Seismicity and Eruptive Activity of Fuego Volcano, Guatemala: February 1975 - January 1977

<p> <p id="x-x-x-"> We examine seismic and eruptive activity at Fuego Volcano (14&deg;29&prime;N, 90&deg; 53&prime;W), a 3800-m-high stratovolcano located in the active volcanic arc of Guatemala. Eruptions at Fuego are typically short-lived vulcanian eruptions producing ash falls and ash flows of high-alumina basalt. From February 1975 to December 1976, five weak ash eruptions occurred, accompanied by small earthquake swarms. Between 0 and 140 (average &asymp; 10) A-type or high-frequency seismic events per day with <em> M </em> &gt; 0.5 were recorded during this period. Estimated thermal energies for each eruption are greater by a factor of 10 ⁶ than cumulative seismic energies, a larger ratio than that reported for other volcanoes. <p id="x-x-x-"> Over 4000 A-type events were recorded January 3&ndash;7, 1977 (cumulative seismic energy &asymp; 10 ⁹ joules), yet no eruption occurred. Five 2-hour-long pulses of intense seismicity separated by 6-hour intervals of quiescence accounted for the majority of events. Maximum likelihood estimates of <em> b </em> -values range from 0.7 &plusmn; 0.2 to 2.1 &plusmn; 0.4 with systematically lower values corresponding to the five intense pulses. The low values suggest higher stress conditions. <p id="x-x-x-"> During the 1977 swarm, a tiltmeter located 6 km southeast of Fuego recorded a 14 &plusmn; 3 microradian tilt event (down to SW). This value is too large to represent a simple change in the elastic strain field due to the earthquake swarm. We speculate that the earthquake swarm and tilt are indicative of subsurface magma movement. </p> </p> </p></p>