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USGS Earthquake Scenario for Southern California
Posted on Thursday, May 22, 2008 @ 11:10 am by Dave Schumaker
The strongest shaking and greatest damage is near the stretch of the San Andreas Fault that extends through the fastest growing areas of Southern California, including the Coachella Valley, Inland Empire and Antelope Valley.
At least 10 million people will be exposed to heavy shaking. California’s efforts at mitigation have concentrated on life safety and have been largely successful. Thus, in spite of the large numbers of people in highly shaken areas, deaths are estimated at only 1,800.
Building types known to be vulnerable to damage and collapse, do indeed sustain major damage. All un-reinforced masonry buildings within 15 miles of the San Andreas Fault are completely destroyed. Those that are not retrofitted kill many occupants. Many other older building types without retrofitting contribute to over $33 billion in damage to buildings.
The fault offsets all lifelines crossing into Southern California at Cajon Pass (Interstate 15), San Gorgonio Pass (Interstate 10) and along Route 14, including pipelines, power lines, roads, railways, telecommunications and aqueducts.
Strong shaking continues in downtown Los Angeles for 55 seconds nearly 8 times longer than in the Northridge Earthquake
The prolonged, strong shaking heavily damages and sometimes collapses hundreds of old brick buildings, thousands of older commercial and industrial concrete buildings, many wood-frame buildings, and even a few, high-rise steel buildings. Over 600,000 buildings suffer at least some damage that causes tens of thousands of injuries and hundreds of deaths, and leaves many thousands of people without homes or jobs.
Fire doubles the fatalities and economic losses. Around Southern California, there will be 1,600 fires started large enough to warrant a 911 call, and some fires merge into conflagrations that burn hundreds of city blocks. Assuming no Santa Ana winds, the models still indicate a further $65 billion in direct losses and $22 billion in indirect losses from the fires.
Nearly two thirds of the hospital beds are non-functional in Los Angeles, Orange, Riverside, and San Bernardino counties. At the same time, 50,000 people will seek treatment at emergency rooms.
Andrew Alden at about.com briefly wrote about this yesterday.
Your First Geology Field Trip?
Posted on Wednesday, May 14, 2008 @ 11:21 pm by Dave Schumaker
The weekend is almost upon us and that means it’s probably time for a new meme to sweep through the geoblogosphere. Last week, it was Pangea Day and before that it was Tag Clouds (I think we’re burning through Accretionary Wedge ideas at an alarming rate).
What was the first geology trip you ever went on? Where did you go, what were your impressions and most important of all; do you have any photos?
Earlier this evening, I uploaded a set of photos I found in my iPhoto library that documents the first geology trip I ever went on as a student at Riverside Community College, way back in the spring of 2001. It was lead by Dr. Jim Mehegan, one of the best professors I have ever had and who had a huge impact on my academic life. Unfortunately, he passed away in 2004 while kayaking the Colorado River.
The field trip in 2001 was for an introduction to geology class and visited the Eastern Mojave Desert over 3 days. Specific features we would look at were the Pisgah Crater, Cima Volcanic Field, Amboy Crater and the area around Essex/Hole in the Wall. The trip was an absolute blast.
About to hike up Amboy Crater
First time hunting for fossils! (FYI, I’m the scrawny guy in the white shirt on the left)
Why do they call it Hole in the Wall?
Welded Tuff
Hiking to the top of the Kelso Dunes
At the top of the Kelso Dunes
Running down the face of the Kelso Dunes. (The Kelso Dunes are known as “barking dunes” for the sound that is made when air in the pore space of the sand grains is compressed and forced out from beneath the surface)
It’s amazing how young and dorky looking I am back then. Fortunately, a lot has changed in the past 7 years since I first started out in geology.
Then again, maybe nothing has changed.
Water Clarity Loss in Lake Tahoe
Posted on Tuesday, May 13, 2008 @ 2:58 pm by Dave Schumaker
Since 1968, researchers have been continuously measuring Lake Tahoe’s famous water clarity and tracking how much it degrades. The degradation of water clarity is caused by runoff and development along the shores of the lake and researchers use it to gauge how healthy the lake is.
New data from UC Davis scientists show that the rate of clarity loss has significantly slowed since 2001, giving residents and scientists interested in the lake cautious optimism that almost $500 million dollars in runoff prevention and treatment may be having a positive effect on the lake.
Schladow cautioned that the data do not pinpoint a specific cause for the recent improvements, but noted that new modeling results show that runoff of fine particles from both urbanized areas and roadways around the lake are the primary factors that influence clarity levels. Fine particles scatter light and limit how far into the lake we can see.
In addition, Schladow and his UC Davis colleagues cautioned that it is difficult to use data from a small number of years (2001 to 2007) to draw conclusions about when the trend might change from a slowdown in clarity decline to an improvement in clarity. “Only with the commitment to long-term monitoring can we truly evaluate environmental changes over time,” he said.
[Via Physorg]
Weekend Adventures - Capitola Fossils
Posted on Sunday, April 27, 2008 @ 11:42 am by Dave Schumaker
On the way back from camping in Monterey last weekend, some friends and I decided to stop by Capitola Beach, in the small beach town of Capitola, California (just east of Santa Cruz). We last visited Capitola in 2005.
It’s a popular destination for tourists and beginning surfers, but it’s also an excellent spot for those interested in collecting Pliocene aged marine fossils that range from common mollusks to seal bones and even whale bones. The best time to visit the beach is at low tide, when the bedrock outcrops usually hidden by surf are accessible. Because of the constant erosion of the cliffs around Capitola, each visit is a new experience in terms of what you will findsee.
We managed to take a few photos of the area as well.
Pieces of bone.
Shell fragments (possible storm bed?).
Larger bones.
Capitola Cliffs
Cliff Face
Shell fragments
Broken Shells.
And what about the geology of Capitola? This PDF file from the Moss Landing Marine Labs explains the deposits.
Here Pliocene Purisima Formation, described by Cummings et al., (1962) as abuff-yellow to light brown and gray, fine-grained sandstone and siltstone, can be seenhere eroding away. This formation has been dated at 3 -1 Ma. At this locality, thePurisima Formation contains numerous dense layers of fossilized mollusk coquinas,ranging from 3-20 cm in thickness. These are interbedded with thin to thickargillitic sandstone beds and thin phosphatic silt and mudstone beds. The alternating fineto coarse-grained bedding is believed to reflect transgressive and regressive periodsassociated with uplift due to wrench tectonics and sea level changes (Clark et al., 1979).Faulting within the formation can be recognized based upon the existence of slickensidespreserved in some of the fractures
Also, here is a fantastic photo gallery by Paul Slocombe and taken in 2007 featuring many different types of Capitola fossils.
All photos taken by Dave Schumaker
More Information:
Capitola Beach 360 Degree VR Photo
Capitola Beach Coastal Monitoring Program [USGS]
Capitola, California [Google Maps]
Collecting Fossils in California
New Forecast for California Earthquakes
Posted on Monday, April 14, 2008 @ 12:22 pm by Dave Schumaker
The USGS released the results of a new study on the probabilities for earthquakes throughout the state of California. Using new modeling techniques, they have found that the possibility of a large earthquake hitting the state of California to be greater than originally thought.
One notable aspect of the study is that it’s the first time that earthquake hazards can be meaningfully compared between Northern and Southern California.
California has more than a 99% chance of having a magnitude 6.7 or larger earthquake within the next 30 years, according scientists using a new model to determine the probability of big quakes.
The likelihood of a major quake of magnitude 7.5 or greater in the next 30 years is 46%-and such a quake is most likely to occur in the southern half of the state.
[...]
The consensus of the scientific community on forecasting California earthquakes allows for meaningful comparisons of earthquake probabilities in Los Angeles and the San Francisco Bay Area, as well as comparisons among several large faults.
The probability of a magnitude 6.7 or larger earthquake over the next 30 years striking the greater Los Angeles area is 67%, and in the San Francisco Bay Area it is 63%, similar to previous Bay Area estimates. For the entire California region, the fault with the highest probability of generating at least one magnitude 6.7 quake or larger is the southern San Andreas (59% in the next 30 years).
For northern California, the most likely source of such earthquakes is the Hayward-Rodgers Creek Fault (31% in the next 30 years). Such quakes can be deadly, as shown by the 1989 magnitude 6.9 Loma Prieta and the 1994 magnitude 6.7 Northridge earthquakes.
The latest episode of the USGS Corecast talks about this study and features an interview with USGS geophysicist Tom Parsons.
[Via USGS]