Seismic Raves: Tremor Observations from an Electronic Dance Music Festival

Abstract

Repetitive signals of sustained amplitude are observed both in music and seismology; in music this is often described as the rhythm, whereas in seismology such signals are often labeled as tremor ( e.g. , Chouet 1996). Tremor is generated by a variety of sources including volcanoes, glaciers, and hydroelectric plants (for examples, see Ferrick et al. 1982) and is often characterized by narrowband spectral features that maintain their amplitude, sometimes for periods of hours or days (so-called harmonic tremor). In this paper we present observations from an unusual anthropogenic source of seismic tremor, generated at an interface between music and seismology: an electronic dance music festival. Music festivals, popular in the summer months across the United Kingdom, provide a meeting point for thousands of enthusiasts to listen to live music. Many of these festivals concentrate on a particular genre of music; e.g. , dance, folk, rock, or world. Previously observed vibrations from rock music festivals have been attributed to large crowds in confined spaces jumping up and down in time to the music, although seismograms were not recorded (Erlingsson and Bodare 1996; Browitt and Walker 1993). Electronic dance music, characterized by strong repetitive rhythms, is the focus for the Glade electronic dance music festival that has been held in the Berkshire countryside for one weekend a year from 2004 to 2007 (see figure 1). The festival consists of a number of music stages and tents, each of which specializes in particular subgenres of electronic dance music. In 2007, approximately 8,500 people enjoyed the festival over the weekend of 20–22 July. To amplify the music to a level suitable for an outdoor concert, the power output of the public address (PA) systems ranged from 2 to 26 kW; the loudspeakers are powerful acoustic sources that are coupled into the ground …