2015 Chilean Earthquake

September 2015 Chilean earthquake and tsunami

The September 16, 2015 earthquake occurred off the north coast of Chile with a magnitude of 8.3. CDIP's Scripps Pier pressure sensor recorded a clear tsunami signal arriving at approximately 11:50 UTC on September 17. Preliminary analysis shows a peak amplitude of close to 4 inches (10 cm).

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Tsunamis are measured through seismic measuring equipment, tide-sea-level instruments, and DART II buoys (different from CDIP wave buoys).  Tsunamis are a separate class of ocean wave altogether. Generated by undersea earthquakes, landslides, and volcanic eruptions instead of wind, tsunamis differ greatly in their dynamics. They have far longer wavelengths and periods than wind-generated waves, and travel at far greater speeds. Instead of periods of 30 seconds or less, tsunamis have periods of several minutes to one hour; instead of traveling at speeds under 100 km/hr, they often move at speeds of 700 km/hr or more.

Since the dynamics of tsunamis contrast so dramatically with wind-generated waves, many of CDIP's sensors are not equipped to measure them. CDIP buoys, for instance, do not measure wave motions with periods greater than 30 seconds; they cannot record tsunamis. The underwater pressure sensors used by CDIP, however, do resolve sea level changes over longer periods, and can be used to study and analyze the motions of tsunamis. Over the years they have recorded a number of tsunamis in the Pacific Ocean.

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tsu-terms-diagram.jpgImage Source: USGS

f20150916_max_energy_sm.pngImage Source: NOAA

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