Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 67-74. / by Keiichiro Ikeda. / M.S.

The 1999 Kocaeli Earthquake (M=7.4) struck northwestern Turkey on August 17, 1999 and caused significant damage in urban areas located along Izmit Bay. The sites that suffered the greatest damages were located primarily in areas of poorest soil conditions, typically containing soft clays and silts and/or loose, liquefiable sands. Because the affected region is heavily developed with infrastructure and there is a preponderance of poor soils, a wide range of soil improvement measures had been used to mitigate anticipated earthquake damages throughout the region. Following the earthquake and significant aftershocks, Virginia Tech researchers traveled to Turkey to investigate the affected area to document geotechnical field performance. Primary focus of the Virginia tech team was given to investigating the performance of improved soil sites and reinforced soil structures. The sites were subjected to ground motions ranging from about 0.10g to 0.35g. The site locations ranged from 0 to 35 km from the zone of energy release. This dissertation presents in detail, the findings from the two most instructive sites. The investigation of these sties involved field reconnaissance, field and laboratory testing of soils, seismic analysis, numerical modeling, and other analytical work. / Ph. D.

Liquefaction is one of the major causes of ground failures during an earthquake. Recent evidence shows that the existing variants of the "simplified" liquefaction evaluation procedure lead to inaccurate results for megathrust earthquakes in subduction interfaces. To overcome this drawback and to achieve better prediction of liquefaction cases in subduction zones, this research intends to develop new empirical models that could be used for the prediction of liquefaction triggering in subduction zones. Towards this goal, new models for number of equivalent cycles (n_eq) and stress-reduction factor (r_d) have been proposed. The models are developed by regressing site response data obtained from 254 pairs of subduction ground motions and 77 representative soil profiles. To account for tectonic differences and magnitude scaling, separate models are developed for interface and intraslab earthquakes. The uncertainties involved in the proposed models are quantified through standard deviations of regression coefficients, event, site, and residual terms. The resulting models differ from other published models, especially the model for number of equivalent cycles. It was found that n_eq is greatly influenced by the fundamental site period. The model for r_d predicts higher values at shallow depths and lower values at deeper layers than other published models. Comparing the factors of safety against liquefaction with those from other existing models revealed that the use of models proposed in this research is more likely to reduce the "false positives" in liquefaction predictions, especially when design ground motion acceleration is high. / Master of Science / During earthquake shaking, loose saturated sands may lose strength and behave more like a liquid than a solid. This phenomenon is referred to liquefaction. Liquefaction has been responsible for infrastructure failure during past earthquakes, thus leading to major economic losses. This prompts the prediction and mitigation of potential liquefaction effects in a building site. However, the current state-of-the-practice for predicting liquefaction is inaccurate for large magnitude earthquakes in subduction zones. This provided the impetus for this research which focusses on developing new liquefaction evaluation models for large magnitude earthquakes. New models for number of equivalent cycles and stress reduction factor are developed by analyzing the representative ground motions and soil strata. These empirical parameters are central to the prediction of liquefaction triggering. Comparing the new models with the existing models revealed that the factor of safety against liquefaction estimated using new models are greater than those obtained using existing models for large magnitude earthquake scenario when the ground acceleration is high. This implies that using the existing models for predicting liquefaction in a site subjected to high values of ground acceleration from a subduction earthquake will lead to "false positives." Developed using a comprehensive dataset and robust regression techniques, the models developed in this research will lead to better predictions of liquefaction due to large subduction events.

On December 22nd, 2003, the Mw=6.5 San Simeon earthquake occurred 12 kilometers east of San Simeon, California, causing damage to buildings, roads, and other infrastructure throughout the central coast. The community of Oceano, 80 kilometers southeast of the epicenter, experienced damage to foundations, roads, and utilities due to liquefaction and lateral spreading. The unique geologic environment in Oceano caused a local amplification of ground motions, liquefaction, and lateral spreading. This study entailed developing ten liquefaction case histories from Oceano during the 2003 San Simeon earthquake. Four of the ten case histories are liquefaction cases and six are non-liquefaction cases, with Cyclic Stress Ratio (CSR) ranging from 0.17 to 0.43 and average corrected cone tip resistance (qc1) ranging from 2.67 to 23.53 kN/m^2. Subsurface data used to represent the geologic conditions in each case history included CPT soundings provided by the United States Geological Survey (Holzer et al., 2004). Ground motion data used to represent the earthquake conditions in each case history included the nearest relatively free field ground motion recordings from the SLO Rec Center Seismic Monitoring Station provided by the PEER strong motion center (PEER Ground Motions Database, 2003). CPT soundings were grouped together to develop representative case histories, allowing for averaging of parameters. The stratum with the single highest potential for liquefaction was selected and used as the ‘critical layer’ in each case history. To accurately represent the ground motion felt by each critical layer, a site response model was used to calculate average shear stress, which was used to calculate Cyclic Stress Ratio. The site response model was built using DEEPSOIL V6.1 with measured seismic shear wave velocities. Velocities were measured using passive geophysical methods in conjunction with Spatial Autocorrelation (SPAC) methods to process the data into shear wave velocity profiles. Measured velocities ranged from approximately 117 to 469 meters per second at depths ranging from 0 to 50 meters below the ground and were normally dispersive.

To understand better the faulting process in the Southern Appalachians, eleven single event focal mechanisms (SEFM) and seven composite focal mechanisms (CFM) are determined from 37 events that occurred in eastern Tennessee between September 1981 and July 1983. Both P-wave polarities and (Sv/P)z amplitude ratios are input to a computer program that systematically searches the focal sphere for solutions acceptable within pre-set error limits. Hypocenter locations, azimuth and departure angles are taken from locations obtained by the Tennessee Earthquake Information Center (TEIG) with a four layer velocity model (GCOl). A second velocity model (STEP2), developed to improve focal depth estimates and to acquire continuously varying departure angles, is used to relocate events for which SEFM and CFM solutions are obtained. The two different velocity models produced focal mechanisms with similar nodal plane and P-axis orientations, indicating stable and reliable results; the differences between average strike, dip, and rake angles of the two data sets range from 2° to 11°. Both SEFM and CFM solutions exhibit predominantly strike-slip motion along nearly vertical north-south (right-lateral) or east-west (left-lateral) oriented nodal planes. Standard deviations for average strike, dip, and rake angles are generally less than 20°. P-axis trends average about N50°E, with a nearly horizontal average plunge, and both have standard deviations of 25° or less. Except for three events in the northernmost region, all earthquakes in the study area result from a maximum compressive stress trending between N40°E and N70°E and plunging between 10° and -30°. / Master of Science

Moment-radius-stress drop relations and composite focal mechanisms were determined for 33 small, shallow, strike slip earthquakes (1.7$MLS4.3) in the Matsushiro region of southwest Honshu, Japan during the period August 1971 through September 1974. Estimates of the scalar moment derived from deconvolved SH displacement amplitude spectra range from 1018 to 1022 dyne-cm. The apparent stress ranges from 0.001 to 3.00 bars and the relationship between apparent stress and moment is approximately linear with a slope of 1. / Ph. D.

Focal mechanisms of earthquakes, two of them in the Gulf of Antalya and one in the eastern Aegean Sea, were determined by using both P-wave polarities and S-wave polarization angles. Additionally, a focal mechanism solution for a third Gulf of Antalya earthquake was determined from P-wave polarities only. The polarity data were read from long period vertical (LPZ) seismograms of World Wide Standard Seismograph Network (WWSSN) stations. Additional polarity data were obtained from published earthquake listings. S-wave polarization angles were determined from particle motion diagrams for both the linear, and non-linear distance ranges. To determine polarization angles for the non-linear range stations, a correction technique by Nuttli (1964) was applied. A revised version of the computer program written by Guinn (1977) was employed to obtain. the mechanism solutions. The focal mechanisms for the Gulf of Antalya events indicated strike-slip normal (28 May 1979 and 26 April 1981 events) and strike-slip thrust faulting (1 June 1977 event). All of the earthquakes occurred in this region are not far more than 50 kilometers from each other with focal depths ranging from 66 to 98 kilometers. The occurrence of opposite type of faults in the Gulf of Antalya indicate a complex tectonics in that region. Additionally, the focal mechanism of the Aegean Sea earthquake showed east-west striking normal faulting. The solution is in agreement with the focal mechanisms of the previous regional events (McKenzie, 1972 and Alptekin, 1973), indicating the continuation of the east-west oriented graben systems of western Turkey in the Aegean Sea. / M.S.

Arrival times from intermediate-depth (110-150 km) earthquakes within the region of flat subduction beneath central Peru provide constraints on the geometry and velocity structure of the subducting Nazca plate. Hypocenters for these events, which are beneath the sub-andean and eastern Peruvian basins, were determined using a best-fitting onedimensional velocity-depth model with a 15-station digitally-recording network deployed in the epicentral region. For that model, P-wave travel times to coastal stations, about 6° trenchward, exhibit negative residuals of up to 4 seconds and have considerably more complexity than arrivals at the network stations. The residuals at coastal stations are conjectured to result from travel paths with long segments in the colder, higher velocity subducting plate. Travel time anomalies were modeled by 3-D raytracing. Computed ray paths show that travel times to coastal stations for the eastern Peru events can be satisfactorilymodeled if velocities relative to the surrounding mantle are 6% lower within the uppermost slab (a 6 km thick layer composed of basaltic oceanic crust) and 8% higher within the cold peridotitic layer (which must be at least 44 km thick). Raytracing runs for this plate model show that "shadow zones" can occur if the source-slab-receiver geometry results in seismic rays passing through regions in which the slab undergoes significant changes in slope. Such geometries exist for seismic waves propagating to some coastal stations from sources located beneath the eastern Peruvian basin. Observed first-arrival times for such cases do in fact have less negative residuals than those for geometries which allow for \direct\ paths. Modeling such arrivals as trapped mode propagation through the high-velocity part of the plate produces arrival times consistent with those observed. / Master of Science

Seismic hazard calculations for sites in eastern North America have traditionally assumed a Poisson process to describe the temporal behavior of earthquakes and have employed the Gutenberg-Richter relationship to define the frequency distribution of earthquake magnitude. For sites in areas where geological information indicates recurrent, large earthquakes, however, such data imply a rate for large events which often exceeds that predicted by the Gutenberg-Richter relationship. One way in which this discrepancy can be reconciled is to assume that the larger events occur as a time-dependent, or renewal, process and possess a "characteristic earthquake" magnitude distribution. The main purpose of this study is to make a quantitative comparison of seismic hazard estimates for Charleston of the influences of 1) the Poisson temporal model assuming the Gutenberg-Richter and characteristic earthquake magnitude recurrence relationships with 2) the renewal temporal model assuming the characteristic magnitude recurrence relationship. Other issues that are examined are the sensitivity of uncertainties of hazard model parameters such as maximum magnitude and seismic source delineation. Probabilistic seismic hazard calculations for the next 50 years were performed at Charleston for all potential seismic sources. The highest estimate of seismic hazard was obtained with the Poisson temporal model and characteristic earthquake recurrence relationship. The lowest hazard was obtained with the renewal temporal model and characteristic magnitude recurrence relationship. The results of this study are in good agreement with hazard estimates for Charleston in the most recent national seismic hazard maps. / Master of Science

Measurements of radon in groundwater before, during and after the 1995 Kobe earth-quake in Japan indicated that there might be a correlation between levels of 222Rn ingroundwater and seismological activity. The artEmis project investigates this possibleconnection with the goal of building a network of detectors in seismically active parts ofEurope. The detectors will be placed in groundwater and measure many factors, one ofthem being the radon level by measuring gamma radiation. The original vision for thedetectors also included alpha detection. The obtained data is analyzed with artificialintelligence. This thesis investigates a possible method for alpha detection under water. Specif-ically by seeing if it is possible for radon dissolved in water to diffuse from the water,through silicone tubes and into the air inside of the silicone tubes. There is a possibilityfor alpha detection of the radon decay if the radon gas could get into the air. This wasinvestigated by submerging an air-filled silicone construction in water with high levelsof radon. The level of radon in the water was increased by placing pieces of lightweightconcrete in the water. The construction was removed after a period of time and itsgamma-ray spectrum was measured. A statistically significant increase in radon levelscompared to the background radiation would indicate that diffusion happened. Measurements of the silicone construction with a germanium detector resulted ingamma spectra that were analyzed with a Python program to determine the activity of222Rn over time. Short measurements, around 1 hour long, showed a significant increaseof radon compared to the background. For longer measurements however, around one ortwo days, this effect was no longer apparent. The conclusion is that radon diffused intothe silicone construction, either into the silicone material itself or into the air inside theconstruction, but it comes out again quickly. If the radon diffused into the air inside ofthe silicone, the use of alpha detection to measure radon levels in groundwater is muchless far-fetched than before. Therefore, the artEmis project might be one step closer tousing alpha detection in their detector network.