Rapid detection and characterization of earthquakes is essential for earthquake early warning systems, which have the ability to alert nearby populations about the approach of potentially damaging seismic waves (e.g. Allen and Kanamori 2003; Kanamori 2005).
The Trimble REF TEK Seismic Recorder, model 130-REN-3 has been specifically designed to meet the key requirements for Earthquake Early Warning (EEW) Systems and Rapid Event Notification (REN) which includes quick delivery of digital data from seismic stations to the acquisition and processing center, and data integrity for real-time earthquake notification in order to provide warning prior to significant ground shaking.
The modified telemetry algorithm in the 130-REN Recorder provides a unique opportunity for customers to meet these critical requirements to detect strong ground shaking at one or several locations and transmit the notification ahead of the seismic energy affecting the populated area.
The 130-REN uses REF TEK Protocol Daemon (RTPD) as the communication server. The new version of RTPD is backward compatible to handle both standard 130 data transmission (RTP) and rapid event notification (REN). The 130-REN Recorder allows output digital data every 0.2 sec. This is a significant reduction in the time delay required for real-time transmission of the currently available digitizers. Modified RTPD receives the digital data and acknowledges data received without error. RTPD forwards all received data in real-time to the processing clients. The 130-REN keeps track of what data has not been acknowledged and re-transmits the data giving priority to current data using backfilling algorithm. When a re-transmitted packet is acknowledged by RTPD, the packet is then stored in Archive by order of time received. The data processing interface receives only real-time data. An advance data transmission algorithm for Rapid Event Notification is shown in the figure below.
Modified RTPD protocol provides:
- Acquire data into 200 msec multiplexed packets
- Digital filter delay is ~150 msec
- Time to construct the packet average 50 msec
- Delay time from sample time to transmission and receive nominally 400 msec
To summarize, data is transmitted every 200 msec and has a 400 msec delay time when decoded across a direct LAN connection.