Precursory seismicity of the 1999–2001 Mayon Volcano eruptions

Abstract

Mayon Volcano is one of the most active volcanoes in the Philippines and is part of the Bicol volcanic chain in the island of Luzon. Prior to and after the eruptions of Mayon Volcano since its geophysical monitoring that started in 1968 activity, the volcano manifested several types of earthquakes representing various source processes. This is one ofthe several parameters that is primarily being used to assess the volcano's condition.
The seismicity that Mayon showed are high and low frequency volcanic earthquakes and tremors. Episodic swarms of earthquakes and tremors preceded the start of the eruption cycle of Mayon Volcano. This swarm of low frequency volcanic earthquakes and tremors is believed to be intrusions of magma from deeper source to shallow reservoir and jerky movement of the viscous magma column in the conduit to the summit crater floor.
High frequency volcanic earthquakes are events with clear P-waves and S-waves and rapidly decaying coda. Low frequency earthquakes are characterized by emergent long-period waveforms and extended codas. Tremors are continuous earthquake signal that last for a few minutes to several hours and even days. Two tremor signals are recorded in Mayon, the high frequency and the low frequency tremors. The low frequency tremor has distinct dominant frequency and the source is internal while the high frequency tremor lacks the distinct dominant frequency and the source is both internal and external processes at the volcano.
Volcanic earthquakes and tremors reflect various complex processes in the plumbing system of a volcano. Proper identification of this volcano related seismicity that occurred within the timescale of the pre-eruptive phase of Mayon Volcano prove to be useful in the timely forecast of an impending eruption.