Variations in slow slip moment rate associated with rapid tremor reversals in Cascadia

During large slow slip events, tremor sometimes propagates in the reverse along-strike direction for a few hours, at speeds 10 to 40 times faster than the forward propagation. We examine the aseismic slip that underlies this rapidly propagating tremor. We use PBO (Plate Boundary Observatory) borehole strainmeter data to search for variations in the slow slip moment rate during 35 rapid tremor reversals (RTRs) that occurred beneath Vancouver Island. The strain records reveal that, on average, the strain rate increases by about 100% ( math formula) during RTRs. Given the Green's functions expected for slip in the RTR locations, these strain rate increases imply 50 to 130% increases in the aseismic moment rate. The median moment released per RTR is between 8 and 21% of the daily slow slip moment, equivalent to that of a MW 5.0 to 5.1 earthquake. By combining the RTR moments with the spatial extents suggested by tremor, we estimate that a typical RTR has peak slip of roughly one-sixth of the peak slip in the main slow slip event, near-front slip rate of a few to ten times the main front slip rate, stress drop around half the main event stress drop, and strain energy release rate around one-tenth that of the main front. Our observations support a picture of RTRs as aseismic subevents with high slip rates but modest strain energy release. RTRs appear to contribute to but not dominate the overall slow slip moment, though they may accommodate most of the slip in certain locations

Short-term earthquake hazard assessment for the San Andreas Fault in southern California

The southernmost 200 km of the San Andreas fault in California, from Cajon Pass southeast to Bombay Beach on the Salton Sea (Figure 1), has not produced a major earthquake within the historic record. Both geodetic evidence of continuing strain accumulation (Savage et al, 1986) and the occurrence of recent prehistoric large earthquakes (Sieh, 1986; Sieh and Williams, 1990), however, lead us to conclude that this fault segment will eventually produce great earthquakes that pose one of the greatest hazards to southern California. An estimated 1.0-1.5 million people now live adjacent to the San Andreas fault within the projected zone of severe shaking for such an earthquake. A magnitude 7.5 to 8.0 earthquake on this segment would also cause widespread damage to San Bernardino, Imperial, Riverside, Orange, and Los Angeles counties, which together have over 12 million inhabitants. For these reasons, the Southern San Andreas Fault Working Group was formed in 1989 to recommend how the scientific community might best respond to anomalous geophysical activity along the fault, increase our understanding of regional seismotectonics, and offer timely scientific advice to state and local governments

Log File Analysis in Cloud with Apache Hadoop and Apache Spark

Proceedings of: Second International Workshop on Sustainable Ultrascale Computing Systems (NESUS 2015). Krakow (Poland), September 10-11, 2015.Log files are a very important set of data that can lead to useful information through proper analysis. Due to the high production rate and the number of devices and software that generate logs, the use of cloud services for log analysis is almost necessary. This paper reviews the cloud computational framework ApacheTM Hadoop R, highlights the differences and similarities between Hadoop MapReduce and Apache SparkTM and evaluates the performance of them. Log file analysis applications were developed in both frameworks and performed SQL-type queries in real Apache Web Server log files. Various measurements were taken for each application and query with different parameters in order to extract safe conclusions about the performance of the two frameworks.The authors would like to thank Okeanos the GRNET’s cloud service for the valuable resources

Evaluation of Zero-Net-Rate Pumping Tests

Accurately estimating the distribution of aquifer properties is key to understanding contaminant movement in the subsurface. The distribution of aquifer properties is typically addressed using slug or constant-rate well tests, and the pros and cons of these tests are well known. Slug tests are appealing because they avoid removing contaminated water, but their results are affected by well skin and the small volume of displaced water limits the volume of aquifer that can be evaluated. Constant-rate well tests have the disadvantage of requiring disposal of potentially contaminated water, but they can generate properties that are more representative than slug tests, and they can be used to estimate well efficiency and storativity, which are difficult to characterize using slug tests. Periodic pumping tests are appealing because they have many of the advantages and few of the disadvantages of slug and constant-rate well tests. This project outlines the current state of conducting and analyzing periodic pumping tests and investigates the potential benefits and limitations of conducting these tests, including identifying zones of heterogeneities in the subsurface and utilizing vadose zone strain signals to characterize an underlying aquifer

Volcanic Processes Monitoring and Hazard Assessment Using Integration of Remote Sensing and Ground-Based Techniques

The monitoring of active volcanoes is a complex task based on multidisciplinary and integrated analyses that use ground, drones and satellite monitoring devices. Over time, and with the development of new technologies and increasing frequency of acquisition, the use of remote sensing to accomplish this important task has grown enormously. This is especially so with the use of drones and satellites for classifying eruptive events and detecting the opening of new vents, the spreading of lava flows on the surface or ash plumes in the atmosphere, the fallout of tephra on the ground, the intrusion of new magma within the volcano edifice, and the deformation preceding impending eruptions, and many other factors. The main challenge in using remote sensing techniques is to develop automated and reliable systems that may assist the decision maker in volcano monitoring, hazard assessment and risk reduction. The integration with ground-based techniques represents a valuable additional aspect that makes the proposed methods more robust and reinforces the results obtained. This collection of papers is focused on several active volcanoes, such as Stromboli, Etna, and Volcano in Italy; the Long Valley caldera and Kilauea volcano in the USA; and Cotopaxi in Ecuador

Analysis of tremor at the San Andreas Fault at Parkfield

Emergent phase arrivals, low amplitude waveforms, and variable event durations make detection and location of tectonic tremor a non-trivial task. In this work I employ a new method to identify tremor in large datasets using a semi-automated technique, which is comprised of an envelope cross-correlation and a Self-Organizing Map (SOM) algorithm to identify and classify event types. Furthermore, I present a new tremor localization method based on time-reversal imaging techniques

Bridges Structural Health Monitoring and Deterioration Detection Synthesis of Knowledge and Technology

INE/AUTC 10.0

50 Years Geophysical Institute Karlsruhe, 1964 to 2014 - Expectations and Surprises

Die Festschrift anlässlich des 50. Geburtstags des Geophysikalischen Instituts in 2014 wurde hauptsächlich von Herrn Dr. Claus Prodehl zusammengestellt. Die einzelnen Beiträge stammen von ehemaligen und aktuellen GPI-Mitarbeitern und Mitarbeiterinnen

Terrestrial Gravity Fluctuations

The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our understanding of terrestrial gravity fluctuations will have great impact on the future development of GW detectors and high-precision gravimetry in general, and many open questions need to be answered still as emphasized in this article.Comment: 151 pages, 52 figures; submitted to Living Reviews in Relativit