75 | | appears in the glass_assoc.d config file. The Nucleator iterates through a set of trial origin times within the potential origin time window. The time delta between iterations in seconds is defined by the !TimeStep command. So if !TimeStep is 5.0, then the Nucleator will iterate between origins that are 5 seconds apart. The smaller the !TimeStep value, the closer the Nucleator should be to the actual origin time and the more processing iterations that will have to be done, so there is a tradeoff between accuracy and processing effort. There are two factors that affect what the TimeStep value should be set to: residual distance limits and locator ability. Because the Nucleator fixes the origin time and depth, any residuals are distance based. If the TimeStep value is set too high, then it increases the artificial distance residual that may be imposed on an origin because the actual event time lay between two iterative steps. So if an event occurs at time 1232.5, !TimeStep is set to 5, and the closest two origin time iterations are 1230.0 and 1235.0, then an artificial time residual of 2.5 seconds is being imposed on the nucleated origin. Because the Nucleator deals only in distance residuals, that 2.5 seconds becomes converted to a distance value. When that residual distance value gets to be too great then the Nucleator will no longer be able to associate the origin. The Nucleator is a tool to associate picks into an Origin, its association is not meant to be the Glass end-all final location answer. Within Glass there is a Locator that will refine solutions after they come out of the Nucleator. So a TimeStep value must be chosen that is not too processing intensive but is also not so wide as to preclude origins based on the artificial residuals between time iterations and actual event time. A !TimeStep of 5.0, results in a maximum artificial window of 2.5 seconds, with a maximum P velocity of about 13km/sec, that ends up at a worst case artificial distance residual of 32km. If the distance Cut is set to 50km, this leaves only 18km available for anomalies due to actual vs. theoretical 1-d travel times, and depth iteration intervals. |
| 75 | appears in the glass_assoc.d config file. The Nucleator iterates through a set of trial origin times within the potential origin time window. The time delta between iterations in seconds is defined by the !TimeStep command. So if !TimeStep is 5.0, then the Nucleator will iterate between origins that are 5 seconds apart. The smaller the !TimeStep value, the closer the Nucleator should be to the actual origin time and the more processing iterations that will have to be done, so there is a tradeoff between accuracy and processing effort. There are two factors that affect what the !TimeStep value should be set to: residual distance limits and locator ability. Because the Nucleator fixes the origin time and depth, any residuals are distance based. If the !TimeStep value is set too high, then it increases the artificial distance residual that may be imposed on an origin because the actual event time lay between two iterative steps. So if an event occurs at time 1232.5, !TimeStep is set to 5, and the closest two origin time iterations are 1230.0 and 1235.0, then an artificial time residual of 2.5 seconds is being imposed on the nucleated origin. Because the Nucleator deals only in distance residuals, that 2.5 seconds becomes converted to a distance value. When that residual distance value gets to be too great then the Nucleator will no longer be able to associate the origin. The Nucleator is a tool to associate picks into an Origin, its association is not meant to be the Glass end-all final location answer. Within Glass there is a Locator that will refine solutions after they come out of the Nucleator. So a !TimeStep value must be chosen that is not too processing intensive but is also not so wide as to preclude origins based on the artificial residuals between time iterations and actual event time. A !TimeStep of 5.0, results in a maximum artificial window of 2.5 seconds, with a maximum P velocity of about 13km/sec, that ends up at a worst case artificial distance residual of 32km. If the distance Cut is set to 50km, this leaves only 18km available for anomalies due to actual vs. theoretical 1-d travel times, and depth iteration intervals. |