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Predicting catastrophic earthquakes
This resource provides an abstract. This article discusses a method based on the magnitude-frequency distribution of previous earthquakes in a region. It is used to examine the probability of a small earthquake growing into a catastrophic one. When a small earthquake is detected in a region where a catastrophic one is expected, early warning systems can be modified to determine the probability that this earthquake will grow in magnitude. It was found that if the observed earthquake magnitude reaches 6.5, the estimated probability that the final magnitude will reach 7.5 is between 25 and 41 percent.
Reassessing the earthquake threat to San Francisco
This resource provides an abstract. New research suggests that authorities may need to reassess the threat posed by the Hayward fault, the fault responsible for San Francisco's highly destructive 1868 earthquake. The authors used a large shaking vehicle to send vibrations into the ground along a 1.6 kilometer portion of the Hayward fault and used the recorded vibrations reflected back from the fault to develop a profile of its shape and location. Findings are described.
Cracks from a Japanese earthquake heal in two years
This resource provides an abstract. Seventeen years of shockwave recordings were used to investigate crack healing after the large March 1997 Tokai region earthquake in Japan. Recordings taken at two stations in Japan from 1986 to 1996 were of shockwaves generated by other earthquakes, which passed through the crust region damaged by the 1997 Tokai quake. Comparing the observations taken before the earthquake to those taken afterwards, the researchers determined that the cracks healed in about two years, a finding similar to that of previous studies of crack repair.
Molten rock makes big earthquakes bigger
This resource provides an abstract. A modified friction welding device was used to spin one small cylinder of granite against another at high speed and pressure in order to simulate two plates sliding against each other. The velocity of the spinning granite cylinders, the force with which they were pushed together, and the temperature at their interface were measured. It was found that high heat generated when large plates slip against each other melts rock which accelerates slipping and results in more violent shaking than expected.
Magma shakes up earthquake locations
Numerical models were employed to examine the relationships between the orientation of volcanotectonic faults and magma movement. It was found that the direction of movement on strike-slip faults should be opposite to that predicted on the basis of regional stresses. The results do not explain the location of some volcanotectonic earthquakes and that the locations of preexisting faults may be more important in influencing the location of these earthquakes.
Improving earthquake warning in Costa Rica
This resource provides an abstract. This study examines seismic waves from a segment of the Middle America subduction zone below Central America that are capable of producing strong earthquakes. Results confirmed the depth of the crust-mantle boundary and mantle seismic velocities in the region. It was found that decreased seismic velocities are evidence that fluid affected nearly 15-25 percent of the mineral structure, leading to serpentinization. This data can contribute to improving earthquake hazard estimates for the area.
Stopping stick-slip seismic events?
This resource provides an abstract. This study models underground frictional resistance in stick-slip seismic events in order to determine the amount of energy needed to weaken a fault plane enough to initiate ground motion and simulate the speed of the recovery after the pressure subsides. The exact moment the slip began the maximum speed of the ground motion were detected. Results indicate that stick-slip events stop spontaneously when frictional melting begins, suggesting a potential way to stop the seismic events.
Using GPS for earthquake imaging
This resource provides an abstract. The authors used a dense array of Global Positioning System (GPS) stations to model how the Earth slipped during the 2003 8.0-magnitude Tokachi-Oki earthquake near Japan. Results indicate that displacements of more than one meter occurred in approximately 20 seconds on Hokkaido. It was found that while satellite data are less precise than traditional seismic data, GPS has the advantage in measuring displacement since seismometers cannot distinguish between the ground's acceleration and rotation.
Simplified modeling method to estimate lava flow
This resource provides an abstract. A numerical model that produces early predictions for the projected path of a lava flow was created. The two dimensional model is based on a generalized set of equations to describe lava flow propagation. Using real data from the 1991 1993 Mount Etna eruption in Italy, the model effectively reproduced the actual lava flow. This preliminary result indicates the usefulness of this method for forecasting lava flow paths for risk mitigation and predicting the damage from future eruptions.
Background on the 1900 Galveston Hurricane
A report on the 1900 hurricane that devastated Galveston, Texas is available on the AGU Web site. It is a chapter from the book, Hurricane!: Coping with Disaster (AGU, 2003), covering the event itself and lessons learned from it.