Empirical relationships between aftershock area dimensions and magnitude for earthquakes in the Mediterranean Sea region

Fault dimension estimates derived from the aftershock area extent of 36 shallow depth (≤ 31 km) earthquakes that occurred in the Mediterranean Sea region have been used in order to establish empirical relationships between length, width, area and surface-wave/moment magnitude. This dataset consists of events whose aftershock sequence was recorded by a dense local or regional network and the reported location errors did not exceed on average 3–5 km. Surface-wave magnitudes for these events were obtained from the NEIC database and/or published reports, while moment magnitudes as well as focal mechanisms were available from the Harvard/USGS catalogues. Contrary to the results of some previously published studies we found no evidence in our dataset that faulting type may have an effect on the fault dimension estimates and therefore we derived relationships for the whole of the dataset. Comparisons, by means of statistical F-tests, of our relationships with other previously published regional and global relationships were performed in order to check possible similarities or differences. Most such comparisons showed relatively low significance levels (< 95%), since the differences in source dimension estimates were large mainly for magnitudes lower than 6.5, becoming smaller with increasing magnitude. Some degree of similarity, however, could be observed between our fault length relationship and the one derived from aftershock area lengths of events in Greece, while a difference was found between our regional and global fault length relationships. A calculation of the ratio defined as the fault length, derived from our relationships, to the length estimated from regional empirical relationships involving surface ruptures showed that it can take a maximum value of about 7 for small magnitudes while it approaches unity at Ms 7.2. When calculating the same ratio using instead global empirical relationships we see the maximum value not exceeding 1.8, while unity is reached at Mw 7.8, indicating the existence of a strong regional variation in the fault lengths of earthquakes occurring in the Mediterranean Sea region. Also, a relationship between the logarithms of the rupture area and seismic moment is established and it is inferred that there is some variation of stress drop as a function of seismic moment. In particular, it is observed that for magnitudes lower than 6.6 the stress drop fluctuates around 10 bar, while for larger magnitudes the stress drop reaches a value as high as 60 bar.     

Stability and P–V–T equation of state of KAlSi3O8-hollandite determined by in situ X-ray observations and implications for dynamics of subducted continental crust material

In situ X-ray diffraction measurements of KAlSi₃O₈-hollandite (K-hollandite) were performed at pressures of 15–27 GPa and temperatures of 300–1,800 K using a Kawai-type apparatus. Unit-cell volumes obtained at various pressure and temperature conditions in a series of measurements were fitted to the high-temperature Birch-Murnaghan equation of state and a complete set of thermoelastic parameters was obtained with an assumed K′_300,0=4. The determined parameters are V _300,0=237.6(2) Å³, K _300,0=183(3) GPa, (?K _T,0/?T) _P =?0.033(2) GPa K^?1, a ₀=3.32(5)×10^?5 K^?1, and b ₀=1.09(1)×10^?8 K^?2, where a ₀ and b ₀ are coefficients describing the zero-pressure thermal expansion: α _T,0 = a ₀ + b ₀ T. We observed broadening and splitting of diffraction peaks of K-hollandite at pressures of 20–23 GPa and temperatures of 300–1,000 K. We attribute this to the phase transitions from hollandite to hollandite II that is an unquenchable high-pressure phase recently found. We determined the phase boundary to be P (GPa)=16.6 + 0.007 T (K). Using the equation of state parameters of K-hollandite determined in the present study, we calculated a density profile of a hypothetical continental crust (HCC), which consists only of K-hollandite, majorite garnet, and stishovite with 1:1:1 ratio in volume. Density of HCC is higher than the surrounding mantle by about 0.2 g cm^?3 in the mantle transition zone while this relation is reversed below 660-km depth and HCC becomes less dense than the surrounding mantle by about 0.15 g cm^?3 in the uppermost lower mantle. Thus the 660-km seismic discontinuity can be a barrier to prevent the transportation of subducted continental crust materials to the lower mantle and the subducted continental crust may reside at the bottom of the mantle transition zone.     

Increasing ore extraction by changing detonator positions in LKAB Malmberget mine

By studying the charging plan of a ring and analysing the propagation of the stress waves caused by blasting in sub-level caving, the effects of detonator positions on ore fragmentation and ore extraction were investigated. Two detonator positions were studied and compared with each other. (1) Detonators were placed at the lowest charged position in a blast hole. This position is used in daily production blasting in Malmberget mine, and a ring with the lowest detonator position is called ordinary ring. (2) Detonators were placed at the middle of a charged blast hole, and a ring with such a detonator position is called a test ring. The study on charging plan and the analysis on stress wave propagation showed that a test ring has the following advantages over an ordinary ring: (a) fewer not-detonated (or initiated) blast holes in a ring; (b) more detonation energy utilized; (c) less back breakage to “eye brow”; (d) better fragmentation; (e) more ore extraction. On the basis of the above analysis, a total of 40 test rings have been tried and the ore extraction in the 40 rings has so far been finished in the mine. Correspondingly, the results from production indicate that: (1) The success rate of the detonated blast holes has been up to 91% according to our measurements to 16 test rings. (2) Severe back breakage has been avoided and common back breakage has been reduced in the test rings. (3) Fragmentation is much better, compared with the ordinary rings. (4) The average ore extraction from all of the test rings is increased by 107%, compared with that from the ordinary rings in the same drifts. Particularly, the lowest ore extraction from the test rings is increased by 80%, compared with that from the ordinary rings. (5) The iron content in extracted ore from the test rings is increased by 7.2% on average, compared with that from the ordinary rings.     

Understanding size and boundary effectsin scaled model blasts - plane problems

This contribution addresses model blasting and focuses on size and boundary effects on wave propagation, fracture pattern development and fragmentation in small scale laboratory size specimen. Small cylindrical specimens are centre-line loaded by linear high velocity of detonation explosive charges and detonated.

Using elastic wave propagation theory and fracture mechanics it is shown that the type of boundary conditions which prevail at the outer boundary of the cylinder control the extension of bore-hole cracking and fragmentation within the body of the cylinder. In the case of a composite cylinder with dissimilar mantel and core materials, the level of fracturing and fragmentation is controlled by the delamination of the interface. This, in turn, depends on the relative diameters of the core and the mantel. The most important parameter though is the ratio between the length of the pulse (space-wise or time-wise) and the characteristic dimensions of the models, i.e. in this case the diameters of the core and the mantel.

The theoretical basis for a simplified two-dimensional plane treatment is developed. Simple or composite, thin, plate-like specimens are centrally loaded; whereas the core is always a circle, the mantel can be either a circle or a square.     

Resource concerns for territorial conflict

The objective of this paper is to engage constructively with literature on armed conflict and resources in order to draw attention both to assumptions that hinder a more accurate or useful understanding of natural resources and their role in territorial conflict as well as to aspects of this field of research that merit further work. In much of the literature on resource conflict, territorial aspects are either implicitly or explicitly tied to resource conflict largely through the assumption that the value of territory is intrinsic. Little of the literature attempts to advance theory, specifically, either on the particular role of resources or on the meaning and objectives of conflict beyond a one-dimensional objective of maintaining or securing control of territory. The paper considers themes of resource scarcity and resource abundance in conflict. A third section focuses on an analysis both of natural resource databases and of conflict databases (both international and civil) which emphasizes problematic results of blending these databases to demonstrate correlations. UIUC territorial conflict management workshop     

Geochemical and biological consequences of groundwater augmentation in lakes of west-central Florida (USA)

We studied sediment cores from four Florida (USA) lakes that have received groundwater hydrologic supplements (augmentation) for >30 years to maintain lake stage. Top samples (0–4 cm) from sediment cores taken in Lakes Charles, Saddleback, Little Hobbs, and Crystal had ²²⁶Ra activities of 44.9, 17.5, 7.6, and 8.5 dpm g⁻¹, respectively, about an order of magnitude greater than values in deeper, older deposits. The surface sample from Lake Charles yielded the highest ²²⁶Ra activity yet reported from a Florida lake core. Several lines of evidence suggest that groundwater augmentation is responsible for the high ²²⁶Ra activities in recent sediments: (1) ²²⁶Ra activity in cores increased recently, (2) the Charles, Crystal, and Saddleback cores display ²²⁶Ra/²¹⁰Pb disequilibrium at several shallow depths, suggesting ²²⁶Ra entered the lakes in dissolved form, (3) cores show recent increases in Ca, which, like ²²⁶Ra, is abundant in augmentation groundwater, and (4) greater Sr concentrations are associated with higher ²²⁶Ra activities in recent Charles and Saddleback sediments. Sr concentrations in Eocene limestones of the deep Floridan Aquifer are high relative to Sr concentrations in surficial quartz sands around the lakes. Historical water quality inferences for the lakes were based on diatom assemblages in sediments. Recent alkalization in Lakes Charles, Saddleback, Little Hobbs, and Crystal was inferred from weighted-averaging calibration (WACALIB). The lakes also show recent trophic state increases based on WACALIB-derived estimates for limnetic total P. Although residential and agricultural sources might contribute to increased P loading, P in augmentation waters probably has had significant influence on eutrophication. Dystrophic diatoms were abundant in the early history of Lakes Saddleback, Little Hobbs, and Crystal, which suggests that these lakes contained more tannic waters during the past than at present, perhaps as a consequence of greater inflows from surrounding wetlands. Ionic content of lake waters increased, as indicated by diatom autecological analysis. Recent geochemical and biological changes detected in cores from these lakes probably are a result of deliberate groundwater augmentation, although inputs of groundwater pumped for agricultural and residential development in the watersheds also might have contributed to limnological changes.     

前陆背景下的两种正断裂现象及其相互作用模式

许多前陆盆地同时存在着下部的裂陷正断裂和上部的造山期的挠曲正断裂。作用在均质不分层和非均质分层板块中的挠曲正断裂具有不同的外观形态和形变的空间协调机制，前者断面陡直、贯穿深远；后者则呈坡坪式形态。裂陷正断裂和挠曲正断裂具有3种相互作用方式、差异甚殊的断裂总体形态和中性面分布位置不同的应力体制。Ⅰ类，挠曲正断裂局限在陆缘期或坳陷期层序中；Ⅱ类，裂陷期正断裂断至断陷期层序，且以裂陷正断裂为基础而存在，二者构成完整而独特的断裂组合；Ⅲ类，挠曲正断裂亦断穿至断陷期层序，但和裂陷正断裂并不存在直接关系。这三类关系对孔隙—裂缝网络体具有不同的影响，并和应力体制一道，对流体尤其是烃类的作用过程有差异很大的影响。地层在跨越同生正断裂和挠曲正断裂时所发生的厚度的变化，起因于二者在物源方向上的完全不同。     

The devastating Muzaffarabad earthquake of 8 October 2005: New insights into Himalayan seismicity and tectonics

The recent earthquake of 8 October 2005 in the Muzaffarabad region in western Himalaya destroyed several parts of Pakistan and the north Indian state of Jammu and Kashmir. The earthquake of magnitude 7.6 claimed more than 80,000 lives, clearly exposing the poor standards of building construction — a major challenge facing the highly populated, earthquake prone, third world nations today. In this paper, we examine variations in the stress field, seismicity patterns, seismic source character, tectonic setting, plate motion velocities, GPS results, and the geodynamic factors relating to the geometry of the underlying subsurface structure and its role in generation of very large earthquakes. Focal mechanism solutions of the Muzaffarabad earthquake and its aftershocks are found to have steep dip angles comparable to the Indian intra-plate shield earthquakes rather than the typical Himalayan earthquakes that are characterized by shallow angle northward dips. A low p-value of 0.9 is obtained for this earthquake from the decay pattern of 110 aftershocks, which is comparable to that of the 1993 Latur earthquake in the Indian shield — the deadliest Stable Continental Region (SCR) earthquake till date. Inversion of focal mechanisms of the Harvard CMT catalogue indicates distinct stress patterns in the Muzaffarabad region, seemingly governed by an overturned Himalayan thrust belt configuration that envelops this region, adjoined by the Pamir and Hindukush regions. Recent developments in application of seismological tools like the receiver function technique have enabled accurate mapping of the dipping trends of the Moho and Lithosphere–Asthenosphere Boundary (LAB) of Indian lithosphere beneath southern Tibet. These have significantly improved our understanding of the collision process, the mechanism of Himalayan orogeny and uplift of the Tibetan plateau, besides providing vital constraints on the seismic hazard threat posed by the Himalaya. New ideas have also emerged through GPS, macroseismic investigations, paleoseismology and numerical modeling approaches. While many researchers suggest that the Himalayan front is already overdue for several 8.0 magnitude earthquakes, some opine that most of the front may not really be capable of sustaining the stress accumulation required for generation of great earthquakes. We propose that the occurrence of great earthquakes like those of 1897 in Shillong and 1950 in Assam have a strong correlation with their proximity to multiple plate junctions conducive for enormous stress build up, like the eastern Himalayan syntaxis comprising the junction of the India, Eurasia plates, and the Burma, Sunda micro-plates.     

Coulomb stress triggering of earthquakes along the Atalanti Fault, central Greece: Two April 1894 M6+ events and stress change patterns

Two M6+ events occurred 15–20 km apart in central Greece on April 20 and April 27, 1894. We identify the April 27, 1894 rupture (2nd in the sequence) with the Atalanti segment of the Atalanti Fault Zone because of unequivocal surface rupturing evidence reported by Skouphos [Skouphos, T., 1894. Die swei grossen Erdbeben in Lokris am 8/20 und 15/27 April 1894. Zeitschrift Ges. Erdkunde zu Berlin, vol. 24, pp. 409–474]. Coulomb stress transfer analysis and macroseismic evidence suggest that the April 20, 1894 event (1st in the sequence) may be associated with the Martinon segment of the same fault zone. Our stress modelling suggests that this segment may have ruptured in an M = 6.4 event producing a 15-km long rupture which transferred 1.14 bar in the epicentral area of the April 27th, 1894 event, thus triggering the second M = 6.6 earthquake along the Atalanti segment and producing a 19-km long rupture. We also examined three alternative fault sources for the first event; however, all these produce smaller stress stresses for triggering the second event. The proposed slip model for the second earthquake is capable of producing coastal subsidence of the order of centimetres to decimetres, which fits the geological data. The 1894 earthquake sequence was followed by a difference in the timing of subsequent M > 5 events in each of the “relaxed” areas (stress shadows; a negative change in Coulomb failure stress > − 0.6 bar), which terminated between 22–37 years (north) and 80 years (south).