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The possibility for earthquakes to be triggered by or related to each other or an external “aseismic” factorimpacts hazard assessment and mitigation. With this dissertation, we have worked towards improvement ofobservation and modeling for earthquake swarms, slow slip associated with episodic tremor and slip, and humaninduced seismicity. Each of these cases has the potential to influence when, where, and to what size an earthquakecan grow. First, we produce geodetic inversions of slow slip events in Cascadia, and highlight two unique instanceswhere slow slip and non-volcanic tremor are not spatially correlated. In Cascadia, the correlation is so strong thattremor has become an accepted proxy for slow slip, but we show that this is not always the case. We show that thedepth of the tremor may resolve this discrepancy. Second, we conduct a search for earthquake swarms along majorconvergent margins and find 180 swarms occurring within the seismogenic megathrust. We find evidence that theseswarms are driven by aseismic slip, and may be broadly anti-correlated with large, destructive megathrust events.Third, we investigate this apparent anti-correlation with large megathrust events in detail by examining all Mw>7.5earthquakes and classify them based on their relationship to swarm-generating regions of the interface. We find thatlarge earthquakes are five times more likely to terminate in swarm regions than they are to propagate through swarmregions, suggesting that swarm regions are delineating where megathrusts are segmented. Lastly, we develop amultiple station waveform cross-correlation technique to investigate local to regional seismic data which is able todetect earthquakes several orders of magnitude smaller than traditional techniques. We use this technique to create a~20 fold increase in detected seismicity during the 2011 Youngstown, Ohio earthquake sequence, allowing us to gowell beyond the standard “proximity test” and conclusively establish a causal relation between wastewater injectionand earthquakes. In total, we expect this dissertation to improve our understanding of how these unique seismicsequences occur, what their underlying mechanism is, and how they may be related to the damaging earthquakessought out by the hazard assessment community. |
