|Observatories and Research Facilities for EUropean Seismology|
|Volume 3, no 1||June 2001||Orfeus Newsletter|
QuakeExplorer - Earthquake Internet Browser and Analysis ToolAnthony Lomax
QuakeExplorer accesses event meta-data in a compact and frequently updated database residing on an Internet server. This meta-data describes hypocentres and provides links to a large quantity of trace data available on the internet from datacentres, networks or individual stations. QuakeExplorer is written in the platform independent Java language and so runs on almost any system. For interactive visualisation and analysis, QuakeExplorer launches the Java applications SeismicityViewer and SeisGram2K.
QuakeExplorer is part of the efforts of ORFEUS and other organisations to promote and enable advanced observation and analysis of seismological information over the Internet (Lomax, 2000ab). The increasing amount of real and near-realtime seismological data available from monitoring networks and data centres, combined with powerful and efficient Internet tools such as QuakeExplorer, creates a dynamic, interactive and accessible work environment for seismologists. This Internet based environment can greatly facilitate the use and dissemination of earthquake information for monitoring, hazard response, research, teaching and public information. ORFEUS-Wilbur system.
The QuakeExplorer browser consists of 2 main user windows: a hypocenter selection window on the left and a trace-table window to the right (Figure 1). The hypocentre selection window allows rapid browsing and selection of earthquake hypocentres in multiple tree diagrams organised by origin time, magnitude, latitude/longitude and depth. Selected hypocentres can be displayed on a 3D, interactive view of the Earth in the application SeismicityViewer. Double-clicking on a hypocentre brings up the trace-table window containing a list of seismic traces available for the hypocentre. The table columns show the station code, channel, distance, azimuth and other trace parameters. The trace-table can be sorted on any parameter by clicking on the corresponding column header, and any combination of z, n or e component can be selected. After one or more traces have been selected, they can be viewed and analysed in the application SeisGram2K or downloaded to disk.
Figure 1. The QuakeExplorer browser window (lower front), the Seismicity Viewer (upper left) and SeisGram2K Seismogram Viewer (upper right).
A QuakeExplorer implementation consists of 2 main elements: a regularly updated database on a host web server (Figure 2), and the QuakeExplorer browser application on each user's computer that accesses this database (Figure 3).
Figure 2. The QuakeExplorer database resides in a web site on a host system. At regular intervals, a Java update program scans the Internet to determine the latest event data available at pre-selected datacentres, networks and stations. The update program writes to the QuakeExlorer database a minimal amount of meta-data containing descriptions of the available events and links to the available trace data.
Figure 3. The QuakeExplorer browser is a Java application that runs on the user's computer. It allows rapid access over the Internet to the lightweight, event meta-data stored in the QuakeExplorer database, and gives the user interactive access to this information. When the user request the viewing or downloading of traces, the (large) data files are transferred directly from the data source to the user's computer over the Internet; only links to trace data are stored in and transferred from the QuakeExplorer database.
The QuakeExplorer browser can read and download trace data from any Internet host because it is a stand-alone application that resides on the user's machine. If QuakeExplorer were implemented as a Java applet that is launched through a web browser (like the current implementation of SeisGram2K on ORFEUS-Wilbur), then the default browser security would only allow the reading of data from the same host containing the QuakeExplorer applet and database. However, an applet version of QuakeExplorer will form a powerful helper tool for accessing a static trace data set, such as an aftershock sequence distributed on a CD or hosted on a single web site. http://www.alomax.net/QuakeExplorer/orfeus/base) presents all events from the last 90 days contained in the ORFEUS-Wilbur system. This database contains all global events with M>5.5 and selected European events; it indexes traces from global broadband stations. The second database (http://www.alomax.net/QuakeExplorer/EDUSeis/base1) presents events from the last 90 days contained in the EDUSeis-Nice system. This database contains global teleseismic events and European local/regional events; it indexes 5 high-school stations of the Nice section of the European EDUSeis project (Virieux, 1999).
In the near future, the EDUSeis QuakeExplorer database will be expanded to include indexing of events from other European high-school seismometer projects. Also, additional information, such as tectonic boundaries and great circle arcs between events and stations will be added to the SeismicityViewer helper application.
Further developments may include the addition of interactive selection of events in a map view window and the creation of an expanded ORFEUS QuakeExplorer database. This expanded database may extend the ORFEUS-Wilbur system (which concerns data residing at ORFEUS) by including internet accessible traces that reside on network and station web servers. http://www.alomax.net/QuakeExplorer. I would greatly appreciate your comments and suggestions on the QuakeExplorer browser and on the content of current and future QuakeExplorer databases.