Earthquake Detective

The Earth Shakes

Though the ground beneath our feet is stable, it is just a small part of many segments on the Earth's surface. These 'plates' are moving on Earth’s interior like leaves on a lake. When two plates of the Earth collide in an earthquake, they release huge amounts of energy as waves that we feel as shaking. In general, any event that sends waves shaking through the Earth is known as a seismic event, coming from the Greek word seien (to shake).

Seismic Waves on the Earth's Surface

Waves generated from a seismic event spread out in all directions from the event, like rays from the sun. They spread into the Earth and across its surface. Waves on the Earth's surface ('surface waves') have the longest duration and highest displacement of all seismic waves. When they pass through a region which is under seismic stress, surface waves may trigger earthquakes or a tremor in locations far away from the source that generated the waves. Determining the frequency and conditions under which seismic events occur will lead to a better understanding of earthquakes.

Detection and the Data Challenge

Instruments for measuring the motion of the Earth's surface continuously record across the USA and around the globe. These recordings of the seismic waves are known as seismograms, documenting the earthquakes that make the news as well as many, many weaker seismic events. These events may be recorded at just one or multiple instrument locations. The number of available seismograms is staggering! Citizen scientists can provide much needed assistance in classifying these events.

Project Execution and Significance

Scientists (known as seismologists) need your help to classify these events. By listening to seismic waves, different seismic events can be classified by anyone. When enough data is classified, seismologists and data scientists can use it to train a machine learning algorithm (an example of artificial intelligence, or AI) to automate the classification of seismograms. Once enough data is classified, seismic models for how, where, when, and why earthquakes happen can be better tested. The work citizen scientists put into this project contributes to the fundamental understanding of our planet that will allow a more sustainable society by allowing professionals to better assess risk for future seismic events.

Earthquakes

Here are a couple of examples of how earthquakes signals can sound. Remember that earthquakes represent waves from a sudden displacement between two plates or along a fault. The sounds you hear represent the sudden release of acoustic/seismic energy. Some people say it sounds like a slamming door.

Tremor

Tremor is different from earthquakes. Tremor is a term that represents
“rumblings" from a slow release of acoustic/seismic energy and can sound, for example, like a train darting over train tracks. Here are a couple of examples of how tremor signals can sound.

None of the Above

The Earth is always shaking a little from long-ago or distant seismic events. However, a nearby noise source (for example, a stampede of a passing herd of buffalo) will cause a distinct seismic signal. A loud concert, sports match, meteorite impact, quarry blast, construction site, etc. near a seismic station, for example, can cause weird sounds in the sped-up seismogram that don't sound like an earthquake or a tremor. If a sped-up seismogram sounds like there is/are one or more event signals in it that is or are unclear or unusual, that classification is just as important as identifying an earthquake or tremor. Don't hesitate to label a sound file as 'none of the above'!

Noise

The Earth is always shaking from long-ago events, distant events, atmospheric and oceanic activity, and even nearby steady sources of noise, such as traffic or machinery. In every seismogram that is sped-up to the audible range, there will be random 'noise' which forms an ever-present 'baseline' for the sound file. If there are no other distinct signals, then the seismogram represents just "noise". Classifying a sped-up seismogram as just noise is just as important as identifying an earthquake or tremor. Don't hesitate to label a sound file as 'noise'!
Noise sounds like whistling wind, or crinkling tin foil. Here are a couple of examples of how noise signals can sound.

References

Brodsky, E. E., and N. J. van der Elst (2014), The Uses of Dynamic Earthquake Triggering, Annu. Rev. Earth Planet. Sci., 42(1), 317–339, doi:10.1146/annurev-earth-060313-054648.
Chao, K., Z. Peng, A. Fabian, and L. Ojha (2012), Comparisons of triggered tremor in California, Bull. Seismol. Soc. Am., 102(2), 900–908, doi:10.1785/0120110151.
Peng, Z., and J. Gomberg (2010), An integrated perspective of the continuum between earthquakes and slow-slip phenomena, Nat. Geosci., 3, 599–607, doi:10.1038/ngeo940.
Rubinstein, J. L., J. Gomberg, J. E. Vidale, A. G. Wech, H. Kao, K. C. Creager, and G. Rogers (2009), Seismic wave triggering of nonvolcanic tremor, episodic tremor and slip, and earthquakes on Vancouver Island, J. Geophys. Res., 114(B00A01), doi:10.1029/2008JB005875.