Determining why earthquake ruptures stop is a central challenge in earthquake science and seismic hazard assessment. The P & uuml;t & uuml;rge segment of the East Anatolian Fault Zone, T & uuml;rkiye, exhibits shallow creep ( 6.5 earthquake ruptures at greater depth. Here, we evaluate whether variations in frictional stability along this segment aided arrest of the 2020 M 6.7 Elazi & gbreve; and 2023 M 7.8 Pazarc & imath;k earthquake ruptures. Analysis of Sentinel-1 Synthetic Aperture Radar imagery indicates the 2023 M 7.8 rupture propagated laterally into a metamorphic massif within the P & uuml;t & uuml;rge segment, where slip rapidly decayed below detection limits. Creepmeters along this segment recorded no significant surface afterslip (<3 mm) in the following year. To investigate this fault-slip behavior, we conducted triaxial friction experiments on P & uuml;t & uuml;rge fault gouge sampled from an outcrop exposure. The gouge, composed primarily of muscovite, quartz, and calcite, is velocity strengthening at conditions approximating 0-2.5 km depth and velocity weakening at 4-5 km depth. This transition to velocity-weakening friction is associated with enhanced comminution and shear localization observed microstructurally. Our results suggest that depth-dependent frictional stability of the P & uuml;t & uuml;rge fault segment facilitates rupture nucleation and propagation at depth while maintaining rupture-arresting behavior near Earth's surface.

The shallower portions of subduction zone megathrust faults host Earth's most hazardous tsunamigenic earthquakes, yet understanding how and when they slip remains elusive because of challenges making seafloor observations. We performed Global Navigation Satellite System Acoustic seafloor geodetic surveys before and ~2.5 months after the 29 July 2021 Mw (moment magnitude) 8.2 Chignik, Alaska, earthquake and determine ~1.4 meters cumulative co- and post-seismic horizontal displacement ~60 kilometers from the megathrust front. Only for the 2011 Mw 9 Tohoku event have closer subduction zone earthquake displacements been observed. We estimate ~2 to 3 meters of megathrust afterslip shallower than 20 kilometers, a portion of the megathrust on which both inter- and co-seismic slip likely had occurred previously. Our analysis demonstrates that by 2.5 months, shallower and deeper moment had effectively equilibrated on the megathrust, suggesting that its tsunamigenic potential remains no more elevated than before the earthquake.

Abstract The 22 July 2020 Mw7.8 Simeonof earthquake was a deep megathrust event that ruptured along the Shumagin segment of the Alaska‐Aleutian subduction zone. This earthquake occurred ∼250 km from a seafloor geodetic GNSS‐Acoustic site IVB1, where we observed a velocity of 3.78 ± 1.15 cm/yr with the down‐going slab prior to the earthquake followed by 0.6 ± 0.7 eastward and −15.5 ± 0.8 cm northward coseismic offset. We computed a slip model of the coseismic rupture using the static offset at IVB1 alongside regional continuous GNSS and strong motion stations. The small static horizontal offset at the site precludes significantly shallower rupture than previously inferred from terrestrial observations, confirming that the Simeonof earthquake was a deep megathrust earthquake. The observed site velocity implies partial locking prior to the earthquake, implying significant shallow strain accumulation such that the small coseismic offset is unlikely to have relieved all of the accumulated strain since the last coseismic rupture.

Abstract Background Robotic surgery is widely spreading in many centers across the United Kingdom. Potential benefits include shorter admissions, fewer complications as well as better surgeon ergonomics and dexterity. Evidence suggests that robotic surgery has a rapid learning curve when first implemented with the number of cases linked to operative time. In this study, we report our preliminary results after implementation of robotic surgery at our upper gastrointestinal unit. Methods This retrospective study included all robotic elective upper gastrointestinal cases since the introduction of robotic surgery at our unit. All cases were performed by two surgeons using Da Vinci XI starting in August 2022. The first 100 cases were completed in 10 months. Both surgeons completed Intuitive training prior to initiating their independent operating lists. Cholecystectomy and anti-reflux surgeries were the main surgeries performed during the study period. Demographics, number of cases per list, console timing and postoperative complications were collected and analysed. Console timing was obtained by Intuitive software. Postoperative complications were graded using the Clavien-Dindo scale. Results 100 UGI robotic surgery cases were analysed consisting of 86 cholecystectomies and 14 anti-reflux operations. Females represented the majority of cases (68%). Mean age was 53.0 years (18-78) while mean ASA and BMI were 2 and 30.3 kg/m2 respectively. Mean console time was 53.3 minutes. Cholecystectomies required 43.0 minutes and anti-reflux surgeries required 119.3 minutes on average. The mean length of stay was 0.90 days for cholecystectomies, and 1.46 days for anti-reflux surgery. There were two readmissions post cholecystectomy for pneumonia and liver bed collection. One cholecystectomy patient developed a Clavien-Dindo grade >3 complication for port site hernia repair. Conclusions Our initial experience has shown favourable outcomes of robotic surgery. There was a noticeable rapid learning curve, encountering only one major post-operative complication. This high effectiveness should stimulate the swift introduction of robotic surgery to other hospitals.

Faults often form through reactivation of pre-existing structures, developing geometries and mechanical properties specific to the system's geologic inheritance. Competition between fault geometry and other factors (e.g., lithology) to control slip at Earth's surface is an open question that is central to our knowledge of fault processes and seismic hazards. Here we use remote sensing data and field observations to investigate the origin of the 2019 M7.1 Ridgecrest, California, earthquake rupture geometry and test its impact on the slip distribution observed at Earth's surface. Common geometries suggest the fault system evolved through reactivation of structures within the surrounding Independence dike swarm (IDS). Mechanical models testing a range of fault geometries and stress fields indicate that the inherited rupture geometry strongly controlled the M7.1 earthquake slip distribution. These results motivate revisiting the development of other large-magnitude earthquake ruptures (1992 M7.3 Landers, 1999 M7.1 Hector Mine) and tectonic provinces within the IDS.

Kenneth W. Hudnut, Benjamin A. Brooks, Katherine Scharer, Janis L. Hernandez, Timothy E. Dawson, Michael E. Oskin, J. Ramon Arrowsmith, Christine A. Goulet, Kelly Blake, Matthew L. Boggs, Stephan Bork, Craig L. Glennie, Juan Carlos Fernandez‐Diaz, Abhinav Singhania, Darren Hauser, and Sven Sorhus. "Airborne Lidar and Electro‐Optical Imagery along Surface Ruptures of the 2019 Ridgecrest Earthquake Sequence, Southern California." Seismological Research Letters 91, no. 4 (2020): 2096–2107. doi: 10.1785/0220190338.

Abstract Quantifying off-fault deformation in the near field remains a challenge for earthquake monitoring using geodetic observations. We propose an automated change detection strategy using geometric primitives generated using a deep neural network, random sample consensus and least squares adjustment. Using mobile laser scanning point clouds of vineyards acquired after the magnitude 6.0 2014 South Napa earthquake, our results reveal centimeter-level horizontal ground deformation over three kilometers along a segment of the West Napa Fault. A fault trace is detected from rows of vineyards modeled as planar primitives from the accumulated coseismic response, and the postseismic surface displacement field is revealed by tracking displacements of vineyard posts modeled as cylindrical primitives. Interpreted from the detected changes, we summarized distributions of deformation versus off-fault distances and found evidence of off-fault deformation. The proposed framework using geometric primitives is shown to be accurate and practical for detection of near-field off-fault deformation.

ABSTRACT The 2019 Ridgecrest, California, earthquake sequence involved predominantly right-lateral strike slip on a northwest–southeast-trending subvertical fault in the 6 July M 7.1 mainshock, preceded by left-lateral strike slip on a northeast–southwest-trending subvertical fault in the 4 July M 6.4 foreshock. To characterize the postseismic deformation, we assemble displacements measured by Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar. The geodetic measurements illuminate vigorous postseismic deformation for at least 21 months following the earthquake sequence. The postseismic transient deformation is particularly well constrained from survey-mode GPS (sGPS) in the epicentral region carried out during the weeks after the mainshock. We interpret these observations with mechanical models including afterslip and viscoelastic relaxation of the lower crust and mantle asthenosphere. During the first 21 months, up to several centimeters of horizontal motions are measured at continuous GPS and sGPS sites, with amplitude that diminishes slowly with distance from the mainshock rupture, suggestive of deeper afterslip or viscoelastic relaxation. We find that although afterslip involving right-lateral strike slip along the mainshock fault traces and their deeper extensions reach a few decimeters, most postseismic deformation is attributable to viscoelastic relaxation of the lower crust and mantle. Within the Basin and Range crust and mantle, we infer a transient lower crust viscosity several times that of the mantle asthenosphere. The transient mantle asthenosphere viscosity is ∼1.3×1017 Pa s, and the adjacent Central Valley transient mantle asthenosphere viscosity is ∼7×1017 Pa s, about five times higher and consistent with an asymmetry in postseismic horizontal motions across the mainshock surface rupture.

Abstract We show that a fixed smartphone network can provide robust Earthquake Early Warning for at least two orders of magnitude less cost than scientific‐grade networks. Our software and cloud‐based data architecture that we have constructed for the Alerta Sismica Temprana Utilizando Teléfonos Inteligentes (ASTUTI; Earthquake Early Warning Utilizing Smartphones) network in Costa Rica is easily scaled and exported. Implementation comprises provisioning and installing modern smartphones in judicious locations. Stand‐up time for regionally operational networks can be on the order of days. We evaluated a non‐parametric ground‐motion detection and alerting strategy that would alert the entire Costa Rican population of any event with a ground motion detection threshold of 0.55–0.65 %g at four neighboring stations. During a 6‐month evaluation period ASTUTI detected and alerted on five of 13 earthquakes with Mw 4.8–5.3 that caused felt Modified Mercalli Intensity shaking levels of 4.3–6. The system did not produce any false alerts and the undetected events did not produce wide‐spread or significant felt shaking. System latencies were less than or similar to scientific‐grade latencies. Alerts for all five detected events would have reached the capital city, San Jose, before strong S‐wave shaking. This would have afforded time for Drop Cover Hold On actions by most residents. Two of the five alerts were triggered by P‐waves suggesting that smartphone‐based networks could approach the fastest theoretical EEW performance, especially with future expected improvements in smartphone sensors and processing algorithms.

Abstract The ShakeAlert earthquake early warning (EEW) system issues public alerts in California and will soon extend to Oregon and Washington. The Cascadia subduction zone presents significant new challenges and opportunities for EEW. Initial publications suggested that EEW algorithms based on Global Navigation Satellite System (GNSS) data could provide improved warning for intraslab events and dramatically improved warning for offshore megathrust events, both of which contribute significantly to hazard in Cascadia. We find that some expectations in these publications were unrealistic, and we demonstrate that in general geodetic algorithms would not produce timely warnings for intraslab events nor warning times of two minutes or more for severe shaking from megathrust earthquakes. Nonetheless, lessons from recent earthquakes in Japan and California, for which alerts from seismic algorithms suffered from magnitude saturation and high data latencies, demonstrate the urgent need for rigorous testing of geodetic EEW as a potential complement to seismic EEW.

High resolution and high accuracy distributed detection of fault creep deformation remains challenging given limited observations and associated change detection strategies. A mobile laser scanning-based change detection method that is capable of measuring centimeter-level near-field (<150 m from fault) deformation is described. The methodology leverages the use of man-made features in the built environment as geodetic markers that can be temporally tracked. The proposed framework consists of a RANSAC-based corresponding plane detector and a combined least squares displacement estimator. Using repeat mobile laser scanning data collected in 2015 and 2017 on a 2 ​km segment of the Hayward fault, near-field fault creep displacement and non-linear creep deformation are estimated. The detection results reveal 2.5 ​± ​1.5 ​cm of accumulated fault parallel creep displacement in the far-field. The laser scanning estimates of displacement match collocated alinement array observations at the 4 ​mm level in the near field. The proposed change detection framework is shown to be accurate and practical for fault creep displacement detection in the near field and the detected non-linear creep displacement patterns will help elucidate the complex physics of surface faulting.

Cite this article as Brooks, B. A., J. Murray, J. Svarc, E. Phillips, R. Turner, M. Murray, T. Ericksen, K. Wang, S. Minson, R. Burgmann, et al. (2020). Rapid Geodetic Observations of Spatiotemporally Varying Postseismic Deformation Following the Ridgecrest Earthquake Sequence: The U.S. Geological Survey Response, Seismol. Res. Lett. XX, 1–16, doi: 10.1785/0220200007. Supplemental Material The U.S. Geological Survey’s geodetic response to the 4–5 July 2019 (Pacific time) Ridgecrest earthquake sequence comprised primarily the installation and/or reoccupation of Global Navigation Satellite System (GNSS) monumentation. Our response focused primarily on theUnited States’Navy’s China Lake Naval AirWeapons Station base (NAWSCL). This focuswas becausemuch of the surface rupture occurred on theNAWSCL and because of NAWSCL access restrictions only permitting Federal and State of California personnel. In total, we measured or are still measuring at 24 sites, 14 of which were on the NAWSCL and, as of this writing, operational. The majority of sites were set up as continuous stations logging at either 1 sample per second or 1 sample per 15 s. Two stationswere recording a 200 m cross-rupture aperture starting ∼10 hr after the M 6.4 event, and they recorded the coseismic displacements of the M 7.1. Approximately, 1 hr after the M 7.1 event, two new stations were recording a ∼200 m cross-rupture aperture of the surface rupture. In the days following, we established the rest of the stations ranging to a distance of ∼ 15 km from the M 7.1 principal rupture trace. The lack of differential displacement across the M 6.4 rupture during the M 7.1 event suggests that it did not reactivate theM 6.4 plane. The lack of differential cross-fault displacement for both events suggests that rapid shallow afterslip did not occur at those two locations. The postseismic time series from these stations shows centimeters of horizontal displacement over periods of a few months. They record a mixture of fault-parallel and fault-normal displacements that, in conjunction with analysis of more spatially complete Interferometric Synthetic Aperture Radar displacement fields, suggest that both poroelastic and afterslip phenomena occur along the M 6.4 and 7.1 rupture planes. Using preliminary data from these and other regional stations, we also explore the Ridgecrest sequence’s effect on regional GNSS time series and the differentiation of long-term postseismic motions and secular deformation rates. We find that redefining a common-mode noise filter using different GNSS stations that are assumed to be unaffected by the earthquakes results in small but systematic differences in the regional velocity field estimate. Introduction The southern California 2019 Ridgecrest earthquake sequence from 4 to 5 July (Pacific time) was a multifault rupture comprising a left-lateral M 6.4 foreshock (∼11:7 km depth) on a northeast-trending fault plane followed ∼34 hr later by a right-lateral M 7.1 (∼8 km depth) mainshock on a 1. Earthquake Science Center, U.S. Geological Survey, Moffett Field, California, U.S.A.; 2. Earthquake Science Center, U.S. Geological Survey, Menlo Park, California, U.S.A.; 3. Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, California, U.S.A.; 4. Earthquake Science Center, U.S. Geological Survey, Pasadena, California, U.S.A.; 5. Earthquake Science Center, U.S. Geological Survey, Vancouver, Washington, U.S.A.; 6. California Geological Survey, Los Angeles, California, U.S.A. *Corresponding author: bbrooks@usgs.gov © Seismological Society of America Volume XX • Number XX • – 2020 • www.srl-online.org Seismological Research Letters 1 Downloaded from https://pubs.geoscienceworld.org/ssa/srl/article-pdf/doi/10.1785/0220200007/5049208/srl-2020007.1.pdf by University of California Berkeley Library user on 01 June 2020 northwest-trending fault plane (Ross et al., 2019; Stewart et al., 2019) (Fig. 1a). Both events produced substantial surface rupture (∼1–5 m) measured over distances of 10s of kilometers (Stewart et al., 2019). Although previously unmapped, the causative faults reside in the Little Lake fault zone, a northwest-trending series of faults that occur in a complicated portion of the Eastern California Shear Zone (ECSZ) that is ∼25 km east of the southern terminus of the southern Sierra Nevada fault zone (itself the western limit of Basin and Range extension) and ∼15 km north of the east-northeast–westsouthwest-trending left-lateral Garlock fault. As a result of this setting, the region experiences a complicated background combination of right-lateral ECSZ-related stress, extensional stress from Basin and Range deformation, and left-lateral, Garlock-related stress (Becker et al., 2005). Given that it was the first major seismic event in southern California for two decades, the Ridgecrest sequence generated a substantial amount of scientific interest and research. Early reports have focused on the surface disruption (Stewart et al., 2019) and multifault nature of the sequence (Ross et al., 2019). Here, we report on the rapid geodetic response to the Ridgecrest sequence led by the U.S. Geological Survey (USGS). Much of the surface rupture for both events occurred within the limits of the United States’ Navy’s China Lake Naval Air Weapons Station base (NAWSCL). Because of NAWSCL access restrictions, USGS and California Geological Survey personnel were the only scientists permitted onsite and to deploy equipment. Immediately following the M 6.4 event, our team maintained close contact and collaboration with the large group of academic geodetic researchers from the Southern California Earthquake Center (SCEC) (Floyd et al., 2020). Our principal scientific objective is to better understand postseismic deformation processes—both the surface deformation they produce and, through inference, the physical processes controlling slip on the fault planes. The spatiotemporal signatures of different postseismic processes such as poroelastic rebound and dilation (Peltzer et al., 1996), fault afterslip (Marone et al., 1991), and viscoelastic relaxation (Pollitz et al., 2001; Bürgmann and Dresen, 2008) are fundamental characteristics of continental lithosphere that can only be studied following infrequent seismic events. The postseismic response to crustal faulting still poses first-order questions: what is the relative contribution of fault afterslip versus viscoelastic mantle relaxation? When and why do poroelastic postseismic responses occur? Why do some faults have shallow afterslip and others not? For instance, the large amount of shallow, rapid afterslip for the Mw 6.0 South Napa earthquake was a surprise (Floyd et al., 2016; Brooks et al., 2017). The shallowest portion of seismogenic faults (<1 km depth) has gained much recent attention, in particular, because of the significant increase in sensing capability for near-field surface 0 75 150 km −122° −120° −118° −116° −114° 34° 36° 38° 40° (a) Figure 1. (a) Regional location map showing western U.S. state boundaries andmapped Quaternary fault traces (red lines). The blue box indicates the study area and Ridgecrest earthquakes surface rupture (black lines) shown in (b). (b) Study area showing the city of Ridgecrest, location of the China Lake Naval Air Weapons Station base (NAWSCL) (cyan lines), mapped Quaternary faults (pink lines), the Ridgecrest earthquake sequence surface rupture trace (red lines, C. B. DuRoss et al., unpublished manuscript, see Data and Resources), Plate Boundary Observatory continuous stations (yellow squares), and stations installed or occupied as part of this study (green squares). Red vectors are coseismic displacements estimated for the M 7.1 event. Note that displacements from stations RCRW and RCRE are so similar, they plot on top of one another. GF, Garlock fault; LLFZ, Little Lake fault zone; SNFZ, Sierra Nevada fault zone. Stations RCRW and RCRE as well as 71RW and 71RE are along Highway 178. Spray-paint markers discussed in the Instrument Deployment and Details section were installed between each of these two locations.(Continued) 2 Seismological Research Letters www.srl-online.org • Volume XX • Number XX • – 2020 Downloaded from https://pubs.geoscienceworld.org/ssa/srl/article-pdf/doi/10.1785/0220200007/5049208/srl-2020007.1.pdf by University of California Berkeley Library user on 01 June 2020 deformation (Nissen et al., 2014; Zinke et al., 2014; Milliner et al., 2015; Brooks et al., 2017). Given that historical surface ruptures predominate in the databases from which empirical relations for seismic hazard analyses are derived (Wesnousky, 2008), it is important to document the prevalence of rapid shallow afterslip. In addition, the presence or absence of rapid shallow afterslip (occurring minutes to days after the mainshock) is critical to the current debate about the amount of coseismic slip that reaches the surface in continental strike-slip faulting events (Simons et al., 2002; Fialko et al., 2005; Dolan and Haravitch, 2014; Xu et al., 2016) and whether a deficit in shallow coseismic slip could be rapidly recuperated by afterslip, as it was, for instance in the 2004 Mw 6.0 Parkfield earthquake (Bilham, 2005; Langbein et al., 2006) and the South Napa event (Lienkaemper et al., 2016; Brooks et al., 2017). Robust quantification of the postseismic deformation field both in the nearand far field of faults also potentially permits placing rheological constraints on the shallowest portion of slipping faults for which, recently, there has been much interest, especially in the field of fault displacement hazard analysis (Petersen et al., 2011). To address these questions, it is critical to rapidly collect geodetic data on surface deformation, especially in the near field. Although space-based instruments have the capability of widespread imaging, their response time (days) is not necessarily adequate to capture the afterslip decay that occurs

ABSTRACTSurface rupture in the 2019 Ridgecrest, California, earthquake sequence occurred along two orthogonal cross faults and includes dominantly left-lateral and northeast-striking rupture in the Mw 6.4 foreshock and dominantly right-lateral and northwest-striking rupture in the Mw 7.1 mainshock. We present >650 field-based, surface-displacement observations for these ruptures and synthesize our results into cumulative along-strike displacement distributions. Using these data, we calculate displacement gradients and compare our results with historical strike-slip ruptures in the eastern California shear zone. For the Mw 6.4 rupture, we report 96 displacements measured along 18 km of northeast-striking rupture. Cumulative displacement curves for the rupture yield a mean left-lateral displacement of 0.3–0.5 m and maximum of 0.7–1.6 m. Net mean vertical displacement based on the difference of down-to-the-west (DTW) and down-to-the-east (DTE) displacement curves is close to zero (0.02 m DTW). The Mw 6.4 displacement distribution shows that the majority of displacement occurred southwest of the intersection with the Mw 7.1 rupture. The Mw 7.1 rupture is northwest-striking and 50 km long based on 576 field measurements. Displacement curves indicate a mean right-lateral displacement of 1.2–1.7 m and a maximum of 4.3–7.0 m. Net vertical displacement in the rupture averages 0.3 m DTW. The Mw 7.1 displacement distributions demonstrate that maximum displacement occurred along a 12-km-long portion of the fault near the Mw 7.1 epicenter, releasing 66% of the geologically based seismic moment along 24% of the total rupture length. Using our displacement distributions, we calculate kilometer-scale displacement gradients for the Mw 7.1 rupture. The steepest gradients (∼1–3 m/km) flank the 12-km-long region of maximum displacement. In contrast, gradients for the 1992 Mw 7.3 Landers and 1999 Mw 7.1 Hector Mine earthquakes are <0.6 m/km. Our displacement distributions are important for understanding the influence of cross-fault rupture on Mw 6.4 and 7.1 rupture length and displacement and will facilitate comparisons with distributions generated remotely and at broader scales.

Poor knowledge of how faults slip and distribute deformation in the shallow crust hinders efforts to mitigate hazards where faults increasingly intersect with the expanding global population at Earth’s surface. Here we analyze two study sites along the 2014 M 6.0 South Napa, California, earthquake rupture, each dominated by either co- or post-seismic shallow fault slip. We combine mobile laser scanning (MLS), active-source seismic tomography, and finite element modeling to investigate how deformation rate and mechanical properties of the shallow crust affect fault behavior. Despite four orders-of-magnitude difference in the rupture velocities, MLS-derived shear strain fields are remarkably similar at the two sites and suggest deceleration of the co-seismic rupture near Earth’s surface. Constrained by the MLS and seismic data, finite element models indicate shallow faulting is more sensitive to lithologic layering and plastic yielding than to the presence of fault compliant zones (i.e., regions surrounding faults with reduced stiffness). Although both elastic and elastoplastic models can reproduce the observed surface displacement fields within the uncertainty of MLS data, elastoplastic models likely provide the most reliable representations of subsurface fault behavior, as they produce geologically reasonable stress states and are consistent with field, geodetic, and seismological observations.

Surface rupture from the 2019 Ridgecrest earthquake sequence, initially associated with the M-w 6.4 foreshock, occurred on 4 July on a-17 km long, northeast-south-west-oriented, left-lateral zone of faulting. Following the M-w 7.1 mainshock on 5 July (local time), extensive northwest-southeast-oriented, right-lateral faulting was then also mapped along a similar to 50 km long zone of faults, including subparallel splays in several areas. The largest slip was observed in the epicentral area and crossing the dry lakebed of China Lake to the southeast. Surface fault rupture mapping by a large team, reported elsewhere, was used to guide the airborne data acquisition reported here. Rapid rupture mapping allowed for accurate and efficient flight line planning for the high-resolution light detection and ranging (lidar) and aerial photography. Flight line planning trade-offs were considered to allocate the medium (25 pulses per square meter [ppsm]) and high-resolution (80 ppsm) lidar data collection polygons. The National Center for Airborne Laser Mapping acquired the airborne imagery with a Titan multispectral lidar system and Digital Modular Aerial Camera (DiMAC) aerial digital camera, and U.S. Geological Survey acquired Global Positioning System ground control data. This effort required extensive coordination with the Navy as much of the airborne data acquisition occurred within their restricted airspace at the China Lake ranges.