Socorro Magma Body Research Articles

Characterization of Earthquake Clustering and Swarms in Central New Mexico from 2002–2009 Associated with the Socorro Magma Body

Characterization of Earthquake Clustering and Swarms in Central New Mexico from 2002–2009 Associated with the Socorro Magma Body

Pressurizing Magma Within Heterogeneous Crust: A Case Study at the Socorro Magma Body, New Mexico, USA

AbstractSurface deformation plays a key role in illuminating magma transport at active volcanoes, however, unambiguous separation of deep and shallow transport remains elusive. The Socorro Magma Body (SMB) lacks an upper crustal magma transport system, allowing us to link geodetic measurements with predictions of numerical models investigating rheologic heterogeneities and magma‐mush interaction in the mid‐/lower crust. New InSAR observations confirm that a pattern of central surface uplift surrounded by a region of subsidence (previously coined “sombrero” deformation) has persisted over >100 years at the SMB. Our models suggest this pattern may reflect the presence of a large (>100 km width), weaker‐than‐ambient, compliant region (CR) surrounding the mid‐crustal magma body. Interactions between a pressurizing (e.g., due to melt injection and/or volatile exsolution) sill‐like magma body and CR drive the sombrero pattern, depending on both viscoelastic relaxation and pressurization timescales, explaining its rare observation and transient nature.

Detection Threshold Estimates for InSAR Time Series: A Simulation of Tropospheric Delay Approach.

We present a method for estimating the detection threshold of InSAR time-series products that relies on simulations of both vertical stratification and turbulence mixing components of tropospheric delay. Our simulations take into account case-specific parameters, such as topography and wet delay. We generate the time series of simulated data with given intervals (e.g., 12 and 35 days) for temporal coverages varying between 3 and 10 years. Each simulated acquisition presents the apparent noise due to tropospheric delay, which is constrained by case-specific parameters. As the calculation parameters are randomized, we carry out a large number of simulations and analyze the results statistically and we see that, as temporal coverage increases, the amount of propagated error decreases, presenting an inverse correlation. We validate our method by comparing our results with ERS and Envisat results over Socorro Magma Body, New Mexico. Our case study results indicate that Sentinel-1 can achieve ≈1 mm/yr detection level with regularly sampled data sets that have temporal coverage longer than 5 years.

Active Deformation Near the Rio Grande Rift and Colorado Plateau as Inferred from Continuous Global Positioning System Measurements

AbstractWe used data from 333 continuous Global Positioning System stations, including 26 stations installed in 2006–2007 as part of a collaborative EarthScope experiment, to investigate how deformation is distributed near the Rio Grande Rift. Our previous analysis, using data from 2006 to 2010, was consistent with a nearly uniform east‐west distributed extensional strain rate of ~1.2 nε/year (nanostrain/year) along five profiles spanning a ~1,000‐km region. We built upon this analysis with additional Global Positioning System networks and longer time series of data spanning varying time ranges between 1993 and 2018. In all five east‐west profiles, extensional strain rates are higher within and west of the fault‐defined rift zone than to the east. There is an east‐to‐west increase in Central New Mexico from 0.7 ± 0.1 to 1.8 ± 0.8 nε/year that is significant at the 95% confidence level. We found elevated extensional and shear strain rates of over 10 nε/year along parts of the central Rio Grande Rift, particularly along the southeast edge of the Colorado Plateau along part of the Jemez lineament, as well as elevated dilatational strain rates and uplift above the Socorro magma body. Results from Euler pole analysis of Global Positioning System velocities for sites within the Colorado Plateau show nonrigid behavior with considerable deformation near the plateau margins and internal east‐west extension. Our results suggest the Rio Grande Rift is actively deforming in an evolving tectonic environment.

Radiogenic isotopes record a ‘drop in a bucket’ – A fingerprint of multi-kilometer-scale fluid pathways inferred to drive fault-valve behavior

Minerals precipitated from fluids carry a chemical signature of fluid origin and transport history. We use this concept to test the hypothesis that a subset of veins precipitated in the Loma Blanca fault zone, Rio Grande rift, NM, USA, record fault-valve behavior. Previous studies of this site show syntectonic calcite veins formed in response to post-seismic fluid discharge following repeated ground-rupturing earthquakes. U-Th ages on veins constrain the timing of fault slip over a period of >400,000 years. The radiogenic isotope (Sr, Pb, and U) data we report here demonstrate that a cluster of earthquakes that occurred at ∼430 ka, when fault-slip frequency increased by nearly one order of magnitude, corresponds with a brief period of particularly large and rapid variations in post-seismic fluid chemistry. Isotopic variations are consistent with fluid input from the Socorro magma body, a large, active, mid-crustal basalt intrusion 19 km below the surface. The short duration of the earthquake cluster (<50,000 years) precludes a role of thermal weakening of the crust in increased extension. We suggest that volatile exsolution and heating of ambient fluids during magma crystallization increased fluid volume and thereby pore-fluid pressure at depth, weakening the fault and driving more frequent failure through fault-valve action. This conclusion could not have been reached using traditional approaches in structural geology, stable isotope geochemistry, or geochronology alone, illustrating the utility of integrated data sets including radiogenic isotope analyses in studies of fluid-fault interactions.

Seismicity of the rocky mountains and Rio Grande Rift from the EarthScope Transportable Array and CREST temporary seismic networks, 2008–2010

AbstractWe developed a catalog of small magnitude (ML −0.1 to 4.7) seismicity across Colorado and New Mexico from the EarthScope USArray Transportable Array and CREST (Colorado Rocky Mountains Experiment and Seismic Transects) seismic networks from 2008 to 2010 to characterize active deformation in the Rio Grande Rift. We recorded over 900 earthquakes in the Rio Grande Rift region, not including induced earthquakes and mine blasts, and find that the rift is actively deforming both broadly and in distinct regions. Seismic events that are likely induced, mostly in the Raton Basin, make up 66% of the catalog (1837 earthquakes). Neogene faults in the northern rift in north central Colorado are seismically active in the North Park Basin and northwestern Colorado. The central rift from the San Luis Basin (southern Colorado) to south of the Socorro Magma Body is the most seismically active rift region, and seismicity delineates the deformation in the Colorado Plateau transition zone, which is spatially correlated with volcanic vents, dikes, and faults within the western Jemez Lineament. The eastern Jemez Lineament is nearly aseismic and surrounded by a halo of seismicity culminating in boundaries defined by recent moderate (Mw 3.9 and Mw 3.3) earthquakes. The southern rift is characterized by diffuse seismicity in Texas and Mexico. This study provides an updated seismic catalog built with uniformity in seismometer coverage and low epicentral uncertainties (~2 km) that allows for regional evaluation of seismicity. During this time period, clusters of seismicity and moderate magnitude earthquakes characterize deformation in a low‐strain rate extensional environment.

Allan R. Sanford (1927–2016)

Allan (Al) R. Sanford, professor of geophysics, emeritus, at New Mexico Tech (NMT) passed away quietly at his home in Woodinville, Washington, on 9 August 2016. He was 89. Al was a pioneer in the recording and interpretation of microearthquake seismograms. For decades, he was the leading authority concerning seismicity across New Mexico and within the Rio Grande rift (RGR). He published numerous papers with graduate students and colleagues on the unique, high‐amplitude reflected phases seen on Socorro‐area microearthquake records. Al and his students eventually attributed these phases to the presence of an extensive midcrustal magmatic sill now known as the Socorro Magma Body (SMB). Figure 1. Allan R. Sanford (1927–2016) Al was born in Pasadena, California. He attended Pomona College, but then entered the Navy to train as a radar specialist during the final 18 months of World War II. Back at Pomona following the war, he completed a B.S. degree in physics in 1949. He then spent time as the “computer” on a seismic crew prospecting for oil across the western United States. This experience led him to graduate school at California Institute of Technology where he gained knowledge in seismology while working for C. F. Richter and he completed his doctorate in geophysics under the guidance of C. H. Dix in 1958. Al was employed as a professor at NMT in Socorro from 1957 to 1997 where he taught courses in exploration geophysics and earthquake seismology, and supervised the research projects of about 50 masters students and about one dozen doctoral students. He joined Seismological Society of …

Determining Location and Magnitude of Historical (Pre‐1963) Events in the Rio Grande Rift Region Using Intensity Information

Abstract We used intensity information from five calibration earthquakes to estimate an intensity attenuation model for the Rio Grande rift region (encompassing west Texas, New Mexico, and southern Colorado). The attenuation model lies between similar models developed for the Basin and Range Province and central and eastern North America. Analysis of two test earthquakes occurring in 1931 and 2014 validated that the intensity attenuation relation adequately predicted the events’ magnitudes and epicenters. We then analyzed intensity information for nine historical (1906–1960) earthquakes to determine their magnitudes and epicenters. Our results indicate that the largest earthquakes of the 1906 Socorro, New Mexico, sequence had intensity magnitudes ( M I ) 5.7–5.9 and may represent north‐to‐south migration of seismicity associated with the Socorro magma body. Moderate earthquakes in 1935 and 1960 also are associated with the magma body. The 1938 Arizona–New Mexico border earthquake sequence occurred about 50 km northeast of the ongoing 2014 Arizona–New Mexico border sequence. The 17 September earthquake of the 1938 sequence had an M I (4.1) that was about 1.0 units less than that of the 29 June 2014 Arizona–New Mexico event ( M I 4.9).

Limited Dynamic Earthquake Triggering in the Socorro Magma Body Region, Rio Grande Rift, New Mexico

Abstract Dynamic earthquake triggering, the process through which stresses transmitted through the passage of seismic waves can trigger remote faults to fail, has been shown to be fairly common throughout the globe and especially in seismically active areas of high heat flow and geothermal activity. We explore the possibility of dynamic earthquake triggering around the Socorro magma body, a feature within the Rio Grande rift in New Mexico that exhibits high heat flow and heightened seismicity. Because the area fits the environment type in which triggering preferentially occurs, we examine 319 global mainshocks with M w ≥6.0 for the possibility of increased seismicity rates following the passage of the mainshock waves. We examine local event locations and origin times relative to mainshock phase arrivals for patterns distinguishing triggering mainshocks from nontriggering mainshocks. We find a small triggering response during the time period analyzed, unlike following the 2002 Denali fault earthquake (DFE). This small response corresponds to smaller peak dynamic stresses than are found in other triggering studies ( M w >7.0), at a regional to small teleseismic distance (

New data reflect on the thermal antiquity of the Socorro magma body locale, Rio Grande Rift, New Mexico

New heat flow data and recent relative Vs (ΔVs/Vs) studies suggest differential crustal warming from prolonged intrusions in the Socorro magma body area. Heat flow above the Socorro magma body, relative to the adjacent Colorado Plateau and Datil-Mogollon region, indicates that ∼8 times more heat has been introduced into the crust than contained in a basaltic Socorro magma body. A combination of relative Vs contours and heat flow data suggests this differential is less, a factor ∼4.5. From relative Vs contours, depth of Socorro magma body, and conduction time constants, the minimum time required to increase heat flow resulting from midcrustal intrusions is ∼1–3 m.y. Recent models indicate that observed historic uplift at the Socorro magma body is explained by viscoelastic response of crustal material surrounding the Socorro magma body. Our estimates suggest that a long time scale (∼10 6 yr) for emplacement of basaltic magma sill(s) and surface uplift need not be directly related. Based on heat flow, we estimate >600 m of basaltic intrusion during Pliocene–Pleistocene time. Compared with adjacent rift basins, the Socorro magma body area shows anomalous landscape instability but no significant uplift of stream terraces across the magma body. Contiguous areas in the Rio Grande Rift have high heat flow but no present magma layer, no historic uplift, and little seismicity. Elliptical relative Vs crustal contours for the area suggest conductive heat transfer. The relative Vs model implies that the Socorro magma body is fed by narrow conduits (dikes) from the upper mantle and that the depth of the sill-like Socorro magma body is primarily controlled by rheology.

Relocation and characterization of the August 2009 microearthquake swarm above the Socorro magma body in the central Rio Grande Rift

Earthquake swarms, often attributed to magma or fluid movement in the uppermost crust, have differing statistics depending on tectonic setting, with volcanic swarms producing b‐values of up to 2.5 and continental rift swarms having b‐values ∼0.8‐1. Along the Rio Grande continental rift (RGR) in the western US, earthquake swarms have occurred in the area of the Socorro Magma Body (SMB), including the 2009 swarm of 431 events (magnitudes −1.0 to 2.5) over 26 days. We characterize the 2009 swarm to define spatial and temporal patterns to help understand the role of the SMB on the swarm. Our relocations suggest a small seismogenic volume of 34.5 km3 and focal mechanisms of the largest events are consistent with regional stress patterns. The b‐value of 0.9 is more characteristic of continental rift zones than volcanic swarms, suggesting more emphasis on the preexisting highly fractured crust rather than direct influence of magmatic movement.

Mechanics of active magmatic intraplating in the Rio Grande Rift near Socorro, New Mexico

We investigate long‐term deformation due to the Socorro Magma Body (SMB), one of the largest active intrusions in the Earth's continental crust, using interferometric synthetic aperture radar (InSAR) observations and finite element simulations. InSAR data spanning 15 years (1992–2007) indicate that the magma body is associated with a steady crustal uplift at a rate of about 2 mm yr−1. Previous work showed that while the pattern of surface uplift is consistent with an elastic inflation of a large sill‐like magma body, the SMB could not have formed via steady elastic inflation because the latter would be outpaced by magma solidification. We resolve this problem using coupled thermo‐visco‐elastic models, and place constraints on the intrusion history as well as the rheology of the ambient crustal rocks. We demonstrate that observations rule out the linear Maxwell response of the ductile crust, but are consistent with laboratory‐derived power law rheologies. Our preferred model suggests that the age of the SMB is of the order of 103 years, and that the apparent constancy of the present‐day uplift may be due to slow heat transfer and ductile deformation in a metamorphic aureole of a giant sill‐like magma intrusion, rather than due to a steady increase in the magma overpressure. The SMB is a contemporaneous example of “magmatic intraplating,” a process by which large volumes of mafic melt stall and spread at midcrustal depths due to density or rheology contrasts.

Magnitude and duration of surface uplift above the Socorro magma body

We use interferometric synthetic aperture radar and geomorphic data to constrain the magnitude and duration of uplift driven by the magma body beneath Socorro, New Mexico, United States. Interferometry spanning 1992–2006 confirms uplift of the Socorro magma body at a rate of ~2.5 mm/yr. However, we find no clear evidence for volcanic uplift after an examination of three rivers (Rio Salado, Rio Puerco, Rio Grande), and two terraces (Llano de Manzano, Llano de Albuquerque) crossing the Socorro magma body. Our geomorphic measurements permit at most 25–50 m of cumulative surface uplift above the Socorro magma body since the middle Pleistocene, but require no long-term uplift. Given previously articulated thermal arguments for the Socorro magma body, we therefore suggest either a recent (within the last few centuries) initiation of uplift at Socorro, or that long-term uplift and subsidence have been essentially equal.

Characteristics of the October 2005 Microearthquake Swarm and Reactivation of Similar Event Seismic Swarms over Decadal Time Periods near Socorro, New Mexico

Seismicity in the Rio Grande rift in central New Mexico, southwestern United States, has been dominated by microearthquakes occurring above the midcrustal Socorro magma body (SMB) for at least the past century. The SMB is a sill-like feature ≥3400 km2 in area, with a top surface at 19-km depth and centered below the inner rift half-graben system. A recent swarm of microearthquakes above the magma body began on 20 October 2005. The activity intensified toward 30 October 2005, with the largest event being a shallow felt local magnitude ( M L) 2.4 earthquake at 02:57:35 (UTC). Seismicity increased in the region following this event, with over 1600 earthquakes detectable at a minimum of one local seismic station during the subsequent month. Seismic waveforms for the earthquakes in this sequence are remarkably similar, implying consistently similar location and faulting geometry. The time–space distribution of earthquakes indicates that this sequence is highly swarmlike, in contrast to tectonic mainshock–aftershock sequences. Given the local tectonic setting and shallow (<8 km) depth of individual events above the SMB, a likely explanation for the Socorro earthquake sequence is fluid flow- or pressure-induced triggering associated with the evolution of the SMB. Swarms such as the 2005 sequence are not uncommon in this area (e.g., prominent previous sequences occurred in May and July of 1983). Here we characterize the 2005 earthquake sequence by presenting composite focal mechanisms, magnitude estimates, and high-precision relative locations based on waveform cross-correlation techniques that capitalize on the similar waveforms. A new waveform scanning technique identifies over 1600 small similar earthquakes during this period from continuous seismic records. Waveforms and locations are also observed to be similar between the 2005 and 1983 sequences, suggesting consistency in source location, geometry, and thus mechanism over decadal time scales.

Evidence for on‐going inflation of the Socorro Magma Body, New Mexico, from interferometric synthetic aperture radar imaging

Interferometric synthetic aperture radar (InSAR) imaging of the central Rio Grande rift (New Mexico, USA) during 1992–1999 reveals a crustal uplift of several centimeters that spatially coincides with the seismologically determined outline of the Socorro magma body, one of the largest currently active magma intrusions in the Earth's continental crust. Modeling of interferograms shows that the observed deformation may be due to elastic opening of a sill‐like intrusion at a rate of a few millimeters per year. Despite an apparent constancy of the geodetically determined uplift rate, thermodynamic arguments suggest that it is unlikely that the Socorro magma body has formed via steady state elastic inflation.

Finite source modelling of magmatic unrest in Socorro, New Mexico, and Long Valley, California

SUMMARY We investigate surface deformation associated with currently active crustal magma bodies in Socorro, New Mexico, and Long Valley, California, USA. We invert available geodetic data from these locations to constrain the overall geometry and dynamics of the inferred deformation sources at depth. Our best-fitting model for the Socorro magma body is a sill with a depth of 19 km, an effective diameter of 70 km and a rate of increase in the excess magma pressure of 0.6 kPa yr x1 . We show that the corresponding volumetric inflation rate is y6r10 x3 km 3 yr x1 , which is considerably less than previously suggested. The measured inflation rate of the Socorro magma body may result from a steady influx of magma from a deep source, or a volume increase associated with melting of the magma chamber roof (i.e. crustal anatexis). In the latter case, the most recent major injection of mantle-derived melts into the middle crust beneath Socorro may have occurred within the last several tens to several hundreds of years. The Synthetic Interferometric Aperture Radar (InSAR) data collected in the area of the Long Valley caldera, CA, between June 1996 and July 1998 reveal an intracaldera uplift with a maximum amplitude of y11 cm and a volume of 3.5r10 x2 km 3 . Modelling of the InSAR data suggests that the observed deformation might be due to either a sill-like magma body at a depth of y12 km or a pluton-like magma body at a depth of y8 km beneath the resurgent dome. Assuming that the caldera fill deforms as an isotropic linear elastic solid, a joint inversion of the InSAR data and two-colour laser geodimeter data (which provide independent constraints on horizontal displacements at the surface) suggests that the inferred magma chamber is a steeply dipping prolate spheroid with a depth of 7‐9 km and an aspect ratio in excess of 2:1. Our results highlight the need for large radar look angles and multiple look directions in future InSAR missions.

A new map of the geographic extent of the Socorro mid-crustal magma body

AbstractFor 35 years, strong reflected phases from the sill-like, mid-crustal Socorro magma body (SMB) have been observed on microearthquake seismograms recorded in the central Rio Grande rift, New Mexico. In 1979, the lateral extent of the SMB was estimated at 1700 km2 by mapping reflection points for 220 observed SzS arrivals. We have remapped the magma body using 697 PzP, 2169 SzP, and 2589 SzS reflections observed on seismograms recorded between 1975 and 1995 by New Mexico Tech seismic networks.These data indicate that the SMB covers an area greater than 3400 km2. By comparing the distribution of observed reflection points with the distribution of all possible reflection points, limits can be set for the northern and southern boundaries of the SMB. The ∼80 km north-south extent of the SMB falls just inside a ∼100-km north-south range of enhanced seismicity near Socorro. This area, the Socorro seismic anomaly (SSA), covers ∼5000 km2 and has the same elliptical shape as the outline of the SMB based on observed reflection points. The close spatial relation between the SSA and the mid-crustal magma body along their northern and southern boundaries suggests that the observed seismicity can be used to place limits on the eastern and western boundaries of the magma body. Using the distribution of earthquakes within the SSA over the last 34 years, the maximum east-west extent of the SMB is &amp;lt;60 km, our reflection based value is ∼50 km.Our data indicates that the upper surface of the magma body displays no regional dip. Considering timing errors, maximum possible relief on the magma body surface is ±0.50 km.

Incorporating Socorro magma body reflections into the earthquake location process

When network station spacing is large relative to event depths, constraining focal depths using direct arrivals is difficult. To help overcome this problem, we incorporated the SzS, SzP, and PzP Socorro magma body reflections into the earthquake location process. To find a velocity model appropriate for combining direct and reflected arrivals, we jointly inverted for 75 hypocenters and a one-dimensional velocity model. We used over 1000 direct arrivals and over 400 reflected arrivals, solving for P velocity ( Vp ) and Poisson's ratio ( v ) above the approximate base of the seismogenic zone, Vp and v below the base of the seismogenic zone, depth to the upper surface of the magma body, and station corrections. High-velocity and low-velocity initial models converged to the same solutions without damping. We found that Vp and v may both decrease slightly below about 10-km depth. Magma body depth is near 18.75 km. A close fit between observed and modeled reflected phase arrival times and an even lateral distribution of positive and negative reflected-phase residuals indicate that the magma body upper surface is nearly flat. In the Socorro area, combining direct and reflected phases reduces average focal depth error by more than a factor of 3 and average origin time error by a factor of 2 compared with using only direct phases. This is because reflected arrivals are more sensitive to changes in focal depth than direct arrivals, and combining upgoing (direct) and downgoing (reflected) times reduces the trade-off between focal depth and origin time. For this method to be successful, phases must be carefully identified. To help identify secondary phases, we used relative arrival time curves, plotting phase-minus- P times versus S -minus- P times. Picking reflection pairs (SzP and SzS, SzP and PzP, or SzS and PzP identified on a single seismogram) significantly reduces the chances of phase misidentification. The SzP-SzS and SzP-PzP pairs also help prevent trade-offs between reflector depth and focal depths.

Crustal extension and magmatic processes: COCORP profiles from Death Valley and the Rio Grande rift

New crustal-scale information on the interaction between normal faulting and magmatic activity is provided by recent COCORP deep seismic reflection profiles in Death Valley, California, and by reprocessing of the COCORP data from the Socorro area of the Rio Grande rift, New Mexico. The most striking feature on the seismic sections from these areas is a prominent, subhorizontal series of reflectors at mid-crustal depth. Previous studies have suggested that thin tabular magma bodies lie within the mid-crustal reflective zones. In addition, because they are traced without apparent offset beneath faults both mapped at the surface and interpreted from the COCORP data, these mid-crustal horizons are here inferred to be detachments or zones of tectonic decoupling. Upper-crustal Cenozoic faults do not appear to penetrate deeper than 15 km in Death Valley and 13 km in the Rio Grande rift. In Death Valley, these faults are relatively planar, with moderate dips (20° to 35°), and appear to bound large basement rocks. One such zone of normal faults can be traced from the magma body inferred at 15 km depth beneath central Death Valley to the surface location of a 690,000-yr-old basaltic cinder cone. Listric and low- to moderate-angle normal faults are evident on the reprocessed New Mexico data and constitute the structural component of upper-crustal extension. In particular, a listric master fault traceable to depths as great as 13 km is inferred to underlie the Albuquerque basin. Unlike the Death Valley data, no faults are observed to merge with the Socorro magma body per se. Rather, subhorizontal to moderately west-dipping packages of reflections are imaged between the base of the faulted upper crust (13 km depth) and the mid-crustal magma body (about 20 km depth). The middle crust marks a major rheological boundary between the faulted upper crust and a ductile lower crust extending by penetrative flow and intrusion. Events seen in the middle and lower crust are generally subhorizontal, and prominent layering is observed. A band of reflections attributed to the crust-mantle boundary is evident on most seismic sections. The upper mantle appears seismically transparent. On some of the profiles, the events attributed to the base of the crust are the deepest in a series of strong and continuous reflections, at least one of which is a layer of magma. This association supports the suggestion that magmatic intrusions are a probable cause for the high reflectivity observed in the deep crust of many extensional terranes.

Evidence of ongoing crustal deformation related to magmatic activity near Socorro, New Mexico

Recent leveling conducted by the National Geodetic Survey in central New Mexico provides new evidence of ongoing tectonic deformation associated with the Rio Grande rift. A 1980–1981 resurvey over suspected midcrustal and shallow magma bodies near Socorro, New Mexico, indicates continued uplift averaging 0.18 cm/yr between 1951 and 1980. Although this rate is somewhat smaller than that reported previously (0.34 cm/yr between 1912 and 1951), the new observations suggest possible systematic errors in the earlier surveys. Reanalysis of the earlier data gives an average rate of 0.23 cm/yr from 1912 to 1951, consistent not only with the new releveling observations but also with geomorphic evidence which indicates an average uplift rate of 0.18 cm/yr over the past 20,000 years. Thus the rate of uplift may be relatively constant. The new releveling measurements also confirm prominent zones of subsidence flanking the central uplift. Modeling the deformation, together with other geophysical observations, suggests that the movements in the Socorro area are likely associated with the 19‐km‐deep Socorro magma body. Although the details of magma movements are not well constrained, plausible models include flow of magma from the periphery toward the central magma chamber and flow from sources in the lower crust into the midcrust. Horizontal strain calculated for these models is generally consistent with the small strain reported from repeated trilateration surveys in the Socorro area. The Rio Grande rift is clearly an important site for future monitoring of crustal deformation.