Interferometric Synthetic Aperture Radar Studies Research Articles

LAND SUBSIDENCE IN WUHAN REVEALED USING A MULTI-SENSOR INSAR TIME SERIES FUSION APPROACH

Abstract. Satellite Interferometric Synthetic Aperture Radar (InSAR) is widely utilized for topographic, geological, and natural resource investigations. However, many existing InSAR studies on ground deformation are limited to relatively short observation periods and single sensors. This paper introduces a novel method for fusing multi-sensor InSAR time series data, specifically designed to address scenarios involving partial overlaps and temporal gaps. The method employs a new Power Exponential Knothe Model (PEKM) to fit and fuse overlaps in the deformation curves, while a Long Short-Term Memory (LSTM) neural network predicts and fuses data during temporal gaps in the series. In this study, the city of Wuhan in China was selected as the experimental area. SAR datasets from COSMO-SkyMed (2011–2015), TerraSAR-X (2015–2019), and Sentinel-1 (2019–2021) were fused to map long-term surface deformation over the past decade. An independent InSAR time series analysis from 2011 to 2020, based on 230 COSMO-SkyMed scenes, was used as a reference for comparison. The correlation coefficient between the fusion algorithm’s results and the reference data is 0.87 in the time overlapping region and 0.97 in the time-interval dataset. The overall correlation coefficient of 0.78 demonstrates that the proposed algorithm achieves a similar trend as the reference deformation curve. Based on the long time series settlement results obtained through fusion, a detailed analysis of the causes of settlement was conducted for several subsidence zones. The subsidence in the Houhu area is primarily attributed to the consolidation and compression of soft soil. Soil mechanics were employed to estimate the expected completion time of subsidence and calculate the degree of consolidation for each year. The COSMO-SkyMed PSInSAR results indicate that the area has entered the late stage of consolidation and compression, gradually stabilizing over time. Furthermore, the subsidence curve observed in the area around Xinrong reveals that the construction of an underground section of subway Line 21 has caused significant settlement in that particular region. The high temporal granularity of the PSInSAR time series also enables precise detection of a rebound phase following a major flooding event in 2016. The experimental results demonstrate the accuracy of the proposed fusion method in providing robust time series for analyzing long-term land subsidence mechanisms. Additionally, these findings unveil previously unknown characteristics of land subsidence in Wuhan, thus clarifying the relationship with urban causative factors.

Multi-sensor InSAR time series fusion for long-term land subsidence monitoring

ABSTRACT Satellite Interferometric Synthetic Aperture Radar (InSAR) is widely used for topographic, geological and natural resource investigations. However, most of the existing InSAR studies of ground deformation are based on relatively short periods and single sensors. This paper introduces a new multi-sensor InSAR time series data fusion method for time-overlapping and time-interval datasets, to address cases when partial overlaps and/or temporal gaps exist. A new Power Exponential Knothe Model (PEKM) fits and fuses overlaps in the deformation curves, while a Long Short-Term Memory (LSTM) neural network predicts and fuses any temporal gaps in the series. Taking the city of Wuhan (China) as experiment area, COSMO-SkyMed (2011–2015), TerraSAR-X (2015–2019) and Sentinel-1 (2019–2021) SAR datasets were fused to map long-term surface deformation over the last decade. An independent 2011–2020 InSAR time series analysis based on 230 COSMO-SkyMed scenes was also used as reference for comparison. The correlation coefficient between the results of the fusion algorithm and the reference data is 0.87 in the time overlapping region and 0.97 in the time-interval dataset. The correlation coefficient of the overall results is 0.78, which fully demonstrates that the algorithm proposed in our paper achieves a similar trend as the reference deformation curve. The experimental results are consistent with existing studies of surface deformation at Wuhan, demonstrating the accuracy of the proposed new fusion method to provide robust time series for the analysis of long-term land subsidence mechanisms.

InSAR Study of Landslides: Early Detection, Three-Dimensional, and Long-Term Surface Displacement Estimation—A Case of Xiaojiang River Basin, China

Landslides, a major natural geohazard, obstruct municipal constructions and may destroy villages and towns, at worst causing significant casualties and economic losses. Interferometric Synthetic Aperture Radar (InSAR) technique offers distinct advantages on landslide detection and monitoring. In this paper, a more systematic workflow is designed for InSAR study of landslides, in terms of three levels: (i) early detection on regional scale, (ii) three-dimensional (3D) surface displacement rates estimation on detailed scale, and (iii) time series analysis on long-term temporal scale. The proposed workflow is applied for landslide research on the Xiaojiang River Basin, China, using ascending and descending Sentinel-1 images acquired from March 2017 to May 2019. First, the landslide inventory has been mapped and updated using InSAR stacking method, supporting geohazard prevention on a regional scale. A total of 22 active landslides are identified, ranging from medium to super large scale. Compared with the existing inventory, three unrecorded landslides are newly detected by our approach, and five recorded landslides are detected significant expansion of their boundaries. Then, specific to a detected landslide, Baobao landslide, a Total Least Squares–Kalman Filter-based approach is presented. Two outcomes are provided for further spatial-temporal pattern analysis: 3D displacement rates, providing an intuitive insight on the spatial characteristics and sliding direction of landslide, which are analyzed to deep the understanding of its kinematic mechanism, and long-term time series, which contribute to deduce the dynamic evolution of landslide, presenting benefits in landslide forecasting.

Permafrost Dynamics Observatory-Part I: Postprocessing and Calibration Methods of UAVSAR L-Band InSAR Data for Seasonal Subsidence Estimation.

Interferometric synthetic aperture radar (InSAR) has been used to quantify a range of surface and near surface physical properties in permafrost landscapes. Most previous InSAR studies have utilized spaceborne InSAR platforms, but InSAR datasets over permafrost landscapes collected from airborne platforms have been steadily growing in recent years. Most existing algorithms dedicated toward retrieval of permafrost physical properties were originally developed for spaceborne InSAR platforms. In this study, which is the first in a two part series, we introduce a series of calibration techniques developed to apply a novel joint retrieval algorithm for permafrost active layer thickness retrieval to an airborne InSAR dataset acquired in 2017 by NASA's Uninhabited Aerial Vehicle Synthetic Aperture Radar over Alaska and Western Canada. We demonstrate how InSAR measurement uncertainties are mitigated by these calibration methods and quantify remaining measurement uncertainties with a novel method of modeling interferometric phase uncertainty using a Gaussian mixture model. Finally, we discuss the impact of native SAR resolution on InSAR measurements, the limitation of using few interferograms per retrieval, and the implications of our findings for cross‐comparison of airborne and spaceborne InSAR datasets acquired over Arctic regions underlain by permafrost.

Explanation of InSAR Phase Disturbances by Seasonal Characteristics of Soil and Vegetation

Seasonal phase disturbances in satellite Interferometric Synthetic Aperture Radar (InSAR) measurements have been reported in other studies to suggest sub-centimetre land surface terrain motion. These have been interpreted in various ways because they correlate with multiple other (sub-)seasonal signatures of, e.g., clay swelling/shrinkage and groundwater level. Recent microwave radar studies mention the occurrence of phase disturbances in different soil types and soil moisture. This study further explored this topic by modeling phase disturbances caused by both soil and vegetation surface characteristics and aimed to interpret what their possible effects on InSAR-interpreted terrain motion is. Our models, based on fundamental microwave reflection and transmission theory, found phase disturbances caused by seasonal variation of soil and vegetation that have the same magnitude as interpreted seasonal land movement in earlier InSAR studies. We showed that small, temporal differences in soil moisture and vegetation can lead to relatively large phase disturbances in InSAR measurements. These disturbances are a result of waves having to comply with boundary conditions at the interface between media with different dielectric properties. The findings of this study explain the seasonal variations found in other InSAR studies and will therefore bring new insights and alternative explanations to help improve interpretation of InSAR-derived seasonal terrain motion.

Interferometric synthetic aperture radar study of recent eruptive activity at Shrub mud volcano, Alaska

Shrub mud volcano is one of three large mud volcanoes that comprise the Klawasi Group in the Copper River Basin of southcentral Alaska. Except for minor discharges in the mid-1950s when the group was first described, Shrub was dormant prior to its reactivation in summer 1996. From 1997 to 1999, Shrub vigorously erupted more than 5 × 105 m3 of saline mud and CO2-rich gas at temperatures as high as 54 °C. Thereafter, activity waned but continued at least through 2015. We analyzed 192 interferograms derived from 106 synthetic aperture radar (SAR) images acquired by the JERS-1 (L-band), ERS-1/2 (C-band), RADARSAT-1 (C-band), and ALOS PALSAR (L-band) satellites to characterize ground deformation at Shrub before, during, and after its reactivation. Collectively, the interferograms span 1992–2000 and 2006–2011. We fit the observations with two deformation sources: a deflating, steeply-dipping, pipe-like body under the summit area and an inflating, shallow-dipping, sill-like body under the southwest flank. Both sources are shallow, with centroids less than 1 km beneath the summit. Prior to reactivation, the flank source inflated ~0.35 × 105 m3/yr from July 1992 to May 1996. During eruptive activity, the summit source deflated at higher rates that peaked at ~8.71 × 105 m3/yr during May–November 1997 and continued at ~0.95 × 105 m3/yr during the 2006–2011 observation window. Cumulative source-volume loss is comparable to the volume of mud erupted. We interpret the summit source as the volcano's feeder conduit that pressurized prior to the first SAR observation in 1992. Also before 1992, the conduit ruptured to feed a lateral intrusion of mud under the southwest flank, perhaps along a bedding plane in underlying glaciolacustrine deposits. The growing sill caused the southwest flank to inflate while it accommodated the mud supply from depth, which explains why we observed pre-eruptive inflation of the flank but not the summit. The summit began deflating when the conduit ruptured to the surface at the onset of eruptive activity. The flank source did not deflate concurrently because the weight of the thin overburden was insufficient to collapse the sill. There is a suggestion in the modern topography that lateral intrusions under Shrub's southwest flank are a common feature of activity there.

Using Persistent Scatterer Interferometry to Map and Quantify Permafrost Thaw Subsidence: A Case Study of Eboling Mountain on the Qinghai‐Tibet Plateau

AbstractPermafrost thaw subsidence, a key indicator of permafrost degradation, remains poorly quantified or understood. It is particularly challenging to detect and measure surface subsidence due to the loss of subsurface ice over a large area because it usually develops gradually, over several years or decades. Here we utilize the persistent scatterer interferometric synthetic aperture radar (PSI) approach to remotely measure gradual surface subsidence on Eboling Mountain in the northeastern region of the Qinghai‐Tibet Plateau, where thermal erosion gullies are well developed. Most of the previous multitemporal interferometric synthetic aperture radar studies on permafrost used the small baseline subset method. By contrast, the PSI approach benefits from the full spatial resolution and is less affected by temporal or geometric decorrelation. In the PSI analysis, we incorporate a piecewise elevation change model that includes periodic subsidence/uplift because of its seasonally varying components as well as its linear subsidence trends. Applying this permafrost‐designated PSI algorithm to 17‐L band ALOS‐1 PALSAR images taken between 2006 and 2011, we find that both the thermal erosion gullies and the surrounding regions (within about 300 m) subside gradually. The subsidence trends range from 0.3 to 3 cm/yr. This suggests that permafrost areas near the gullies are more vulnerable to gradual thawing and degradation. This study demonstrates the potential of using PSI to study permafrost thaw processes and of assessing its impacts over vast areas on the Qinghai‐Tibet Plateau and in the Arctic.

An L-band interferometric synthetic aperture radar study on the Ganos section of the north Anatolian fault zone between 2007 and 2011: Evidence for along strike segmentation and creep in a shallow fault patch

We utilize L-band interferometric synthetic aperture radar (InSAR) data in this study to retrieve a ground velocity map for the near field of the Ganos section of the north Anatolian fault (NAF) zone. The segmentation and creep distribution of this section, which last ruptured in 1912 to generate a moment magnitude (Mw)7.3 earthquake, remains incompletely understood. Because InSAR processing removes the mean orbital plane, we do not investigate large scale displacements due to regional tectonics in this study as these can be determined using global positioning system (GPS) data, instead concentrating on the close-to-the-fault displacement field. Our aim is to determine whether, or not, it is possible to retrieve robust near field velocity maps from stacking L-band interferograms, combining both single and dual polarization SAR data. In addition, we discuss whether a crustal velocity map can be used to complement GPS observations in an attempt to discriminate the present-day surface displacement of the Ganos fault (GF) across multiple segments. Finally, we characterize the spatial distribution of creep on shallow patches along multiple along-strike segments at shallow depths. Our results suggest the presence of fault segmentation along strike as well as creep on the shallow part of the fault (i.e. the existence of a shallow creeping patch) or the presence of a smoother section on the fault plane. Data imply a heterogeneous fault plane with more complex mechanics than previously thought. Because this study improves our knowledge of the mechanisms underlying the GF, our results have implications for local seismic hazard assessment.

Which Fault Segments Ruptured in the 2008 Wenchuan Earthquake and Which Did Not? New Evidence from Near‐Fault 3D Surface Displacements Derived from SAR Image Offsets

The 2008 M w 7.9 Wenchuan earthquake ruptured a complex thrust‐faulting system at the eastern edge of the Tibetan plateau and west of Sichuan basin. Though the earthquake has been extensively studied, several details about the earthquake, such as which fault segments were activated in the earthquake, are still not clear. This is in part due to difficult field access to the fault zone and in part due to limited near‐fault observations in Interferometric Synthetic Aperture Radar (InSAR) observations because of decorrelation. In this study, we address this problem by estimating SAR image offsets that provide near‐fault ground displacement information and exhibit clear displacement discontinuities across activated fault segments. We begin by reanalyzing the coseismic InSAR observations of the earthquake and then mostly eliminate the strong ionospheric signals that were plaguing previous studies by using additional postevent images. We also estimate the SAR image offsets and use their results to retrieve the full 3D coseismic surface displacement field. The coseismic deformation from the InSAR and image‐offset measurements are compared with both Global Positioning System and field observations. The results indicate that our observations provide significantly better information than previous InSAR studies that were affected by ionospheric disturbances. We use the results to present details of the surface‐faulting offsets along the Beichuan fault from the southwest to the northeast and find that there is an obvious right‐lateral strike‐slip component (as well as thrust faulting) along the southern Beichuan fault (in Yingxiu County), which was strongly underestimated in earlier studies. Based on the results, we provide new evidence to show that the Qingchuan fault was not ruptured in the 2008 Wenchuan earthquake, a topic debated in field observation studies, but show instead that surface faulting occurred on a northward extension of the Beichuan fault during or immediately following the mainshock. [Electronic Supplement:][1] Parallel ascending‐orbit track coseismic deformation. [1]: http://www.bssaonline.org/lookup/suppl/doi:10.1785/0120160126/-/DC1

Mapping ground surface deformation using temporarily coherent point SAR interferometry: Application to Los Angeles Basin

Multi-temporal interferometric synthetic aperture radar (InSAR) is an effective tool to detect long-term seismotectonic motions by reducing the atmospheric artifacts, thereby providing more precise deformation signal. The commonly used approaches such as persistent scatterer InSAR (PSInSAR) and small baseline subset (SBAS) algorithms need to resolve the phase ambiguities in interferogram stacks either by searching a predefined solution space or by sparse phase unwrapping methods; however the efficiency and the success of phase unwrapping cannot be guaranteed. We present here an alternative approach – temporarily coherent point (TCP) InSAR (TCPInSAR) – to estimate the long term deformation rate without the need of phase unwrapping. The proposed approach has a series of innovations including TCP identification, TCP network and TCP least squares estimator. We apply the proposed method to the Los Angeles Basin in southern California where structurally active faults are believed capable of generating damaging earthquakes. The analysis is based on 55 interferograms from 32 ERS-1/2 images acquired during Oct. 1995 and Dec. 2000. To evaluate the performance of TCPInSAR on a small set of observations, a test with half of interferometric pairs is also performed. The retrieved TCPInSAR measurements have been validated by a comparison with GPS observations from Southern California Integrated GPS Network. Our result presents a similar deformation pattern as shown in past InSAR studies but with a smaller average standard deviation (4.6 mm) compared with GPS observations, indicating that TCPInSAR is a promising alternative for efficiently mapping ground deformation even from a relatively smaller set of interferograms.

Global compilation of interferometric synthetic aperture radar earthquake source models: 1. Comparisons with seismic catalogs

[1] While many earthquakes have now been studied using interferometric synthetic aperture radar (InSAR) data, a full assessment of the quality and additional value of InSAR source parameters compared to seismological techniques is still lacking. We compile a catalog of source models obtained using InSAR and estimate the corresponding centroid moment tensor (CMT) parameters; we refer to this compilation as the ICMT archive. We compare source parameters from over 70 InSAR studies of 57 global earthquakes with those in the Global CMT (GCMT), International Seismological Centre (ISC) and Engdahl‐Hilst‐Buland (EHB) seismic catalogs. We find an overall good agreement between fault strike, dip and rake values in the GCMT and ICMT archives. Likewise, the differences in seismic moment between these two archives are relatively small, and we do not find support for previously suggested trends of InSAR leading to larger moments than seismic data. However, epicentral locations show substantial discrepancies, which are larger for the GCMT (median differences of ∼21 km) than for the EHB and ISC catalogs (median differences of ∼10 km). Since InSAR data have a high spatial resolution, and thus should map epicentral locations accurately, this allows us to obtain a first independent estimate of epicentral location errors in the seismic catalogs. Earthquake depths from InSAR are systematically shallower than those in the EHB catalog, with a median of differences of ∼5 km. While this trend may be partly due to unmodeled crustal complexity, it is also compatible with the observation that the rupture of crustal earthquakes tends to propagate upward in the seismogenic layer.

On the importance of path for phase unwrapping in synthetic aperture radar interferometry

Phase unwrapping is a key procedure in interferometric synthetic aperture radar studies, translating ambiguous phase observations to topography, and surface deformation estimates. Some unwrapping algorithms are conducted along specific paths based on different selection criteria. In this study, we analyze six unwrapping paths: line scan, maximum coherence, phase derivative variance, phase derivative variance with branch-cut, second-derivative reliability, and the Fisher distance. The latter is a new path algorithm based on Fisher information theory, which combines the phase derivative with the expected variance to get a more robust path, potentially performing better than others in the case of low image quality. In order to compare only the performance of the paths, the same unwrapping function (phase derivative integral) is used. Results indicate that the Fisher distance algorithm gives better results in most cases.

A structural, geomorphological and InSAR study of an active rock slope failure development

AbstractFew studies of rockslides have addressed the relationships between structures, geomorphological expression and direct evidence for movement. We employ structural geology, geomorphology and interferometric synthetic aperture radar (InSAR) to investigate the evolution of the surface features developed in response to movement of the Gamanjunni rockslide site in Troms County in northern Norway. The slide is located on a west-facing mountainside, and is bounded by two angled back scarps and a 20°–30° basal sliding plane. The volume is estimated at 24 Mm3 and is therefore among the largest potential rockslides in Norway. InSAR provides a new method to measure the movement of potential rockslides, and thus provides a direct link between qualitative movement data and field observations. We document the relationship between variations in ground movement rates and changing back-scarp geomorphology at the Gamanjunni site as well as movement patterns within the incipient rockslide. We demonstrate that variations in InSAR documents millimetre variations in scarp displacement and that this is reflected in the evolving back-scarp geometry. We conclude that InSAR can provide important information to complement field observations. The ability of InSAR to document landslide movement patterns greatly extends our knowledge of back-scarp evolution and active landslide processes.

Applying InSAR technique to accurately relocate the epicentre for the 1999Ms= 5.6 Kuqa earthquake in Xinjiang province, China

SUMMARY The 1999 M s = 5.6 Kuqa earthquake occurred in a seismically active belt between the Tianshan Mountain and the Traim basin. Because of the sparse seismic network and complex crustal structure, it is very difficult to accurately locate the epicentre for this event using seismic waves. The epicentres located by different research groups vary over a spatial range of 20– 40 km. Interferometric synthetic aperture radar (InSAR) is a geodetic technique with fine spatial resolution, good precision and wide coverage. An interferometric map of the epicentral region constrains the epicentre of this event. The arid climate and sparsely vegetation in the Kuqa region provide excellent conditions for InSAR studies. In this paper, we firstly construct a interferogram to map the coseismic deformation field due to the 1999 Kuqa earthquake using a coseismic interferometric pair of radar images acquired by the ESA ERS-2 satellite. Then, we develop a new geocoding method and apply it to the interferogram. Next, we infer the geometry of the seismogenic fault according to its focal mechanism and tectonic setting. To model the interferogram, we assume a dislocation buried in a uniform elastic half-space. Finally, we infer the epicentre of this earthquake to be located at (82.80 ◦ E, 41.92 ◦ N), which is close to the results of the National Earthquake Information Center of USGS and China Earthquake Administration. The epicentre location inferred from InSAR falls in the six-level isoseismal contour described by Xinjiang earthquake administration using the field investigations.

Monitoring post-mining subsidence in the Nord-Pas-de-Calais coal basin (France): comparison between interferometric SAR results and levelling

The interferometric synthetic aperture radar (InSAR) technique is used to detect surface deformations in the French Nord-Pas-de-Calais coal mining basin. Several subsiding areas had already been observed at the sites of Lens, Billy-Montigny, Courrières and Ostricourt during the 1992–2000 period. InSAR deformation measurements are compared with ground-based levelling measurements and an analysis of the results shows a good agreement for the relative deformations. However, the InSAR study reveals a systematic bias of the absolute levelling values. Our interpretation is that the stability points of the ground-based monitoring network probably moved during the study period. Such cross-checking is particularly important considering the current legal value of the levelling measurements.

Structure and mechanical properties of faults in the North Anatolian Fault system from InSAR observations of coseismic deformation due to the 1999 Izmit (Turkey) earthquake

We study the structure and mechanical properties of faults in the North Anatolian Fault system by observing near‐fault deformation induced by the 1999 Mw 7.4 Izmit earthquake (Turkey). We use interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System observations to analyze the coseismic surface deformation in the near field of the Izmit rupture. The overall observed coseismic deformation is consistent with deformation predicted by a dislocation model assuming a uniform elastic crust. Previous InSAR studies revealed small‐scale changes in the radar range across the nearby faults of the North Anatolian fault system (in particular, the Mudurnu Valley and Iznik faults) (e.g., Wright et al., 2001). We demonstrate that these anomalous range changes are consistent with an elastic response of compliant fault zones to the stress perturbation induced by the Izmit earthquake. We examine the spatial variations and mechanical properties of fault zones around the Mudurnu Valley and Iznik faults using three‐dimensional finite element models. In these models, we include compliant fault zones having various geometries and elastic properties and apply stress changes deduced from a kinematic slip model of the Izmit earthquake. The best fitting models suggest that the inferred fault zones have a characteristic width of a few kilometers, depth in excess of 10 km, and reductions in the effective shear modulus of about a factor of 3 compared to the surrounding rocks. The characteristic width of the best fitting fault zone models is consistent with field observations along the North Anatolian Fault system (Ambraseys, 1970). Our results are also in agreement with InSAR observations of small‐scale deformation on faults in the Eastern California Shear Zone in response to the 1992 Landers and 1999 Hector Mine earthquakes (Fialko et al., 2002; Fialko, 2004). The inferred compliant fault zones likely represent intense damage and may be quite commonly associated with large crustal faults.

InSAR Imaging of Volcanic Deformation over Cloud-prone Areas – Aleutian Islands

Interferometric synthetic aperture radar (INSAR) is capable of measuring ground-surface deformation with centimeter-tosubcentimeter precision and spatial resolution of tens-ofmeters over a relatively large region. With its global coverage and all-weather imaging capability, INSAR is an important technique for measuring ground-surface deformation of volcanoes over cloud-prone and rainy regions such as the Aleutian Islands, where only less than 5 percent of optical imagery is usable due to inclement weather conditions. The spatial distribution of surface deformation data, derived from INSAR images, enables the construction of detailed mechanical models to enhance the study of magmatic processes. This paper reviews the basics of INSAR for volcanic deformation mapping and the INSAR studies of ten Aleutian volcanoes associated with both eruptive and noneruptive activity. These studies demonstrate that all-weather INSAR imaging can improve our understanding of how the Aleutian volcanoes work and enhance our capability to predict future eruptions and associated hazards.

Interferometric synthetic aperture radar study of Okmok volcano, Alaska, 1992–2003: Magma supply dynamics and postemplacement lava flow deformation

Okmok volcano, located in the central Aleutian arc, Alaska, is a dominantly basaltic complex topped with a 10‐km‐wide caldera that formed circa 2.05 ka. Okmok erupted several times during the 20th century, most recently in 1997; eruptions in 1945, 1958, and 1997 produced lava flows within the caldera. We used 80 interferometric synthetic aperture radar (InSAR) images (interferograms) to study transient deformation of the volcano before, during, and after the 1997 eruption. Point source models suggest that a magma reservoir at a depth of 3.2 km below sea level, located beneath the center of the caldera and about 5 km northeast of the 1997 vent, is responsible for observed volcano‐wide deformation. The preeruption uplift rate decreased from about 10 cm yr−1 during 1992–1993 to 2 ∼ 3 cm yr−1 during 1993–1995 and then to about −1 ∼ −2 cm yr−1 during 1995–1996. The posteruption inflation rate generally decreased with time during 1997–2001, but increased significantly during 2001–2003. By the summer of 2003, 30 ∼ 60% of the magma volume lost from the reservoir in the 1997 eruption had been replenished. Interferograms for periods before the 1997 eruption indicate consistent subsidence of the surface of the 1958 lava flows, most likely due to thermal contraction. Interferograms for periods after the eruption suggest at least four distinct deformation processes: (1) volcano‐wide inflation due to replenishment of the shallow magma reservoir, (2) subsidence of the 1997 lava flows, most likely due to thermal contraction, (3) deformation of the 1958 lava flows due to loading by the 1997 flows, and (4) continuing subsidence of 1958 lava flows buried beneath 1997 flows. Our results provide insights into the postemplacement behavior of lava flows and have cautionary implications for the interpretation of inflation patterns at active volcanoes.