LOCSAT

Locator in SeisComP for computing source time and hypocenter coordinates from phase picks.

Description

LOCSAT is a locator in SeisComP for computing source time and hypocenter coordinates from phase picks considering:

  • Pick time,

  • Backazimuth,

  • Slowness.

The LOCSAT locator interface implements a wrapper for the LocSAT locator by Bratt and Nagy [39] (according to the README file shipped with the LocSAT distribution) referred to as LOCSAT in SeisComP.

Travel-time tables

SeisComP ships with two predefined travel time tables: tab and iasp91. LOCSAT travel time tables are located under share/locsat/tables/.

The default profile is iasp91.

Travel-time interface

LOCSAT provides an interface for computing travel times based on coordinates and depth.

Use “LOCSAT” as a value for the travel-time interface when configurable, e.g. by FixedHypocenter.

Configuration in SeisComP modules

Use “LOCSAT” as a value for the locator type or interface when configurable, e.g. by screloc or scolv.

Station corrections

LOCSAT does not support station corrections natively. At least checking the code:

sta_cor[i]  = 0.0;    /* FIX !!!!!!*/

However the SeisComP wrapper adds this feature. It allows to define a .stacor file which defines corrections of observation times in seconds. A correction is subtracted (not added) from the observation time to be compatible with the NonLinLoc [49] station correction definitions.

Each LOCSAT profile (travel time table) can have an associated station correction file. To use station corrections for the iasp91 tables, the file $SEISCOMP_ROOT/share/locsat/tables/iasp91.stacor needs to be created.

A station correction table takes the form:

# LOCDELAY code phase numReadings delay
LOCDELAY GE.MORC P 1 -0.1

with

  • code (string) station code (after all alias evaluations)

  • phase (string) phase type (any of the available travel time tables)

  • numReadings (integer) number of residuals used to calculate mean residual/delay (not used by NLLoc, included for compatibility with the format of a summary, phase statistics file)

  • delay (float) delay in seconds, subtracted from observed time

Note

The fourth column (numReadings) is ignored and just provided for compatibility reasons with NonLinLoc.

Module Configuration

Note

LOCSAT.* Locator parameters: LOCSAT

LOCSAT.profiles

Type: list:string

Defines a list of available LOCSAT travel-time tables. Default is iasp91, tab.

LOCSAT.depthInit

Type: double

Unit: km

The initial depth estimate for LOCSAT. Default is 20.0.

LOCSAT.usePickUncertainties

Type: boolean

Whether to use pick time untertainties for arrival deltim rather than a fixed time error. If true then the uncertainties are retrieved from each individual pick object. If they are not defined then the default pick time uncertainty will be used as fallback. Default is false.

LOCSAT.defaultTimeError

Type: double

Unit: s

The default pick time uncertainty assigned to LOCSAT’s arrival deltim attribute if pick uncertainties are not going to be used or if they are absent. A time uncertainty of 0 s may result in errors of the SVD decomposition in LOCSAT. Default is 1.0.

LOCSAT.usePickBackazimuth

Type: boolean

Whether to forward pick backazimuth to LOCSAT or not. In an automatic mode backazimuth measurements might be inaccurrate and disabling their usage in LOCSAT can be controlled with this parameter. Default is true.

LOCSAT.usePickSlowness

Type: boolean

Whether to forward pick horizontal slowness to LOCSAT or not. In an automatic mode slowness measurements might be inaccurrate and disabling their usage in LOCSAT can be controlled with this parameter. Default is true.

LOCSAT.degreesOfFreedom

Type: int

Number of degrees of freedom. Default is 9999.

LOCSAT.confLevel

Type: double

Confidence level between 0.5 and 1.0. Default is 0.9.

LOCSAT.enableConfidenceEllipsoid

Type: boolean

Compute the confidence ellipsoid from covariance matrix in 3D. Default is false.