Recent earthquakes in california northridge12/24/2023 ![]() "While similar post-seismic movements have been seen after earthquakes in other regions, this observation is significant because it highlights the difficulty of fully accounting for all of the strain that can potentially lead to earthquakes. Granada Hills is a foothill community just to the north of the city of Northridge. What is clear is that the force of the after-slip has added about 16 centimeters (about 6 inches) to the Granada Hills since the earthquake. "Our GPS processing techniques are now better refined, making it easier to resolve vertical as well as horizontal movements of the Earth's surface." "It is not clear yet if this continued post-Northridge 'after-slip' represents a loss of stress along a fault or if it is a transfer of stress to other areas," Lyzenga said. Scientists at JPL can determine the position of a user with a GPS receiver to better than 1 centimeter (0.4 inches) per day by correlating signals from the satellites and knowing the satellite orbital locations very accurately. The satellites are arranged so that several of them are "visible" from any point on the surface of the Earth at any time. GPS uses data transmitted from a constellation of 24 Earth- orbiting satellites that are jointly operated by the departments of Defense and Transportation. SCIGN uses an array of permanent GPS receivers placed throughout the region. These temporary GPS sites were part of a preliminary earthquake study that helped lead to a large effort called the Southern California Integrated GPS Network (SCIGN). Andrea Donnellan studied data from about a dozen GPS receivers that continuously measure the constant, yet nearly physically imperceptible, movements of earthquake faults throughout Southern California. "The amount of motion that happened because of this 'stealth' earthquake is equivalent to the displacement that would accompany a magnitude 6.0 earthquake." Gregory Lyzenga, a JPL geophysicist and professor at Harvey Mudd College, Claremont, CA. However, the sedimentary layers of rock, in the top five kilometers located just below the surface near the epicenter, have continued to move in a fluid- like manner - sort of like honey flowing off a spoon - since the earthquake," said Dr. "The Northridge quake occurred on a thrust fault that did not break all the way to the surface. Scientists from NASA's Jet Propulsion Laboratory will present their findings this week at the annual Fall meeting of the American Geophysical Union in San Francisco. ![]() Earthquake researchers measuring the movement of the Earth's surface with the Global Positioning System (GPS) have concluded that the Northridge earthquake has continued in a "quiet" way and the Granada Hills have risen about 16 centimeters (about 6 inches) since that first jolt in January 1994. ![]()
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