Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Los Angeles ’big squeeze’ continues, straining earthquake faults


Northern metropolitan Los Angeles is being squeezed at a rate of five millimeters [0.2 inches] a year, straining an area between two earthquake faults that serve as geologic bookends north and south of the affected region, according to NASA scientists.

The compression of the Los Angeles landscape is being monitored by a network of more than 250 precision global positioning system (GPS) receivers, known as the Southern California Integrated Global Positioning System Network (SCIGN), as well as by measurements from interferometric synthetic aperture radar (InSAR) satellites operated by the European Space Agency (ESA).

Information from these two sources of precision ground deformation measurements is accumulating and enhancing our knowledge of the forces shaping the land surface in the Los Angeles region. These forces include motions of the North American and Pacific tectonic plates and ground movement caused by human activities, such as oil drilling and pumping water into and out of local aquifers.

A team of scientists from NASA’s Jet Propulsion Laboratory and University of California at Los Angeles, led by Donald Argus, set out to distinguish between motions induced by human activity and those generated by movements of Earth’s tectonic plates. Their results, published in the Journal of Geophysical Research (Solid Earth) in April, indicate human-caused motions are very slow and could not account for the significant ground shift observed in northern Los Angeles.

The new study used space-based navigation to determine the exact position of hundreds of points around the metropolitan area to measure the strain building up across faults. Scientists expect that the strain will ultimately be released in earthquakes much like the 1994 Northridge temblor. The study also suggests which faults might be most likely to rupture. "These findings remove uncertainty about the rate at which strain is building up in northern metropolitan Los Angeles," Argus said. "In addition, by taking into account the effects of humans and observations from the many new global positioning system sites established in the past few years, we can identify the areas where strain is building the fastest."

He cautioned, however, that more studies are needed, since scientists do not yet fully understand the consequences and risks of this stress accumulation. "Nevertheless, these data have important implications for hazard management and retrofitting strategies," he said.

The study finds strain is rapidly accumulating within an area 12 to 25 kilometers [7.5 to 16 miles] south of the San Gabriel Mountains, primarily in the San Gabriel and San Fernando Valleys and nearby hills. The region is located between the Puente Hills fault, which begins south of downtown Los Angeles and extends east, and the Sierra Madre fault, which runs along the base of the San Gabriel Mountains

The new analysis indicates the crust above the Los Angeles segment of the Puente Hills Fault is being squeezed the most. The finding suggests that the Puente Hills Fault and nearby faults in the area, such as the upper Elysian Park Fault, may be more likely to break than those elsewhere in metropolitan Los Angeles. Previous studies have estimated the Puente Hills Fault might generate an earthquake of magnitude 6.6 to 7.5.

The researchers constructed models of the accumulating strain, varying which faults "creep" (move continuously without producing earthquakes), how fast they creep, and the depths at which the faults go from being "locked" in place (and building strain) to creeping. The model that best fit the actual global positioning system observations is one in which a thrust fault (a fault where one block of Earth shifts up or down relative to the other) is locked above six kilometers [four miles] deep and creeps at about nine millimeters [0.4 inches] a year beneath that depth. From that model, they inferred that the deep part of the Los Angeles segment of the Puente Hills Fault is creeping, as is a deep unknown buried fault east of downtown that lies north of the Whittier Fault and south of the Sierra Madre Fault. The model does not allow the researchers to determine which fault segments are locked.

Argus said a significant discrepancy exists between the relatively shallow locking depth of their model and the historical record of the depth of earthquakes that struck the region in 1971 and 1994, which were much deeper. Scientists speculate the discrepancy may be due to the presence of sediments filling parts of the Los Angeles basin. Further studies are planned to examine how these sediments may be affecting fault strain in the region.

The study used InSAR data collected from 1992 to 2000 from ESA’s European Remote Sensing satellite to estimate vertical ground motion. Horizontal strain buildup measurements were made from SCIGN observations from 1994 to 2004.

Harvey Leifert | EurekAlert!
Further information:

More articles from Earth Sciences:

nachricht Wandering greenhouse gas
16.03.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung

nachricht Unique Insights into the Antarctic Ice Shelf System
14.03.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

Im Focus: Surveying the Arctic: Tracking down carbon particles

Researchers embark on aerial campaign over Northeast Greenland

On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...

Im Focus: Unique Insights into the Antarctic Ice Shelf System

Data collected on ocean-ice interactions in the little-researched regions of the far south

The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...

Im Focus: ILA 2018: Laser alternative to hexavalent chromium coating

At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.

When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...

Im Focus: Radar for navigation support from autonomous flying drones

At the ILA Berlin, hall 4, booth 202, Fraunhofer FHR will present two radar sensors for navigation support of drones. The sensors are valuable components in the implementation of autonomous flying drones: they function as obstacle detectors to prevent collisions. Radar sensors also operate reliably in restricted visibility, e.g. in foggy or dusty conditions. Due to their ability to measure distances with high precision, the radar sensors can also be used as altimeters when other sources of information such as barometers or GPS are not available or cannot operate optimally.

Drones play an increasingly important role in the area of logistics and services. Well-known logistic companies place great hope in these compact, aerial...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

International Virtual Reality Conference “IEEE VR 2018” comes to Reutlingen, Germany

08.03.2018 | Event News

Latest News

Wandering greenhouse gas

16.03.2018 | Earth Sciences

'Frequency combs' ID chemicals within the mid-infrared spectral region

16.03.2018 | Physics and Astronomy

Biologists unravel another mystery of what makes DNA go 'loopy'

16.03.2018 | Life Sciences

Science & Research
Overview of more VideoLinks >>>