# Earthworm Modules:
Evanstrig and Evansassoc Overview

(last revised 24 July, 1998)

The evanstrig program is an adaptation of lptrig. Evanstrig runs John Evans' long-period trigger algorithm on single-channel TYPE_TRACEBUF messages and produces single-channel triggers. These triggers can then be associated into "events" by the moduleevansassoc.

The evansassoc program associates long-period triggers from several scn's. The association rule is that triggers from a certain number of scn's must be received within a specified time interval. The association parameters are specified in evansassoc 's parameter file .

NOTE: evanstrig will only work on 100 hz data!

The details of John Evans' long period trigger algorithm are discussed in the following two papers:

A Teleseism-Specific Detection Algorithm for Single Short-Period Traces, Bull. Seism. Soc. Am. 73, 1173-1186, Evans and S.S. Allen, 1983.

Reliable Automatic Detection of Long-Period Volcanic Earthquakes at Long Valley Caldera, California, Bull. Seism. Soc. Am. 85, 1518-1522, Evans and Pitt, 1995.

Module Index | Evanstrig Commands | Evansassoc Commands