Ground‐coupled air waves and diffracted infrasound from the Arequipa earthquake of June 23, 2001

Abstract

On June 23, 2001, a strong earthquake measuring Mw 8.4 occurred along the coast of south‐central Peru. Coherent infrasonic waves were detected over a period of one hour by the IS08 infrasound station in Bolivia. Analysis of the ground‐coupled air waves shows that the rupture propagated from the northwestern to the southeastern part of the fault with a rupture velocity of 3.3 km/s. The azimuth variation of the infrasonic waves is attributed to a distribution of secondary sources along the highest mountain ranges, which excite infrasonic waves that are diffracted to the ground. The predominant source of infrasound is likely distributed along the Andean Cordillera. Using the azimuth and arrival time determination, the horizontal scale size of the distant source regions of infrasonic waves is reconstructed over distances greater than 400 km.

Use of hydroacoustic and seismic arrays to observe rupture propagation and source extent of the Mw = 9.0 Sumatra earthquake

“…The small array analysis allows to estimate the azimuth time evolution and to follow the rupture front. This property was already observed [Le Pichon et al, 2002] but in the present case of the Sumatra M w = 9.0 earthquake we can take advantage of the complementary hydroacoustic and seismology technologies. The quality of CTBT array makes this present analysis unique.…”

“…Small arrays of sensors are the main technology of the International Monitoring System because they increase the detection sensitivity. The utility of array records at regional distances has already been underlined in terms of description of the rupture propagation for a major earthquake [Le Pichon et al, 2002]. Indeed the result of the array analysis in terms of azimuth and velocity time-evolution allows us to directly observe the propagation of the rupture along the fault.…”

The source of infrasound associated with long‐period events at Mount St. Helens

“…The simplest explanation for the infrasonic signals is that they are sourced by seismic-acoustic conversion at the ground-air interface. It is known that infrasound and acoustic gravity waves are generated by large tectonic earthquakes both from strong ground displacement and deformation near the source epicenter [e.g., Bolt, 1964;Mikumo, 1968], and interaction of surface waves with topography [Le Pichon et al, 2002, 2003, 2006Mutschlecner and Whitaker, 2005, and references therein]. In addition, P/SV and Rayleigh wave energy can be locally radiated into the atmosphere for even relatively small magnitude earthquakes [e.g., Press and Ewing, 1951;Kitov et al, 1997;Mutschlecner and Whitaker, 2005;Sylvander et al, 2007], providing an explanation for reports of low-frequency sounds accompanying earthquakes [Benioff et al, 1951].…”

Infrasonic Signals Associated with the Aftershocks of LuShan Earthquake of April 20th, 2013

“…It is well known that infrasound waves can be generated by earthquakes through several mechanisms, e.g., [1][2][3]. The development of cracks in the crust of the Earth is accompanied by a generation of seismic waves, which causes elastic motions of ground surface.…”

“…The infrasound is then propagated through the atmosphere to the infrasonic station at a mean signal speed of about 300 m/s, and travels through the station area [1,[6][7][8]. Diffracted infrasound is associated with the passage of seismic surface waves through an area of extreme topography such as mountains or cliffs [2,8,9].…”