The Whittier Narrows quake struck 30 years ago this Sunday, Oct. 1. It wasn’t the most deadly or most costly temblor in California, but it set many things in motion to help us deal with future earthquakes.
LESSONS FROM WHITTIER
The magnitude 5.9 earthquake caused eight deaths and an estimated $358 million in damage (adjusted to 2008 dollars). Homes were damaged in Los Angeles, Orange and Ventura counties in the strongest quake in Southern California since 1971.
The quake occurred on a previously unrecognized fault and was the first sign that the Los Angeles basin was on what is now called a blind thrust fault. The second major quake from such a fault was the Northridge shaker in 1994, which killed 57 and inflicted $44 billion in damage.
The search for blind thrust faults has been on since the early 1990s.
What lurks beneath
The Whittier quake took place in the Puente Hills thrust system, considered one of the highest-risk faults in the U.S. because it is underneath a heavily populated area.
Matter of magnitude
Measuring earthquakes accurately has come a long way since 1987. The USGS website shows earthquakes occurring around the world in real time and what their magnitude is.
Shown above are examples of magnitudes and how vast the difference of fault slippage is. California has not had a magnitude 8 quake since records have been kept.
The energy released in a magnitude 7 earthquake is about 30 times more than the energy released in a magnitude 6 earthquake.
Getting the alert out
There were just a few seismic monitoring stations in California before the Whittier quake, and now there are 740. California is trying to fund an earthquake early-warning system that can send a message to your computer or mobile device seconds to minutes in advance.
How the system works:
When an earthquake occurs, it sends out three types of waves: P-waves, S-waves and surface waves. The P-wave is the initial wave detected by seismometers. It travels the fastest.
Sensors detect the P-wave and immediately transmit data to an earthquake analysis center, where the location and size of the quake are determined. The surface and S-waves are the wave types that mark the start of potential damage from shaking. They follow the P-wave.
An alert from the analysis center is immediately transmitted to computers or mobile phones. Using GPS coordinates, the system calculates the arrival time of the shaking.
The Whittier Narrows (1987), Loma Prieta (1989) and Hector Mine (1999) quakes occurred in the month of October but earthquakes can occur all year long, at any moment.
The last earthquake of magnitude 5 or higher in California was in 2014.
Source: USGS; Lucy Jones, USGS seismologist; Geology.com; Science.org; Geophysical Journal International; Southern California Earthquake Center
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