Comparison of satellite and air photo based landslide susceptibility maps

Landslide susceptibility maps can be prepared in a variety of ways. Many geoscientists favour the use of an overlay model approach in which several map layers are combined by some arithmetic rules to determine the potential for sliding in an area or region. The resulting susceptibility maps, although based on a subjective weighting of relevant factors, can often be of high accuracy and utility. In order to obtain the relevant input data for this type of analysis, remotely sensed data are often used. To date, susceptibility mapping, just as the mapping of historic and individual landslides, has tended to require higher-resolution imagery. This has somewhat limited the application of landslide susceptibility mapping. While high-resolution air photo or satellite imagery is superior to lower resolution imagery for the purpose of mapping of historic and individual landslides, such higher levels of resolution may not be required for the development of landslide susceptibility maps. In order to determine if medium-resolution satellite imagery, such as SPOT or ASTER, could provide the needed data for landslide susceptibility mapping, a comparison was undertaken of landslide susceptibility model output resulting from the use of stereo NAPP aerial photography versus the use of data obtained from stereo SPOT imagery. The test area selected for this study consisted of two watersheds, Pena Canyon and Big Rock Canyon, situated west of Santa Monica, California, USA, along the Pacific Coast Highway. Both watersheds have a long and well-documented history of landslide activity and sufficient geologic variability and complexity to provide a good test site. The specific overlay model used in this evaluation required input data consistent with the needs of many other models of this type. The model output derived from the two different data sources and presented here in the form of susceptibility maps were virtually identical. Statistical and difference analysis confirmed that both methods of obtaining input data provide similar results and successfully identified landslide prone areas. These results suggest that satellite imagery, in this instance, SPOT images, could potentially be used in lieu of conventional air photos, to evaluate landslide susceptibility. In many situations, especially in the case of remote locations and/or developing countries, this capability should result in substantial savings in terms of time, financial resources, and overall viability.     

Late Triassic initial subduction of the Bangong‐Nujiang Ocean beneath Qiangtang revealed: stratigraphic and geochronological evidence from Gaize,Tibet

Sedimentological and geochronological studies along a north–south traverse across the Bangong‐Nujiang suture zone (BNSZ) in Gaize, Tibet provide evidence for a Late Triassic–Jurassic accretionary wedge accreted to the south margin of Qiangtang. This wedge, preserved as the Mugagangri Group (MG), records evidence for the northward subduction of the Bangong‐Nujiang Ocean (BNO) beneath Qiangtang. The MG strata comprise two coarser intervals (lower olistostromes and upper conglomerates) intercalated within sandy turbidites, which are consistent with timing and forearc stratigraphy during subduction initiation predicted by geodynamic modelling. Following the model, the northward subduction of the BNO beneath Qiangtang and subsequent arc‐magmatism are inferred to have begun, respectively, at ca. 220 Ma and ca. 210 Ma, with respect to depositional ages constrained by youngest detrital‐zircon ages. The initiation of arc‐magmatism is also supported by provenance transition reflected by sandstone detrital modes and age patterns of detrital zircons. Previously, evidence for an incipient arc was lacking, but the timing of Late Triassic BNO subduction and related arc‐magmatism is coincident with an important Late Triassic magmatic event in central Qiangtang that probably represents the ‘missing’ arc. Other Qiangtang events, such as exhumation of the Qiangtang metamorphic belt as a source area, and development of the Late Triassic Nadigangri deposits and bimodal volcanism, are more easily explained in the tectonic context of early northward subduction of the BNO beneath Qiangtang, beginning at about 220 Ma.     

Late Quaternary lake-level changes of Lake El'gygytgyn, NE Siberia

Lake El'gygytgyn is situated in a 3.6 Ma old impact crater in northeastern Siberia. Presented here is a reconstruction of the Quaternary lake-level history as derived from sediment cores from the southern lake shelf. There, a cliff-like bench 10 m below the modern water level has been investigated. Deep-water sediments on the shelf indicate high lake levels during a warm Mid-Pleistocene period. One period with low lake level prior to Marine Oxygen Isotope Stage (MIS) 3 has been identified, followed by a period of high lake level (10 m above present). In the course of MIS 2 the lake level dropped to − 10 m. At the end of MIS 2 the bench was formed and coarse beach sedimentation occurred. Subsequently, the lake level rose rapidly to the Holocene level. Changes in water level are likely linked to climate variability. During relatively temperate periods the lake becomes free of ice in summer. Strong wave actions transport sediment parallel to the coast and towards the outlet, where the material tends to accumulate, resulting in lake level rise. During cold periods the perennial lake ice cover hampers any wave activity and pebble-transport, keeping the outlet open and causing the lake level to drop.     

陆相盆地中的海侵层序特征:中欧盆地三叠系与松辽盆地白垩系对比研究

中欧盆地三叠系是典型的海陆过渡相沉积,松辽盆地白垩系是含有海侵事件记录的陆相河湖盆地。两盆地的共同特点是：①大陆克拉通上长期发育的大型坳陷盆地;②靠近古大洋和（或）有向海通道;③主要由互层状泥岩、粉砂岩、碳酸盐岩和膏盐层组成;④无典型海相化石,可能发育有半咸水和（或）高盐度生物;⑤海侵层中自生矿物的δ^34S,δ^13C,δ^18O同位素比值及介质盐度指数（Sr/Ba）、碱度指数（Ca Mg)／（Si Al）、还原性指标（Zn Ni)/Ga、硫沉积通量指数（归一化硫含量）等显著高于相邻层位背景值。     

Perspectives on basaltic magma crystallization and differentiation: Lava-lake blocks erupted at Mauna Loa volcano summit, Hawaii

Explosive eruptions at Mauna Loa summit ejected coarse-grained blocks (free of lava coatings) from Moku'aweoweo caldera. Most are gabbronorites and gabbros that have 0–26 vol.% olivine and 1–29 vol.% oikocrystic orthopyroxene. Some blocks are ferrogabbros and diorites with micrographic matrices, and diorite veins (≤ 2 cm) cross-cut some gabbronorites and gabbros. One block is an open-textured dunite.

The MgO of the gabbronorites and gabbros ranges  7–21 wt.%. Those with MgO > 10 wt.% have some incompatible-element abundances (Zr, Y, REE; positive Eu anomalies) lower than those in Mauna Loa lavas of comparable MgO; gabbros (MgO < 10 wt.%) generally overlap lava compositions. Olivines range Fo_83–58, clinopyroxenes have Mg#s  83–62, and orthopyroxene Mg#s are 84–63 — all evolved beyond the mineral-Mg#s of Mauna Loa lavas. Plagioclase is An_75–50. Ferrogabbro and diorite blocks have  3–5 wt.% MgO (TiO₂ 3.2–5.4%; K₂O 0.8–1.3%; La 16–27 ppm), and a diorite vein is the most evolved (SiO₂ 59%, K₂O 1.5%, La 38 ppm). They have clinopyroxene Mg#s 67–46, and plagioclase An_57–40. The open-textured dunite has olivine  Fo_83.5. Seven isotope ratios are ⁸⁷Sr/⁸⁶Sr 0.70394–0.70374 and ¹⁴³Nd/¹⁴⁴Nd 0.51293–0.51286, and identify the suite as belonging to the Mauna Loa system.

Gabbronorites and gabbros originated in solidification zones of Moku'aweoweo lava lakes where they acquired orthocumulate textures and incompatible-element depletions. These features suggest deeper and slower cooling lakes than the lava lake paradigm, Kilauea Iki, which is basalt and picrite. Clinopyroxene geobarometry suggests crystallization at < 1 kbar P. Highly evolved mineral Mg#s, < 75, are largely explained by cumulus phases exposed to evolving intercumulus liquids causing compositional ‘shifts.’ Ferrogabbro and diorite represent segregation veins from differentiated intercumulus liquids filter pressed into rigid zones of cooling lakes. Clinopyroxene geobarometry suggests < 300 bar P. Open-textured dunite represents olivine-melt mush, precursor to vertical olivine-rich bodies (as in Kilauea Iki). Its Fo_83.5 identifies the most primitive lake magma as  8.3 wt.% MgO. Mass balancing and MELTS show that such a magma could have yielded both ferrogabbro and diorite by ≥ 50% fractional crystallization, but under different fO₂: < FMQ (250 bar) led to diorite, and FMQ (250 bar) yielded ferrogabbro. These segregation veins, documented as similar to those of Kilauea, testify to appreciable volumes of ‘rhyolitic’ liquid forming in oceanic environments. Namely, SiO₂-rich veins are intrinsic to all shields that reached caldera stage to accommodate various-sized cooling, differentiating lava lakes.     

Experimental study on dynamic characteristics of granular materials under axial high-frequency vibration

The fundamental understanding of the behavior of granular materials by the effect of vibration is necessary to properly address a number of engineering issues, such as long-term settlement of high-speed railway, vibratory pile driving in sandy stratum, and earthquake-induced geotechnical disaster. Triaxial compression tests of dry Pingtan sand were carried out by a modified triaxial apparatus, where axial high-frequency vibration was super-imposed on the specimen at pre-peak, peak, and post-peak stress states during monotonic shearing. The influences of vibration conditions, confining pressure, and the initial relative density on the vibration-induced responses of Pingtan sand are mainly considered. It is shown that the super-imposed vibration leads to significant deviatoric stress reduction and vibro-induced additional axial strain. This owes to the fact that the static inter-particle friction turns to dynamic friction, and consequently, the frictional resistance has a considerable reduction when vibration is applied to the sand specimen. The vibration-induced stress–strain behavior of sand specimen is characterized into three states by two thresholds concerning vibration intensity and confining pressure: (1) stable state, (2) vibro-compression state and (3) vibro-instability state. For the vibro-compression state, the deviatoric stress reduction has a positive linear correlation with the increase in vibration intensity, while the vibro-induced additional axial strain follows a power-law increase with vibration intensity. Given a vibration condition, the deviatoric stress reductions and the vibro-induced additional axial strains at pre-peak, peak, and post-peak stress state follow a descending order. Besides, the influences of vibration on shear strength and critical state were also discussed.

     

Ergebnisse neuer Untersuchungen über Fazies und Bildung von Trias und Jura in Südwest-Deutschland

Ohne Zusammenfassung     

Indicator geostatistics for reconstructing Baton Rouge aquifer-fault hydrostratigraphy, Louisiana, USA

The complex siliciclastic aquifer system underneath the Baton Rouge area, Louisiana (USA), is fluvial in origin and is characterized by strongly binary heterogeneity of sand units and mudstones as pervious and impervious hydrofacies. The east–west trending Baton Rouge fault and Denham Springs-Scotlandville fault cut across East Baton Rouge Parish and play an important role in groundwater flow and aquifer salinization. This study reconstructs the Baton Rouge aquifer-fault system architecture for a Miocene-Pliocene depth interval that consists of the 1,200-foot sand to the 2,000-foot sand. The results show the spatial extent of sand units, their interconnections, and flow paths within each sand unit. The regional-scale formation dip, the sand unit offset on the faults, and the volumetric spatial extent of individual sand units are quantified. The study reveals the complexity of the Baton Rouge aquifer-fault system where the sand deposition is non-uniform, different sand units are interconnected, the sand unit displacement on the faults is significant, and the spatial distribution of flow pathways through the faults is sporadic. The identified locations of flow pathways through the Baton Rouge fault provide useful information on possible windows for saltwater intrusion from the south.