Generation of High Frequency P and S Wave Energy by Rock Fracture During a Buried Explosion

• Main Author: Sammis, Charles G.
• Other Authors: CALIFORNIA UNIV LOS ANGELES DEPT OF EARTH AND SPACE SCIENCES
• Format: Text
• Language: English
• Published: 2007
• Subjects: Acoustics; Explosions; *UNDERGROUND EXPLOSIONS; *FRACTURE(MECHANICS); *MICROMECHANICS; *ULTRASONIC FREQUENCIES; COUPLING(INTERACTION); ICE; PERMAFROST; SEISMOLOGY; CHEMICAL REACTIONS; EXPERIMENTAL DATA; ALASKA; NONLINEAR SOURCE MECHANICS; *FROZEN CRYSTALLINE ROCKS; SEISMIC RADIATION; PE62601F; WUAFRL1010SMA1; Ice; permafrost; Alaska
• Online Access: http://www.dtic.mil/docs/citations/ADA477146; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA477146

The micromechanical damage mechanics developed by Ashby and Sammis (1990) was used to explore the effects of rock fracture on the seismic coupling of explosions. An important focus was the effect of ice in the fractures. The main effect of ice in the cracks of crystalline rock is to bridge the existing cracks forming a larger number of smaller cracks. Ice also increases the coefficient of friction on the cracks resulting in a significant increase in both elastic stiffness and fracture strength, both of which are temperature and strain-rate dependent. The damage mechanics model was used to interpret laboratory data on frozen rock and a field experiment in which chemical explosions were detonated above and below the permafrost layer in Alaska to directly observe the effect of ice in rock on the seismic coupling. Finally, we used the equivalent elastic medium model for an explosive source developed by Johnson and Sammis (2001) to explore the effect of an increase in both elastic stiffness and compressive strength on the amplitude of far-field seismic radiation. Our conclusion is that an explosion in frozen rock should have a smaller apparent yield than the same explosion in rock at temperatures above the freezing point and that the effect should be larger in limestone than in granite. The original document contains color images.