Archive for January, 2011
A decade ago, the most common earthquake exercise for high school students or college freshmen involved locating the epicenter of a seismic event. All you needed were the arrival times of P- and S-waves for three seismic stations, a time-distance graph, a map, and a pencil and thread. A steady hand was a bonus.
Today a search for earthquake exercises at DLESE (Digital Library for Earth Science Education yields 980 resources. Some are descriptive in nature and offer little in the way of student interaction with the material. But DLESE offers up a whole host of exercises tailored for certain grade levels and at different tiers of difficulty. Contributors range from high school and university faculty, to conservation organizations, to federal agencies, to professional societies and educational think tanks.
A grab-bag list of several of the dozens of DLESE earthquake lab exercises, with several entries from DLESE’s highly vetted “reviewed collection”, includes:
And yes, plotting earthquakes, is included, too, and remains a stalwart of introductory Earth science lab books.
Of course, a multitude of choices carries with it it’s own problem – selection, and while that’s not trivial, it’s a problem Earth science educators can afford.
Mike Conway, 31 January 2011
Earlier this month, we blogged about new findings on the moon’s interior structure, Moonquake ~ Liquid Core in, blue cheese out. Matt Fouch of Arizona State University’s (ASU) School of Earth and Space Science Exploration saw the blog and pointed out an important omission: the Arizona-lunar connection.
Rene Weber while at the USGS Astrogeology Branch in Flagstaff, Arizona, was a driving force behind revisiting the old Apollo seismic data and applying it to understanding lunar structure. At this fall’s AGU meeting in San Francisco, Rene presented a poster entitled, The use of deep moonquakes for constraining the internal structure of the Moon.
ASU’s Ed Garnero and graduate student Patty Lin contributed as well by recommending an analytical approach, array processing, that allows a series of weak signals to be evaluated in concert. ASU News quoted Lin as saying, “… when we add the signals together, that core reflection amplitude becomes visible, which lets us map the deep Moon” (http://asunews.asu.edu/20110106_lunarcore).
As a result of this Arizona-lunar connection, we know now quite a bit more about lunar structure. For more on lunar core research, see Seismic Detection of the Lunar Core, 2011, by Weber, Lin, Garnero, Williams and Lognonne, Science, v. 331, #6015, p. 309-312. You can view the abstract at: http://www.sciencemag.org/content/331/6015/309
Image – False-color image of Earth’s moon released by NASA on 16 March 2002.
Mike Conway, 23 January 2011
A new report on the condition of Utah’s school buildings suggests that 60% of the structures have inadequate seismic resistance in the event of a major earthquake, and as many as 8% appeared “virtually certain” to collapse when the “big one” hits the Wasatch front.
For more specifics about the Utah Seismic Safety Commission report visit: http://www.sltrib.com/sltrib/home/51092127-76/buildings-seismic-utah-schools.html.csp?page=1
The results are relevant because the 240 mile long fault that runs along eastern edge of the Salt Lake region is made up of several 25 mile-long segments which are independently known to generate significant (magnitude 6.5-7.5) earthquakes every 1,300 years. The last of these events was around 1,300 years ago. Additionally, because the urban areas of the Wasatch Front are built in the soft lake sediments of prehistoric Lake Bonneville, the area stands to experience severe damage during the next large Wasatch Fault event.
The May, 2010 investigation on the Wasatch Fault Zone, prepared by the USGS and the Utah Geological Survey, can be found here: http://www.sltrib.com/sltrib/home/51092127-76/buildings-seismic-utah-schools.html.csp?page=1
With Federal and State budget crunches we often lack the means to implement comprehensive mitigation strategies immediately. The more that is known about the dynamics of active faulting in the region the more impetus state officials and city planners have to enact appropriate legislation. In the meantime there are things that individuals can do to minimize the dangers to their families in the event of an earthquake. The Handbook offered at http://ussc.utah.gov/putting_down_roots.html is just one resource of many on the web.
LIDAR Illuminating Earthquake Hazards
Visualizing geologic processes is a challenge. But the payoff in graphics or animations that help geoscientists better understand and communicate how geologic processes operate is beyond measure. A new video on how scientists use LIDAR to examine young fault systems is a wonderful addition to the Earth sciences cinematic portfolio.
LIDAR (Light Detection and Ranging) involves laser pulses to collect detailed information about the ground surface, providing a much higher resolution image than is normally available; it has the added advantage, too, of seeing through vegetation. The raw data constitutes a point cloud of millions of data points that are rendered into digital elevation models (DEM) that represent the ground surface at sub-meter resolution. LIDAR applications range broadly from hydrology to biology, archaeology, meteorology, and geophysics – and that’s just scratching the surface.
Video. The video begins with an earthquake propagation animation on the San Andreas fault system (source, Southern California Earthquake Center), then quickly moves to a freshly trenched fault trace in the Mystic Lake area and discussion on the hazards earthquakes pose to people. That’s followed up by marvelous 3-D models of California’s major fault systems manufactured using LIDAR data and complemented by a primer on how LIDAR works.
Ken Hudnut (USGS) does an excellent job describing how LIDAR provided new insight into recent slip events along a section of the San Andreas Fault.
Open Topography (www.opentopography.org) receives especial attention here as a purveyor of high resolution topographic data and tools.
If you have nine-minutes to spare and an interest in fault systems and how new topographic modeling greatly illuminates subtle ground features, this video is for you.
LIDAR Illuminating Earthquake Hazards
Director ~ Sarah Robinson
Cinematography and Audio ~ Andrew Whitesides
Narrator ~ Michael Ihrig
Michael Conway, 21 January 2011
Imagine 8 million people simultaneously dropping to the ground, scurrying beneath a table, and crouching there on all fours while firmly gripping a table leg until the all-clear is sounded. Sound familiar? It should, at least to people in the Southwestern U.S., because that describes last October’s ”The Great California Shakeout”.
Earthquake prediction is a shaky business and a long way from providing a measure of safety to the tens of millions living in earthquake country here and abroad. In the contiguous U.S., California is arguably the state with the greatest potential for large magnitude (M 7.0+) earthquakes in the near term. State officials there recognize the dire need for aggressive earthquake prevention outreach and mitigation: hence, the Great Shakeout approach.
But earthquakes happen elsewhere in the U.S., and the Great Shakeout phenomenon is sweeping east and south. Now states in the central U.S. — Missouri, Illinois, Indiana, Kentucky, Tennessee, South Carolina, Georgia, Alabama, Mississippi, and Arkansas – are planning the “Great Central U.S. ShakeOut” for 28 April at 10:15 a.m. (Indiana’s scheduled to participate on 19 April.)
The Great Central U.S. Shakeout ~ http://www.shakeout.org/centralus/
The Great California Shakeout ~ http://www.shakeout.org/
Mike Conway, 17 January 2011
If you own a computer – and who doesn’t these days – you own a device capable of detecting and reporting on ground acceleration, i.e., earthquakes. Earth Trek – Global Citizen Science Program is managing the Quake-Catcher Network. The image at right shows the distribution of U.S. computers participating in Quake-Catcher.
According to EarthTrek, Quake-Catcher, which comprises internet-connected computers – both laptops and desktops, constitutes the world’s largest, low-cost, strong-motion seismic network. Most computers now come with the necessary hardware to join the network.
One of Quake-Catcher’s chief goals is to serve as an early alert system for schools, hospitals, civil authorities, and the public.
Interested? You’ll find more information at the Quake-Catcher website: http://www.goearthtrek.com/QCN/QCN.html
Since the onset of historical records in the 1830s, Arizona has been rattled, rocked, and rolled by thousands of earthquakes. Most are instrumental events requiring modern seismometers to detect and record them. Many but not all originated in Arizona along young, active faults. Some originated in surrounding states – California is the usual suspect, but the Earth’s fractured crust in Utah, Nevada and New Mexico has contributed, too. Large magnitude earthquakes in Sonora and Baja California, Mexico, have had their impact as well; most recently on Easter Sunday of 2010.
Now Google Earth Users can sample a time-series of Arizona earthquakes from the Arizona Earthquake Information Center (AEIC) at Northern Arizona University. AEIC serves up their catalog of earthquake activity in Arizona as a KML file that includes 1100 events stretching from 1830 to 2010.
Go to AEIC’s catalog page at http://www4.nau.edu/geology/aeic/eq_history.html
At “NEW: download AEIC earthquake catalog in Google Earth (GE) kmz file updated to November 2010 here “, select here. The catalog will upload to your GE application.
A time-series control tool appears in the upper left corner of GE. Select the wrench and you can control the rate at which the seismic events pop up on the screen. To start the animation, select the clock icon to the right of the magnifying glass. All that is missing is a solid thud and swinging chandelier as earthquake after earthquake shakes Arizona.
Mike Conway, 15 January 2011
The sensitivity of modern seismometers can’t be overstated. They can detect ground acceleration imparted by tremulous tree roots as the tree canopy overhead sways in the wind, or pond waves lapping onto the shore on a calm winter day.
And as a recent article in the Seattle Times shows, they can be used as a stethoscope to measure the fortunes of the home team favorite. On 8 January 2011, NFL’s underdog Seattle Seahawks met the New Orleans Saints at Seattle’s Quest Field in the first round of the NFL playoffs. The Seahawks won the game with one of the year’s best performances.
Fans elated by the Seahawks play stomped their feet and clapped their hands imparting energy – seismic waves – into the stadium, which then delivered it to the Earth’s surface. A nearby seismometer performed masterly in capturing and quantifying the crowd’s energy; energy equivalent to a M1 to M2 earthquake.
The seismogram to the right, published by the Seattle Times, captures for posterity the elation of Seattle fans.
Mike Conway, 13 January 2011
NOVA’s Deadliest Earthquakes: Earthquake Science & Masterful Cinematography
The film begins with devastating and heart wrenching scenes of the destruction of Port-au-Prince, Haiti, on 11 January 2010. The camera captures terrified people running through ruined streets. What follows is a helicopter shot showing a broken, bloodied, and battered city.
The scene shifts to the arrival of a seismologist from Purdue University. He discusses how GPS-based research allows him to quantify the amount of movement on the fault that produced the 7.0 M killer earthquake.
Fabulous graphics showing earth structure, plate boundaries, and corrugated fault surfaces follow. Then a magnificent graphic of the exponential nature of seismic magnitude.
The Purdue research documents that only a small section of fault ruptured, leaving the remaining section with a large and unreleased stress load.
The film makers shift suddenly to western California and the San Andreas Fault. Arnold Schwarzenegger is standing at a podium deliberating on CA’s Great Shakeout program – one of the great science outreach events in the world. There are great shots of field research along the Elsinore fault in Anza Borrego State park – the graphics showing downhole placement of seismic equipment is remarkably telling.
Then on to Chile where, at 3:00 AM on 27 Feb 2010, a magnitude 8.8 event occurs. The result: half a million homes destroyed, hundreds dead, and Earth’s day shortened by the tiniest fraction of a second.
The film shows much more as it bounces from place to place across the Earth’s fractured surface. And as the participating scientists point out again and again, earthquake prediction remains an elusive prize.
A fantastic film well worth a look.
Mike Conway, 11 January 2010
Yesterday, Sunday, 9 January 2011, marked the 153-year anniversary of the 1857 Fort Tejon earthquake. The earthquake, a 7.9 M event, occurred as the San Andreas Fault ruptured from Cajon Pass to northwest of San Bernardino in western California . Shaking lasted for several minutes and maximum ground displacement in
the Carrizo Plain SE of Parker, California, was on the order of 9 meters – about 27 ft!
Fort Tejon was not proximal to the event, but because of the severe damage done there, they won – whether they liked it or not — crowing rights. Damage reports from the Fort indicate two buildings declared unsafe, three others suffered extensive damage, while several others suffered moderate damages.
Imagine for a moment the impact that a 7.9M event would incur today; damage would undoubtedly be in the billions of dollars.
You would have liked – and who would not have liked – the earthquake to have happened in the middle of some desert …, Jean-Jacques Rousseau in his famous response to Voltaire’s cold statements following the cataclysmic Lisbon, Portugal, earthquake of 1755.
Mike Conway, 10 January 2010
Additional Information at US Geological Survey. http://earthquake.usgs.gov/earthquakes/states/events/1857_01_09.php