News & Science: How To Read Earthquake And Tsunami Diagrams

USGS Shakemap
Image from USGS/EPA

These days when we hear news about earthquakes near coastal areas, what we fear most is the magnitude of such earthquakes because the higher it is, the higher the chance a tsunami will be triggered. The result can be devastating!

The image above is a ShakeMap, a map colour-indicated by the instrumental intensity of the earthquake, according to the perceived shaking, potential damage, peak ground acceleration (measured in g-force) and peak ground velocity (measured in centimetre per second).

Another diagram we often see once there is a threat of a tsunami is this Tsunami Travel Times. As stated in the subheading, "tsunami travel time contours in hours, beginning from the earthquake origin time". What we need to look closely at are the yellow and red dots on the map and in the legend. Red dots are the DARTs while yellow dots are tide gage / gauge.

DART Easy to Deploy (ETD) buoy
Image from DART

DART® (Deep-ocean Assessment and Reporting of Tsunamis) real-time tsunami monitoring systems, developed by PMEL, are positioned at strategic locations throughout the ocean and play a critical role in tsunami forecasting.

NDBC DART® Program
Image from NDBC

The location and warnings from the DART can be checked through the NDBC DART® Program website at National Data Buoy Center.

Tide gage / gauge are, according to Wikipedia, "is a device for measuring the change in sea level relative to a datum. Sensors continuously record the height of the water level with respect to a height reference surface close to the geoid. Water enters the device by the bottom pipe (far end of the tube, see picture), and electronic sensors measure its height and send the data to a tiny computer."

Energy map as of 1st Aril 2014
Image from National Tsunami Warning Center

Finally, the last diagram you will see is the Tsunami Propagation Forecast, which shows the "contours of forecasted maximum wave amplitudes above sea level [in centimetre], detailing tsunami energy propagation". The only problem with this diagram is that it only measures the wave amplitude above sea level up to 100cm, or in fact, anything above 40cm will be completely red, thus it is hard to see how much higher than 100cm the tsunami could be. That said, maybe anything above 40cm is destructive enough and will not make much difference from a 200cm one. Oh no! I'm starting to doubt what I have just said.

Let's hope that the people living at the coastal areas are safe.

Resources:
Hawaii on Alert After Huge Quake Hits Off Chile @ TIME
http://time.com/46206/chile-earthquake/

Peak ground velocity @ Wikipedia
http://en.wikipedia.org/wiki/Peak_ground_velocity

Peak ground acceleration @ Wikipedia
http://en.wikipedia.org/wiki/Peak_ground_acceleration

DART (Deep-ocean Assessment and Reporting of Tsunamis) @ NOAA Center of Tsunami Research
http://nctr.pmel.noaa.gov/Dart/

NDBC DART® Program @ National Data Buoy Center
http://www.ndbc.noaa.gov/dart.shtml

National Tsunami Warning Center
http://wcatwc.arh.noaa.gov/

Tsunami warning Antofagasta @ YouTube
https://www.youtube.com/watch?v=ai5e8Lpm0AU