Previously comparison of tilt with the seismic data has been done using RSAM (seismic amplitude) data. RSAM (Endo and Murray, 1991) peaks have been matched with the peaks in the tilt cycles. This has been interpreted as the Hybrid and LP events being involved in the pressurisation of the volcanic edifice (Voight et al, 1998).

When these cycles are looked at more closely, it can be seen that sometimes the peaks match and at othertimes the RSAM precedes the tilt and vice versa.

The RSAM data contains all seismic data, including rockfall, hybrids, long period events, etc., so the tilt cycles really need to be compared with the energy of the low-frequency events (hybrids, LP's), to see if the tilt cycles match up to the release of low-frequency energy and other seismic parameters.

When you compare the low frequency energy to the tilt (trace (a) above), you can see that there is a time delay between the increase in the tilt signal and the increase in the seismic energy, although both traces appear to decrease about the same time.

If we assume that the tilt is the equivilant to the pressure of the system, then the derivative of the tilt is equivilant to the pressurisation of the system. If we compare the low-frequency energy to the pressurisation (trace(b) above), then we see that the seismicity is linked to the depressurisation of the volcanic edifice (Powell and Neuberg, 2003).

more information

References:

Endo E.T. and Murray T.L., 1991. Real-time seismic amplitude measurment (RSAM), a volcano monitoring and prediction tool. Bulletin of Volcanology, 53, 533-545.

Powell T.W. and Neuberg J., 2003.Variations of seismic parameters during different activity levels of the Soufriere Hills Volcano, Montserrat. EGS - AGU - EUG Joint Assembly, Nice, France, April 2003.

Voight B., Hoblitt R., Clarke A., Lockhart A., Miller A., Lynch L. and McMahon J., 1998. Remarkable cyclic ground defomation monitored in real-time on Montserrat, and its use in eruption forcasting. Geophysical Research Letters, 24, 3405-3408.