Subduction along the Kuril‐Kamchatka arc has been proposed as a primary example in which subducted lithosphere plunges steeply into the lower mantle with little deformation. The occurrence of several unusual earthquakes along this arc during the last few years places new constraints on the configuration and the state of strain of the down‐going slab. We systematically determined the source parameters of 27 large‐ to moderate‐sized earthquakes (mb≥5.5) that occurred between 1963 and 1990 at depths greater than 200 km along this subduction zone. To our surprise, our results show that the configuration and strain due to earthquakes in subducted lithosphere are highly variable along both the strike and dip of the arc. Approximately 75 km farther west of the deepest earthquakes in the northern portion of the arc, the earthquake of August 14, 1988, occurred at a comparable depth of 636±17 km. Thus at least part of the slab has been displaced in a direction perpendicular to the overall strike of the Wadati‐Benioff zone. Earthquakes in the central part of the arc delineate shoaling of the subducted slab at a depth of approximately 570 km, reminiscent of the configuration of subducted lithosphere along the Tonga arc. Both observations indicate that the subducted slab is deforming, probably in response to resistance encountered near the 670‐km discontinuity. For all earthquakes north of 48°N, focal mechanisms of all events deeper than 200 km show a remarkably consistent pattern of downdip compression (strain). In the Southern Kuril, the Sakhalin Island earthquake (M0∼8×1019N m)of May 12, 1990, is one of three large deep‐focus earthquakes that have occurred over 150 km farther west of the well‐defined Wadati‐Benioff zone. The relationship between the source region of these events and the rest of the subducted slab is equivocal due to the lack of background seismicity. Nonetheless, for earthquakes south of 48°N, net downdip extension dominates between depths of 200–450 km before switching to downdip compression below 540 km. Thus the strain field within the slab is segmented both along strike and dip. If the slab in southern Kuril‐Kamchatka can serve as a stress guide down to depths of 615 km, the changeover from extension to compression occurs at an unusually large depth within the transition zone of the upper mantle. Alternatively, the deep‐focus events west of the island of Sakhalin could have occurred in a detached piece of lithosphere. As a whole, the configuration and state of strain of the subducted slab along the Kuril‐Kamchatka arc are highly variable, close to a microcosm of variations among different deep subduction systems observed on a global scale. In particular, the subducted lithosphere is apparently undergoing considerable deformation as it approaches the base of the upper mantle. Our results do not preclude the possibility of subducted lithosphere ever reaching the lower mantle. Nevertheless, it seems unlikely that the down‐going slab along the Kuril‐Kamchatka arc penetrates into the lower mantle unhindered.

No abstract

No abstract

S U M M A R YThe high resolution of broad-band seismic data is highly effective in studying ruptures associated with deep-focus earthquakes. In this study, we report results from an analysis of P and S H waveforms from eight of the largest deep-focus earthquakes that occurred between 1987 and 1992 along the north-western Pacitic. In this region, broad-band data recorded at close-in distances. directly above the source zone, offer an unusual source-receiver geometry that complements observations at teleseismic distances. Among the eight earthquakes studied, six showed clear indications of directivity. The best constraint on the extent of rupture came from the steeply dipping Izu-Bonin Wadati-Benioff zone, where subhorizontal ruptures typically originate in the interior of subducted slab and propagate toward the top at high angles. In particular, rupture of the 1988 September 7 event consists of two en echelon line sources. At a depth of approximately 480 km. the overall rupture length of this earthquake constrains the minimum thickness of the seismogenic zone to be 27 f 12 km. At this depth, our estimated thickness of the seismogenic zone seems remarkably close to the maximum thickness (-35 km) predicted by the metastable olivine wedge model of seismogenesis. This model interprets deep-focus earthquakes as a result of transformational faulting within a region bounded approximately by the 700 "C isotherm. The extent of rupture during the largest events in this region seems to be only slightly larger than the 20-25 km spacing between the two layers of a double seismic zone. found at depths between 300 and 400 km in the same general area. Beneath the Island of Sakhalin, a rupture speed greater than that of the shear wave is not required for the large, deep-focus earthquake (-615 km) of 1990 May 12. Almost all complexity in observed waveforms for this event can be explained by a northward propagating, subhorizontal rupture composed of only two subevents.

-The quantitative forecasting of spectral imaging system performance is an important capability. The ability to accurately predict the effects on utility of the data due to scene conditions, sensor performance, or even algorithm parameters, can be very important. To this end, an analytical modeling tool has been under development to predict end-to-end spectroradiometric remote sensing system performance, and to understand the relative impact of various system parameters on that performance. Recently, data were collected by NASA's EO-1 Hyperion space-based hyperspectral imager over an area in Southern California including spatially unresolved buildings of known size. The area of interest was also imaged with previous low-altitude overflights of NASA/JPL's AVIRIS airborne imaging spectrometer. The AVIRIS data provided an opportunity to investigate the accuracy of unmixing analysis applied to the Hyperion image as well as to serve as a source of input data in model forecasts. This paper describes the results of analysis of the remotely sensed data as well as comparisons to predictions made by the analytical performance prediction model. While the empirical analyses provide point results in terms of the abundance of the buildings per pixel, the model predicts the anticipated variation in the abundance estimates given inherent variability of the building roof material and nearby backgrounds. The model is also exercised to show the impact on the abundance estimates from various remote sensing system parameters including sensor noise, radiometric calibration error, and the number of endmembers assumed in the unmixing algorithm. In the example studied, the natural surface variability and the use of endmembers in the unmixing that were not present in the scene were found to have the most impact on the abundance estimates.