Mayra Vaca’s research while affiliated with National Polytechnic School and other places

The Instituto Geofísico (IG-EPN) was created in 1983 by faculty of the Escuela Politécnica Nacional, a public university in Quito, Ecuador, with the objective of assessing volcanic hazard in the country. Since then, the IG-EPN has established and developed an instrumental monitoring network and from 1999 has faced the eruption of five continental-arc volcanoes (Guagua Pichincha, Tungurahua, Reventador, Cotopaxi, and Sangay) which displayed varied hazards, eruptive dynamics, eruption durations, and socio-economic contexts. At the same time, mainly effusive eruptions took place in Galápagos archipelago, which has undergone an increase in local population over the last two decades and hence in the risk posed by volcanic eruptions. The outstanding handling of these volcanic crises was the reason why IG-EPN was granted with the 2020 Volcanic Surveillance and Crisis Management IAVCEI Award. Now, the IG-EPN manages a country-wide network of about 500 instruments to monitor both volcanic and tectonic activity with a highly qualified staff of 80 people. This manuscript describes the history of IG-EPN, the main volcanic hazard studies and resulting hazard maps; the instrumental networks; and the volcanic crises that the IG-EPN faced during the last forty years.

The Instituto Geofísico of the Escuela Politécnica Nacional (IGEPN) is in charge of the monitoring and study of seismic and volcanic activity in the Ecuadorean territory. This institution currently maintains the Servicio Nacional de Sismología y Vulcanología (The National Seismology and Volcanology Service), which includes monitoring via modern seismic, volcanic, and geodetic networks with 81 seismic stations, 117 strongmotion sensors, 85 Global Positioning System (GPS) stations, and 8 first- and second-level volcano observatories (at least 2 independentmonitoring techniques).This systemis supported by a real-time transmission network that relies on different and independent technologies (satellite, microwave, fiber-optic, and digital radio). It also maintains the National Processing Center for Issuing Seismic and Volcanic Alerts (TERRAS center),which operates 24/7 and supplies the information by email, fax, radio, Skype, Facebook, Twitter, website, and SMS, and the national seismic and volcanic data center, which maintains raw and processed seismic, volcanic, and geodetic data. Evolution, coverage, and characteristics of these networks are described in this article.

In 1988, the Instituto Geofisico (IG) began a permanent surveillance of Ecuadorian volcanoes, and due to activity on Guagua Pichincha, SP seismic stations and EDM control lines were then installed. Later, with the UNDRO and OAS projects, telemetered seismic monitoring was expanded to Tungurahua, Cotopaxi, Cuicocha, Chimborazo, Antisana, Cayambe, Cerro Negro, and Quilotoa volcanoes. In 1992 an agreement with the Instituto Ecuatoriano de Electrificacion strengthened the monitoring of Tungurahua and Cotopaxi volcanoes with real-time SP seismic networks and EDM lines. Thus, background activity levels became established, which was helpful because of the onset of the 1999 eruptive activity at Tungurahua and Guagua Pichincha. These eruptions had a notable impact on Baños and Quito. Unrest at Cotopaxi volcano was detected in 2001-2002, but waned. In 2002 Reventador began its eruptive period which continues to the present and is closely monitored by the IG. In 2006 permanent seismic BB stations and infrasound sensors were installed at Tungurahua and Cotopaxi under a cooperative program supported by JICA, which allowed us to follow Tungurahua's climatic eruptions of 2006 and subsequent eruptions up to the present. Programs supported by the Ecuadorian Secretaria Nacional de Ciencia y Tecnologia and the Secretaria Nacional de Planificacion resulted in further expansion of the IG's monitoring infrastructure. Thermal and video imagery, SO2 emission monitoring, geochemical analyses, continuous GPS and tiltmeters, and micro-barometric surveillance have been incorporated. Sangay, Soche, Ninahuilca, Pululahua, and Fernandina, Cerro Azul, Sierra Negra, and Alcedo in the Galapagos Islands are now monitored in real-time. During this time, international cooperation with universities () has introduced the use of new technologies and methods. An agreement with the Secretaria de Gestion de Riesgos fortifies the communication flow to society, officials, and risk managers. Today the IG has the challenge of offering real-time information through a web-based net of virtual observatories.

Due to the scarcity of local stations, seismicity at the Galapagos Islands is under-represented. Using the ISC catalogue, we found a magnitude of homogeneity of 4.5 mb for the 1970-2010 period. The largest magnitude recorded by the global network in this period is 5.6 mb. In 1996 the Instituto Geofisico installed a seismic network composed of six short-period stations with UHF telemetry linkage, located on Fernandina, Isabela, Bartolome and Santa Cruz. Using this network, in 2000, a clear seismic swarm was located at the western edge of the Galapagos platform about 50 km from Cerro Azul and Fernandina volcanoes. This swarm coincides with expected central mantle plume upwelling. A seismic swarm near Alcedo volcano persisted between 2000 and 2001. Between 1999 and 2003 a temporary network was deployed for a hotspot tomography project using teleseismic events (Hooft et al, 2003,Villagomez et al., 2007). Seismic events with epicenters in Alcedo were also reported in the SIGNET project (See Ebinger et al. at this session) consisting of 16 temporal stations. In order to monitor seismic and volcanic activities at the Islands and contribute to research studies on seismic sources and stress states at an active hotspot near a spreading zone, the Instituto Geofisico with the support of an Ecuadorian Science and Technology Secretariat`s grant will install next year a new permanent seismic network of 6 broad-band stations distributed on Alcedo, Sierra Negra, Cerro Azul and Fernandina volcanoes. This network will transmit real-time data to the Instituto Geofisico via satellite connections. This project is also supported by the Galapagos National Park through an institutional agreement.

We systematically used two approaches to analyze broadband seismic signals for monitoring active volcanoes: one is waveform inversion of very-long-period (VLP) signals assuming possible source mechanisms; the other is a source location method of long-period (LP) events and tremor using their amplitudes. The deterministic approach of the waveform inversion is useful to constrain the source mechanism and location but is basically only applicable to VLP signals with periods longer than a few seconds. The source location method assumes isotropic radiation of S waves and uses seismic amplitudes corrected for site amplifications. This simple approach provides reasonable source locations for various seismic signals such as a VLP event accompanying LP signals, an explosion event, and tremor associated with lahars and pyroclastic flows observed at five or fewer stations. Our results indicate that a frequency band of about 5-12 Hz and a Q factor of about 60 are appropriate for the determination of the source locations. In this frequency band the assumption of isotropic radiation may become valid because of the path effect caused by the scattering of seismic waves. The source location method may be categorized as a stochastic approach based on the nature of scattering waves. Systematic use of these two approaches provides a way to better utilize broadband seismic signals observed at a limited number of stations for improved monitoring of active volcanoes.

Ecuador has 55 active volcanoes in the northern half of the Ecuadorian Andes. There, consequences of active volcanism include ashfalls, pyroclastic flows (fast moving fluidized material of hot gas, ash, and rock), and lahars (mudflows), which result in serious damage locally and regionally and thus are of major concern to Ecuadorians. In particular, Tungurahua (elevation, 5023 meters) and Cotopaxi (elevation, 5876 meters) are high‐risk volcanoes. Since 1999, eruption activity at Tungurahua has continued and has produced ashfalls and lahars that damage towns and villages on the flanks of the volcano. More than 20,000 people live on these flanks.

Tungurahua and Cotopaxi are andesitic active volcanoes in Ecuadorian Andes. Tungurahua continues its eruptive activity since 1999, in which explosive eruptions accompanying pyroclastic flows occurred in July- August, 2006. Cotopaxi is one of the world's highest glacier-clad active volcanoes, and its seismic activity remains high since 2001. To enhance the monitoring capability of these volcanoes, we have installed broadband seismometers (Guralp CMG-40T: 60 s-50 Hz) and infrasonic sensors (ACO TYPE7144/4144: 10 s- 100 Hz) on these volcanoes through the technical cooperation program of Japan International Cooperation Agency (JICA). Three and five stations are currently installed at Tungurahua and Cotopaxi, respectively, and additional two stations will be installed at Tungurahua. Both seismic and infrasonic waveform data at each station are digitized by a Geotech Smart24D datalogger with a sampling frequency of 50 Hz, and transmitted by a digital telemetry system using 2.4 GHz Wireless LAN to the central office in Quito. The Tungurahua's eruptive activity accompanying pyroclastic flows in July-August 2006 was monitored in real-time by the network. The observed waveforms show a wide variety of signatures in response to various eruption styles: intermittent tremor during Strombolian eruptions, five-hour-long continuous strong tremor during heightened eruptions, very-long-period (VLP) seismic signals (10-50 s) associated with pyroclastic flows, and impulsive seismic and infrasonic events of explosions. At Cotopaxi Volcano, VLP signals (2 s) accompanying long- period signals (1-2 Hz) were detected by our network. Similar events occurred in 2002, and are interpreted as gas-release process from magma in an intruded dike beneath Cotopaxi (Molina et al, submitted to JGR). The present observation of the same type of events suggests that the intruded dike is still active beneath Cotopaxi. These signals detected by our networks are highly useful to understand volcanic processes beneath Tungurahua and Cotopaxi, which contribute to improve the monitoring capability of these volcanoes.