SEIS-SOUND is an NSF NGF data product that transforms traditional seismic recordings into synchronized audio–visual media. By converting ground motion into sound and pairing it with visual representations of the waveform and its frequency content, SEIS-SOUND makes it possible to hear and see how an earthquake signal evolves through time.

Each SEIS-SOUND product conveys the data in four complementary ways:

• an image of the original seismogram
• an image of a filtered version of the seismogram
• an image of the spectrogram of the filtered trace
• an audio playback of the seismic signal that is time-compressed and amplitude-normalized so that the sound is audible to human ears (roughly 20 Hz–20 kHz)

The temporal evolution of the seismogram is depicted by the trace gradually shifting from light gray to dark black as time progresses. A pink vertical line in each subplot marks the current playback time, as does the timer in the upper right. Because real earthquake signals unfold over minutes to hours—and much of their frequency content is below human hearing—the playback is sped up by the factor shown on the x-axis. For example, a 500× speed-up shifts energy from 0.5–40 Hz into the audible 250–20,000 Hz range. Both the spectrogram and audio are generated after applying a 0.5 Hz high-pass filter. For the best experience, we recommend using earbuds or high-quality speakers.

Transforming seismic data so that both high- and low-frequency signals are simultaneously audible is challenging, because each band would require a different speed-up factor. To address this, we apply an appropriate speed-up factor to render the higher-frequency (> 0.5 Hz) energy audible. For the lower-frequency energy, we use MATLAB’s voltage-controlled oscillator (vco) function to create a tone that oscillates around an audible center frequency, with its modulation tracking the amplitude of the low-frequency seismic signal¹. This modulated channel is then made the same duration as the time-compressed high-frequency channel, allowing the two to be saved together as a stereo sound pair². Hearing both bands in stereo, alongside the synchronized video, helps reveal relationships between low-frequency surface waves and high-frequency triggered earthquakes or tremor when present.

In the spectrogram, warm colors represent higher amplitudes and cool colors represent lower amplitudes. The amplitudes shown are the base-10 logarithm of the normalized amplitude, multiplied by a scale factor of 10. All SEIS-SOUND products use identical scaling to enable direct comparison between events and stations.

The first line of the title displays information about the earthquake, while the second line shows information about the seismic station, including its distance and azimuth to the event. The top y-axis label indicates the type of seismogram (e.g., velocity) and its channel code (e.g., BHZ). Optional seismic phase arrival times—such as P, S, SKS, and R1—can be displayed as short blue vertical lines with corresponding labels.

Use the filter controls below to limit the events by time, location, etc. Then click on the desired event, to play. Visit the SEIS-SOUND product page for more information .