Thomas J. Owens
OF DRUMS AND NEEDLES ... DISAPPEARING ICONS OF SEISMOLOGY?
It's the New Year and the ES finds himself pondering the good ol' days of analog seismology. Remember the soothing sight of the rotating paper drum? The buzz in the hallway when a large earthquake began to dance across the paper? Friday afternoon record reading where you learned to interpret seismograms from the Masters? A lot was learned about the Earth from those records and a lot still remains to be learned from those willing to dig through acres of archives around the world. But progress is inevitable and those paper drums have been replaced by ... hey, wait a minute ... what have we replaced them with? The hallways are silent until our e-mails beep telling us of a large earthquake. Then, we rush down the hall to see ... what? The icons of our science are disappearing and important educational, research, and social aspects of our science may be too. Do students crowd around your computer screen every Friday afternoon to look at seismograms? Do you print 12" x 36" plots of the best records of the week so everyone can interact and feel like a community? Are important chance discoveries being lost because we are not looking at seismograms just for fun on Friday afternoon? The ES worries about these things.
So much for the upbeat New Year ES nostalgia column, eh? But it's not all bad. First, the helicorders are not all gone. Granted, most come now with a crabby technician and a box of spare parts. But at the ES's home turf, we've added a raggedy old sofa in front of them so the ES and others can watch at their leisure. Through the wonders of real-time data, in the time it would take the ES to change paper on those old drums, he can assemble a record section of seismograms from around the world. And discoveries about the Earth continue through creative ideas and processing. So the researchers will probably make it through this transition. But what about students and the general public? The public and the media really like drum recorders.
The ES has had many conversations with colleagues about these pitfalls of digital seismology. The subject comes to the ES column because Bob Mereu offered his concerns and a solution through a short SRL submission. When the ES read it, he realized there are a number of potential solutions out there and so this column has brief summaries from several folks. The scope of the offerings range from Bob's Fortran-based approach to Alan Jones' Windows® display for a local seismometer to Philip Crotwell's new-fangled Java-language code that allows real-time viewing of data from Antarctica if desired to Mitch Withers' short opinion pointing out the possibility that the ES's world may not be coming to an end. This month's ES Panel of Experts mainly focuses on the impact our digital era may have on the presentation of our science to students and the general public. That multiple solutions for these audiences do exist is calming to the ES, but his doomsday gene still spawns concerns that certain aspects of our science will suffer as well, that our delicate social fabric will collapse, that chaos will reign. Ahhh ... some things will stay the same. Happy New Year! The ES thanks his panelists for taking the time to offer solutions and hopes anyone pondering our disappearing icons will find an approach to his liking.
SIMULATING A MECHANICAL PEN RECORDER WITH A COMPUTER PROGRAM
R. F. Mereu
For years mechanical pen recorders have been used at seismic observatories and educational centers (e.g., universities, schools, and museums) to display live seismic data from various stations of a seismic network. These displays have not only been useful to research seismologists but have always attracted a lot of popular interest, particularly just after a large earthquake. People in general seem to be fascinated by watching the mechanical pen write the seismograms on the paper of the recorder.
In the days when instrumentation was mostly analog, the mechanical recorders were ideally suited for displaying the analog traces. In recent years, most of the analog instrumentation has given way to much more powerful digital systems. Computer monitors are the natural method to display the digital seismograms, as the displays and formats can easily be controlled by suitable graphic software programs.
Because of the high speed of the modern computer, seismograms are plotted almost instantly or are plotted in spurts as the digital packets are received from the source station. What is lost in all of this new technology is the fun of watching a mechanical pen trace out the large and small amplitudes of a seismogram in real-time and watching it suddenly jump into action and swing back and forth energetically when an event arrives at a station.
We have written a computer graphics subroutine package which shows how you can restore a real-time moving pen back into the seismograph displays while still retaining all the advantages of digital systems. These subroutines may easily be incorporated into larger software packages which configure the output graphics into any desired format with appropriate labels. Two examples are:
We have implemented these display methods in our hallway to enable students to view both live data from the Southern Ontario Seismic Network and stored data of interesting earthquakes. Examples of seismograms from this network are presented at our Web site, http://www.gp.uwo.ca.
Our subroutines were written using the PGPLOT plotting subroutines on a Linux operating system. Information on the PGPLOT graphics routines may be obtained from http://www.astro.caltech.edu/~tip/pgplot. Copies of our subroutines and further information on how the programs may be incorporated into other plotting systems may be obtained from the author.
AmaSeis: A COMPUTER HELICORDER PROGRAM FOR SCHOOL SEISMOMETERS
Alan L. Jones
AmaSeis is a Windows® program which displays the output of a simple seismometer on a helicorderlike display. It acts like the pen recorders of old in that students can watch the "pen" move up and down in real-time as an event is arriving. AmaSeis is one part of a suite of educational programs for seismology that will be described in an article that I have submitted with Larry and Sheryl Braile to a special educational issue of Seismological Research Letters to be published in the summer of 2003. The other programs in this suite are Seismic/Eruption, Seismic Waves, and EqLocate.
AmaSeis is a program to receive continuous data from a single-channel seismometer. It was originally designed for use with the AS-1 (Amateur Seismologist: http://www.amateurseismologist.com) seismometer (http://www.jjlahr.com/science/psn/as1) but now supports several analog-to-digital devices (DATAQ DI-151RS, DATAQ DI-154RS, DATAQ DI-194RS: http://www.dataq.com). IRIS has placed AS-1 seismometers in more than 50 schools. The seismometer costs less than $500. It incorporates a simple design so that the principles of a seismometer and the recording of ground motions can be understood. The main AmaSeis screen is a helicorder display which can show 24 hours of data. When an earthquake is observed on the helicorder screen, the user can select the trace with the mouse and then click on the "Extract" icon. The trace is then shown on its own screen. At this point, the seismogram can be filtered by applying a low-pass, high-pass, or band-pass filter. The package has a number of features designed to help students pick phases, determine station-event distance, etc. In addition to processing seismograms collected with AmaSeis, the program can also import waveforms in SAC, PEPP (Princeton Earth Physics Project), or PSN (Public Seismic Network) formats.
AmaSeis is designed for use with a local seismometer. It is ideal for a classroom situation or potentially a museum display. The seismometer should be in full view of students or the public, who can view the effects of their own motions. AmaSeis is supplemented by a Web site, http://www.eas.purdue.edu/~braile, with teaching suggestions for using the AS-1. The information includes examples of recorded seismograms and seismograms that are filtered using the AmaSeis software to enhance specific wave arrivals or reduce noise; calculating magnitude from AS-1 recordings; a discussion of calibration of the AS-1 instrument; and ideas for classroom use such as maintaining a catalog of seismograph recordings, comparing AS-1 seismograms with records from other stations, and generating a map of earthquake locations and seismograms for events recorded by the AS-1 station in the school.
REAL-TIME VIEWING WITH THE GLOBAL EARTHQUAKE EXPLORER
H. Philip Crotwell
Several facets of the old paper helicorder records have not translated well into the digital age. Of course there is the excitement of watching the needle jitter and bounce across the page, and knowing that there is a direct connection between its movements and the movement of the ground underneath. Somehow the whirl of a hard drive and the blinking of an LED just don't have the same romance as the slowly rotating drum of yesteryear. While it is hard to point to any scientific or educational value from watching data flow in, it is undeniably a crowd-pleaser.
Another aspect may have more actual educational impact, if perhaps less nostalgia. Paper records give you the ability to see a whole day at a glance and to discover an earthquake not by an e-mail or database query but by actually seeing the waveform. This point of discovery, excitement, and curiosity can be a stepping stone for students and the public toward learning about the Earth and earthquakes. The challenge is to bring the dancing needle and its 24-hour record into the digital era.
The Global Earthquake Explorer, or GEE, is an education and outreach application being developed at the University of South Carolina. In addition to being a general seismic data viewer, it also has the ability to view a whole day of data as well as real-time data. The design of the real-time viewer is based on seeing a relatively short time window before the current time, at most a few tens of minutes. At this scale it is possible to see an effect similar to the movement of the helicorder pen. The rotation of the drum is simulated by shifting the display to the left in real-time. Two problems with this must be overcome. The first is that data arrives in discrete chunks, and the effect of adding 30 seconds of data all at once is not nearly as pleasing as having it flow onto the screen. We solve this by having the right hand side of the screen offset from now by a couple of minutes to allow time for the chunks to arrive.
One nice feature of the real-time player in GEE is that the display code for real-time data is the same as that for regular seismograms. Normal display functions such as zooming in and out and dragging work. This allows you to go quickly from watching the latest data flow in while zoomed in on the end, to looking at a previous section of data, to zooming out to view all the data in memory. The player also has play, pause, fast forward, and rewind buttons.
Another problem with real-time data, even with analog helicorders, is that you can not make an earthquake happen when you want it to. We have also added a real-time playback that allows data from an old earthquake to be played back as if it were happening now. This sets the first data point in the seismogram to be just off the right hand side of the screen, and then lets it flow across the screen at a real-time rate. While it does not quite have the same excitement level as the real real-time, it is more predictable for demo and classroom use, and the fast forward feature is a life-saver for distant earthquakes!
To simulate the whole day at a time view of seismic data provided by the analog helicorder, we have a seismic day viewer as part of GEE. For a particular channel and day, it displays the whole day of data. Of course, actually receiving a whole day's worth of data is more than most Internet connections can handle in a reasonable amount of time, so we have only a highly decimated version, called a Plottable, that can represent the data but be much smaller. It is not an image of the data but stores only the minimum and maximum values for each column of pixels. This allows the display to look exactly like the real data, at least at the specific resolution, but has the added advantage of scaling the amplitudes. This is particularly important for several of our high school stations (http://www.seis.sc.edu/scepp) as they are located near train tracks, and the noise from the trains causes large spikes that cause any real data to be scaled very small. This ability to zoom in amplitude allows you to ignore the spikes and focus on the lower amplitude signal. One nice feature that we have not yet implemented is having the day viewer update the display periodically. Due to the scale, it would not need to update nearly as often as the real-time player, but it would make a nice display piece. A Plottable server is in the works at the IRIS DMC so 24-hour records from anywhere in the world will be available, but for now only stations of the South Carolina Earth Physics Project are available through the GEE day-view.
For GEE, ease of use is particularly important, so all data access is done via the FISSURES Data Handling Infrastructure, or DHI. It allows GEE to get the latest information for seismic events, networks, stations, and channels, as well as actual data, in a robust, easy-to-code manner. We also try to hide as much of the complexity of seismic data, such as channel naming and data request methods, from the user as possible. We hope that GEE will become widely used in and out of the education and outreach community, and invite you to try it out. It is available from either the SCEPP Web site, http://www.seis.sc.edu/scepp, or the IRIS DMC Web site, http://www.iris.washington.edu/DHI/clients.html.
REAL-TIME VIEWING WITH THE GLOBAL EARTHQUAKE EXPLORER
When the ES asked me to contribute a section to his review of real-time waveform displays, my first reaction was, "Who cares?" Automated algorithms and processing systems have advanced to the point of removing much of the drudgery of scanning thousands of paper records. This begs the question, is real-time display even necessary? Yes, for two principal reasons: testing and troubleshooting, and education and outreach. Whether it is Antelope, Earthworm, Xdetect, or SeisAn, most seismic acquisition and processing packages include the ability for real-time testing and feedback. IRIS has combined the AS-1 demonstration seismometer with Alan Jones' AmaSeis software into a product that does an outstanding job of meeting the E&O need to see the Earth move in schools and museums.
Unfortunately, or perhaps necessarily, most digital real-time viewers are tied to a specific type of instrumentation and/or acquisition software. Further, most large permanent network operators do not allow unplanned real-time connections to their network data. This is necessary to avoid bandwidth peaks and overloading critical systems. Given that troubleshooting and E&O needs are met, the important tools are offline and "pretty quick" viewers such as SAC and the Earthworm heli_ewII module (see, for example, http://quake.wr.usgs.gov/recent/helicorders/index.html).
The media always want to see the old analog paper recorders rather than digital viewers. When performing temporary deployments, even the old MEQ systems provide a useful and quick daily assessment of the number of events. Digital systems are not a replacement for analog systems, nor vice versa. Neither is end of life about to be declared on either. Rather, the roles and needs are changing.
SRL encourages guest columnists to contribute to the "Electronic Seismologist." Please contact Tom Owens with your ideas. His e-mail address is firstname.lastname@example.org.
Posted: 24 February 2003