Gareth J. Funning

The 2003 Bam (Iran) earthquake: Rupture of a blind strike-slip fault

A magnitude 6.5 earthquake devastated the town of Bam in southeast Iran on 26 December 2003. Surface displacements and decorrelation effects, mapped using Envisat radar data, reveal that over 2 m of slip occurred at depth on a fault that had not previously been identified. It is common for earthquakes to occur on blind faults which, despite their name, usually produce long-term surface effects by which their existence may be recognised. However, in this case there is a complete absence of morphological features associated with the seismogenic fault that destroyed Bam.

Shallow fault-zone dilatancy recovery after the 2003 Bam earthquake in Iran

Earthquakes radiate from slip on discrete faults, but also commonly involve distributed deformation within a broader fault zone, especially near the surface. Variations in rock strain during an earthquake are caused by heterogeneity in the elastic stress before the earthquake, by variable material properties and geometry of the fault zones, and by dynamic processes during the rupture. Stress changes due to the earthquake slip, both dynamic and static, have long been thought to cause dilatancy in the fault zone that recovers after the earthquake. Decreases in the velocity of seismic waves passing through the fault zone due to coseismic dilatancy have been observed followed by postseismic seismic velocity increases during healing. Dilatancy and its recovery have not previously been observed geodetically. Here we use interferometric analysis of synthetic aperture radar images to measure postseismic surface deformation after the 2003 Bam, Iran, earthquake and show reversal of coseismic dilatancy in the shallow fault zone that causes subsidence of the surface. This compaction of the fault zone is directly above the patch of greatest coseismic slip at depth. The dilatancy and compaction probably reflects distributed shear and damage to the material during the earthquake that heals afterwards. Coseismic and postseismic deformation spread through a fault zone volume may resolve the paradox of shallow slip deficits for some strike-slip fault ruptures.

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.

El Mayor‐Cucapah (Mw 7.2) earthquake: Early near‐field postseismic deformation from InSAR and GPS observations

El Mayor-Cucapah earthquake occurred on 4 April 2010 in northeastern Baja California just south of the U.S.-Mexico border. The earthquake ruptured several previously mapped faults, as well as some unidentified ones, including the Pescadores, Borrego, Paso Inferior and Paso Superior faults in the Sierra Cucapah, and the Indiviso fault in the Mexicali Valley and Colorado River Delta. We conducted several Global Positioning System (GPS) campaign surveys of preexisting and newly established benchmarks within 30 km of the earthquake rupture. Most of the benchmarks were occupied within days after the earthquake, allowing us to capture the very early postseismic transient motions. The GPS data show postseismic displacements in the same direction as the coseismic displacements; time series indicate a gradual decay in postseismic velocities with characteristic time scales of 66 ± 9 days and 20 ± 3 days, assuming exponential and logarithmic decay, respectively. We also analyzed interferometric synthetic aperture radar (InSAR) data from the Envisat and ALOS satellites. The main deformation features seen in the line-of-sight displacement maps indicate subsidence concentrated in the southern and northern parts of the main rupture, in particular at the Indiviso fault, at the Laguna Salada basin, and at the Paso Superior fault. We show that the near-field GPS and InSAR observations over a time period of 5 months after the earthquake can be explained by a combination of afterslip, fault zone contraction, and a possible minor contribution of poroelastic rebound. Far-field data require an additional mechanism, most likely viscoelastic relaxation in the ductile substrate.

Spatial variations in fault friction related to lithology from rupture and afterslip of the 2014 South Napa, California, earthquake

Following earthquakes, faults are often observed to continue slipping aseismically. It has been proposed that this afterslip occurs on parts of the fault with rate-strengthening friction that are stressed by the main shock, but our understanding has been limited by a lack of immediate, high-resolution observations. Here we show that the behavior of afterslip following the 2014 South Napa earthquake in California varied over distances of only a few kilometers. This variability cannot be explained by coseismic stress changes alone. We present daily positions from continuous and survey GPS sites that we remeasured within 12 h of the main shock and surface displacements from the new Sentinel-1 radar mission. This unique geodetic data set constrains the distribution and evolution of coseismic and postseismic fault slip with exceptional resolution in space and time. We suggest that the observed heterogeneity in behavior is caused by lithological controls on the frictional properties of the fault plane.

Matrix Profile II: Exploiting a Novel Algorithm and GPUs to Break the One Hundred Million Barrier for Time Series Motifs and Joins

Time series motifs have been in the literature for about fifteen years, but have only recently begun to receive significant attention in the research community. This is perhaps due to the growing realization that they implicitly offer solutions to a host of time series problems, including rule discovery, anomaly detection, density estimation, semantic segmentation, etc. Recent work has improved the scalability to the point where exact motifs can be computed on datasets with up to a million data points in tenable time. However, in some domains, for example seismology, there is an insatiable need to address even larger datasets. In this work we show that a combination of a novel algorithm and a high-performance GPU allows us to significantly improve the scalability of motif discovery. We demonstrate the scalability of our ideas by finding the full set of exact motifs on a dataset with one hundred million subsequences, by far the largest dataset ever mined for time series motifs. Furthermore, we demonstrate that our algorithm can produce actionable insights in seismology and other domains.

Kinematic modeling of fault slip rates using new geodetic velocities from a transect across the Pacific-North America plate boundary through the San Bernardino Mountains, California

©2015. American Geophysical Union. All Rights Reserved. Campaign GPS data collected from 2002 to 2014 result in 41 new site velocities from the San Bernardino Mountains and vicinity. We combined these velocities with 93 continuous GPS velocities and 216 published velocities to obtain a velocity profile across the Pacific-North America plate boundary through the San Bernardino Mountains. We modeled the plate boundary-parallel, horizontal deformation with 5-14 parallel and one obliquely oriented screw dislocations within an elastic half-space. Our rate for the San Bernardino strand of the San Andreas Fault (6.5±3.6mm/yr) is consistent with recently published latest Quaternary rates at the 95% confidence level and is slower than our rate for the San Jacinto Fault (14.1±2.9mm/yr). Our modeled rate for all faults of the Eastern California Shear Zone (ECSZ) combined (15.7±2.9mm/yr) is faster than the summed latest Quaternary rates for these faults, even when an estimate of permanent, off-fault deformation is included. The rate discrepancy is concentrated on faults near the 1992 Landers and 1999 Hector Mine earthquakes; the geodetic and geologic rates agree within uncertainties for other faults within the ECSZ. Coupled with the observation that postearthquake deformation is faster than the pre-1992 deformation, this suggests that the ECSZ geodetic-geologic rate discrepancy is directly related to the timing and location of these earthquakes and is likely the result of viscoelastic deformation in the mantle that varies over the timescale of an earthquake cycle, rather than a redistribution of plate boundary slip at a timescale of multiple earthquake cycles or longer.

MERIS Atmospheric Water Vapor Correction Model for Wide Swath Interferometric Synthetic Aperture Radar

A major source of error for repeat-pass interferometric synthetic aperture radar is the phase delay in radio signal propagation through the atmosphere, particularly the part due to tropospheric water vapor. These effects become more significant for ScanSAR observations due to their wider coverage (e.g., 400 km × 400 km for ENVISAT Advanced Synthetic Aperture Radar (ASAR) wide swath (WS) mode versus 100 km × 100 km for ASAR image mode). In this letter, we demonstrate for the first time that a Medium Resolution Imaging Spectrometer water vapor correction model can significantly reduce atmospheric water vapor effects on ASAR WS interferograms, with the phase variation in non-deforming areas decreasing from 3.8 cm before correction to 0.4 cm after correction.

Use of a GPS-Derived Troposphere Model to Improve InSAR Deformation Estimates in the San Gabriel Valley, California

We evaluate the potential of troposphere models derived from ground meteorological data (pressure, temperature, and relative humidity) and Global Positioning System (GPS) data to improve InSAR measurements and models derived from them. We test this approach on an ERS-2/Envisat data set collected during a transient surface deformation episode that occurred from January to July 2005 in the San Gabriel Valley, southern California, USA. We find that the interferometric phase change observed over the corresponding period cannot be solely attributed to hydrological uplift associated with rising groundwater levels but also includes a significant contribution from differential tropospheric delay due to differing quantities of water vapor in the troposphere on the two SAR observation dates. We show that, if the tropospheric phase contribution is mistakenly interpreted as the range change associated with changes in groundwater storage, both the surface displacement and the groundwater storage coefficient may be overestimated by up to 30%. This method could be applied in real time where meteorological measurements are available near one or more GPS permanent site(s).

Testing the inference of creep on the northern Rodgers Creek fault, California, using ascending and descending persistent scatterer InSAR data†

Author(s): Jin, L; Funning, GJ | Abstract: ©2017. American Geophysical Union. All Rights Reserved. We revisit the question of whether the Rodgers Creek fault in northern California is creeping, a question with implications for seismic hazard. Using imagery acquired by Envisat between 2003 and 2010, we process two persistent scatterer interferometric synthetic aperture radar (InSAR) data sets, one from an ascending track and the other from a descending track, covering the northernmost segment of the Rodgers Creek fault between the cities of Santa Rosa and Healdsburg. The two different viewing geometries provided by the two different tracks allow us to distinguish vertical velocities, which may reflect nontectonic deformation processes, from fault-parallel velocities, which can be used to identify creep. By measuring offsets in InSAR line-of-sight velocity from 12 fault-perpendicular profiles through both data sets, we identify seven locations where we have a high degree of confidence that creep is occurring (estimated creep rate is more than two standard deviations above zero). The preferred creep rates at these locations are in the range 1.9–6.7 mm/yr, consistent within uncertainty with alignment array measurements. Creep is probable (P≥0.70) at another three locations, defining a creeping zone ∼20 km long in total, extending northwest from Santa Rosa. We also estimate the map patterns of fault-parallel and vertical velocities in the region covered by both data sets; these suggest that the Rodgers Creek fault immediately southeast of Santa Rosa remains locked.