High‐precision earthquake location and three‐dimensional P wave velocity determination at Redoubt Volcano, Alaska

Abstract

[1] Redoubt Volcano, Alaska poses significant volcanic hazard to the Cook Inlet region and overlying flight paths. During and following the most recent eruption in [1989][1990] the Alaska Volcano Observatory deployed up to 10 seismometers to improve real-time monitoring capabilities at Redoubt and continues to produce an annual earthquake catalog with associated arrival times for this volcano. We compute a three-dimensional P wave velocity model using double-difference tomography combined with waveform cross-correlation techniques to identify families of similar earthquakes and increase earthquake location precision at Redoubt. Absolute and differential times for well-constrained events are used to simultaneously invert for hypocenter location and P wave velocity structure. Shot and earthquake arrival times recorded by temporary stations deployed on Redoubt in July 1991 supplement the catalog picks. Double-difference tomography reduces uncertainties associated with absolute and relative earthquake locations and provides a clearer picture of three-dimensional velocity heterogeneity. All Redoubt data available through November 2005 are relocated through the three-dimensional model, and we investigate seismicity associated with the 1989-1990 eruption and compare cross-correlation coefficients to identify similar earthquakes within the catalog. Waveform similarity is high at Redoubt, especially during the eruptive phases, and event families include long-period shallow summit, hybrid, and both shallow summit and midcrust level volcano-tectonic earthquakes. We do not resolve a low-velocity feature in the three-dimensional P wave model that can be interpreted as a source magma chamber and prefer the idea of an interconnected body of dikes and sills as the source of magma erupted in 1989-1990. Citation: DeShon, H. R., C. H. Thurber, and C. Rowe (2007), High-precision earthquake location and three-dimensional P wave velocity determination at Redoubt Volcano, Alaska,

Seismicity and structure of Akutan and Makushin Volcanoes, Alaska, using joint body and surface wave tomography

“…Relocations at both volcanoes show considerably more complex seismicity distributions than at several other Alaskan volcanoes (Figure ) [e.g., Caplan‐Auerbach and Peterson , ; DeShon et al ., ; Syracuse et al ., ; Ohlendorf et al ., ]. In comparison to catalog locations from AVO, earthquakes at Akutan moved on average 0.7 km deeper, with locations concentrated between the surface and 6 km depth, while earthquakes at Makushin moved 0.9 km shallower and are concentrated between 4 and 10 km depth.…”

“…Previous passive‐ and active‐source velocity tomography studies of other volcanoes have found a variety of types of features in the subsurface. Compiling results from 23 active arc volcanoes (Aso [ Sudo and Kong , ], Augustine [ Syracuse et al ., ], Mount Etna [ Aloisi et al ., ; Laigle et al ., ], Mount Fuji [ Nakamichi et al ., ], Great Sitkin [ Pesicek et al ., ], Iwate [ Tanaka et al ., ], Katmai [ Murphy et al ., ], Kirishima [ Tomatsu et al ., ], Klyuchevskoy [ Koulakov et al ., ], Long Valley Caldera [ Seccia et al ., ], Montserrat [ Paulatto et al ., ], Mount St. Helens [ Lees , ; Waite and Moran , ], Naruko [ Nakajima and Hasegawa , ], Nevado del Ruiz [ Londoño and Sudo , ], Okmok [ Masterlark et al ., ; Ohlendorf et al ., ], Popocatépetl [ Berger et al ., ; Kuznetsov and Koulakov , ], Rainier [ Moran et al ., ], Redoubt [ DeShon et al ., ], Taranaki [ Sherburn et al ., ], Tongariro [ Rowlands et al ., ], Tungurahua [ Molina et al ., ], Unzen [ Ohmi and Lees , ], and Vesuvius [ Piana Agostinetti and Chiarabba , ]) show that upper crustal low‐velocity regions, potentially indicative of hotter or melt‐rich areas, are as common as high‐velocity regions, generally interpreted to be cooled basaltic rocks intruded during previous eruptions and near which magma travels to the surface. It is possible that all volcanoes contain both these features, but resolution limitations prevent their observation.…”

“…Since 1996, Alaska Volcano Observatory (AVO) has seismically monitored Makushin and Akutan Volcanoes with multiple short‐period and broadband instruments. In addition to real‐time earthquake monitoring, the seismic instrumentation of numerous volcanoes by AVO has allowed the tomographic imaging of the subsurface to tens of kilometers depth at some volcanoes (Redoubt [ DeShon et al ., ], Katmai [ Jolly et al ., ; Murphy et al ., ], Great Sitkin [ Pesicek et al ., ], Okmok [ Masterlark et al ., ; Ohlendorf et al ., ], and Augustine [ Syracuse et al ., ]). In the context of these previous studies, seismic imaging of Makushin and Akutan Volcanoes deepens the understanding of the variety of seismicity patterns and types of magma storage systems possible at volcanoes in Alaska and globally.…”

Seismic activity near the Moriyoshi-zan volcano in Akita Prefecture, northeastern Japan: implications for geofluid migration and a midcrustal geofluid reservoir

“…In Figure 10, we aligned seismograms on the catalog P-wave picks, which is not adequate for that purpose. The alignment and stacking of waveforms of similar earthquakes based on the CC picks may be useful, as Rowe et al (2004) and DeShon et al (2007) have shown. Thus, increasing the spatial resolution of hypocenters and pressure sources as well as the scattering structure near the geofluid reservoir would be the next step of this study, using waveforms of smaller earthquakes we have not analyzed in this paper.…”

Characterization of seismic events during the 2009 eruption of Redoubt Volcano, Alaska

“…In this study we have also successfully tested automated procedures for removing noise using event metric thresholds listed in B. Additionally, the success of single-station detection combined with correlation detection have worked sufficiently to make manual event review and selection unnecessary. Previous studies by DeShon et al (2007DeShon et al ( , 2010 have used event similarity among events within the analyst reviewed catalog to more accurately determine phase arrival times from aligned waveform stacks. Because the catalog only represents a small percentage of the total seismic events occurring during an eruption, we assume that a great majority of multiplet events are also being omitted.…”