Volcanoes produce highly scattered seismic wavefields, which are characterized by the scattering mean free path (l0) and the quality factor of medium attenuation for S waves (Qi). Previous studies have estimated scattering mean free paths at various volcanoes to be around 100–1,000 m, but their depth distributions remain to be determined. We estimated one‐dimensional l0 and Qi structures using the envelope widths of volcano‐seismic events at Taal (Philippines) and at Nevado del Ruiz (Colombia) in a high‐frequency band (5–10 Hz). We performed Monte Carlo envelope simulations in various one‐dimensional models, and compared the simulated and observed envelope widths. Our results indicate that a highly heterogeneous (l0 = 1,000 m) and attenuative (Qi = 100) surface layer exists to a depth of 1 km, below which l0 and Qi are comparable to those in the normal crust. The surface layer may consist of unconsolidated materials with hydrothermal fluids and/or altered clay minerals, which cause strong scattering and attenuation effects beneath these volcanoes. Our results suggest that strong heterogeneities observed at volcanoes exist only in a thin surface layer.

Nevado del Ruiz is part of a large volcano complex in the northern Andes of Colombia. Interferometric synthetic aperture radar observations from the RADARSAT‐2 satellite since 2011 show steady inflation of the volcano since 2012 at 3–4 cm/yr. The broad (>20 km) deformation pattern from both ascending and descending track data constrain source models for either point or spheroidal sources, both located at >14 km beneath the surface (mean elevation 4.2 km) and 10 km SW of Nevado del Ruiz, below nearby Santa Isabel Volcano. Stress change computations for both sources in the context of a compressive regional stress indicate that dikes propagating from the source should become trapped in sills, possibly leading to a more complex pathway to the surface and explaining the significant lateral separation of the source and Nevado del Ruiz Volcano.

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The Servicio Geológico Colombiano (SGC) was created in 1916 and has been dedicated to the research and monitoring of active volcanoes in the country since the disaster resulting from the eruption of Nevado del Ruíz Volcano in 1985, where more than 25000 people died due to lahars. Today the SGC has three Volcanological and Seismological Observatories in the cities of Manizales (SGC-OVSM), Popayán (SGC-OVSPop), and Pasto (SGC-OVSP), from where 23 active volcanoes are monitored. The three observatories manage an instrumental network of about 740 stations (permanent and portable) as well as signal repeaters, and cover the disciplines of seismology, geodesy, geochemistry, and potential field, amongst others. Volcanic hazard assessment is also carried out by the SGC, producing hazard maps and reports. These tasks are complemented by programs for promoting geoscience knowledge transfer to the public, developed through different strategies. Although at this time, data derived from volcanic monitoring are not available online, the SGC is analysing this need, for implementation in the near future. El Servicio Geológico Colombiano (SGC) fue creado en 1916, y se ha dedicado a la investigación y monitoreo de los volcanes activos en el país desde el desastre resultante de la erupción del volcán Nevado del Ruíz en 1985, donde más de 25000 personas murieron debido a la ocurrencia de lahares. Hoy en día, el SGC tiene tres Observatorios Vulcanológicos y Sismológicos en las ciudades de Manizales (SGC-OVSM), Popayán (SGC-OVSPop) y Pasto (SGC-OVSP), desde donde se monitorean 23 volcanes activos. Los tres observatorios manejan una red instrumental de aproximadamente 740 estaciones (permanentes y portátiles), como también repetidoras de señal, y cubren las disciplinas de sismología, geodesia, geoquímica y campos de potencial, entre otras. La evaluación de la amenaza volcánica también es realizada por el SGC, produciendo mapas e informes. Estas tareas se complementan con programas para promover transferencia de conocimientos geocientíficos al público, desarrollados a través de diferentes estrategias. Aunque en este momento los datos derivados del monitoreo volcánico no están disponibles en línea, el SGC está analizando esta necesidad para su implementación en un futuro cercano.