Seismic swarms in 2009 and 2012

Within the last five years, Instituto Nicaragüense de Estudios Territoriales (INETER) reported at least two seismic swarms at Apoyeque, and between the Chiltepe Peninsula and the city of Managua (~15 km SE) (figure 1). Our last report also highlighted swarms which lasted several hours and days in 2001 and 2007 (BGVN 34:04). Intermittent seismicity was reported within the region during 2009-2012, but events were rarely larger than M 2.5.

Figure 1. Regional maps showing Apoyeque and the tectonic setting. (A) Sketch map highlighting volcanic centers in Central America relative to the active subduction of Cocos Plate beneath the Caribbean Plate. In Nicaragua active volcanism is concentrated inside the Nicaragua Depression (ND). The red box labeled "B" refers to the 50 x 50 km area that includes Apoyeque on the Chiltepe Peninsula. (B) This Landsat 7 image corresponds to the extent of the red box labeled "B" in the sketch map "A"; the Nejapa-Miraflores fault (NMF) marks an offset in the main arc and frequently generates seismicity. (C) Along the NMF, mainly monogenetic volcanoes have formed W of Managua city. Modified from Pardo and others, 2009.

2009 swarm. INETER reported a seismic swarm on 29 September 2009. It began at 1800 local time in an area W of Apoyeque volcano. The main event occurred at 1817 local time, with a ML 3.1 event at a depth of 5 km. The earthquake was felt by the population in Sandino City, ~5 km W of the earthquakes. The seismic swarm lasted until 2 October 2009; the total number of detected earthquakes was not disclosed.

2012 swarm. INETER reported a swarm that began at 1727 local time on 6 September 2012. The National Seismic Network detected and located the series of earthquakes between Apoyeque and the Nejapa-Miraflores fault (figure 1).

More than 20 earthquakes were detected and the two largest had magnitudes of 2.3 and 3.8, with depths of 2.8 and 6 km respectively; the largest event occurred at 1937 (figure 2). None of these earthquakes were reportedly felt by local populations and the event was assigned an Intensity II. The swarm lasted ~2 hours.

Figure 2. Epicenters of the largest earthquakes from the Apoyeque swarm are plotted. INETER detected ~20 earthquakes on 6 September 2012 all within 30 km depth. Courtesy of INETER.

Avellán and others (2012) described the polygenetic Apoyeque volcano as belonging to the Nejapa volcanic field (figure 1), which is bound by the Nejapa fault system. There were 23 eruptions from the field within the last ~30 ka; 13 of these events were explosive (VEI 2). The most recent eruption was dated between 2,130 ± 40 and 1,245 ± 120 years BP. With respect to hazards implications, clear vent migration patterns were seemingly absent for this volcanic field. The authors concluded that there is a high probability of future, similar eruptions, particularly phreatomagmatic ones, within this area of Nicaragua.

References: Avellán, D.R., Macías, J.L., Pardo, N., Scolamacchia, T., and Rodriguez, D., 2012, Stratigraphy, geomorphology, geochemistry and hazard implications of the Nejapa Volcanic Field, western Managua, Nicaragua, Journal of Volcanology and Geothermal Research, 213-214: 51-71.

Pardo, N., Macías, J.L., Giordano, G., Cianfarra, P., Avellán, D.R., and Bellatreccia, F., 2009, The ~1245 yr BP Asososca maar eruption: The youngest event along the Nejapa-Miraflores volcanic fault, Western Managua, Nicaragua, Journal of Volcanology and Geothermal Research, 184: 292-312.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/).

Information is preliminary and subject to change. All times are local (unless otherwise noted)

January 1988 (SEAN 13:01) Cite this Report

Sulfur smell from active fumaroles

The surface temperature of the crater lake was 28.1-28.8°C on 16 January at 0900. A slight smell of sulfur was evident at the N caldera rim, probably originating from fumaroles 100-200 m below. Fumaroles also remained active in Laguna Jiloa.

Information Contacts: B. van Wyk de Vries, H. Rymer, and G. Brown, Open Univ; P. Hradecky and H. Taleno, INETER.

April 1989 (SEAN 14:04) Cite this Report

Lake temperature measured

Surface temperature of the lake (measured with an 8-14 micrometer bandpass radiometer) varied between 28 and 30°C during fieldwork 8 April. A water temperature measured near the N shore was 25.5°C.

Information Contacts: C. Oppenheimer, Open Univ.

April 2009 (BGVN 34:04) Cite this Report

Repose continues, punctuated by occasional seismic swarms in 2001 and 2007

Seismic swarms took place during 2001 and 2007. The last overview of Apoyeque (BGVN14:04) reported slight variations of the crater lake's surface temperature of between 25 and 30°C (which began to rise in 1988). Faint sulfurous odors were noted as well as some active fumaroles.

Swarms were reported by INETER (Instituto Nicarag?ense de Estudios Territoriales) in a 23 September 2007 report. The first swarm, during January 2001, included earthquakes up to MR 5.2. This swarm was felt strongly in the cities of Managua (~ 8 km away) and in Ciudad Sandino. No damage was reported. The second swarm began on 21 September 2007, becoming more intense on 23 September, by which time there had been 10 earthquakes up to MR 2.8. Scores of smaller earthquakes were also detected at a seismometer in Apoyeque's crater.

INETER stated that, based on past cases at this volcano, such swarms can continue for days and might reach M 4-M 5 (as they had in January 2001). The typical pattern is for a series of smaller volcanic earthquakes to precede one or more larger ones. This is in contrast to earthquakes associated with the subduction of the Cocos plate, where larger earthquakes often precede substantially smaller ones.

Apoyeque remains in repose without documented historical eruptions. Tephrochronology (the study of ash layers, in this case including radiometric dating) indicates the most recent eruption here was large and took place about 50 BC (? 100 years) depositing the Chiltepe tephra. That tephra deposit has an estimated 4 km³ on-land volume and a total volume (including the offshore component) of about 18 km³(Kutterolf and others, 2008).

Reference. Kutterolf, S., Freundt, A., and Perez, W., 2008, Pacific offshore record of Plinian arc volcanism in Central America: 2. Tephra Volumes and erupted masses: Geochemistry, Geophysics, Geosystems (G³), v. 8, Q02S02, doi: 10.1029/2007GC001791.

Information Contacts: Instituto Nicaraguense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua.

October 2013 (BGVN 38:10) Cite this Report

Seismic swarms in 2009 and 2012

Within the last five years, Instituto Nicaragüense de Estudios Territoriales (INETER) reported at least two seismic swarms at Apoyeque, and between the Chiltepe Peninsula and the city of Managua (~15 km SE) (figure 1). Our last report also highlighted swarms which lasted several hours and days in 2001 and 2007 (BGVN 34:04). Intermittent seismicity was reported within the region during 2009-2012, but events were rarely larger than M 2.5.

Figure 1. Regional maps showing Apoyeque and the tectonic setting. (A) Sketch map highlighting volcanic centers in Central America relative to the active subduction of Cocos Plate beneath the Caribbean Plate. In Nicaragua active volcanism is concentrated inside the Nicaragua Depression (ND). The red box labeled "B" refers to the 50 x 50 km area that includes Apoyeque on the Chiltepe Peninsula. (B) This Landsat 7 image corresponds to the extent of the red box labeled "B" in the sketch map "A"; the Nejapa-Miraflores fault (NMF) marks an offset in the main arc and frequently generates seismicity. (C) Along the NMF, mainly monogenetic volcanoes have formed W of Managua city. Modified from Pardo and others, 2009.

2009 swarm. INETER reported a seismic swarm on 29 September 2009. It began at 1800 local time in an area W of Apoyeque volcano. The main event occurred at 1817 local time, with a ML 3.1 event at a depth of 5 km. The earthquake was felt by the population in Sandino City, ~5 km W of the earthquakes. The seismic swarm lasted until 2 October 2009; the total number of detected earthquakes was not disclosed.

2012 swarm. INETER reported a swarm that began at 1727 local time on 6 September 2012. The National Seismic Network detected and located the series of earthquakes between Apoyeque and the Nejapa-Miraflores fault (figure 1).

More than 20 earthquakes were detected and the two largest had magnitudes of 2.3 and 3.8, with depths of 2.8 and 6 km respectively; the largest event occurred at 1937 (figure 2). None of these earthquakes were reportedly felt by local populations and the event was assigned an Intensity II. The swarm lasted ~2 hours.

Figure 2. Epicenters of the largest earthquakes from the Apoyeque swarm are plotted. INETER detected ~20 earthquakes on 6 September 2012 all within 30 km depth. Courtesy of INETER.

Avellán and others (2012) described the polygenetic Apoyeque volcano as belonging to the Nejapa volcanic field (figure 1), which is bound by the Nejapa fault system. There were 23 eruptions from the field within the last ~30 ka; 13 of these events were explosive (VEI 2). The most recent eruption was dated between 2,130 ± 40 and 1,245 ± 120 years BP. With respect to hazards implications, clear vent migration patterns were seemingly absent for this volcanic field. The authors concluded that there is a high probability of future, similar eruptions, particularly phreatomagmatic ones, within this area of Nicaragua.

References: Avellán, D.R., Macías, J.L., Pardo, N., Scolamacchia, T., and Rodriguez, D., 2012, Stratigraphy, geomorphology, geochemistry and hazard implications of the Nejapa Volcanic Field, western Managua, Nicaragua, Journal of Volcanology and Geothermal Research, 213-214: 51-71.

Pardo, N., Macías, J.L., Giordano, G., Cianfarra, P., Avellán, D.R., and Bellatreccia, F., 2009, The ~1245 yr BP Asososca maar eruption: The youngest event along the Nejapa-Miraflores volcanic fault, Western Managua, Nicaragua, Journal of Volcanology and Geothermal Research, 184: 292-312.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/).