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If the quality is not high enough the software waits until a fourth accelerometer reports detection of a P-wave. Then the Direct Grid Search runs again. In additional addition another algorithm called Linearized Least Squares also analyzes the four P-wave times. The mean value of the output of both algorithms is reported as the epicenter. Knowing the distance from the epicenter to the sensors, the time of origin of the earthquake can be determined.
In addition the The magnitude of the earthquake is estimated using two methods. One method compares the Tau (period) values reported by the accelerometers, which is expected to be the same at all sensors. The magnitude is proportional to the Tau on a logarithmic scale. The other method uses the Pd or maximum vertical acceleration reported by each of the sensors. The Pd is attenuated by the distance to the sensor on a logarithmic scale. So after factoring in the attenuation due to distance, the magnitude is logarithmically proportional to the Pd.
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