Plate convergence measured by GPS across the Sundaland/Philippine Sea Plate deformed boundary: the Philippines and eastern Indonesia

The western boundary of the Philippine Sea (PH) Plate in the Philippines and eastern Indonesia corresponds to a wide deformation zone that includes the stretched continental margin of Sundaland, the Philippine Mobile Belt (PMB), extending from Luzon to the Molucca Sea, and a mosaic of continental blocks around the PH/Australia/Sunda triple junction. The GPS GEODYSSEA data are used to decipher the present kinematics of this complex area. In the Philippines, the overall scheme is quite simple: two opposing rotations on either side of the left-lateral Philippine Fault, clockwise to the southwest and counterclockwise to the northeast, transfer 55 per cent of the PH/Sundaland convergence from the Manila Trench to the northwest to the Philippine Trench to the southeast. Further south, 80 per cent of the PH/Sunda convergence is absorbed in the double subduction system of the Molucca Sea and less than 20 per cent along both continental margins of northern Borneo. Finally, within the triple junction area between the Sundaland, PH and Australia plates, from Sulawesi to Irian Jaya, preferential subduction of the Celebes Sea induces clockwise rotation of the Sulu block, which is escaping toward the diminishing Celebes Sea oceanic space from the eastward-advancing PH Plate. To the south, we identify an undeformed Banda block that rotates counterclockwise with respect to Australia and clockwise with respect to Sundaland. The kinematics of this block can be defined and enable us to compute the rates of southward subduction of the Banda block within the Flores Trench and of eastward convergence of the Makassar Straits with the Banda block. The analysis made in this paper confirms that this deformation is compatible with the eastward motion of Sundaland with respect to Eurasia determined by the GEODYSSEA programme but is not compatible with the assumption that Sundaland belongs to Eurasia, as was often assumed prior to this study.     

Block-and-ash flow deposition: A conceptual model from a GPR survey on pyroclastic-flow deposits at Merapi Volcano, Indonesia

In 2006, a series of block-and-ash flows swept the southwestern and southern flanks of Merapi Volcano, Java, Indonesia. In the K. Gendol valley, near the village of Kaliadem, we conducted a GPR survey on the most distal lobe of the June 14th second block-and-ash flow deposit. For this 100 m-long transect, we used a commercial GPR RAMAC© mounted with 100 MHz antennas. We measured the topography with a synchronized GPS and a laser rangefinder. Back at the laboratory, we processed the dataset with the software REFLEX®. Data of the subsurface reveals a series of layers, separated by strong reflective horizons. These horizons are the manifestation of intercalations of fine materials in between more coarse layers. The architecture of these layers presents progradation, retrogradation and aggradation patterns that we relate to the block-and-ash flow deposition process. Based on these observations we proposed a relative chronology of the deposition and a simple conceptual model of the deposition. The model show that the block-and-ash flow can deposit either long, close to horizontal single layers, or shorter layers that imbricate themselves, following different patterns (progradation, retrogradation or aggradation). Nevertheless we remained cautious, since we only studied a very short portion of the deposit, and similar experiences need to be repeated. Moreover there are reflections in the radargram that we could not identify, and further studies need to be conducted.     

The influence of seasonal and local weather conditions on rock surface changes on the shore platform at Kaikoura Peninsula, South Island, New Zealand

A traversing micro-erosion meter (TMEM) was used to measure micro-scale surface changes in a 45 cm² area of an intertidal mudstone shore platform on Kaikoura Peninsula, New Zealand, with hourly readings taken over 5 days for two seasons, within 4 h either side of low tide. For all monitoring events, the relative height of a total of 120 co-ordinates were obtained, resulting in 4200 and 4800 measurements for the summer and winter seasons respectively. Within seasons, samples were grouped according to the presence of rain or no rain. Significant changes were found in the micro-topography with variations in temperature and among rain and no rain sample groups. For both seasons, in the absence of rain, there were positive linear relationships between rock surface temperatures and rock surface elevations, and regression analysis explained 42.3% and 46.5% of this variation for the summer (y = 0.098 + 0.004x; p-value = 0.007) and winter (y = 0.007 + 0.012x; p-value < 0.001) seasons respectively. It is suggested that incorporating weather readings alongside measurements of surface change could not only improve extrapolations of shore platform erosion from short-term studies, but also differentiate fluctuations in rock surfaces due to changes in rock surface temperatures from other processes involved in shore platform erosion.     

GPS、GIS技术在西庄河流域滑坡灾害研究中的应用

本文采用了GPS辅助下的野外调查、野外实地填固进行数据采集和室内GIS(ArcInfo7．0)辅助下的数据储存、分析方法，以西庄河山地流域过去发生的滑坡事件为研究对象，初步分析了该山地流域内滑坡事件的时空分布特征及近期滑坡发生的可能趋势。最后，指出GPS和GIS技术在流域滑坡灾害研究中具有广泛的应用前景和优越性。     

A test of the possible influence of seabird activity on the <Superscript>210</Superscript>Pb flux in high Arctic ponds at Cape Vera,Devon Island,Nunavut: implications for radiochronology

A large seabird colony of northern fulmars (Fulmarus glacialis) at Cape Vera on Devon Island in the Canadian high Arctic has been shown to act as an effective biological pump, transporting large quantities of marine-derived nutrients and contaminants to the ponds beneath their nesting sites. Previous research has shown that seabirds also have the potential to elevate radionuclide concentrations in their immediate surroundings. Here, we assess the influence of the Cape Vera seabird colony on the ²¹⁰Pb budgets of six affected ponds and one control site, and discuss potential implications with respect to ²¹⁰Pb dating methodologies. In general, fluxes of ²¹⁰Pb at Cape Vera were similar to, or less than, those measured at other Arctic locations not influenced by seabirds. Plots of unsupported ²¹⁰Pb activity versus depth showed a number of non-monotonic features in all sediment cores, necessitating the use of the constant-rate-of-supply (CRS) model to derive age-depth profiles. We conclude that seabird activity has not dramatically increased the ²¹⁰Pb flux to the ponds at Cape Vera. Overall, the low flux of excess ²¹⁰Pb made accurate dating problematic for some of the study cores, necessitating the use of independent dating markers (e.g., ¹³⁷Cs and PCB concentrations) to verify the reliability of the chronologies.