Dissolved organic nitrogen as an indicator of livestock impacts on soil biochemical quality

Soil degradation in the Mediterranean and other arid and semi-arid regions of the world is caused mainly by cultivation and grazing. A consequence of de-vegetation due to overgrazing has been a decrease in organic matter (litter) input to soil and a decrease of aggregate size and stability making soils more susceptible to erosion and to organic matter losses. This study provided evidence linking the Dissolved Organic Nitrogen (DON) export from river basins to livestock grazing intensity and the resulting decrease in vegetation. Koiliaris River Basin in Crete was selected to study the effects of livestock grazing on water quality because it offers a unique morphologic situation due to its karstic hydrogeology draining the upland grazing areas through karstic springs. Mass balance calculations of N loads indicated that organic N is behaving as a conservative substance. It is postulated that the two potential mechanisms of Mineralization–Immobilization-Turnover and Direct Uptake did not operate in the degraded soils of the karst and arguments are presented justifying the hypothesis. De-vegetated soils of the area had lower C and N content, the same bacterial count, but lower microbial activity, lower fungi counts and species richness and lower mineralizable N compared to naturally vegetated soils. DON was the predominant N species in both extracted soluble N pools. De-vegetated soils had lower decomposition potential compared to vegetated soils. Mineralization and plant uptake appeared to be restricted and leaching of soluble low aromaticity organic matter was favored. A linear relationship between DON export and livestock N load was obtained for five Greek basins suggesting a mechanism that operates on regional scales. The de-vegetation of grazing lands in Koiliaris River highland calcaric leptosols was shown to be a primary factor causing the decline of soil biochemical quality and DON can be used as a reliable indicator for livestock grazing impacts to soil biochemical quality.     

Application of the stress evolutionary model along the Xiaojiang fault zone in Yunnan Province,Southeast China

The Xiaojiang fault zone constitutes part of the major Xianshuihe-Xiaojiang left lateral structure that bounds the rhombic-shaped block of Yunnan-Sichuan to the east. Long strike slip fault zones that have repeatedly accommodated intense seismic activity, constitute a basic feature of southeast China. Known historical earthquakes to have struck the study area are the 1713 Xundian of M6.8, 1725 Wanshou mountain of M6.8, the 1733 Dongchuan of M7.8, and the strongest one, the 1833 Songming of M8.0. Although instrumental record did not report events of this magnitude class, the 18th century clustering as well as the 19th century large event prompted the investigation of stress transfer along this fault zone. Coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic half-space, and taking into account both the coseismic slip in strong (M ≥ 6.8) earthquakes and the slow tectonic stress buildup along the major fault segments. Geological and geodetic data are used to infer the geometry of these faults and long term slip rates on them, as well as for the fault segments that slipped. Evidence is presented that the strong historical events as well as the ones of smaller magnitude that occurred during the instrumental era, are located in areas where the static stress was enhanced. By extending the calculations up to present, possible sites for future strong events are identified.     

Long-term earthquake prediction along the western coast of South and Central America based on a time predictable model

The repeat times,T, of strong shallow mainshocks in fourteen seismogenic sources along the western coast of South and Central America have been determined and used in an attempt at long-term forecasting. The following relation was determined: $$\log T = 0.22M_{\min } + 0.21M_p + a$$ between the repeat time,T, and the magnitudes,M _min, of the minimum mainshock considered andM _p , of the preceding mainshock. No dependence of the magnitude,M _f , of the following mainshock on the preceding intervent time,T, was found. These results support the idea that the time-predictable model is valid for this region. This is an interesting property for earthquake prediction since it provides the ability to predict the time of occurrence of the next strong earthquake. A strong negative dependence ofM _f onM _p was found, indicating that a large mainshock is followed by a smaller magnitude one, andvice versa. The probability for the occurrence of the expected strong mainshocks (M _s ≥7.5) in each of the fourteen seismogenic sources during the next 10 years (1992–2002) is estimated, adopting a lognormal distribution for earthquake interevent times. High probabilities (P ₁₀>0.80) have been calculated for the seismogenic sources of Oaxaca, Chiapas and Southern Peru.     

A study of the interaction among mining-induced seismic events in the Legnica-Głogów Copper District,Poland

We applied the Coulomb stress transfer technique to investigate interactions among seismic events induced by mining works in the Rudna mine in the Legnica-Glogów Copper District in Poland. We considered events with energy greater than 10⁵ J from the period 1993–1999. We examined the influence of the cumulative static stress changes (ΔCFF) due to previous events on the generation of subsequent ones. The results indicate that in many cases strong mining tremors produce changes in the state of stress of a sufficient magnitude to influence subsequent events. The location of over 60% of events is consistent with stress-enhanced areas where the values of ΔCFF were above 0.01 MPa. For most of the events located inside areas of a calculated negative ΔCFF, their modelled rupture zone was partially located inside stress enhanced area, providing thus additional evidence for possible triggering at the nucleation point.     

Rupture model of the great AD 365 Crete earthquake in the southwestern part of the Hellenic Arc

An M8.3 earthquake struck the southwestern part of the Hellenic Arc, near the Island of Crete, in AD 365, generating a tsunami that affected almost the entire eastern Mediterranean region. Taking into account that the time history of seismicity in this region is fairly complete for such earthquakes in the historical catalog, which can be dated as back as the 5th century B.C., there is no indication that this segment of plate boundary has been fully ruptured again. The seismic hazard associated with this part of the Hellenic Arc necessitates the evaluation of the rupture characteristics of this great event. The constraint of the faulting geometry was initially achieved by using information from seismicity, and the focal mechanisms of earthquakes that occurred during the instrumental period. A rupture model for this great earthquake is constructed by assuming an elastic medium and calculating the theoretical surface displacements for various fault models that are matched with the observed surface deformation gleaned from historical reports. The resulted fault model concerns thrust faulting with a rupture length of 160 km and a seismic moment of 5.7 × 10²⁸ dyn·cm, an average slip of 8.9 m and a corresponding moment magnitude equal to 8.4, in excellent agreement with the macroseismic estimation. The absence of such events recurrence is an indication of the lack of complete seismic coupling that is common in subduction zones, which is in accordance with the back arc spreading of the Aegean microplate and with previous results showing low coupling for extensional strain of the upper plate.     

Thessaloniki–Gerakarou Fault Zone (TGFZ): the western extension of the 1978 Thessaloniki earthquake fault (Northern Greece) and seismic hazard assessment

Active faulting and seismic properties are re-investigated in the eastern precinct of the city of Thessaloniki (Northern Greece), which was seriously affected by two large earthquakes during the 20th century and severe damage was done by the 1759 event. It is suggested that the earthquake fault associated with the occurrence of the latest destructive 1978 Thessaloniki earthquake continues westwards to the 20-km-long Thessaloniki–Gerakarou Fault Zone (TGFZ), which extends from the Gerakarou village to the city of Thessaloniki. This fault zone exhibits a constant dip to the N and is characterised by a complicated geometry comprised of inherited 100°-trending faults that form multi-level branching (tree-like fault geometry) along with NNE- to NE-trending faults. The TGFZ is compatible with the contemporary regional N–S extensional stress field that tends to modify the pre-existing NW–SE tectonic fabric prevailing in the mountainous region of Thessaloniki. Both the 1978 earthquake fault and TGFZ belong to a ca. 65-km-long E–W-trending rupture fault system that runs through the southern part of the Mygdonia graben from the Strymonikos gulf to Thessaloniki. This fault system, here called Thessaloniki–Rentina Fault System (TRFS), consists of two 17–20-km-long left-stepping 100°-trending main fault strands that form underlapping steps bridged by 8–10-km-long ENE–WSW faults. The occurrence of large (M6.0) historical earthquakes (in 620, 677 and 700 A.D.) demonstrates repeated activation, and therefore the possible reactivation of the westernmost segment, the TGFZ, could be a major threat to the city of Thessaloniki. Changes in the Coulomb failure function (ΔCFF) due to the occurrence of the 1978 earthquake calculated out in this paper indicate that the TGFZ has been brought closer to failure, a convincing argument for future seismic hazard along the TGFZ.