Seismic transmission of elephant vocalizations and movement

Abstract

Seismic signals were recorded during periods of vocalizations and movement by African and Asian elephants. Initially, vocalizations were detected in both microphone and geophone recordings. To test whether these sounds are propagated separately in the air and the ground, recordings were made with a four-channel data acquisition system, processing signals simultaneously from microphone/geophone pairs at near and remote points ranging from 20–130 m distances from the elephants. These recordings indicate that elephant vocalizations and movement produce Rayleigh waves, a type of ground surface wave. This paper quantifies the propagation of elephant vocalizations in the air and ground and compares the rates of signal attenuation within each of the two media. A normalized cross-correlation coefficient was performed on rumble and movement signals in the ground, resulting in a time lag between near and remote sensors corresponding to Rayleigh wave velocity. Rayleigh waves travel slower than airborne sound waves (approximately 250 m per second versus 340 m per second), but they can travel further and more reliably than those transmitted through the air. The presence of seismic properties in elephant vocalizations and movement suggests a possibility for their use in long distance communication.