal temperature of the intrusive was cooling from 500°C to 400°C. Taking into account the initial (7.5 mm/yr) rate of uplift and effects of erosion, an optimal temperature–time–depth window is proposed: for 500°C at 1.54–1.57 Ma and 5.2±0.9 km (drilling) depth; and 400°C at 1.36–1.38 Ma and 3.3±0.8 km (drilling) depth, which is within the capabilities of modern drilling technologies, and similar to measured temperature–depth profiles in other active hydrothermal systems (e.g. at Kakkonda, Japan). 相似文献
16.
断层岩的粒度分布包含岩石破裂机制、摩擦性质和地震能量分配等重要信息。筛分-称重和激光测量是分析断层岩三维粒度的2种有效方法,但每一种方法的测量范围仅有3个量级,难以全面反映断层岩的粒度分布特征。利用上述2种方法对汶川地震断层滑动带上的断层岩（简称断层岩）的粒度分布进行了测量,粒径测量范围从0.2μm至16mm,跨度达到5个数量级。结果显示：1）存在临界粒径dc（0.95～1.90μm）。粒度大于和小于dc的颗粒满足不同的颗粒数（Nd）-粒径（d）分布关系,表明该断层岩的粒径分布不具有自相似性特征。2）利用粒度大于dc的颗粒计算出的分形维数与断层岩类型有很好的相关性,即断层带边缘的角砾岩的平均分形维数为2.6,核部压碎角砾岩的平均分形维数约为3.0,中心断层泥的分形维数约为3.5。粒径小于dc的颗粒的分形维数为1.7～2.1。分形维数的突变反映出断层破裂机制的复杂性,即在不同的粒度域,岩石的破裂机制不尽相同。3）依据粒度分析结果,估算出汶川地震断层泥的单位破裂能（Es）为0.63MJ/m2。 相似文献
17.
In this work,the fractal dimension of granulometric composition in the fault gouge from the Yishu fault zone and northwest-trending faults on its west side is calculated and studied based on the fractal theory of rock fragmentation.The seismo-geological implications of the fractal dimension of granulometric composition in fault gouges are also discussed.The results show that the Yishu fault zone is more active than the northwest-trending faults and the Anqiu-Juxian fault is the most active in the Yishu fault zone.The fractal dimension of fault gouge is a parameter describing the relative active age and rupture mode of the fault and forming age of the fault gouge.The fractal dimension value is also related to the parent rock,thickness,structural position,and clay content of the fault gouge. 相似文献
18.
— Analysis of the Koyna-Warna earthquake catalog (1968–1996) shows that on an average there is a positive correlation between the b value (decrease) and fractal dimensions (decrease in both D2s and D2t) of earthquake epicenters 0.5 and 2.5 years prior to 1973 (M5.2) and 1980 (M5.5) events, respectively, except a negative correlation for about five years (1988–1993) prior to the 1993/1994 sequence (M5.4). This positive correlation indicates a weaker clustering, or that the epicenters tend to fill the two-dimensional plane. While the origin of the negative correlation seems to be that during periods of large events (low b value), there is strong clustering around the main shock epicenter (high fractal dimension). Interestingly, during the last year (1995–1996) of the studied period both the b value and correlation dimensions rose significantly, suggesting that stress release occurs through increased levels of low magnitude and increasingly scattered seismicity, suggesting an increased risk of larger magnitude events. Incidentally, during 2000 three earthquakes of magnitude M 5.0, one earthquake of M 4.0, 45 earthquakes of magnitude M 3.0–3.9, and several thousand earthquakes of M < 3 have occurred in the region. Thus it can be inferred that at local scales the relationship yields both positive and negative correlation that appears to be controlled by different modes of failure within the active fault complex.Acknowledgement. The authors are grateful to Dr. B.K. Rastogi of NGRI for providing the catalog of Koyna earthquakes and for useful scientific discussions. The comments of Dr. I. G. Main have improved the quality of paper for which we extend to him our sincere thanks. One of the authors (AOM) thanks the Third World Academy of Science and the Council of Scientific and Industrial Research, India for the Postdoctoral Fellowship award under which this work was carried out. 相似文献
19.
沂沭断裂带及其附近断裂的断层泥分形特征及其地震地质意义 总被引：7，自引：0，他引：7
利用岩石碎裂数目的分形理论，分析，计算了沂沭断裂带及其西侧北西向断裂的断层泥粒度成分的分维值，讨论了断层泥粒度成分分维的地震地质意义，研究结果表明，沂沭断裂带内的断裂活动的强度大于北西向断裂活动强度；Ｆ２是沂沭断裂带中活动最强的一条断裂，断层泥粒度成分分维值可作为表征断裂活动时代，破裂形式和断层泥形成斫代等的参量；分维值还与断层泥的母岩，厚度，粘土矿物含量和所处的断裂部位等相关。 相似文献
20.
Self-organized Fractal Seismicity and b Value of Aftershocks of the 2001 Bhuj Earthquake in Kutch (India) 总被引：1，自引：0，他引：1
— The devastating intraplate earthquake of Mw 7.7 of 26 January, 2001 took place along the south-dipping reverse fault in the lower crust ( 23 km) of Kutch, Gujarat, India, obliterating some 14,000 people. The aftershock activity has ensued for three years. We analyzed 997 aftershocks of M 3.0 to study the b value and fractal correlation dimensions in time and space. The b value is found to be 0.8 ± 0.03 from the Gutenberg-Richter relation and 0.76 ± 0.02 from the maximum-likelihood, suggesting a typical value for the intraplate region. The spatial correlation is 1.71 ± 0.02, indicating that events are approaching a two-dimensional region. Further, the temporal correlation dimension is estimated to be 0.78 ± 0.02, confirming the structure is mono-fractal in time domain. The depth section of b value shows a peak at 15–35 km depth range coinciding with the maximum occurrence of aftershocks ( 47%), which is inferred as a fluid-filled highly fractured rock matrix with fractures of high density. It will be important to note that tomographic results also suggest a low Vp, low Vs and a large Poissons ratio for the same depth range, further confirming this inference. Additionally, we have studied the variation of D2s and b value with time. During the first two months of aftershock activity the results show a marked negative correlation between spatial correlation dimension D2 (large) and b value (low), indicating the predominance of large events associated with weak clustering. The negative correlation means the stress release along faults of a larger surface area. After two months the fractal dimension (D2s) and b value suggests a positive correlation implying more numerous smaller shocks with stress release along faults of a smaller surface area. This would indicate a reduced probability of large magnitude earthquakes due to fragmentation of the fault zone.Acknowledgement. The authors thank Dr. V.P. Dimri, Director, NGRI for his encouragement and kind permission to publish this work. The Department of Science and Technology, New Delhi supported this study. 相似文献