The seismogenic potential of subducting sediments

This thesis examines the seismic behavior of sediments in shallow subduction zones. In the traditional view of the seismogenic zone, the upper stability limit is controlled by a transition to velocity-strengthening (frictionally stable) clay-rich sediments at shallow depths in the accretionary prism. However, recent observations have emphasized that these shallow sediments can host a wide range of seismic behaviors. On one end of the seismic spectrum, the March 2011 Mw9.1 Tohoku-oki earthquake demonstrated that peak slip in a megathrust rupture can be hosted at the shallowest depths. At the other end of the spectrum, observations at the Hikurangi trench off the North Island of New Zealand have revealed that spontaneous, periodic slow slip events (SSEs) can nucleate in the shallowest portions of a subduction zone. The Japan Fast Trench Drilling Project (JFAST, IODP Expedition 343) drilled through the plate boundary faults in the Japan Trench to investigate the structure that hosted the Tohoku-oki earthquake. In Chapter 2, I use a trace element-based stratigraphy to identify several large displacement faults within the bottom ~15 m of the JFAST core. This work highlights that there are multiple candidate structures that could host a megathrust rupture and that not all displacement is accommodated along a weak pelagic clay layer recovered in the JFAST core. However, this method is incapable of determining which of these faults experienced significant seismic slip. In Chapter 3, I develop a novel paleoseismic indicator appropriate for faults hosted in seafloor sediments. This tool takes advantage of the fact that organic material (molecular biomarkers) in sediments degrades as a function of time and temperature. In this study, I determine the kinetics of thermal maturation for alkenones (coccolithophore-derived molecules) and n-alkanes (plant leaf wax-derived molecules) found in western Pacific sediments. In Chapter 4, I apply these kinetics to measured biomarker anomalies in JFAST samples to determine which faults recovered in the JFAST core could have hosted a megathrust event such as the Tohoku-oki earthquake. This approach reveals that multiple faults in the plate boundary region have likely hosted megathrust events and that the occurrence of seismic slip is not confined to a particular lithology. This implies that small differences in frictional behavior in subducting sedimentary lithologies are not the primary control on the occurrence of shallow seismic slip. In Chapter 5, I turn to a different type of shallow seismic behavior and focus on SSEs in the shallowest portion of the Hikurangi trench. In this study, I measure friction and velocity-dependence of the input sediments for this subduction zone at a range of pressures and temperatures relevant to the shallow portion of the slab where SSEs have been observed. These experiments demonstrate that the sediment here becomes frictionally weak at effective stresses expected deeper than ~2 km. At the same effective stresses, the sediment becomes less velocity strengthening, and under some conditions exhibits velocity neutral behavior. A plate-rate experiment exhibits velocity-weakening behavior and two spontaneous SSEs, indicating that at slow velocities, the sediment subducting at the Hikurangi trench is capable of unstable frictional behavior required to promote shallow SSEs. These results demonstrate that subducting sediments can exhibit a variety of frictional properties that can support unstable behavior in the shallowest reaches of the subduction zone

Earthquake slip surfaces identified by biomarker thermal maturity within the 2011 Tohoku-Oki earthquake fault zone.

Extreme slip at shallow depths on subduction zone faults is a primary contributor to tsunami generation by earthquakes. Improving earthquake and tsunami risk assessment requires understanding the material and structural conditions that favor earthquake propagation to the trench. We use new biomarker thermal maturity indicators to identify seismic faults in drill core recovered from the Japan Trench subduction zone, which hosted 50 m of shallow slip during the Mw9.1 2011 Tohoku-Oki earthquake. Our results show that multiple faults have hosted earthquakes with displacement ≥ 10 m, and each could have hosted many great earthquakes, illustrating an extensive history of great earthquake seismicity that caused large shallow slip. We find that lithologic contrasts in frictional properties do not necessarily determine the likelihood of large shallow slip or seismic hazard

Impact of anti‐immigrant rhetoric and policies on frontline health and social service providers in Southeast Michigan, U.S.A

Rising hostility towards immigrants characterised the 2016 Presidential election in the United States (US) and subsequent policy priorities by the new presidential administration. The political shift towards aggressive policies targeting undocumented immigrants is far‐reaching and extends into other communities that convive con—or coexist with—immigrant communities. Our study aims to examine the rippling effects of these anti‐immigrant policies and rhetoric on health and social service providers in Southeast Michigan who predominantly serve Latino immigrants. Between April and August 2018, we conducted in‐depth individual interviews in two Federally Qualified Health Centers and a non‐profit social service agency at a county health department. We interviewed 28 frontline health and social service providers. After coding and thematic analyses, we found that staff members’ experiences in supporting immigrant clients was congruent with definitions of secondary trauma stress and compassion fatigue, whereby exposure to clients’ trauma combined with job burden subsequently impacted the mental health of providers. Major themes included: (a) frontline staff experienced a mental and emotional burden in providing services to immigrant clients given the restrictive anti‐immigrant context; and (b) this burden was exacerbated by the increased difficulties in providing these services to their clients. Staff described psychological and emotional distress stemming from exposure to clients’ immigration‐related trauma and increased mental health needs. This distress was exacerbated by an increased demand to meet clients’ needs, which involved explaining or translating documents into English, assisting with legal paperwork, referring clients to mental health resources, addressing increased transportation barriers, and reestablishing trust with the community. Our findings add qualitative data on the mental health implications for frontline providers who support Latino immigrant clients impacted by immigration and highlights the need for further research and resources that address the workplace‐related stress generated by heightened immigration enforcement.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163387/2/hsc13012.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163387/1/hsc13012_am.pd

Tropical surface singularities

In this paper, we study tropicalisations of singular surfaces in toric threefolds. We completely classify singular tropical surfaces of maximal-dimensional type, show that they can generically have only finitely many singular points, and describe all possible locations of singular points. More precisely, we show that singular points must be either vertices, or generalized midpoints and baricenters of certain faces of singular tropical surfaces, and, in some cases, there may be additional metric restrictions to faces of singular tropical surfaces.Comment: A gap in the classification was closed. 37 pages, 29 figure

A qualitative study on the impact of the 2016 US election on the health of immigrant families in Southeast Michigan

Abstract Background Given the anti-immigrant rhetoric and policy proposals by President Donald Trump during the 2016 presidential campaign and afterwards, his election to president in November 2016 and subsequent policy changes has affected immigrant families. In this study, we aim to better understand how post-election policy change may have impacted the health and well-being, including health and social service utilization, of Latino immigrants in Southeastern Michigan. Methods We conducted 28 in-depth interviews with frontline staff at two Federally Qualified Health Centers and a non-profit agency. These staff had intimate knowledge of and insights into the lived experiences of the mixed-status immigrant families they serve. The interviews were audio recorded, transcribed, and analyzed thematically. Results Our findings show three major themes: (1) An increased and pervasive fear of deportation and family separation among mixed-status immigrant clients, (2) The fear of deportation and family separation has resulted in fractures in community cohesion, and (3) Fear of deportation and family separation has had an impact on the healthcare utilization and health-related behaviors of mixed-status families. Staff members report that these three factors have had an impact on physical and mental health of these immigrant clients. Conclusions These results add to previous literature on the effect of immigration policies on the health and provide key insights for interventions to improve the health of immigrants within this socio-political environment.https://deepblue.lib.umich.edu/bitstream/2027.42/152129/1/12889_2019_Article_7290.pd

Perturbed Field Ionization for Improved State Selectivity

Selective field ionization (SFI) is used to determine the state or distribution of states to which a Rydberg atom is excited. By evolving a small perturbation to the ramped electric field using a genetic algorithm, the shape of the time-resolved ionization signal can be controlled. This allows for the separation of signals from pairs of states that would be indistinguishable with unperturbed SFI. Measurements and calculations are presented that demonstrate this technique and shed light on how the perturbation directs the pathway of the electron to ionization. Pseudocode for the genetic algorithm is provided. Using the improved resolution afforded by this technique, quantitative measurements of the 36p3/2 + 36p3/2 --\u3e 36s1/2 + 37s1/2 dipole–dipole interaction are made

Cluster K Mycobacteriophages: Insights into the Evolutionary Origins of Mycobacteriophage TM4

Five newly isolated mycobacteriophages –Angelica, CrimD, Adephagia, Anaya, and Pixie – have similar genomic architectures to mycobacteriophage TM4, a previously characterized phage that is widely used in mycobacterial genetics. The nucleotide sequence similarities warrant grouping these into Cluster K, with subdivision into three subclusters: K1, K2, and K3. Although the overall genome architectures of these phages are similar, TM4 appears to have lost at least two segments of its genome, a central region containing the integration apparatus, and a segment at the right end. This suggests that TM4 is a recent derivative of a temperate parent, resolving a long-standing conundrum about its biology, in that it was reportedly recovered from a lysogenic strain of Mycobacterium avium, but it is not capable of forming lysogens in any mycobacterial host. Like TM4, all of the Cluster K phages infect both fast- and slow-growing mycobacteria, and all of them – with the exception of TM4 – form stable lysogens in both Mycobacterium smegmatis and Mycobacterium tuberculosis; immunity assays show that all five of these phages share the same immune specificity. TM4 infects these lysogens suggesting that it was either derived from a heteroimmune temperate parent or that it has acquired a virulent phenotype. We have also characterized a widely-used conditionally replicating derivative of TM4 and identified mutations conferring the temperature-sensitive phenotype. All of the Cluster K phages contain a series of well conserved 13 bp repeats associated with the translation initiation sites of a subset of the genes; approximately one half of these contain an additional sequence feature composed of imperfectly conserved 17 bp inverted repeats separated by a variable spacer. The K1 phages integrate into the host tmRNA and the Cluster K phages represent potential new tools for the genetics of M. tuberculosis and related species

Expanding the diversity of mycobacteriophages: insights into genome architecture and evolution.

Mycobacteriophages are viruses that infect mycobacterial hosts such as Mycobacterium smegmatis and Mycobacterium tuberculosis. All mycobacteriophages characterized to date are dsDNA tailed phages, and have either siphoviral or myoviral morphotypes. However, their genetic diversity is considerable, and although sixty-two genomes have been sequenced and comparatively analyzed, these likely represent only a small portion of the diversity of the mycobacteriophage population at large. Here we report the isolation, sequencing and comparative genomic analysis of 18 new mycobacteriophages isolated from geographically distinct locations within the United States. Although no clear correlation between location and genome type can be discerned, these genomes expand our knowledge of mycobacteriophage diversity and enhance our understanding of the roles of mobile elements in viral evolution. Expansion of the number of mycobacteriophages grouped within Cluster A provides insights into the basis of immune specificity in these temperate phages, and we also describe a novel example of apparent immunity theft. The isolation and genomic analysis of bacteriophages by freshman college students provides an example of an authentic research experience for novice scientists