The Mechanism And Effect Analysis Of Using Dual Waves In Source Location

Geological dynamic disasters,such as rockbursts,have always been threatening the safety production in deep mines.Microseismic monitoring is an ideal tool for studying all kinds of dynamic disasters in geotechnical engineering.Source location is a basic and unique advantage of microseismic monitoring.Most of the source location techniques,however,use only P-wave,and their effective monitoring area is small.The location errors outside of the monitoring network are large,and the stability of the location results is very poor.To improve the source location accuracy,increase the effective monitoring area of the monitoring network,enhance the reliability of the monitoring results,and further strengthen the role of microseismic monitoring in the monitoring and early warning of various geological dynamic disasters,and improve the capability of microseismic monitoring in the monitoring and early warning of various types of dynamic disasters,this research paper would focus on simultaneously utilizing P-and S-waves,which is represented by dual waves.Theoretical derivation and analysis,program development,computer numerical simulation,and some other research methods are utilized in the thesis,and the mechanism of using both P-and S-waves in source location is investigated.Also,the location effects,after including S-wave,in both two-dimensional case and three-dimensional space are carefully analyzed.The influence of velocity error and arrival-time error on the location result is systematically studied as well.At the same time,the location accuracy of using dual-waves and using P-wave only is compared in different sensor arrays,different sizes of sensor array and arrays consist of different numbers of sensors.The location accuracy of the monitoring network in a coal mine has been studied.The main conclusions are as follows:(1)The principle of conventional source location,which is arrival-time-difference approach that utilizes P-wave only,is reviewed.Meanwhile,the mechanism of simultaneous using P-wave and S-wave in source location is studied.And after the theoretical analysis,the mechanism is revealed.The essential causes for the improvement of the location effect after adding S-waves is presented as well.As follows:①The source location method,which is most commonly used,is the arrival-time-difference approach,but this method only utilizes P-wave.Its principle,in two-dimensional case,is the hyperbolic field,and the location accuracy mainly depends on the density of the hyperbolic intersections.Inside the sensor array,the source location accuracy is high.And outside the array,the location error is relatively high.Also,as the increase of the distance from the center of the sensor array,the location error increases rapidly.In three-dimensional space,the principle of source location is a hyperboloid field,and the location effect is similar to that in two-dimensional case.The location accuracy mainly depends upon the intersection of hyperboloids,or the density of the intersections.At the center of a monitoring network,the accuracy is the highest,and the error is the smallest.As the source moves out,the location accuracy decreases.However,the location effect is overall better in the monitoring network.When the source moves out of the monitoring network,the location accuracy drops rapidly,and the location error rises rapidly.②The mechanism of source location has changed when dual waves are utilized.There is accuracy control in the radial direction of a monitoring network when S-wave is used.In two-dimensional case,a circle is added around each sensor,and in three-dimensional case,a sphere is added around each sensor.Therefore,the source location accuracy depends on not only the density of intersections of hyperbolas or hyperboloids,but also the density of intersections between hyperbolas and circles or hyperboloids and spheres.After S-wave is included,the monitoring network can not only accurately locate the AE/MS events occurring inside the monitoring network,but also locate the AE/MS events occurring in a certain range outside the network relatively accurately.Of course,the location error increases with the increase of the distance from the network,and the error is large for the AE/MS events that occur at a far location.(2)A computer numerical simulation program was developed,and this program was used to study and compare the location effect of different sensor arrays,sensor arrays with different sizes and the arrays consist of different numbers of sensors in the case of using P-wave only and using dual waves.Therfore,the location result of different sensor arrays and the influence of geometrical size of an array and the sensor number of an array on location result are obtained.The details are as follows:①By Matlab software,a Simplex source location algorithm based on the least squares method(L2 norm statistic method)was selected to develop the computer program of numerical simulation.And this program can be used to analyze the location errors of different sensor arrays,which laid the foundation for the follow-up research.②For differently distributed sensor arrays,the location accuracy is high within the array,but it drops rapidly and the location error increases fast outside the array in the case of utilizing only P-wave,whether it is a ring array or a diamnd array.However,after the S-wave is added,the location accuracy is high not only within the network,but also within a certain area outside the network,and the location error increases slowly.Therefore,the location accuracy is improved for the area outside the array,the effective monitoring area of an entire monitoring network is increased,and the stability of the location result is greatly enhanced as well after the S wave is added.③For arrays with different geometrical sizes,similarily,the location accuracy is high and the location effect is good for the AE/MS events occurring within the geometrical distribution of the sensor,but the location error increases rapidly and the location effect deteriorates rapidly for the AE/MS events occur out of the distribution if only P-wave is used.The array distribution can accurately locate AE/MS events not only within the geometry of the sensor,but within a certain range outside the geometric distribution if S-waved is used as well.And the stability of the results is greatly improved.The research showed that,when only P-wave is included,as the increase of the geometric size of a monitoring network,at the very behinning,the high-accuracy area is constantly increasing.But the effective monitoring area of the network keep a constant value of area and no longer increases when the geometrical size of the network reached a certain value.However,the effective monitoring area does not increase with the increase of the size of the network geometry,but maintains a constant value when using dual waves in source location.④For monitoring networks consisting of different numbers of sensors,the effective monitoring area,where there is high location accuracy,increases with the increase of the sensor number when using only P-wave data.But the effective monitoring area remains unchanged,which means it will not change with the increase of the number of sensors when the S-wave data is also used.For a sensor configuration,the location error is low and the result is good within the configuration regardless of S-wave is added or not.However,the location error rises rapidly and the accuracy declines to the unacceptable level very fast out of the configuration if S-wave is not used.The location error increases evenly slow if S-wave is used.Therefore,even if outside the sensor configuration,there is a relatively high location accuracy and good location result for the area just out of the array boundary.The stability of the location results has been greatly improved after adding S-wave.(3)To study the location effect of using both P-and S-waves in source location in three-dimensional space,the location effect of three typical three-dimensional monitoring networks is analyzed,and compared this with the effect of these which using only P-wave.Also,the microseismic monitoring scheme in a coal mine was deeply studied.The details are as follows:①The numerical simulation results of the three-dimensional monitoring networks indicate that the lcoation accuracy in the vertical direction can be greatly improved,the high-accuracy area in the vertical direction can be expanded,and the stability of the lcoation results in the vertical direction can be enhanced if both waves are utilized in source location.Therefore,the vertical location result can be improved after including S-wave.The location result is similar to that in two-dimensional case in horizontal direction.This is very important in the case where deep-hole operations are required to install sensors for source location and in earthquake location.②The research on the field test scheme shows that only the area within the monitoring network has high location accuracy,for the areas outside the network,the location accuracy falls rapidly to an unacceptable level when only P-wave is used.Outside the two ends of the monitoring network,there is a blind area,where there is no accuracy control.The blind area disappears and the location accuracy is relatively high within a certain area beyond the geometrical distribution of the sensor after the S-wave is added,although the location error is still increasing.It is slowly increasing,so the location result is more stable than that of not using S-wave.(4)Velocity error of waves and arrival-time error are two key factors that affect the location accuracy of the source.This article uses the above-mentioned third numerical simulation scheme and field test scheme as an example to systematically study the wave-velocity error and arrival error for the source location.The effect of error.The influences of the wave-velocity error and the arrival error on the location accuracy were studied when the P-wave and S-wave were applied simultaneously and only the P-wave was applied.The results show:①Velocity error is the main source of source location error.The results show that the location error decreases with the decrease of the wave velocity error and increases with the increase of the wave velocity error.However,the negative wave speed error,that is,the calculation of the use of the wave speed is smaller than the actual wave speed,the positioning error caused by the equal wave velocity error caused by the equivalent location error.With the same velocity error,when dual waves are applied,that is,when P-wave and S-wave are applied simultaneously,the location results are much more accurate than the application of P-waves only.No matter whether it is within the monitoring station network or the station network,whether it is the horizontal direction or not.Still vertical.That is,the dual-wave monitoring station network is far more capable of processing the wave velocity error than the P-wave network.②The arrival-time error is another key factor that affects the location accuracy.The results show that the location error is positively correlated with the arrival error,that is,the location error increases with the increase of the error.In the horizontal direction,the two are basically linear,but in the vertical direction,the change in location error is sometimes small.When S-wave is added,the entire monitoring network can greatly increase the processing time error.In the horizontal direction,it is mainly reflected in the geometric distribution of the network,and the overall improvement in the vertical direction.