October Geology and GSA Today media ...(alog for the entire Cascadia subduction ...)

Date:9/25/2007

alog for the entire Cascadia subduction zone, offshore western North America, and compare the patterns with a variety of along-strike trends for the subducting and overriding plates. Correlated ground vibrations and strain observations are found all along the subduction zone, demonstrating that ETS is an inherent part of the subduction process. There are three broad (300500 km), coherent zones with different recurrence intervals (14 2, 19 4, 10 2 months), where the interval duration is inversely proportional to upper plate topography and the spatial extent correlates with geologic terranes. These zones are further divided into segments of ETS that occur at times typically offset from each other. The seven largest (100200 km) segments appear to be located immediately landward from forearc basins interpreted as manifestations of megathrust asperities, implying that there is a spatial link between ETS and earthquake behavior. It is not yet clear if any temporal link exists, but the regional time between ETS episodes could be controlled by strength variations due to composition of geologic terranes.

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Quantification of soil erosion rates related to ancient Maya deforestation
Flavio S. Anselmetti, Geological Inst. ETHZ, Earth Sciences, Universittsstr. 16, CHN H70, Zurich, ZH 8092, Switzerland; et al. Pages 915-918.

Anselmetti et al. address an important issue of how the ancient Maya civilization of Mesoamerica impacted the environment through its agricultural activities. For the first time, Anselmetti et al. have quantified soil erosion rates over 6000 years during the period of Maya occupation in a lake basin in northern Guatemala. They found that soil erosion was greatest (almost 1000 t/ km2yr1) in the Pre-Classic period when estimated population densities were still low. Erosion rate unexpectedly declined in the Early and Late Classic periods as Maya population densities rose exponentially. Anselmetti et al. infer that a pulse
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Contact: Ann Cairns acairns@geosociety.org 303-357-1056 Geological Society of America Source:Eurekalert

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