Advanced S-Phase Detector

The scanloc package provides the enhanced S-phase detectors, S-AIC and S-AIC-V, as well as the debugger.

Overview

The scanloc package includes two S phase pickers: S-AIC and S-AIC-V, enhancing the performance of the picker with respect to the OpenSource S-L2. Both picker apply an AIC algorithm in order to detect S phases after a P pick was maked. Therefore S phases are only detected after a P detection. Using the S-AIC, S picks are determined on the vectorial sum of the horizontal componentes (L2 trace). The S-AIC-V works like the S-AIC but it picks S phases on the vertical component.

The method which was applied to make the pick can be read

• In the method column of the arrival table in the Location tab of scolv [18],

• In the picker window from the letter within brackets following a phase type,

• In the picker window from the hint which appears when hovering over a pick.

Figure 41: Read the method applied to make a pick in the arrival table of scolv or in the picker window.

The performance of the pickers have been tested by comparison of automatic with manual picks (see the Figure showing the comparison).

Figure 42: Performance comparison showing the differences in pick time from manual picks and the optimally tuned pickers S-L2, S-AIC and S-AIC-V for local earthquakes in West-Bohemia/Vogtland. The area is typical of local earthquake monitored at short epicentral distances of a few tens of kilometers. The distribution of the differences in the automatic pick times with respect to the manual ones shows the increased performance using the S-AIC.

Picker configuration

1. Global module parameters: Add the plugin saic to the configuration of scautopick or the global module configuration for making use of the S-AIC or the S-AIC-V:

   plugins = ${plugins},saic
   

2. Module parameters: Activate one of the S-phase ickers (S-L2, S-AIC, S-AIC-V) by changing the name of the S picker in the module configuration of scautopick. Deactivating killPendingSPickers will allow to pick S phases even if more P phases were detected before:

   spicker = "S-AIC"
   killPendingSPickers = false
   

3. Bindings parameters: Configure the S-picker parameters under spicker in global section of the bindings of scautopick e.g. for S-AIC in local earthquake monitoring. For tuning the values based on actual data you may use the graphical debugger:

   detecFilter = "RMHP(10)>>ITAPER(30)>>BW(4,4,20)>>STALTA(0.2,20)"
   timeCorr = 0
   
   spicker.AIC.noiseBegin = -10
   spicker.AIC.signalBegin = 0.5
   spicker.AIC.filter = "ITAPER(4)>>BW_HP(4,3)"
   spicker.AIC.detecFilter = ""
   spicker.AIC.step = 0.5
   spicker.AIC.minSNR = 5
   spicker.AIC.minCnt = 5
   

   The AIC parameters spicker.AIC. are used for S-AIC and for S-AIC-V. The parameters of the S-phase pickers can be configured in the global section of the bindings profile of scautopick. The meaning of some parameters are shared between the S-phase pickers:

   Parameter	Picker type	Description
   noiseBegin	S-AIC, S-AIC-V, S-L2	Data window added before the p pick on order to compensate for effects due to the data processing, filtering and to compute the SNR.
   signalBegin	S-AIC, S-AIC-V, S-L2	Start of the data processing relative to the reference P pick.
   signalEnd	S-AIC, S-AIC-V, S-L2	End of the data processing relative to the reference P pick.
   filter	S-AIC, S-L2	Filter applied before forming the L2 trace.
   detectFilter	S-AIC, S-AIC-V, S-L2	Filter applied on the L2 trace before AIC analysis.
   step	S-AIC, S-AIC-V	Step size in which the time windows are enlarged.
   minSNR	S-AIC, S-AIC-V, S-L2	Minimum SNR in order to accept a pick.
   minCnt	S-AIC, S-AIC-V	Minimum number the AIC minimum must be found for subsequent time windows.
   uncertainty	S-AIC, S-AIC-V	Pick uncertainty. Unused by the picker but part of the output pick element.

Picker tuning: Debugger

The debugger GUI allows the graphics-assisted tuning of the S pickers, S-L2, S-AIC, S-AIC-V. In order to make use of the S picker debugging GUI:

1. Global module parameters: Add the plugin spickdbg to the global configuration of scolv [18] (scolv.cfg)

   plugins = ${plugins}, spickdbg
   

2. Global bindings: Configure the initial parameters in the global bindings of the considered stream. You may adopt parameters from the ones used by the spicker for a good inital guess.

The debugger GUI can be started from the picker window of scolv. If there is an existing P pick, the debugger window can be opened with a right click on the P pick. In the dropdown menu the S picker type can be chosen.

Figure 43: Selection of S-picker debugger by right-clicking on a P phase.

A new pop-up window opens where the P pick (red line) and the newly determined S pick (light blue line) are shown and the parameters can be tested.

Figure 44: S-picker debugger example showing the filtered horizontal traces, the computed L2 trace and the resulting S pick (light blue line).

The example above shows the debugger GUI for a local earthquake:

• Top traces: original filtered data.

• Bottom trace: Resulting trace e.g. L2.

• First red line: the time of the referenced pick. A pick pick should be selected.

• Additional phase picks are shown on top of the data.

• Light blue line: the S pick which would be made based on the selected parameters. The number next to ‘AIC’ indicates the SNR.

• Lower section: Parameters which can be adjusted.

The initial parameters are read from the global binding configuration from the selected stream. Change the parameters to find the optimum values. Click on the Update button to apply them in the GUI. In order to make use of the tested parameters their values must be configured in the bindings parameter of scautopick or the respective alias.

Parameter	Description
N	Start of the noise window
S0	Start of the AIC window
S1	End of the AIC window
AIC0	Start of the data processing relative to the reference P pick.
AIC	S pick based on the current parameters with number indicating the SNR.
AIC1	End of the data processing when meeting MinSNR and MinCnt.
Pick	Pick time at AIC.