A low-noise, low-power broadband borehole seismometer is required for use in networks of seismic stations for monitoring underground nuclear explosions. This project will apply the latest technology from surface broadband instrumentation to the borehole application, leading to two prototype instruments that will be suitable for noise and stability testing at a seismically quiet site. Phase I will resolve the remaining noise issues of the electronics and complete the design, including drawings for building prototypes in Phase II. Feasibility tests will be conducted on breadboards, as required for proof of concept. Commercial Applications and Other Benefits as described by awardee: A low cost, low-power, low-noise borehole triaxial seismometer should open the technology to more customers. For example, research programs are often prohibited from using borehole instruments because of the very high cost.