100th Anniversary of the Great San Francisco Earthquake Will be Recognized at the (Seismological Society of America) Annual Meeting

On April 18th, 1906, at 5:12am local time, one of the largest earthquakes in the history of the United States rumbled through the city of San Francisco, waking everyone with terror. After a full minute of shaking, those who believed the worst was over were severely mistaken. The entire city of San Francisco was destroyed by the ensuing fire which was caused by the earthquake. Ruptured water lines prevented fire crews from fighting the fires, and many roads were blocked with debris. The image below shows the destruction of the entire city of San Francisco, taken some five weeks after the quake. Note the lack of buildings and total destruction even at the most distant of visible areas on the horizon. Nearly every single building was destroyed or at least compromised due to the earthquake and fire. This earthquake sparked the interest that was needed to study the effects of earthquakes, and challenged the brilliant minds of those early generations to develop key insights to seismology that paved the way for the theories and laws that are still used by modern seismology today.

The 2006 SSA Meeting will be attended by nearly all of the top research seismologists in the world. The meeting will be the largest of its kind, and will allow politicians, scientists, educators, students, first-responders, engineers, and business professionals to gather and share ideas via one of the largest venues ever for an SSA Meeting.

To learn more, or to find out how to attend the 2006 SSA Meeting, click here.

M7.2 Earthquake off the coast of Eureka, CA

At 7:50PM local time (PDT), there was a M_W7.2 earthquake located 91 miles (146 km) WNW off the coast of Eureka, CA. This earthquake was felt widely along the west coast of the United States, and felt as far away as Seattle, WA, Los Angeles, CA, and as far east as the Sierra Nevada mountain range in central CA. The event was approximately 10 miles deep, and was located in the middle of the Gorda Plate, east of the Mendocino Triple-Junction, where the Gorda Plate, North American Plate, and the Pacific Plate meet. The event triggered the West Coast/Alaska Tsunami Warning Center to issue a tsunami warning, but this bulletin was quickly cancelled when more analysis of the earthquake showed that it was not an earthquake that generated a tsunami.

There are no reports of damage or injury, but this earthquake serves as a reminder that we do live in earthquake country, and should always be prepared with a plan of action in the event of a major earthquake and/or tsunami. This event provided an excellent opportunity for a tsunami drill, which will give authorities insight to the problems that exist in the tsunami warning system, in addition to the issues that arose during evacuation of some nearby towns (in the northernmost portion of CA and southernmost portion of OR). This will better help us understand how to prepare for tsunamis, in addition to creating a better, more efficient tsunami warning system.

To learn more about this quake, go to http://www.cisn.org/special/evt.05.06.15/.

Map of M7.2 Earthquake of 6/14/05

Dr. Kate Hutton Explains the Magnitude Change for the 6/12/05 Anza Earthquake from M_L5.6 to M_W5.2

			The "local magnitude" (ML, in this case 5.6) is the traditional form of earthquake magnitude that we have been using for 70 years, based on Charles Richter and Beno Gutenburg's original work, adapted to modern technology.  It is based on the logarithm of the peak "pen" (or virtual equivalent) deflection on a certain type of short-period seismometer.  With our current software, the local magnitude is available within a minute of the occurrance of the earthquake, so the initial notifications by e-mail, pager, world-wide web, etc. use it. Moment magnitude (MW, in this case 5.2) is more complicated.  It involved matching a computer model of the earthquake source to long-period seismograms.  Ideally, it is a better indication of how much rock moved how far during the earthquake.
At the moment, MW is computed automatically, but sometimes the computer needs a little extra help from a seismologist.  For this reason, at the moment, MW requires human review & is therefore not available in the first few minutes when the notifications go out. Because MW is a better measure of the energy released in the earthquake, seismologists prefer it.  This is why we switched from reporting ML to reporting MW.  If we had been able to make the change right away, we would have done it then.  Once the media reporting began, however, we thought it less confusing to stick with our original estimate through the day. It is unrealistic to expect ML and MW to be exactly the same, because earthquakes are complex, and the methods of measurement are completely different.  They are like the proverbial apples and oranges, both round and about the same size, but totally different fruit. Kate Hutton Staff Seismologist, Caltech Dr. Kate Hutton has worked as a staff seismologist with the Caltech Seismological Laboratory for nearly 30 years. Known to many as "That Earthquake Lady", Southern Californians have come to expect to see her on the television news after a local earthquake. Click here to learn more about SCSN magnitude calculations

New Study Models Puente Hills Fault Hazard and Probability for M7.5 Event, One-quarter Trillion Dollar Losses Estimated

USGS scientist Ned Field estimates that a M7.5 event on the recently discovered Puente Hills Fault could generate $250 billion in losses, and could cause more than 15,000 fatalities in the Los Angeles Basin. Large magnitude events (M7.2-7.5) generally occur every 3,000 years on the fault, which has ruptured four times in the past 11,000 years. The fault was discovered in 1999, which created an immediate interest in research, and thereby prompted more than fifty scientists to study the fault and create earthquake scenarios, such as the Puente Hills Earthquake Scenario ShakeMap, and the Percent Building Loss Estimate, shown below. To read the full press release, visit either the USGS Website or the SCEC Website.

New State of California Earthquake Probability Maps

The USGS, in conjunction with Caltech Seismological Lab, UC Berkeley Seismological Lab, and the California Geological Survey recently released to the public new 24 hour earthquake probability maps for the entire state of California. These maps do not predict earthquakes, but simply display the statistical probability of an earthquake based on previous earthquake activity. The map, shown below, is generated every hour, and whenever an earthquake with a magnitude larger than 3 occurs. To learn more about these probability maps, or to view the map at any time, visit: http://pasadena.wr.usgs.gov/step/.

SCSN.org has replaced Trinet.org with a more functional site that is user-friendly. The new SCSN site will be updated with the most current relative information, targeted to an audience with a background in seismology, geology, geophysics, network administration, IT, and hazard mitigation.

Check this page often to learn about the most current information relating to Southern California earthquakes. We welcome input relating to SCSN.org, and encourage you to contact us at webmaster@scsn.org .