scholarly journals A New Analysis of Caldera Unrest through the Integration of Geophysical Data and FEM Modeling: The Long Valley Caldera Case Study

2021 ◽  
Vol 13 (20) ◽  
pp. 4054
Author(s):  
Fabio Pulvirenti ◽  
Francesca Silverii ◽  
Maurizio Battaglia
Keyword(s):  
Sierra Nevada ◽  
Volume Fraction ◽  
Gravity Data ◽  
Deformation Source ◽  
Hydrothermal Fluids ◽  
Gravity Potential ◽  
Baseline Length ◽  
Fem Modeling ◽  
Long Valley Caldera ◽  
Long Valley

The Long Valley Caldera, located at the eastern edge of the Sierra Nevada range in California, has been in a state of unrest since the late 1970s. Seismic, gravity and geodetic data strongly suggest that the source of unrest is an intrusion beneath the caldera resurgent dome. However, it is not clear yet if the main contribution to the deformation comes from pulses of ascending high-pressure hydrothermal fluids or low viscosity magmatic melts. To characterize the nature of the intrusion, we developed a 3D finite element model which includes topography and crust heterogeneities. We first performed joint numerical inversions of uplift and Electronic Distance Measurement baseline length change data, collected during the period 1985–1999, to infer the deformation-source size, position, and overpressure. Successively, we used this information to refine the source overpressure estimation, compute the gravity potential and infer the intrusion density from the inversion of deformation and gravity data collected in 1982–1998. The deformation source is located beneath the resurgent dome, at a depth of 7.5 ± 0.5 km and a volume change of 0.21 ± 0.04 km3. We assumed a rhyolite compressibility of 0.026 ± 0.0011 GPa−1 (volume fraction of water between 0% and 30%) and estimated a reservoir compressibility of 0.147 ± 0.037 GPa−1. We obtained a density of 1856 ± 72 kg/m3. This density is consistent with a rhyolite melt, with 20% to 30% of dissolved hydrothermal fluids.

The 2011-2020 long-term sustained inflation at Long Valley Caldera:  investigation of the interaction of magmatic and tectonic processes

2021 ◽  
Author(s):  
Erica De Paolo ◽  
Elisa Trasatti ◽  
Cristiano Tolomei ◽  
Emily K. Montgomery-Brown
Keyword(s):  
Ground Deformation ◽  
Deformation Source ◽  
Deformation Pattern ◽  
Seismic Zone ◽  
The South ◽  
Long Valley Caldera ◽  
Tectonic Processes ◽  
Sustained Inflation ◽  
Long Valley

<p>The Long Valley Caldera, California (USA), has been restless over the past few decades, experiencing seismic swarms and ground deformation episodes. The last inflation began in late 2011, when a radially symmetric tumescence was detected coinciding with a large resurgent dome within the caldera. Since then, a continuous inflation with quasi-steady rate of ~1.5 cm/yr has been observed.<span>  </span>Earthquakes mostly occur within the caldera along the South Moat Seismic Zone, to the south of the maximum deformation area. Although the area is tectonically active, increased seismic activity has been documented during periods of renewed inflation since the onset of this tumescence in 1978. In this study, we aim to investigate the nature and dynamics of the long-term unrest at Long Valley Caldera, as well as to provide new insights into the interaction between magmatic and tectonic processes. For this purpose, we consider a variety of datasets including geodetic and seismic records over the period spanning from late 2011 to the end of 2020. A complete seismic catalog supports our study, with more than 200 M2.5-4.5 earthquakes recorded since 2011, most with epicenters located within the caldera. Measurements from a dense network of continuous GPS stations collected in the last 10 years are analyzed in combination with high resolution Interferometric Synthetic Aperture Radar (InSAR) data. For full temporal coverage, we integrate InSAR velocities obtained from the acquisition of different satellite missions. We use, in particular, data from SAR systems operating with X and C-bands such as TerraSAR-X, COSMO-SkyMed and Sentinel-1. The multi-sensor dataset (i.e., GPS and multi-mission InSAR data) compensate the limitations of each technique, with reliable mapping of the deformation pattern evolving over several years. Data analysis highlights uplift velocities with peaks of ~2 cm/yr within the caldera and beyond its southern rim. Moreover, compared to the first half of the period of analysis (2011-2014), the area affected by high deformation rates is broader in the last several years (2017-2020). Models based on the geodetic data are developed to constrain the deformation source and to better interpret the observed signals. This study is motivated as a contribution to the understanding of this long-lived caldera unrest, for a more reliable hazard assessment.</p>

Study of Volcanic Sources at Long Valley Caldera, California, Using Gravity Data and a Genetic Algorithm Inversion Technique

2004 ◽  
Vol 161 (7) ◽  
pp. 1399-1413 ◽  
Author(s):  
M. Charco ◽  
J. Fern�ndez ◽  
K. Tiampo ◽  
M. Battaglia ◽  
L. Kellogg ◽  
...  
Keyword(s):  
Genetic Algorithm ◽  
Gravity Data ◽  
Long Valley Caldera ◽  
Inversion Technique ◽  
Long Valley

Magnetotelluric transect of Long Valley caldera: Resistivity cross‐section, structural implications, and the limits of a 2-D analysis

Geophysics ◽  
1991 ◽  
Vol 56 (7) ◽  
pp. 926-940 ◽  
Author(s):  
P. E. Wannamaker ◽  
P. M. Wright ◽  
Zhou Zi‐xing ◽  
Li Xing‐bin ◽  
Zhao Jing‐xiang
Keyword(s):  
Apparent Resistivity ◽  
Transverse Electric ◽  
Hydrothermal Fluids ◽  
Bishop Tuff ◽  
Long Valley Caldera ◽  
Low Resistivity ◽  
Te Mode ◽  
Tm Mode ◽  
Long Valley ◽  
North And South

Twenty‐four magnetotelluric (MT) soundings have been collected in an east‐west profile across the center of Long Valley caldera. The average station spacing is approximately 1 km and appears adequate to sample the important features of the upper crustal and deeper resistivity structures. Additional control on the shallowest resistivity is provided by a continuous profile of time domain electromagnetic soundings coincident with the western portion of the MT line. Our MT data set reveals numerous resistivity structures which illuminate the evolution and present state of the Long Valley system. Many of these have been quantified through two‐dimensional (2-D) finite element modeling emphasizing the transverse magnetic (TM) mode. Important structural components include low‐resistivity layers 0.5–1.5 km deep under the eastern half of the caldera, beneath the axial graben of the resurgent dome, and under the west caldera moat. Most of this layering appears to lie in post‐caldera Early Rhyolite tuffs, and the uppermost unwelded Bishop Tuff. These rhyolite units have been observed to be porous and highly altered and to commonly contain Pleistocene intercalated lacustrine clays. The remainder and majority of the Bishop Tuff appears highly resistive. A low resistivity layer also occurs below the axial graben near the base of the Bishop Tuff (1.5 km). Hydrothermal fluids or alteration in precaldera volcanic strata or, less likely, carbonaceous metasediments may be the cause of this. Resistive, probably crystalline basement at high levels is apparent beneath the center of resurgence. Low resistivities are modeled at a depth around 5 km below the entire west moat and central graben and may represent a zone of hydrothermal fluids released from magma crystallization, with potential magmatic contributions at greater depths. The correspondence between this low resistivity and teleseismic delay and low density zones found in other studies is quite striking. A subtle anomaly in the transverse electric (TE) mode impedance is weakly suggestive of a midcrustal conductive axis centered beneath the central graben and resurgent dome. However, it cannot be simulated by two‐dimensional transverse electric calculations and requires a full three‐dimensional evaluation to ensure that the anomaly does not represent resistivity complexity in just the upper few kilometers. A fundamental, caldera‐wide 3-D effect is documented by comparison of observed and computed TE impedance and vertical magnetic field data. The abrupt termination of conductive caldera sediments less than 10 km north and south of our profile greatly depresses the observed TE apparent resistivity and vertical magnetic field relative to the model calculations for periods greater than 0.3 s for the central and eastern caldera. Analysis of the TE mode data also suggests that a similar finite‐strike effect lies in the response at periods greater than 3 s due to the mid‐crustal west moat conductor. The TM mode measurements are judged to also contain some large‐scale departure from the 2-D assumption related to horizontal current gathering from the north and south. This inflates the apparent resistivity and decreases the phase somewhat around 10 s over the central portion of the caldera relative to the 2-D model response. The regional profile of resistivity for the data at hand can be modeled with a 40 ohm‐m basal half‐space beneath 30 km of crust of 1000 ohm‐m or more. Although stations outside the caldera are very desirable to constrain this deep profile better, there is no evidence for a discrete low‐resistivity layer deep below Long Valley in contrast to our interpretation in the northeastern Basin and Range.

Long Valley Caldera and the UCERF Depiction of Sierra Nevada Range-Front Faults

2015 ◽  
Vol 105 (6) ◽  
pp. 3189-3195 ◽  
Author(s):  
David P. Hill ◽  
Emily Montgomery-Brown
Keyword(s):  
Sierra Nevada ◽  
Long Valley Caldera ◽  
Long Valley

scholarly journals Hydrologically Induced Deformation in Long Valley Caldera and Adjacent Sierra Nevada

2020 ◽  
Vol 125 (5) ◽  
Author(s):  
F. Silverii ◽  
E. K. Montgomery-Brown ◽  
A. A. Borsa ◽  
A. J. Barbour
Keyword(s):  
Sierra Nevada ◽  
Long Valley Caldera ◽  
Long Valley

scholarly journals Joint interpretation of displacement and gravity data in volcanic areas. A test example: Long Valley Caldera, California

2001 ◽  
Vol 28 (6) ◽  
pp. 1063-1066 ◽  
Author(s):  
J. Fernández ◽  
M. Charco ◽  
K. F. Tiampo ◽  
G. Jentzsch ◽  
J. B. Rundle
Keyword(s):  
Gravity Data ◽  
Long Valley Caldera ◽  
Long Valley ◽  
Joint Interpretation

Bibliography of literature pertaining to Long Valley Caldera and associated volcanic fields

2005 ◽  
Author(s):  
John W. Ewert ◽  
Christopher J. Harpel ◽  
Suzanna K. Brooks
Keyword(s):  
Long Valley Caldera ◽  
Long Valley ◽  
Volcanic Fields
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