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+/- 0.3 are typical for local micro magnitude scales (Thatcher, 1973), and are due not only to <br />instrument variation but also to uncertainties in the basic definitions of magnitude scales. <br />Magnitude values for detected and located events should be analyzed with consideration of these <br />uncertainties. <br />This process is ongoing but the use of stable stations within MSSN will allow the correlations to be <br />continually refined. As recorded ground motions and station distances are applied to these <br />magnitude determinations, the magnitude scale can be extrapolated to the smaller, more <br />numerous events. <br />Location Analysis <br />Events recorded by the triggered system with clear arrivals on eight or more stations are analyzed. <br />The program "SUDSVIEW V2.0" is used to display the data from each station. The arrivals are <br />time registered by the recording system, thus the picking of the onset of the first arrival is <br />facilitated. This program also corrects for the DC shift of the accelerometer data and reports the <br />maximum digital signal received on each of the three channels transmitted from each station. <br />These data, the arrival times for each station and the maximum digital signal on each component <br />are recorded for computer analysis. The arrival time data is put into HYPOINVERSE 2000,2002) <br />and the calculations, based on the station locations, arrival times, and delay time corrections if <br />any, are preformed. Output of the location program includes the latitude, longitude and depth for <br />each event and the distance to the hypocenter for each station. <br />The quality of the location is based on several metrics including the residuals (mismatch of model- <br />based-calculated-arrival-time and observed arrival time) and the root-mean-squared total error. A <br />contributor to the quality is the "gap", the maximum angle between stations from the perspective of <br />the hypocentrl location. A well located event within one of the subnets will have a gap of 70-90 <br />degrees. An event outside of the network (or a subnet) may often have a gap of 180-190 degrees. <br />Event locations are converted from latitude and longitude to UTM coordinates (in feet) and plotted <br />with respect to the network stations. <br />The distance from each station to the hypocenter is another output of the location program. A <br />preparation program for the input data converts the digital counts to acceleration and calculates <br />the largest calculated acceleration. These data (distances, accelerations, and locations) are then <br />output as Table 4. <br />Threshold Analysis <br />Large events are detected and analyzed by NEIC in Golden, NIOSH in Spokane, MSSN in Grand <br />Junction. An exceptional event may be felt by mine personnel. Quantitative analysis currently <br />generally is available within 24 to 48 hours from NIOSH. A threshold reaction program for <br />inspection or mitigation is under development for use when mining approaches non-mine owned <br />structures. <br />• <br />