Wilfried Strauch

Trench‐parallel translation of the Central American Forearc (CAFA) is the result of strain partitioning along the Cocos and Caribbean (CA) convergent margin. Unlike the tectonics of northwestern Costa Rica and El Salvador, CAFA‐CA relative motion in Nicaragua is not accommodated on margin‐parallel fault systems. Rather, the northwest‐trending dextral shear is accommodated on margin‐normal sinistral strike‐slip faults that approximate the motion of a margin‐parallel fault (i.e., bookshelf faulting). We compare a new Global Positioning System interseismic horizontal velocity field to analytical and numerical models to show that the bookshelf faulting model can produce the observed velocity field and provide insight into the kinematics and configuration of the margin‐normal fault system. We find that a fault system with 20 km‐long parallel to sub‐parallel margin‐normal sinistral faults, spaced ∼5 km apart, locked from the surface to 5 km depth, and with interseismic slip deficits of 4 mm yr⁻¹, can replicate the observed velocity field. These findings have implications for the region's seismic hazard where shallow moderate‐magnitude earthquakes will have reoccurrence intervals of ∼50 years. These findings are also important for volcanic hazard estimation and unrest forecasting because the margin‐normal faults are in the volcanic arc and magma‐tectonic interactions have been documented along the CAFA.

Strain partitioning in oblique convergent margins results in margin‐parallel shear in the overriding plate. Margin‐parallel shear is often accommodated by margin‐parallel strike‐slip faults proximal to active volcanic arcs. Along the Nicaraguan segment of the Central American Forearc (CAFA) in the Cocos‐Caribbean plate convergent margin, there are no well‐expressed right‐lateral faults that accommodate CA‐CAFA relative motion. Instead, historical earthquakes and mapped fault orientations indicate that the ∼12 mm/yr of dextral motion is accommodated on arc‐normal, left‐lateral faults (i.e., bookshelf faults). We investigate three upper‐plate earthquakes; the 10 April 2014 (M_w 6.1), 15 September 2016 (M_w 5.7), and 28 September 2016 (M_w 5.5), using Global Position System co‐seismic displacements and relocated earthquake aftershocks. Our analyses of the three earthquakes indicate that the 10 April 2014 earthquake ruptured an unmapped margin‐parallel right‐lateral fault in Lago Xolotlán (Managua) and the September 2016 earthquakes ruptured arc‐normal, left‐lateral and oblique‐slip faults. These earthquakes represent a triggered sequence whereby the 10 April 2014 earthquake promoted failure of the faults that ruptured in September 2016 by imparting a static Coulomb stress change (ΔCFS) of 0.02–0.07 MPa. Likewise, the 15 September 2016, earthquake additionally promoted failure (ΔCFS of 0.08–0.1 MPa) on sub‐parallel faults that ruptured in two subsequent earthquakes. We also present an instance of magma‐tectonic interaction whereby the 10 April 2014 earthquake dilated (10s of μStrain) the shallow magmatic system of Momotombo Volcano, which led to magma injection, ascent, and eruption on 1 December 2015, after ∼100 years of quiescence.

Gas and particulate matter (PM) emissions from Masaya volcano, Nicaragua, cause substantial regional volcanic air pollution (VAP). We evaluate the suitability of low-cost SO₂ and PM sensors for a continuous air-quality network. The network was deployed for six months in five populated areas (4-16 km from crater). The SO₂ sensors failed and recorded erroneous values on multiple occasions, likely due to corrosion, requiring significant maintenance commitment. The PM sensors were found to be robust but data required correction for humidity. SO₂ measurements could not be used as stand-alone tools to detect occurrence of VAP episodes (VAPE), but SO₂/PM correlation reliably achieved this at near-field stations, as confirmed by meteorological forecasts and satellite imagery. Above-background PM concentrations reliably identified VAPE at both near-field and far-field stations. We suggest that a continuous network can be built from a combination of low-cost PM and SO₂ sensors with a greater number of PM-only sensors.

Gas and particulate matter (PM) emissions from Masaya volcano, Nicaragua, cause substantial regional volcanic air pollution (VAP). We evaluate the suitability of low-cost SO2 and PM sensors for a continuous air-quality network. The network was deployed for six months in five populated areas (4-16 km from crater). The SO2 sensors failed and recorded erroneous values on multiple occasions, likely due to corrosion, requiring significant maintenance commitment. The PM sensors were found to be robust but data required correction for humidity. SO2 measurements could not be used as stand-alone tools to detect occurrence of VAP episodes (VAPE), but SO2/PM correlation reliably achieved this at near-field stations, as confirmed by meteorological forecasts and satellite imagery. Above-background PM concentrations reliably identified VAPE at both near-field and far-field stations. We suggest that a continuous network can be built from a combination of low-cost PM and SO2 sensors with a greater number of PM-only sensors.

Many of Earth's volcanoes experience well‐defined states of “quiescence” and “unrest,” with unrest occasionally culminating in eruption. Some volcanoes, however, experience an unusually protracted (i.e., decades‐long) period of noneruptive unrest and are thus categorized as “persistently restless volcanoes” (PRVs). The processes that drive persistently restless volcanism are poorly understood, as our knowledge of PRVs is currently based on a small number of case studies. Here we examine multidisciplinary observations of the 2015 eruptive episode at Telica Volcano, Nicaragua, in the context of its long‐term behavior. We suggest that the latter phases of the 2015 eruption were ultimately driven by destabilization of its shallow magma reservoir. Based on previous geodetic‐seismic studies of Telica (Geirsson et al., 2014, https://doi.org/10.1016/j.jvolgeores.2013.11.009; Rodgers et al., 2013, https://doi.org/10.1016/j.jvolgeores.2013.08.010 and 2015, https://doi.org/10.1016/j.jvolgeores.2014.11.012) and on multiparameter observations at Telica over a 7‐year period, we propose that three distinct states of unrest occur at Telica over decadal timescales: a stable open state involving steady conduit convection and two distinct “unstable” states that may lead to eruptions. In the “weak sealing” state, phreatic explosions result from steady conduit convection underlying a weak seal. In the “destabilized” state, destabilization of the top of the convecting magma in the conduit leads to rapid accumulation of high pressures leading to strong/impulsive phreatomagmatic explosions. Our observations and interpretations suggest that continuous seismic, ground‐based deformation, gas emission, and thermal monitoring and interpretation of these data within a paradigm of sustained conduit convection modulated by episodes of sealing and destabilization of shallow magma reservoirs may allow robust forecasting of eruption potential, energy, and duration at Telica and similar PRVs worldwide.

We report on seismic and tsunami monitoring and early warning systems in Nicaragua and Central America, regions that are bordered by plate boundaries and subduction zones with related high seismic and tsunami risks. These systems were established in Nicaragua only after big earthquake and tsunami disasters (that took place in Managua in 1972 and the Pacific coast in 1992, respectively). The Nicaraguan seismic network is well developed, and the National Tsunami Warning System (NTWS) is a model for the Central American region. In 2015, the Central American countries and the Intergovernmental Oceanographic Commission (IOC) of the United Nations Educational, Scientific and Cultural Organization (UNESCO), along with the Tsunami Warning Systems (TWS) for the Pacific and the Caribbean, accepted Nicaragua’s proposal to create a regional TWS that would improve tsunami services for Central America. In 2016, Instituto Nicaragüense de Estudios Territoriales (INETER) started to develop the Central American Tsunami Advisory Center (CATAC) and intensified cooperation and real‐time data exchange with regional seismic networks and civil protection institutions. INETER initiated a project with the Japanese cooperation to reinforce CATAC until full services would be established in 2019. Since 2016, INETER has been cooperating with the Swiss Seismological Service (SED) to develop earthquake early warnings (EEW) in Nicaragua and Central America. EEW, besides being favorable for tsunami warning, could help compensate for the extreme seismic vulnerability of millions of homes in Nicaragua and Central America that are made from adobe or other bad construction materials. Alerts, received just a few seconds before the destructive shaking, could permit inhabitants of adobe houses to leave their collapsing homes, thus saving their lives.