Intensive microearthquake swarms with the appearance of volcanic tremor have been observed in the southwest part of Long Valley caldera, southeastern California. This activity, possibly associated with magma injection, began 6 weeks after several strong (magnitude 6+) earthquakes in an area south of the caldera and has continued sporadically to the present time. The earthquake sequence and magmatic activity are part of a broad increase in tectonic activity in a 15,000-square-kilometer region surrounding the "White Mountains seismic gap," an area with high potential for the next major earthquake in the western Great Basin.

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Shallow earthquakes around the southwest boundary of Long Valley caldera, west of the Hilton Creek fault, are characterized by lack of S‐waves at regional seismic network stations to the northwest, north and northeast, and P‐waves for these same station‐event combinations are deficient in frequencies higher than about 2‐3 Hz. Earthquakes east of the Hilton Creek fault and southeast of the caldera have normal P‐ and S‐wave signatures at the same stations. These effects are explained by propagation through a magma chamber in the south‐central part of Long Valley caldera, at depth greater than 7‐8 km.

A new catalog of seismicity at magnitudes above 2.5 for the period in the Iran region is assembled from arrival times reported by global, regional, and local seismic networks. Using in-country data we have formed new events, mostly at lower magnitudes that were not previously included in standard global earthquake catalogs. The magnitude completeness of the catalog varies strongly through time, complete to about magnitude 4.2 prior to 1998 and reaching a minimum of about 3.6 during the period [1998][1999][2000][2001][2002][2003][2004][2005]. Of the 25,722 events in the catalog, most of the larger events have been carefully reviewed for proper phase association, especially for depth phases and to eliminate outlier readings, and relocated.To better understand the quality of the data set of arrival times reported by Iranian networks that are central to this study, many waveforms for events in Iran have been re-picked by an experienced seismic analyst. Waveforms at regional distances in this region are often complex. For many events this makes arrival time picks difficult to make, especially for smaller magnitude events, resulting in reported times that can be substantially improved by an experienced analyst. Even when the signal/noise ratio is large, re-picking can lead to significant differences. Picks made by our analyst are compared with original picks made by the regional networks. In spite of the obvious outliers, the median (-0.06 s) and spread (0.51 s) are small, suggesting that reasonable confidence can be placed in the picks reported by regional networks in Iran.This new catalog has been used to assess focal depth distributions throughout Iran. A principal result of this study is that the geographic pattern of depth distributions revealed by the relatively small number of earthquakes (~167) with depths constrained by waveform modeling (+/-4 km) are now in agreement with the much larger number of depths (~1229) determined using reanalysis of ISC arrival-times (+/-10 km), within their respective errors. This is a significant advance, as outliers and future events with apparently anomalous depths can be readily identified and, if necessary, further investigated. The patterns of reliable focal depth distributions have been interpreted in the context of Middle Eastern active tectonics. Most earthquakes in the Iranian continental lithosphere occur in the upper crust, less than about 25-30 km in depth, with the crustal shortening produced by continental collision apparently accommodated entirely by thickening and distributed deformation rather than by subduction of crust into the mantle. However, intermediate-depth earthquakes associated with subducted slab do occur across the central Caspian Sea and beneath the Makran coast.A multiple-event relocation technique, specialized to use different kinds of near-source data, is used to calibrate the locations of 24 clusters containing 901 events drawn from the seismicity catalog. The absolute locations of these clusters are fixed either by comparing the pattern of relo...

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