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Earthquake statistics is a growing field of research with direct application to probabilistic seismic hazard evaluation. The earthquake process is a complex spatio-temporal phenomenon, and has been thought to be an example of the self-organised criticality (SOC) paradigm, in which events occur as cascades on a wide range of sizes, each determined by fine details of the rupture process. As a consequence, deterministic prediction of specific event sizes, locations, and times may well continue to remain elusive. However, probabilistic forecasting, based on statistical patterns of occurrence, is a much more realistic goal at present, and is being actively explored and tested in global initiatives. This thesis focuses on the temporal statistics of earthquake populations, exploring the uncertainties in various commonly-used procedures for characterising seismicity and explaining the origins of these uncertainties. Unlike many other SOC systems, earthquakes cluster in time and space through aftershock triggering. A key point in the thesis is to show that the earthquake inter-event time distribution is fundamentally bimodal: it is a superposition of a gamma component from correlated (co-triggered) events and an exponential component from independent events. Volcano-tectonic earthquakes at Italian and Hawaiian volcanoes exhibit a similar bimodality, which in this case, may arise as the sum of contributions from accelerating and decelerating rates of events preceding and succeeding volcanic activity. Many authors, motivated by universality in the scaling laws of critical point systems, have sought to demonstrate a universal data collapse in the form of a gamma distribution, but I show how this gamma form is instead an emergent property of the crossover between the two components. The relative size of these two components depends on how the data is selected, so there is no universal form. The mean earthquake rate—or, equivalently, inter-event time—for a given region takes time to converge to an accurate value, and it is important to characterise this sampling uncertainty. As a result of temporal clustering and non-independence of events, the convergence is found to be much slower than the Gaussian rate of the central limit theorem. The rate of this convergence varies systematically with the spatial extent of the region under consideration: the larger the region, the closer to Gaussian convergence. This can be understood in terms of the increasing independence of the inter-event times with increasing region size as aftershock sequences overlap in time to a greater extent. On the other hand, within this high-overlap regime, a maximum likelihood inversion of parameters for an epidemic-type statistical model suffers from lower accuracy and a systematic bias; specifically, the background rate is overestimated. This is because the effect of temporal overlapping is to mask the correlations and make the time series look more like a Poisson process of independent events. This is an important result with practical relevance to studies using inversions, for example, to infer temporal variations in background rate for time-dependent hazard estimation.

A great number of the urban areas in Ethiopia are situated within the Great Rift Valley of Ethiopia, a system consisting of depressions and large faults. As a region with significant seismic activities, it is vital that careful planning is implemented to avoid constructing buildings on flat surfaces as they can amplify ground motion in the case of an earthquake.   This study was conducted in Adama, a city located within the rift system, to map and characterize the subsurface of a construction site with seismic refraction and investigate whether this is an optimal area to construct a building should an earthquake occur. Seismic refraction is based on Snell’s law, specifically the case of the critical angle, which is when the refracted angle is at 90 degrees and a number of the energy from the wave is rebounded back to the surface in accordance with Huygen’s Principle.       Seismic waves were generated with a sledgehammer and recorded with 24 vertical geophones. The acquired data was then analysed with SeisImager and produced a 2D-tomography of the site with the corresponding velocity layers for a P-wave. Comparing the P-wave velocities to a table of Seismic Velocities of Rocks and Various Materials, one could determine that the subsurface layers consisted of rock soils, sand and silt. These are incredibly loose materials that will amplify ground motion during earthquake crisis and are therefore not optimal or ideal for constructing buildings.

The tremendous growth in the serious games market presents the opportunity to help people learn through playing games. Defying Disaster is a 2D side scroller serious game designed to teach people how to prepare for and handle an earthquake. Players do a series of mini games that provide earthquake survival tips while interacting with a larger world after an earthquake disaster. An evaluation with thirty people compared learning disaster knowledge through reading materials versus playing games. The results show people learn better through playing Defying Disaster than reading materials.

An accurate seismic hazard assessment can only be carried out if a homogeneous and sufficiently complete catalogue for the study area is available. Since the catalogue for southern Africa was last updated in the early 1990s for the Global Seismic Hazard Assessment Program (GSHAP), it is necessary that a new updated, homogeneous and complete earthquake catalogue be compiled that includes data acquired during the last two decades. The process of compiling the new earthquake catalogue for southern Africa (South Africa, Lesotho, Swaziland, Botswana, and Namibia) was done as part of the Global Earthquake Modelling (GEM) project. The data from published and unpublished sources, and databases from the South African National Seismograph Network (SANSN), Bulawayo (BUL), the Geological Survey of Botswana, the National Earthquake Information Centre (NEIC), the Advanced National Seismic System (ANSS), and the International Seismic Centre (ISC) were retrieved and evaluated. After the data from the different sources were merged, duplicates and induced earthquakes were removed. The catalogue was unified with all magnitude types converted to moment magnitude (MW). Unifying the southern African catalogue to one magnitude scale had multiple challenges, considering that the catalogue is mostly incomplete, and it was therefore not easy to derive relations between different magnitude scales. The question of which method and relations are most suitable for converting all magnitude scales to MW had to be addressed. To ensure that all the events are independent, several procedures were carried out to decluster the catalogue and most suitable method selected. The final catalogue includes all available events, i.e. historical, and instrumental events from 1690 to December 2011, excluding fore- and aftershocks and induced events. This catalogue has 920 events with MW ≥ 4 whereas GSHAP has only 100 events with MS ≥ 4 in the southern African region. The largest event in the final catalogue occurred in 1952 and is located in the Okavango Delta region in Botswana with magnitude MW = 6.7. The maximum likelihood method was used at each point on a grid covering the study area, to estimate the spatial distribution of the b-value and the activity rate. The maximum curvature method was used for estimating the spatial distribution of magnitude of completeness, which was also substantiated with the Gutenberg-Richter, time-scale and spatial-scale magnitude of completeness graphs.

Thesis advisor: John E. Ebel / Earthquake activity in New England has been studied since the area was settled in the 17th century; however, the mechanism for this activity has yet to be determined. This thesis studied earthquake activity in Amesbury and Newburyport, Massachusetts, a region that has a history of significant seismic activity, including the 1727 Newbury earthquake. Earthquake data was collected by portable seismic devices set up in the Amesbury-Newburyport region as well as from the regional seismic network (New England Seismic Network). This data was analyzed to determine the absolute and relative locations of recorded events to improve upon previously calculated earthquake epicenters. The determined locations were then mapped in order to draw conclusions regarding the events’ relations and any possible common focal mechanism. / Thesis (BA) — Boston College, 2010. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: College Honors Program. / Discipline: Geology and Geophysics.

Thesis advisor: John E. Ebel / Studies of aftershock sequences in the Central Virginia Seismic Zone (CVSZ) provide critical details of the subsurface geologic structures responsible for past and (possibly) future earthquakes in an intraplate setting. The 23 August 2011 MW 5.8 Mineral, Virginia, earthquake, the largest magnitude event recorded in the CVSZ, caused widespread damage and generated a lengthy and well-recorded aftershock sequence. Over 1600 aftershocks were recorded using a dense network of seismometers in the four months following the mainshock, offering the unique opportunity to study the fault structure responsible for the post-main event seismicity. Previous work has not accurately determined the geometry of the fault structure or the migration of post-mainshock seismicity and association of the 2011 event with a known fault has been unsuccessful. In this study, relative locations of recorded aftershocks were calculated using a version of the double-difference location method outlined in Ebel et al. (2008) to generate an accurate model of the fault structure. The moment tensor inversion technique of Ebel and Bonjer (1990) was used to generate focal mechanisms of dozens of the aftershocks at various locations on the fault structure. Results from the double-difference and moment tensor inversion methods were used to map the structure responsible for the aftershock sequence in high resolution. The calculated fault structure has planes with similar strikes and dips as known faults and geologic structures in the CVSZ. In-depth analysis of this aftershock sequence provides seismologists with the opportunity to better understand the seismic hazards present in poorly understood intraplate seismic zones. / Thesis (MS) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Thesis advisor: John E. Ebel / The seismicity of the mid Atlantic Ridge (MAR) was compared in space and time with the seismicity along the Atlantic continental margins of Europe, Africa, North America, the Carribean and South America in a bid to appraise the level of influence of the ridge push force at the MAR on the Atlantic coastal seismicity. By analyzing the spatial and temporal patterns of many earthquakes (along with the patterns in their stress directions) in diverse places with similar tectonic settings, it is hoped that patterns that might be found indicate some of the average properties of the forces that are causing the earthquakes. The spatial analysis of the dataset set used shows that areas with higher seismic moment release along the north MAR spatially correlate with areas with relatively lower seismic moment release along the north Atlantic continental margins (ACM) and vice versa. This inverse spatial correlation observed between MAR seismicity and ACM seismicity might be due to the time (likely a long time) it takes stress changes from segments of the MAR currently experiencing high seismic activity to propagate to the associated passive margin areas presently experiencing relatively low seismic activity. Furthermore, the number of Atlantic basin and Atlantic coast earthquakes occurring away from the MAR is observed to be independent of the proximity of earthquake’s epicenters from the MAR axis. The effect of local stress as noted by Wysession et al. (1995) might have contributed to the independence of Atlantic basin and Atlantic coast earthquake proximity from the MAR. The Latchman (2011) observation of strong earthquakes on a specific section of the MAR being followed by earthquakes on Trinidad and Tobago was tested on other areas of the MAR and ACM. It was found that that the temporal delay observed by Latchman does not exist for the seismicity along other areas along the MAR and ACM. Within the time window used for this study, it appears that seismicity is occurring randomly in space away from the MAR. The weak anticorrelations between ACM and MAR seismicity show that the ridge push force probably has some level of influence on the ACM seismicity. However, as revealed from previous research on the study area, the forces resulting from lateral density contrasts related to topographic features and lateral density variations between oceanic and continental crust also appear to significantly influence the seismicity of the Atlantic coastal margins. / Thesis (MS) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Thesis advisor: Ruth McRoy / In January 2010, Haiti experienced a phenomenon no living Haitian had ever known. A devastating earthquake of 7.0 magnitude ravaged the already destitute island nation, killing over 230,000, leaving over one million living in tent cities or open spaces, and affecting millions of Haitians on the island and in the diasporas. This study examines the trauma and resilience of women who survived Haiti's 2010 earthquake and relocated to Boston, MA. A phenomenological qualitative design was used in this research in which 1-2 hour in-depth interviews were conducted with eight Haitian women who were living in Haiti and directly experienced the effects of earthquake. They all subsequently sought refuge from the destruction and chaos by coming to the U.S. This research aimed 1) to discover the culturally specific ways Haitian women survivors respond to trauma and exhibit resilience in the aftermath of a natural disaster and 2) to determine the factors that effect adjustment and wellbeing for Haitian women survivors in Boston. This inquiry was guided and informed by ecological resilience theory. A linguistically and culturally competent research team was formed in order to conduct the study in Haitian Creole, transcribe the narrative data, thematically code and analyze the data in the original language, and then provide clear translations that capture the meaning of the participants' narratives. Findings revealed that barriers such as unresolved legal status, financial stress, empathic stress, and family separation, threatened successful adaptation to their new reality. Ecological factors such as supports from friends, family and community organizations were found to promote resilience in the women survivors. Cultural values promoting connections to Haiti, the power of women, education, and spirituality, also served as motivating factors for acclimating to their relocation. The findings of this study suggest that social workers serving the relocated victims of the recent Haitian earthquake, recognize that the stress of family separation and the legal challenges of immigration, are major factors affecting the resilience of this population. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Social Work. / Discipline: Social Work.

The Oregon coast is facing the dual perils of climate change and the catastrophic Cascadia subduction zone earthquake and tsunami, yet many communities remain unprepared. Using qualitative interviews with residents of Coos Bay, Oregon, this study traces how communities facing these perils socially construct their visions of change by “remembering the future” and how this future memory influences unsettlement that, in turn, can trigger revision of strategies of action to deal with environmental risk. Participants understood these risks through three interrelated themes: analogy to familiar circumstances such as regular winter flooding, narratives of isolation and self-reliance based in collective history, and visions of symbolic preparedness. Each of these themes drew the conversation away from the material reality of environmental catastrophe, reducing relative unsettlement. Since the way that communities collectively understand environmental risk may influence preparatory action, these observations can help to explain the disjunction between knowledge of risks and response.