H. Tomita: Department of Physics, Sophia University, Tokyo, Japan.
5. Tremor activity changes following two San Andreas Fault earthquakes
Large earthquakes change the stress on faults. This can either accelerate or decelerate deep fault creep, as suggested by changes in tremor activity rates. Analyzing tremor data from the San Andreas Fault in central California, Shelly and Johnson find that the 2003 San Simeon earthquake, with a magnitude 6.5, created a "stress shadow" north of Parkfield, causing tremor to stop abruptly there for about a month, while tremor south of Parkfield continued. On the other hand, tremor increased sharply following the 2004 magnitude 6.0 Parkfield earthquake. The authors examine the spatial and temporal variability of post-earthquake effects on the San Andreas Fault and note a depth dependence of tremor recurrence patterns. The study provides new information on the properties of these sections of the fault, as well as new insight into how earthquakes affect stress on a fault and deep fault motion.
Geophysical Research Letters, doi:10.1029/2011GL047863, 2011
Title: Tremor reveals stress shadowing, deep postseismic creep, and depth-dependent slip recurrence on the lower-crustal San Andreas fault near Parkfield
Authors: David R. Shelly: U.S. Geological Survey, Menlo Park, California, USA;
Kaj M. Johnson: Dept. of Geological Sciences, Indiana University, Bloomington, Indiana, USA.
6. Droughts in Amazon forest increasing
In 2005 a severe, once-in-a-century drought struck the Amazon rain forest. Just 5 years later, an even more severe and widespread drought struck the region. How do these extreme events fit into the context of historical droughts? Marengo et al. looked at historical
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American Geophysical Union