Live Seismograms from the Net

Charles R. Hutt and Harold Bolton
USGS Albuquerque Seismological Laboratory

Figure 1. The 24-hour seismogram was plotted from 1 sample-per-second seismic data from the GSN station at Scott Base, Antarctica (SBA) collected in near real-time by the LISS running at ASL. The regional Mb 4.6 event, seen on the plot, occurred near the Balleny Islands on July 6, 1999, at a distance of 16.2 degrees.

Live seismic data are now available on the Internet. Both Data Collection Centers of the Global Seismographic Network (GSN) have developed near real-time servers that make data from GSN stations directly available. Both types of data servers are known by their acronyms:

LISS - Live Internet Seismic Server was developed by the USGS Albuquerque Seismological Laboratory (ASL); NRTS - Near Real-Time System was developed by the University of California, San Diego (see following article).

Although this article concentrates on the LISS, NRTS has similar functionality.

Seismographic Networks
ASL currently operates about 75 GSN stations and the UCSD IDA group approximately 33 GSN stations. Both of these numbers are growing as the two groups expect to complete the installation of a total of about 150 GSN stations over the next 2­3 years. This will complete the installation phase of the GSN, developed by IRIS. (Figure 2)

Near real-time data are now available from many of these GSN stations. The LISS operating at ASL currently collects data from 36 GSN stations (Figure 2). The data from these stations can be obtained from the LISS in raw digital form (miniSEED) and are displayed at the LISS web site as heliplots covering the past 24 hours. The number of stations with near real-time data is increasing as connections to stations via the Internet and satellite links become more widely available. There are also plans to include near real-time data via the LISS from the US National Seismic Network (USNSN) stations in the near future.

Figure 2. The ASL LISS currently provides data from 36 stations of the GSN (plotted as red circles). Data from Chinese and Russian stations are received by the LISSes in their respective countries, and then served to the primary LISS located in Albuquerque, New Mexico (as indicated by the heavy green and blue lines).

Figure 3. ASL field engineer Neil Ziegelman performs maintenance on radio telemetry equipment at Vanda Station, Antarctica (VNDA). This type of telemetry link is commonly used at remotely located seismograph stations to send real-time data to the LISS.

What can you use it for?
Internet Surfing: Heliplots (as in Figure 1) emulate the appearance and function of the old standard WWSSN photographic paper seismograms that were created by writing a trace of magnified ground motion on a long piece of paper wrapped around a drum. These heliplots are available on the LISS website to anyone with access to a computer, a web browser and Internet connectivity. In addition to the seismograms, the LISS website includes a world map showing the earthquakes of the past 24 hours as reported by the USGS National Earthquake Information Center (NEIC). The heliplots and map are updated every 30 minutes, so it is easy for seismo-surfers to keep themselves informed of the world's current seismicity. There are also links to other informative earthquake oriented websites, including sites displaying live seismic data and related educational material.

Seismic displays: The LISS provides a near real-time (1-3 minutes delay) source of waveforms from GSN stations for several public seismic displays that are connected via the Internet. These seismic displays are generally equipped with an Internet connected computer and receive live data streams from several GSN stations that are displayed on analog drum recorders. Such a display strikes a chord with the general public, since a live moving pen on a drum recorder seems more like a "real" seismogram than a computer display. IRIS and ASL have, in fact, cooperated in producing several of these displays, one of which is operating at IRIS headquarters (Figure 4). Similar displays are operating at the New Mexico Museum of Natural History and Science in Albuquerque, NM, at the American Museum of Natural History in New York, and at the Carnegie Museum of Natural History in Pittsburgh. In addition, the first seismic display developed and built as a cooperative effort by IRIS, ASL, and the NM Museum of Natural History, is currently touring the US as part of the Franklin Institute's "Powers of Nature" exhibit.

Figure 4. Robert Woodward discusses global seismicity using a LISS seismicity display at IRIS headquarters in Washington, DC.

Professional use: The use of LISS data by seismologists is still in its infancy. It is not exactly clear what directions may ensue, but many practical applications are in use or in development. The LISS has the ability to maintain a large number of simultaneous connections, to any or all of the data collected. This allows for an unprecedented amount of versatility in the projects that are designed to use the data. An obvious application is real-time monitoring. These data can provide for quicker and more accurate earthquake source information and are ideal for hazards groups such as the USGS NEIC and tsunami warning centers. Already being constructed are 'virtual networks' (see related article on page 7) where workers are able to collect data from a subset of stations that enhance the specific goals of individual projects. These data are also proving to be invaluable to the individual Data Centers as a tool to enhance quality control (QC). Rather than having to wait (sometimes up to several months) for data tapes to be mailed from stations in the field to the Data Centers, the QC analyst can, at a glance, detect overt problems (Figure 5) at a station and initiate the appropriate corrective actions.

Figure 5. "Thumbnails" from six of the 35 heliplots available on the LISS website. Stations HKT and KONO have transients that can be easily identified by a quality control analyst scanning for station problems.

How the LISS works, How to connect
The primary LISS site is currently ocated at the USGS Albuquerque Seismological Laboratory. ASL will soon have a secondary LISS located at another site with much higher bandwidth capabilities. This change should be transparent to the user. The most basic feature of the LISS is that it can provide many users access to the data from a single station while only the LISS server is actually connected to the station (Figure 6). As the LISS can connect to many stations, its versatility is greatly enhanced. Currently, the LISS pulls over the entire set of channels from a station which has been preprogrammed by the station's software engineers. If one LISS site were to die, it would then be possible to turn on another LISS site to gather each station's data without having to reprogram each individual station. The broadband miniSEED data records from each station typically contain about 30 seconds of data. Each station has a record ready to be pulled about 120 seconds after the initial record is acquired. The LISS servers then broadcast these records to any clients connected to the LISS server.

All the software and documentation that are necessary to connect to the LISS are free and available to anyone willing to download them from the LISS web site. Currently the software has been tested on Solaris and FreeBSD platforms and, if demand warrants, could be extended to various Linux and perhaps Windows systems. Users are encouraged to use and adapt the software in any manner they wish.

Figure 6. Data flow diagram of the LISS connected to a single seismograph station while serving several users. The LISS actually connects to many stations simultaneously, as well as to other LISS servers.

Future Directions
Second generation LISS software is currently under active development at ASL. A primary goal of this development will be to have redundant LISS servers that can be automatically switched for load leveling and as backup should there be a primary failure. Also to be included are the use of user 'select files' for choosing which stations and channels are to be received. Other features will be driven by user requests. The LISS source code will be freely made available for development work.

Additional information on LISS connectivity and current global seismicity can be found at the LISS website http://www.liss.org.