The thresh_subtrig module builds station subnets for each station in a network. The amplitude threshold alerts of each station in a subnet are monitored and a threshold subnet trigger is issued if a specified number of stations in the subnet has an amplitude threshold crossing within a certain time-period.
The thresh_subtrig modules reads a list of stations from a file in Hypoinverse station file format. For each station in the station list, a station subnet is created by collecting nearby stations. A configurable maximum number of nearby stations are searched in a circular area defined by a minimum and maximum search radius in the config file.
The thresh_subtrig module reads TYPE_THRESH_ALERT messages created by module ewthresh. A subnet trigger is issued, if the main station and a configurable number of subnet stations show an amplitude threshold crossing within a certain time-period. The time period is related to the maximum distance of the center station (main station) to the related subnet stations and a configurable minimum seismic velocity. The time-period for each subnet should represent the maximum time that a seismic wave needs to cover the maximum radius of the subnet.
The thresh_subtrig module writes TYPE_THRESH_SUBNET_TRIGGER messages to a ringbuffer. These can be read and processed using the module thresh_bindsubtrig.