How To Make Your Own Seismogram!
It's easy, just fill in the blanks, and press the create plot button. After a few seconds, a GIF file will be created and loaded. The size of the file will vary depending on the parameters you use, but the default parameters usually create a GIF file of about 34K bytes. The program that creates the GIF file takes 10 - 20 seconds to to build the GIF file from the earthquake data files. In some cases, data will need to be retrieved from the BDSN archive on the Northern California Earthquake Data Center, which may add up to a minute delay to your request. Add that time to the time it usually takes you to load a 34K GIF file.
The material below describes the input parameters and their use.
- Disclaimers and qualifiers
Usually we have continuous data for all of the available stations and
channels. If a station or telemetry channel is undergoing maintenance, we
may not have data available at the time of your request. Not all
stations have operated for all time, so data may not be available
for all sites at all times.
- Station names
These stations are part of the
Digital Seismic Network. Select a station of interest (see the
map for site locations) for your seismogram. In general, the
stations in the Sierra (such as CMB) are the quietest and the stations
near the coast are the noisiest (such as JRSC). If you are interested in
a local earthquake, you may wish to choose a station close to the
- Channel parameters
There are six data channels available in 2 different frequency bands:
- Long-Period channels LHZ, LHN, and LHE
- These three channels are sampled 1 time per second and record longer periods, which is useful for viewing distant earthquakes. Since the lower sampling rate also makes it easier to view longer time series, we suggest using these channels for a quick look at an earthquake.
- Broadband channels BHZ, BHN, and BHE
- These three channels are sampled 20 times per second and record higher frequencies, which is useful for viewing local or regional earthquakes.
- Date,Time parameters
You can specify a beginning and an end for a time period to be viewed.
Date and time parameters can be specified in one of two formats:
- yyyy = year (1992-present)
- doy = day-of-year (1-366)
- mm = month (1-12)
- dd = day-of-month(1-31)
- HH = hour UTC (0-23)
- MM = minute (0-59)
- SS = second (0-59.9999)
If the date is not specified, it defaults to the current day. Time is assumed to be in Universal Time (UTC), which is PST + 8 hours, and will default to midnight if unspecified. There cannot be any blanks between the date and time, or within the date,time string. The year must be specified with 4 digits.
The amount of data displayed is subject to the plotting parameters used. If all of the data cannot fit on a single plot, the requested data will be truncated.
Your requests are currently limited to a maximum of 1 hour of Broadband data and 24 hours of Long Period data. More data than that does not easily fit on a single page.
If you want to view a recent earthquake but don't know when it occurred, try checking a list of recent events in northern and central California or a list of recent global earthquakes to find the event you want.
- Plotting parameters
There are three parameters that control the size of the
final image, and the amount of data (time) displayed in
- Compression controls the number of data samples compressed into a horizontal pixel. For example, the default of value of 40 plots 40 time samples in the space of one pixel. Keep your channel selection in mind when you set this parameter. Since low band channels are sampled at 1/20th the rate of broad band channels, a compression rate of 2 would give the same effective time compression as a compression rate of 40 for broad band.
- Amplitude scaling Data samples are multiplied by this scale factor. Increasing this number will amplify the waveforms, enhancing the signals from smaller earthquakes. Decreasing this number will reduce the the overlap between traces for a large earthquake.
- Scan spacing controls the distance between horizontal scans in the seismogram. The value is specified in pixels. Larger values give you more space between scans, and may make data easier to see but you can't get as many scans on the screen at one time. Larger values also mean you are creating a larger image, so loading time will go up.
- Create plot and Reset
Press the create plot button to start the image
Press the reset form button to reset all parameters to their default values.