Tectonic and volcano-tectonic seismicity below Tungurahua volcano (Ecuador) between 2013 and 2018

<p class="western" align="left"><span lang="en-US">Tungurahua (5023 m a.s.l.) is an andesitic stratovolcano located in Central Ecuador. The more recent eruptive cycle started in September 1999 and lasted until March 2016 with repeated phases of enhanced activity. </span><span lang="en-US">I</span><span lang="en-US">ts activity included the occurrence of distinct eruptive phases separated by periods of quiescence, both lasting from few weeks to months. From October 2013 until March 2018, we operated </span><span lang="en-GB">at Tungurahua a temporary seismic network including up to 13 broadband stations. It complemented the permanent monitoring network </span><span lang="en-GB">operated </span><span lang="en-US"> by the </span><span lang="en-US">Instituto Geof&#237;sico de la Escuela Polit&#233;cnica Nacional </span><span lang="en-US">(IG-EPN)</span> <span lang="en-US">and </span><span lang="en-GB">included stations up to 4275 m a.s.l. as well as stations on the remote Eastern flank. </span></p> <p class="western" align="left"><span lang="en-US">Using IG-</span><span lang="en-US">EPN</span><span lang="en-US"> catalogs </span><span lang="en-US">and </span><span lang="en-US">cross-correlation techniques, we identified several clusters of shallow and deep (volcano-)tectonic earthquakes. For these clusters, we manually picked a selection of larger events and used them to pick automatically other </span><span lang="en-US">similar events</span><span lang="en-US">. A visual inspection of the pickings was performed to confirm the absence of major biases. The comparison of P-phase times shows differences less than 0.1 s. </span><span lang="en-US">R</span><span lang="en-US">egarding S-phases, the cross correlation technique detected by far more S-phases per event, providing a general </span><span lang="en-US">improvement</span><span lang="en-US"> in the location of events. Additionally we used seismic amplitudes </span><span lang="en-US">and their decay as a function of distance</span><span lang="en-US"> to locate tremor and explosion quake sources during eruptive phases.</span></p> <p class="western" align="left"><span lang="en-US">The seismicity below sea level defines 4 main clusters spread around the volcano between 2 and 10 km b.s.l.. The temporal evolution of these clusters displays a rather steady behavior for 3 of them and a swarm-type behavior for the fourth. Their relation with </span><span lang="en-US">the </span><span lang="en-US">eruptive </span><span lang="en-US">phases</span> <span lang="en-US">is, however,</span><span lang="en-US"> unclear. Above sea level a single cluster of small volcano-tectonic events is observed about 2-3 km below the summit. This </span><span lang="en-US">cluster</span><span lang="en-US"> displays a rather clear relationship with the eruptive phases and often preceded </span><span lang="en-US">phases with strong explosive onsets.</span><span lang="en-US"> Most of tremor and explosion quake sources are </span><span lang="en-US">found</span><span lang="en-US"> just above this cluster.</span></p> <p class="western" align="left"><span lang="en-US">This study emphasizes the importance of dense, geographically well distributed networks, to identify seismic precursors </span><span lang="en-US">and decipher volcanic plumbing systems</span><span lang="en-US">.</span></p>