The PASSCAL instrumentation performed very well in the Tibetan Plateau Seismic Experiment. This experiment has demonstrated the viability of recording high-quality broadband data at temporary sites in extreme environments. It also highlights some areas where further development is needed. Primarily, more effort is needed to develop more versatile triggering options for the PASSCAL instruments. Such developments could both increase the instrument's success at recording low magnitude teleseismic events for travel-time studies and save disk space when recording local events, thus further increasing the feasibility of long deployments in remote regions. Although the use of the PASSCAL instrument's calibration circuitry for sensor recentering is a valuable technique, more experience is needed in the construction of sensor pads to minimize tilt problems that require site visits to relevel the seismometer such as we experienced at a few sites in the winter. This may also lead to improved low-frequency noise levels, although signals with periods greater than 200 sec can be recovered from these sites.
The most exciting aspect of the data we have collected is its broad frequency content and spatial density. We anticipate that this type of experiment will be increasingly useful in the study of lithospheric interactions as well as deep Earth structure. This data was delivered to the IRIS Data Management Center in early September 1993 and is available to the community. Two other broadband passive-seismic experiments, the Baikal Rift experiment (Gao et al. 1992) and the Rocky Mountain Front experiment (Sheehan et al. 1992) should be delivered to the IRIS DMC in the Fall of 1993 as well. Temporary broadband seismic experiments represent an extension of the permanent Global Seismic Network (GSN). We encourage the seismological community to incorporate these data into any research using GSN data in order to maximize the potential utility of this new mode of seismic recording.