HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) References Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Xie, X.-B. Articles by Lay, T. Search for Related Content GeoRef GeoRef Citation

The excitation of Lg waves by explosions: A finite-difference investigation

Institute of Tectonics University of California, Santa Cruz, California 95064

Abstract

Several mechanisms have been proposed to explain the excitation of the regional Lg phase by explosions. We examine some of these mechanisms with finite-difference simulations. An energy-flux technique is used to analyze the synthetic signals. The method is adapted from conventional array-analysis techniques and gives a clear characterization of wave-field intensity, wave slowness, and propagation direction. The vector energy flux in the model is studied instead of the scalar distribution of energy in the space-time domain. The calculations show that for an explosive source in a high P-wave velocity crust, P-wave energy cannot be effectively trapped in the crust, and the nongeometrical phase S* may be the primary contributor to the Lg phase. For an explosive source buried in a low-velocity upper crust (i.e., where the P-wave velocity is lower than the upper-mantle S-wave velocity), part of the pS wave can be trapped in the crustal wave guide to form the Lg phase. The relative Lg excitation depends on the ratio between the P-wave velocity in the source region and the S-wave velocity in the uppermost mantle. Scattering effects can transfer P-wave or surface-wave energy into Lg, but the efficiency strongly depends on both the wave frequency and the characteristic size of the scatterers. Any source process that directly excites S waves is more efficient for generating Lg than the aforementioned mechanisms. Spall directly generates S-wave energy, and consequently is an efficient source for Lg. For actual explosions, all of these factors may simultaneously contribute to Lg excitation. Determining their relative importance and interactions requires additional observations.

This article has been cited by other articles:

				J. L. Bonner, M. R. Leidig, C. Sammis, and R. J. Martin Explosion Coupling in Frozen and Unfrozen Rock: Experimental Data Collection and Analysis Bulletin of the Seismological Society of America, April 1, 2009; 99(2A): 830 - 851. [Abstract] [Full Text] [PDF]

				Y. He, X.-B. Xie, and T. Lay Explosion-Source Energy Partitioning and Lg-Wave Excitation: Contributions of Free-Surface Scattering Bulletin of the Seismological Society of America, April 1, 2008; 98(2): 778 - 792. [Abstract] [Full Text] [PDF]

				X. Yang, T. Lay, X.-B. Xie, and M. S. Thorne Geometric Spreading of Pn and Sn in a Spherical Earth Model Bulletin of the Seismological Society of America, December 1, 2007; 97(6): 2053 - 2065. [Abstract] [Full Text] [PDF]

				X.-B. Xie, Z. Ge, and T. Lay Investigating Explosion Source Energy Partitioning and Lg-Wave Excitation Using a Finite-Difference plus Slowness Analysis Method Bulletin of the Seismological Society of America, December 1, 2005; 95(6): 2412 - 2427. [Abstract] [Full Text] [PDF]

				S. Hartzell, M. Guatteri, P. M. Mai, P.-C. Liu, and M. Fisk Calculation of Broadband Time Histories of Ground Motion, Part II: Kinematic and Dynamic Modeling Using Theoretical Green's Functions and Comparison with the 1994 Northridge Earthquake Bulletin of the Seismological Society of America, April 1, 2005; 95(2): 614 - 645. [Abstract] [Full Text] [PDF]

				Strong Lg Attenuation in the Tibetan Plateau Bulletin of the Seismological Society of America, October 1, 2003; 93(5): 2264 - 2272.

				Seismic Wave Propagation and Scattering in Heterogeneous Crustal Waveguides Using Screen Propagators: I SH Waves Bulletin of the Seismological Society of America, April 1, 2000; 90(2): 401 - 413.

				K. S. Vogfjord Effects of explosion depth and earth structure on the excitation of Lg waves: S* revisited Bulletin of the Seismological Society of America, October 1, 1997; 87(5): 1100 - 1114. [Abstract] [PDF]

				I. N. Gupta, T. R. Zhang, and R. A. Wagner Low-frequency Lg from NTS and Kazakh nuclear explosions--observations and interpretation Bulletin of the Seismological Society of America, October 1, 1997; 87(5): 1115 - 1125. [Abstract] [PDF]

				H. E. Hartse, S. R. Taylor, W. S. Phillips, and G. E. Randall A preliminary study of regional seismic discrimination in central Asia with emphasis on western China Bulletin of the Seismological Society of America, June 1, 1997; 87(3): 551 - 568. [Abstract] [PDF]

				Z. Xu, S. Y. Schwartz, and T. Lay Seismic wave-field observations at a dense, small-aperture array located on a landslide in the Santa Cruz Mountains, California Bulletin of the Seismological Society of America, June 1, 1996; 86(3): 655 - 669. [Abstract] [PDF]

				T.-R. Zhang and T. Lay Why the Lg phase does not traverse oceanic crust Bulletin of the Seismological Society of America, December 1, 1995; 85(6): 1665 - 1678. [Abstract] [PDF]

				X.-B. Xie and T. Lay The log (rms Lg)-mb scaling law slope Bulletin of the Seismological Society of America, June 1, 1995; 85(3): 834 - 844. [Abstract] [PDF]

				H. J. Patton and S. R. Taylor Analysis of Lg spectral ratios from NTS explosions: Implications for the source mechanisms of spall and the generation of Lg waves Bulletin of the Seismological Society of America, February 1, 1995; 85(1): 220 - 236. [Abstract] [PDF]