Physical constraints on speleothem deformations caused by earthquakes, seen from a new perspective: Implications for paleoseismology

Abstract

Fractured speleothems, important earthquake environmental effects used in paleoseismological studies worldwide, are particularly effective for dating. Here, we discuss physical phenomena that can damage caves. We supplement the discussion with information (frequency characteristics and ground-motion parameters) from areas of mine openings threatened by induced seismicity, as analogs of cave conduits, as both, from a physical point of view, are underground voids affected by oscillations. Theoretical considerations indicate the use of bulk (P-wave) and shear (S-wave) moduli instead of Young's modulus, depending on the type of seismic wave affecting a given speleothem. Application of P-wave and shear moduli enables the calculation of a speleothem's natural frequency, based on measured P- and S-wave velocities as well as on the height and diameter of the speleothem. The relationship between the natural frequency, the acceleration causing speleothem failure, and the height and diameter of speleothems has been determined. Moreover, this acceleration value was compared to expected PGA values in order to find similarities between the two acceleration values. We highlight a phenomenon not previously considered in relation to cave environments, i.e., tunnel waves, which can appear in cave walls. This effect significantly changes oscillation characteristics in a cave, which can result in damage to speleothems which had not been expected to fail. Finally, we present the potential for estimating the minimum magnitude required to damage a cave at a given distance from its source.