Intrinsic and Scattering Seismic Attenuation in Southwestern Anatolia

The intrinsic dissipation and scattering attenuation in southwestern (SW) Anatolia, which is a tectonically active region, is studied using the coda waves. First the coda quality factor (Q_c) assuming single scattering is estimated from the slope of the coda-wave amplitude decay. Then the Multiple Lapse Time Window (MLTW) analysis is performed with a uniform earth model. Three non-overlapping temporal data windows are used to calculate the scattered seismic energy densities against the source-receiver distances, which, in turn, are used to calculate separate estimates of the intrinsic and scattering factors. In order to explore the frequency dependency, the observed seismograms are band pass-filtered at the center frequencies of 0.75, 1.5, 3.0, 6.0 and 12.0. The scattering attenuation (Q_s⁻¹) is found lower than the intrinsic attenuation (Q_i⁻¹) at all frequencies except at 0.75 Hz where the opposite is observed. Overall the intrinsic attenuation dominates over the scattering attenuation in the SW Anatolia region. The integrated energy curves obtained for the first energy window (i.e., 0–15 s) are somewhat irregular with distance while the second (i.e., 15–30 s) and third (i.e., 30–45 s) data windows exhibit more regular change with distance at most frequencies. The seismic albedo B₀ is determined as 0.61 at 0.75 Hz and 0.34 at 12.0 Hz while the total attenuation factor denoted by L_e⁻¹ changes in the range 0.034–0.017. For the source-station range 20–180 km considered the scattering attenuation is found strongly frequency dependent given by the power law Q_s⁻¹ = 0.010*f^−1.508. The same relations for Q_i⁻¹, Q_t⁻¹ (total), Q_c⁻¹ and (expected) hold as Q_i⁻¹ = 0.0090*f^−1.17, Q_t⁻¹ = 0.019*f^−1.31, Q_c⁻¹ = 0.008*f^−0.84 and respectively. Compared to the other attenuation factors Q_c⁻¹ and are less dependent on the frequency.     

Site and laboratory investigation of the Slano blato landslide

The Slano blato landslide is situated above the village of Lokavec, in the western part of Slovenia. This area is one of the seismically most active parts of the country. Considering just the last decade, movement of the landslide was observed in November 2000, when the displaced material reached a velocity of 60–100 m/day. Silty and clayey gravel above flysch layers of marl and sandstone formed the landslide mass.Geotechnical investigations of the landslide were performed in 2003 and 2004, when the depth of the landslide was determined, as well as the geotechnical parameters and the sliding mechanism. Rheological tests were also carried out for further analysis. Based on the investigation results and the observed landslide velocity, the landslide was classified as an earth flow. Inclinometer measurements showed that the landslide has two shear surfaces, with different behaviour shown as each.A stability analysis was carried out numerically by applying the Mohr–Coulomb and Burger elasto–plastic models. The Mohr–Coulomb model indicated that the high water level influences the landslide instability. In the case of the Burger elasto-plastic model, a higher velocity was calculated, at a water content of between 35 and 40%.     

Application of lithospheric rheology in structural metallogenesis: taking BIF-type iron-rich ore deposits as an exampleEI北大核心CSCD

Based on the basic theory and recent progresses of rock rheology, this paper addresses the critical role of rock rheological properties in the structural metallogenesis. The worldwide, metamorphic banded iron formation-type (BIF) iron-ore deposits are referred as example to delineate and evaluate the influences of structural deformation and rock rheological properties on the formation of this type of ore deposit. It is concluded that due to rheological differentiation, folding induced by ductile shearing and high-temperature plastic flow played a particularly key role in the formation of the high-grade, BIF-type Fe-rich ore deposits. Therefore, we propose that a combination between structural metallogenesis and rock rheology may be of help to our understanding of the tectono-physicochemical characteristics of large to super-large ore deposits. ©, 2015, Science Press. All right reserved.     

岩石圈流变学：一种研究地球深部岩体变形的新方法

岩石圈流变学是大陆岩石变形的主导因素之一,是一种研究地球深部岩体变形的新方法。简要介绍流变学对大陆动力学研究的影响,并对当前流变学研究进展进行评述。岩石圈流变学在岩石圈地层、造山带和大型盆地动力学和动力学特征研究中的应用非常广泛。近年来,岩石圈流变学在脆-塑性转换、岩石流变含水性、“三明治”结构及岩石流变律等方面有重大进展。最后,指出目前岩石圈流变学还存在一些亟待解决的问题,如时间因素。     

Rheological implications of the strong seismic reflector in the Kakkonda geothermal field, Japan

We re-processed the seismic reflection survey data of the Kakkonda geothermal field. The pre-stack migration delineates a strong and continuous reflector between 1800- and 2800-m depth, below which formations are not reflective. Earthquake data exhibit seismicity in the upper crust. The lower boundary of seismogenic layer is interpreted as the brittle–ductile transition. The thermal structure is thought to be the major factor controlling its depth. We compared the strong reflector with the thermal and rheological structure from drillholes. The depth of the reflector corresponds to the top of the highly–very highly fractured zone observed from formation microscanner imagery (FMI) logging in the Miocene formations. The density of fracture in the Kakkonda granite is very low, suggesting that granite corresponds to the nonreflective zone. The temperature–depth profile of well WD-1a shows that the temperature at the highly–very highly fractured zone is about 350 °C. This corresponds to a hydrothermal convection zone filled with two-phase geothermal fluid. The cut-off depth of seismicity that indicates the brittle–ductile transition lies at the isotherm of 300–350 °C near the reflector. We conclude that the strong seismic reflector is a strong contrast in acoustic impedance at the top of the fractured layer. The fractured layer could be a decoupling plane caused by different tectonic behaviors between the upper brittle and the lower ductile layers or a dehydration front by thermal diffusion. The similarity between the strong reflector and K-horizon, the strong reflector, found in southern Tuscany, Italy suggests that the P-wave reflector at the top of highly fractured zone at the brittle–ductile transition be common in areas with magmatic activity.     

Thermal and mechanical structure of the central Iberian Peninsula lithosphere

The central Iberian Peninsula (Spain) is made up of three main tectonic units: a mountain range, the Spanish Central System and two Tertiary basins (those of the rivers Duero and Tajo). These units are the result of widespread foreland deformation of the Iberian plate interior in response to Alpine convergence of European and African plates. The present study was designed to investigate thermal structure and rheological stratification in this region of central Spain. Surface heat flow has been described to range from 80 to 60 mW m⁻². Highest surface heat flow values correspond to the Central System and northern part of the Tajo Basin. The relationship between elevation and thermal state was used to construct a one-dimensional thermal model. Mantle heat flow drops from 34 mW m⁻² (Duero Basin) to 27 mW m⁻² (Tajo Basin), and increases with diminishing surface heat flow. Strength predictions made by extrapolating experimental data indicate varying rheological stratification throughout the area. In general, in compression, ductile fields predominate in the middle and lower crusts and lithospheric mantle. Brittle behaviour is restricted to the first 8 km of the upper crust and to a thin layer at the top of the middle crust. In tension, brittle layers are slightly more extended, while the lower crust and lithospheric mantle remain ductile in the case of a wet peridotite composition. Discontinuities in brittle and ductile layer thickness determine lateral rheological anisotropy. Tectonic units roughly correspond to rheological domains. Brittle layers reach their maximum thickness beneath the Duero Basin and are of least thickness under the Tajo Basin, especially its northern area. Estimated total lithospheric strength shows a range from 2.5×10¹² to 8×10¹² N m⁻¹ in compression, and from 1.3×10¹² to 1.6×10¹² N m⁻¹ in tension. Highest values were estimated for the Duero Basin.Depth versus frequency of earthquakes correlates well with strength predictions. Earthquake foci concentrate mainly in the upper crust, showing a peak close to maximum strength depth. Most earthquakes occur in the southern margin of the Central System and southeast Tajo Basin. Seismicity is related to major faults, some bounding rheological domains. The Duero Basin is a relative quiescence zone characterised by higher total lithospheric strength than the remaining units.     

软岩流变过程与强度研究

文中通过分析软岩流变特征找出流变速度与作用载荷之间的关系。利用U-相关曲线确定能够反映流变过程的4个特征点(流变起始点、等速流变起始点、加速流变起始点、流变破坏点).根据4个特征点的变化规律确定临界等速流变应力的方法和流变强度取值原则。     

流变介质中亚临界扩展前地震孕育过程的能量积累

本文用流变断裂力学研究了地震孕育过程.与弹性力学不同,它是一个不可逆的时空过程.由于介质的粘性,外力功的一部分花在粘性耗散上,只有弹性应变能是地震发生及震后过程可利用的能量.我们将弹性应变能从总能量中分离出来,并就标准线性体给出了简洁公式.以海城地震为例,计算了两个共线不等长断层在地震孕育过程中其周围区域的应力场和能量场的时空变化图象及应变能积累曲线.结果表明,应变能分布复杂,在时间和空间上都很不均匀,能量积累在孕震初期较快而在后期渐趋平缓.由此讨论了某些地震前兆,认为当能量增加速率较大时某些早期前兆可能出现,比如唐山地震10年前出现的某些异常可能就是这种早期前兆表现.