The Effect of Regional Borders when Using the Gutenberg-Richter Model, Case Study: Western Anatolia

A probabilistic seismic hazard analysis (PSHA) for Western Anatolia is presented using the Gutenberg-Richter (G-R) frequency-magnitude relation. Since the modeling is sensitive to the location of seismotectonics boundaries, to use the information content of the observed earthquake data, as a general rule the borders of the affected area are extended. In this study, the effect of the region’s definition on the G-R model is debated on the Western Anatolian region, which is one of the most seismically active and rapidly deforming regions of the world throughout the ages. Calculations are carried out for two subregions and one combined region as a whole using the seismic catalog from 1900 to 2005. The data sets are determined by the region’s borders with the parameters computed according to these data sets by the least-squares and maximum likelihood methods, and then future predictions are estimated via these parameters. Comparing the results with historical earthquake records, most appropriate regional borders for Western Anatolia are defined, and for this new region G-R model parameters are obtained.     

Assessment of Petrophysical Surface Data of the Har?it Granitoid in Trabzon, in Northeastern Turkey

The Har?it granitoid in northeastern Turkey, comprises four separate granite units that are apparently unfoliated. The Har?it granitoid was investigated here by using microstructural, petrofabric and anisotropy of magnetic susceptibility (AMS) data. The structural data of the granitoid were found to be highly compatible with the zonation recognized from AMS measurements. The orientation of magnetic fabrics within the granite units indicates that tectonic deformation might have occurred coevally with the magmatic emplacement of the intrusion. When we evaluated the manners on the scale of the pluton that the disruption took place in the form of uplifting, probably related to a rapid migration of the volcanic front and the documented change from deep sea sedimentation predominant until late Cretaceous to shallower environments during the Paleocene. The possible tectonic control of fault systems on the ascent and emplacement of the granitic magma in the study area, however, cannot be completely ruled out because the Har?it granitoid is situated at or very near the NAF systems in northern Anatolia. In any case, the intrusion is clearly discordant to the regional deformational features formed during the collisional events between the Eurasia and Anatolia plates in northern Turkey.     

A new approach to liquefaction hazard zonation: Application to Laoag City,Northern Philippines

To help mitigate liquefaction hazards in the Philippines, an inexpensive yet effective approach to liquefaction hazard zonation was developed in this study. The proposed approach is also useful in other areas especially where funds for more rigorous procedures may not be available. The approach utilizes the geomorphology-based criteria to identify liquefaction-prone deposits based on geology and grain characteristics, and generate a preliminary liquefaction susceptibility map. Then, microtremor recordings, popularly used in site effect estimation, are gathered to derive qualitative information on the density and thickness of these deposits and generate a site classification map. This latter map is also essentially a ground shaking hazard map in that it shows those areas where thick, soft deposits likely to amplify and prolong the duration of ground motion can be found. Therefore, it also identifies areas where seismic demand can be high that the possibility of liquefaction being triggered is likewise high. Combining the two maps, an integrated liquefaction hazard zonation map is produced which provides not only an improved characterization of the soils’ capacity to resist liquefaction but also integrates qualitative information on the seismic demand on these deposits as well. With information about the relative thickness of the deposits, the severity of potential damage can likewise be inferred from the map since thicker deposits relate to more serious damage. The proposed approach was applied to Laoag City, Northern Philippines, where it was shown to reliably identify areas that are vulnerable to the hazard.     

Analysis of faulting in porous sandstones

Faults in porous sandstones occur in three forms: deformation bands about 1-mm thick and tens of m long and across which offsets are a few mm; zones of deformation bands constituted of many closely spaced deformation bands across which offsets are a few cm or dm; and slip surfaces, that is, distinct surfaces within zones of deformation bands across which offsets are a few m to a few tens of m. Deformation bands represent highly localized deformation; analogous localization within a field of homogeneous deformation is theoretically possible in inelastic materials with certain ranges of constitutive parameters. Crushing and consolidation of sandstone within a band cause the material there to become stiffer than the surrounding porous sandstone. A zone of deformation bands behaves mesoscopically much as a stiff inclusion in a soft matrix. According to the constitutive model assumed to investigate the formation of deformation bands, an instability can develop, and strain increments within the zone of deformation bands can become boundlessly large when the far-field stresses reach critical values. This instability is here associated with the formation of slip surfaces.     

Geochemical and Sr–Nd–Pb isotopic compositions of the Eocene Dölek and Sariçiçek Plutons, Eastern Turkey: Implications for magma interaction in the genesis of high-K calc-alkaline granitoids in a post-collision extensional setting

The major and trace elements and Sr–Nd–Pb isotopes of the host rocks and the mafic microgranular enclaves (MME) gathered from the Dölek and Sariçiçek plutons, Eastern Turkey, were studied to understand the underlying petrogenesis and geodynamic setting. The plutons were emplaced at  43 Ma at shallow depths ( 5 to 9 km) as estimated from Al-in hornblende geobarometry. The host rocks consist of a variety of rock types ranging from diorite to granite (SiO₂ = 56.98–72.67 wt.%; Mg# = 36.8–50.0) populated by MMEs of gabbroic diorite to monzodiorite in composition (SiO₂ = 53.21–60.94 wt.%; Mg# = 44.4–53.5). All the rocks show a high-K calc-alkaline differentiation trend. Chondrite-normalized REE patterns are moderately fractionated and relatively flat [(La/Yb)_N = 5.11 to 8.51]. They display small negative Eu anomalies (Eu/Eu = 0.62 to 0.88), with enrichment of LILE and depletion of HFSE. Initial Nd–Sr isotopic compositions for the host rocks are ε_Nd(43 Ma) = − 0.6 to 0.8 and mostly I_Sr = 0.70482–0.70548. The Nd model ages (T_DM) vary from 0.84 to 0.99 Ga. The Pb isotopic ratios are (²⁰⁶Pb/²⁰⁴Pb) = 18.60–18.65, (²⁰⁷Pb/²⁰⁴Pb) = 15.61–15.66 and (²⁰⁸Pb/²⁰⁴Pb) = 38.69–38.85. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with I_Sr ranging from 0.70485 to 0.70517, ε_Nd(43 Ma) − 0.1 to 0.8 and with Pb isotopic ratios of (²⁰⁶Pb/²⁰⁴Pb) = 18.58–18.64, (²⁰⁷Pb/²⁰⁴Pb) = 15.60–15.66 and (²⁰⁸Pb/²⁰⁴Pb) = 38.64–38.77. The MMEs have T_DM ranging from 0.86 to 1.36 Ga. The geochemical and isotopic similarities between the MMEs and their host rocks indicate that the enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and mantle-derived magmas. All the geochemical data, in conjunction with the geodynamic evidence, suggest that a basic magma derived from an enriched subcontinental lithospheric mantle, probably triggered by the upwelling of the asthenophere, and interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on the Sr–Nd isotope data indicates that  77–83% of the subcontinental lithospheric mantle involved in the genesis. Consequently, the interaction process played an important role in the genesis of the hybrid granitoid bodies, which subsequently underwent a fractional crystallization process along with minor amounts of crustal assimilation, en route to the upper crustal levels generating a wide variety of rock types ranging from diorite to granite in an extensional regime.