Aftershock sequence simulations using synthetic earthquakes and rate-state seismicity formulation

We use an efficient earthquake simulator that incorporates rate-state constitutive properties and uses boundary element method to discretize the fault surfaces, to generate the synthetic earthquakes in the fault system. Rate-and-state seismicity equation is subsequently employed to calculate the seismicity rate in a region of interest using the Coulomb stress transfer from the main shocks in the fault system. The Coulomb stress transfer is obtained by resolving the induced stresses due to the fault patch slips onto the optimal-oriented fault planes. The example results show that immediately after a main shock the aftershocks are concentrated in the vicinity of the rupture area due to positive stress transfers and then disperse away into the surrounding region toward the background rate distribution. The number of aftershocks near the rupture region is found to decay with time as Omori aftershock decay law predicts. The example results demonstrate that the rate-and-state fault system earthquake simulator and the seismicity equations based on the rate-state friction nucleation of earthquake are well posited to characterize the aftershock distribution in regional assessments of earthquake probabilities.     

Dinosaur tracks from the Cretaceous of South Korea: Distribution, occurrences and paleobiological significance

Abstract   Abundant dinosaur fossils including dinosaur footprints, eggs and nests, teeth and bones have been found from the Cretaceous non-marine deposits of Korea. Among them, dinosaur tracks are the most distinctive, and some track sites are among the most famous in the world. Until now, 27 dinosaur track localities have been discovered from the Cretaceous strata in the Gyeongsang Basin and several small basins. Ornithopod tracks are most abundant at most Korean track sites, and most of them are identified as Caririchnium ; that is, large ornithopod footprints with wide hoof impressions. Most theropod tracks are found in Neungju Basin and they consist of various types of small or medium-sized bird-like footprints, and other large footprints. Sauropod tracks are also abundant in the Gyeongsang Basin. The sauropod tracks vary in size, shape, and pattern of trackway, and suggest that diverse sauropods existed in this area. These diverse tracks in South Korea suggest that various dinosaurs flourished at the margins of lakes distributed in the southern part of the Korean Peninsula during the Cretaceous.     

Ensemble-based landslide susceptibility maps in Jinbu area, Korea

Ensemble techniques were developed, applied and validated for the analysis of landslide susceptibility in Jinbu area, Korea using the geographic information system (GIS). Landslide-occurrence areas were detected in the study by interpreting aerial photographs and field survey data. Landslide locations were randomly selected in a 70/30 ratio for training and validation of the models, respectively. Topography, geology, soil and forest databases were also constructed. Maps relevant to landslide occurrence were assembled in a spatial database. Using the constructed spatial database, 17 landslide-related factors were extracted. The relationships between the detected landslide locations and the factors were identified and quantified by frequency ratio, weight of evidence, logistic regression and artificial neural network models and their ensemble models. The relationships were used as factor ratings in the overlay analysis to create landslide susceptibility indexes and maps. Then, the four landslide susceptibility maps were used as new input factors and integrated using the frequency ratio, weight of evidence, logistic regression and artificial neural network models as ensemble methods to make better susceptibility maps. All of the susceptibility maps were validated by comparison with known landslide locations that were not used directly in the analysis. As the result, the ensemble-based landslide susceptibility map that used the new landslide-related input factor maps showed better accuracy (87.11% in frequency ratio, 83.14% in weight of evidence, 87.79% in logistic regression and 84.54% in artificial neural network) than the individual landslide susceptibility maps (84.94% in frequency ratio, 82.82% in weight of evidence, 87.72% in logistic regression and 81.44% in artificial neural network). All accuracy assessments showed overall satisfactory agreement of more than 80%. The ensemble model was found to be more effective in terms of prediction accuracy than the individual model.     

Estimation of the methane flux from mud volcanoes along Chishan Fault,southwestern Taiwan

Because of the increasing public awareness of the greenhouse effect, geological emissions of methane (GEM) have gained more attention. The Intergovernmental Panel on Climate Change included GEM in the natural sources of methane category in the Fourth Assessment Report in 2007. The methane flux from mud volcanoes (MVs) is the second leading source within GEM. However, given that gas flux from MVs has been measured directly only in Sicily and Azerbaijan, the global methane estimation is still a conservative assumption based on limited data. The behavior of MV activities is seldom reported. This study attempts to estimate annual methane emissions through MVs by using a video recorder to record MV activities along the Chishan Fault and determining the bubble size and flux rate of each MV. Observation results, after a 1 year observation period, indicate that the annual emissions of the 19 MVs along the Chishan Fault are 0.1–0.2% of the global methane flux from MVs, highlighting that the methane emission from these MVs should not be neglected. In addition, the continuous monitoring of a particular MV disclosed periodic characteristics of MV activities. These results manifest the spatial and temporal variations of MV activities along the Chishan Fault. The spatial variations are related to the extensional kinematics of the Chishan fault, while the temporal variation relates to the earth-tide-related MV activities. The estimated annual methane emissions from the study are far more than those of previous studies and are still considered conservative. Results of this study may provide valuable information for researchers attempting to estimate the quantity of GEM.     

Melt extraction and melt refertilization in mantle peridotite of the Coast Range ophiolite: an LA–ICP–MS study

The middle Jurassic Coast Range Ophiolite (CRO) is one of the most important tectonic elements in western California, cropping out as tectonically dismembered elements that extend 700 km from south to north. The volcanic and plutonic sections are commonly interpreted to represent a supra-subduction zone (SSZ) ophiolite, but models specifying a mid-ocean ridge origin have also been proposed. These contrasting interpretations have distinctly different implications for the tectonic evolution of the western Cordillera in the Jurassic. If an SSZ origin is confirmed, we can use the underlying mantle peridotites to elucidate melt processes in the mantle wedge above the subduction zone. This study uses laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) to study pyroxenes in peridotites from four mantle sections in the CRO. Trace element signatures of these pyroxenes record magmatic processes characteristic of both mid-ocean ridge and supra-subduction zone settings. Group A clinopyroxene display enriched REE concentrations [e.g., Gd (0.938–1.663 ppm), Dy (1.79–3.24 ppm), Yb (1.216–2.047 ppm), and Lu (0.168–0.290 ppm)], compared to Group B and C clinopyroxenes [e.g., Gd (0.048–0.055 ppm), Dy (0.114–0.225 ppm), Yb (0.128–0.340 ppm), and Lu (0.022–0.05 ppm)]. These patterns are also evident in orthopyroxene. The differences between these geochemical signatures could be a result of a heterogeneous upper mantle or different degrees of partial melting of the upper mantle. It will be shown that CRO peridotites were generated through fractional melting. The shapes of REE patterns are consistent with variable degrees of melting initiated within the garnet stability field. Models call for 3% dry partial melting of MORB-source asthenosphere in the garnet lherzolite field for abyssal peridotites and 15–20% further partial melting in the spinel lherzolite field, possibly by hydrous melting for SSZ peridotites. These geochemical variations and occurrence of both styles of melting regimes within close spatial and temporal association suggest that certain segments of the CRO may represent oceanic lithosphere, attached to a large-offset transform fault and that east-dipping, proto-Franciscan subduction may have been initiated along this transform.     

Hybrid continuum–discrete simulation of granular impact dynamics

Acta Geotechnica - Granular impact—the dynamic intrusion of solid objects into granular media—is widespread across scientific and engineering applications including geotechnics....     

Distribution and Sources of Dissolved and Particulate Heavy Metals (Mn,Co, Ni,Cu, Zn,Cd, Pb) in Masan Bay,Korea

Ocean Science Journal - In this study, we investigated the spatial and temporal distribution and sources of dissolved and particulate heavy metals in Masan Bay, an area that for a long time has...     

Probabilistic seismic performance assessment of lap-spliced RC columns retrofitted by steel wrapping jackets

In this study, the seismic fragility curves of two reinforced concrete (RC) columns that were lap-spliced at the bottom and retrofitted with steel wrapping jackets were generated. Their seismic performance was probabilistically assessed in comparison to that of lap-spliced or continuous reinforcement RC columns. This study used two types of steel wrapping jackets, a full jacket and a split jacket. Analytical models of the four types of columns were developed based on the experimental results of the columns using OpenSEES, which is effective in conducting nonlinear time history analyses. A suite of ten artificial ground motions, modified from recorded ground motions, was used to perform nonlinear time history analyses of the analytical models with scaling of the peak ground acceleration from 0.1 g to 1.0 g in increments of 0.1 g. The steel wrapping jackets did not increase the medians for yield (slight damage state) of the lap-spiced column and did not exceed the corresponding median of the continuous reinforcement column. However, the two steel jackets increased the medians for failure by 1.872 and 2.017 times, respectively, and exceeded the corresponding median of the continuous reinforcement column by 11.8% and 20.5%, respectively.