An automatic detection algorithm of P-wave arrival time for a microearthquake is described. A function based on normalized fourth-order cumulant, kurtosis, is used to detect both provisional P-wave arrival time and the end of microseismic signal. The contrast function has the maximum value near the P-wave arrival time. After detection of the provisional P-wave arrival time, maximum likelihood analysis is applied to evaluate residuals between microseismic signal and its AR model, which is made based on the provisional P-wave arrival time. 100 of microseismic events are used to examine the performance of this automatic detection. Errors of the automatic detection are within 3 ms in the 97 events. 3 ms is as long as a quarter of a period of P-wave because dominant frequency of P-wave is 80 Hz.
Distribution of the darcy velocity of groundwater flow in aquifers in the Nobi plain is estimated to understand suitable area for installation of ground-coupled heat pumps. The velocity of groundwater flow is calculated from hydraulic gradient and permeability coefficient of aquifers. Distribution of hydraulic gradient is estimated from interpolated distribution of water table of wells using kriging. Permeability coefficient of aquifers is assumed to be a constant value of 10-3m/s. In any area of the Nobi plain, the velocity of groundwater flow in the aquifer is not expected to be >10-5m/s. In the most part of the alluvial fan area, the gravel is dominant in the formation and the velocity is >10-6m/s. In the southwestern area, the velocity is ≤6.3×10-7m/s. This difference of groundwater velocity would affect effective heat conductivity of formations and heat transfer under the ground.