Source model for the Copahue volcano magma plumbing system constrained by InSAR surface deformation observations. Issue 7 (20th July 2017)

• Record Type: Journal Article
• Authors: Lundgren, Paul; Nikkhoo, Mehdi; Samsonov, Sergey V.; Milillo, Pietro; Gil‐Cruz, Fernando; Lazo, Jonathan
• Is Part Of: Journal of geophysical research. Volume 122:Issue 7(2017)
• Page Start: 5729
• Page End: 5747
• Publication Date: 2017-07-20
• Subjects: InSAR -- Copahue volcano -- volcano deformation -- volcano seismicity; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2017JB014368
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Copahue volcano straddling the edge of the Agrio‐Caviahue caldera along the Chile‐Argentina border in the southern Andes has been in unrest since inflation began in late 2011. We constrain Copahue's source models with satellite and airborne interferometric synthetic aperture radar (InSAR) deformation observations. InSAR time series from descending track RADARSAT‐2 and COSMO‐SkyMed data span the entire inflation period from 2011 to 2016, with their initially high rates of 12 and 15 cm/yr, respectively, slowing only slightly despite ongoing small eruptions through 2016. InSAR ascending and descending track time series for the 2013–2016 time period constrain a two‐source compound dislocation model, with a rate of volume increase of 13 × 10 6 m 3 /yr. They consist of a shallow, near‐vertical, elongated source centered at 2.5 km beneath the summit and a deeper, shallowly plunging source centered at 7 km depth connecting the shallow source to the deeper caldera. The deeper source is located directly beneath the volcano tectonic seismicity with the lower bounds of the seismicity parallel to the plunge of the deep source. InSAR time series also show normal fault offsets on the NE flank Copahue faults. Coulomb stress change calculations for right‐lateral strike slip (RLSS), thrust, and normal receiver faults show positive values in the north caldera for both RLSS and normal faults, suggesting that northward trending seismicity and Copahue fault motion within the caldera are caused by the modeled sources. Together, the InSAR‐constrained source model and the seismicity suggest a deep conduit or transfer zone where magma moves from the central caldera to Copahue's upper edifice. Plain Language Summary: Copahue volcano straddling the edge of the Agrio‐Caviahue caldera along the Chile‐Argentina border in the southern Andes has been in unrest since inflation began in late 2011. Its asymmetric deformation pattern extending into the caldera observed by radar interferometry suggests a complex magma plumbing system. We constrain models of its plumbing system with satellite and airborne interferometric synthetic aperture radar (InSAR) surface displacement observations. Displacement time series from RADARSAT‐2 and COSMO‐SkyMed satellite data span the entire inflation period from 2011 to 2016, with their initially high rates of 12 and 15 cm/yr, respectively, slowing only slightly through 2016. InSAR observations for the 2013–2016 time period constrain a two‐source compound dislocation model, with a rate of volume increase of 13 × 10 6 m 3 /yr. They consist of a shallow, near‐vertical, elongated source centered at 2.5 km beneath the summit, and a deeper, shallowly plunging source centered at 7 km depth connecting the shallow source to the deeper caldera. The deeper source is located directly beneath the volcano tectonic seismicity with the lower bounds of the seismicity parallel to the plunge of the deep source. This suggests a deep conduit or transfer zone where magma moves from the central caldera to Copahue's upper edifice. Key Points: InSAR time series reveal an asymmetric deformation pattern concurrent with eruptive activity Two nonstandard sources are required: shallow summit and a deeper conduit system plunging into the caldera Compared to seismicity, we suggest that the summit connects via the deep source to the central caldera