Geomorphic and geologic controls of geohazards induced by Nepal’s 2015 Gorkha earthquake

The Gorkha earthquake (M 7.8) on 25 April 2015 and later aftershocks struck South Asia, killing ~9,000 and damaging a large region. Supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone, our team undertook a satellite image survey of the earthquakes’ induced geohazards in Nepal and China and an assessment of the geomorphic, tectonic, and lithologic controls on quake-induced landslides. Timely analysis and communication aided response and recovery and informed decision makers. We mapped 4,312 co-seismic and post-seismic landslides. We also surveyed 491 glacier lakes for earthquake damage, but found only 9 landslide-impacted lakes and no visible satellite evidence of outbursts. Landslide densities correlate with slope, peak ground acceleration, surface downdrop, and specific metamorphic lithologies and large plutonic intrusions

A Non-Hohmann Method for Orbital Element Database Pre-Processing

One major obstacle to successful orbital debris remediation is the determination of which pieces of debris are the most viable targets for capture and de-orbit. The viability of a target is determined by some combination of the debris’ risk factor (a combination of its size, composition, andthe orbit it occupies), the anticipated resource cost to find and capture the debris, and the underlying probability of successful intercept and capture of that target. The problem of selecting debris for capture by a multi-capture capable spacecraft is fundamentally a traveling salesman problem in which the traveler only has the resources to reach a very limited subset of the available destinations. Therefore, rapidly identifying the sets of destinations (i.e. pieces of debris) which are either too expensive to reach or insufficiently valuable to justify targeting will reduce the target destination set; this would significantly enhance the efficiency of the solution. This problem of intelligently reducing the space of possible solutions can be partially solved by performing a preliminary filtering and sorting of orbital debris database entries using known spacecraft orbital parameters and maneuvering ∆V-budget to reduce the number of possible destinations for an optimizer to those which are in fact accessible from the spacecraft’s initial orbit. The chosen algorithm for analyzing and filtering the data is a two-burn node-to-node non-Hohmann transfer, which was used to estimate the ∆V-cost for transfer from the capture spacecraft’s initial orbit to an orbit near the target piece of debris. Once the ∆V-cost was calculated for each transfer orbit, entries with excessive fuel costs were removed from consideration, and the fuel cost to access each remaining orbit was appended to its entry. This method was capable of reducing a 10,400-item list of debris to less than 100 accessible targets in under 3 seconds on an ordinary laptop computer. This reduction in database size brought the number of targets down to a practical size for processing by a more computationally expensive optimization algorithm suitable for selecting final targets for a multi-capture spacecraft

Surface ruptures on cross-faults in the 24 November 1987 Superstition Hills, California, earthquake sequence

Left-lateral slip occurred on individual surface breaks along northeast-trending faults associated with the 24 November 1987 earthquake sequence in the Superstition Hills, Imperial Valley, California. This sequence included the M_s = 6.2 event on a left-lateral, northeast-trending “cross-fault” between the Superstition Hills fault (SHF) and Brawley seismic zone, which was spatially associated with the left-lateral surface breaks. Six distinct subparallel cross-faults broke at the surface, with rupture lengths ranging from about Formula to 10 km and maximum displacements ranging from 30 to 130 mm. About half a day after the M_s = 6.2 event, an M_s = 6.6 earthquake nucleated near the intersection of the cross-faults with the SHF, and rupture propagated southeast along the SHF. Whereas right-lateral slip on the SHF occurred dominantly on a single trace in a narrow zone, the cross-fault surface slip was distributed over several stands across a 10-km-wide zone. Also, whereas afterslip accounted for a large proportion of total slip on the SHF, there is no evidence for afterslip on the cross-faults. We present documentation of these surface ruptures. A simple mechanical model of faulting illustrates how the foreshock sequence may have triggered the main rupture. Displacement on other cross-faults could trigger an event on the southern San Andreas fault by a similar mechanism in the future

Fault‐Slip Distribution of the 1999 M_w 7.1 Hector Mine Earthquake, California, Estimated from Postearthquake Airborne LiDAR Data

The 16 October 1999 Hector Mine earthquake (M_w 7.1) was the first large earthquake for which postearthquake airborne Light Detection and Ranging (LiDAR) data were collected to image the fault surface rupture. In this work, we present measurements of both vertical and horizontal slip along the entire surface rupture of this earthquake based on airborne LiDAR data acquired in April 2000. We examine the details of the along‐fault slip distribution of this earthquake based on 255 horizontal and 85 vertical displacements using a 0.5 m digital elevation model derived from the LiDAR imagery. The slip measurements based on the LiDAR dataset are highest in the epicentral region, and taper in both directions, consistent with earlier findings by other works. The maximum dextral displacement measured from LiDAR imagery is 6.60±1.10  m, located about 700 m south of the highest field measurement (5.25±0.85  m). Our results also illustrate the difficulty in resolving displacements smaller than 1 m using LiDAR imagery alone. We analyze slip variation to see if it is affected by rock type and whether variations are statistically significant. This study demonstrates that a postearthquake airborne LiDAR survey can produce an along‐fault horizontal and vertical offset distribution plot of a quality comparable to a reconnaissance field survey. Although LiDAR data can provide a higher sampling density and enable rapid data analysis for documenting slip distributions, we find that, relative to field methods, it has a limited ability to resolve slip that is distributed over several fault strands across a zone. We recommend a combined approach that merges field observation with LiDAR analysis, so that the best attributes of both quantitative topographic and geological insight are utilized in concert to make best estimates of offsets and their uncertainties

The Ursinus Weekly, March 15, 1965

Sig Nu and inactive Demas win Sorority-Fraternity Song Fest • Roving reporter • The grammarian\u27s funeral, or Easy does it • Silent generation whispers, non-quiet editor speaks • Upper classmen reveal soph shingles technique • Editorial: Come on, girls! • A view of fraternity bids • Letter to the editor • Admissions Office, Spring 1960 • Campus song: Addendum • Advice column • To a seminar in Spring • Greek gleaningshttps://digitalcommons.ursinus.edu/weekly/1243/thumbnail.jp

Continuous GPS Observations of Postseismic Deformation Following the 16 October 1999 Hector Mine, California, Earthquake (M_w 7.1)

Rapid field deployment of a new type of continuously operating Global Positioning System (GPS) network and data from Southern California Integrated GPS Network (SCIGN) stations that had recently begun operating in the area allow unique observations of the postseismic deformation associated with the 1999 Hector Mine earthquake. Innovative solutions in fieldcraft, devised for the 11 new GPS stations, provide high-quality observations with 1-year time histories on stable monuments at remote sites. We report on our results from processing the postseismic GPS data available from these sites, as well as 8 other SCIGN stations within 80 km of the event (a total of 19 sites). From these data, we analyze the temporal character and spatial pattern of the postseismic transients. Data from some sites display statistically significant time variation in their velocities. Although this is less certain, the spatial pattern of change in the postseismic velocity field also appears to have changed. The pattern now is similar to the pre-Landers (pre-1992) secular field, but laterally shifted and locally at twice the rate. We speculate that a 30 km × 50 km portion of crust (near Twentynine Palms), which was moving at nearly the North American plate rate (to within 3.5 mm/yr of that rate) prior to the 1992 Landers sequence, now is moving along with the crust to the west of it, as though it has been entrained in flow along with the Pacific Plate as a result of the Landers and Hector Mine earthquake sequence. The inboard axis of right-lateral shear deformation (at lower crustal to upper mantle depth) may have jumped 30 km farther into the continental crust at this fault junction that comprises the southern end of the eastern California shear zone

Co-Seismic Displacements of the 1994 Northridge, California, Earthquake

The 17 January 1994 Northridge, California, earthquake significantly deformed the Earth's crust in the epicentral region. Displacements of 66 survey stations determined from Global Positioning System (GPS) observations collected before and after the earthquake show that individual stations were uplifted by up to 417 ± 5 mm and displaced horizontally by up to 216 ± 3 mm. Using these displacements, we estimate parameters of a uniform-slip model. Fault geometry and slip are estimated independent of seismological information, using Monte Carlo optimization techniques that minimize the model residuals. The plane that best fits the geodetic data lies 1 to 2 km above the plane indicated by aftershock seismicity. Modeling for distributed slip on a coplanar, yet larger model fault indicates that a high-slip patch occurred up-dip and northwest of the mainshock hypocenter and that less than 1 m of slip occurred in the uppermost 5 km of the crust. This finding is consistent with the lack of clear surface rupture and with the notion that the intersection with the fault that ruptured in 1971 formed the up-dip terminus of slip in the Northridge earthquake. Displacements predicted by either of these simple models explain most of the variance in the data within 50 km of the epicenter. On average, however, the scatter of the residuals is twice the data uncertainties, and in some areas, there is significant systematic misfit to either model. The co-seismic contributions of aftershocks are insufficient to explain this mismatch, indicating that the source geometry is more complicated than a single rectangular plane

Superficial simplicity of the 2010 El Mayor–Cucapah earthquake of Baja California in Mexico

The geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation, propagation and arrest of seismic ruptures. The fault system that runs from southern California into Mexico is a simple strike-slip boundary: the west side of California and Mexico moves northwards with respect to the east. However, the M_w 7.2 2010 El Mayor–Cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike-slip fault. Here we use geodetic, remote-sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake. We find that the earthquake produced a straight 120-km-long fault trace that cut through the Cucapah mountain range and across the Colorado River delta. However, at depth, the fault is made up of two different segments connected by a small extensional fault. Both segments strike N130° E, but dip in opposite directions. The earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike-slip motion. We show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves. We conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone