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The papers in this volume illustrate a number of approaches that are becoming increasingly common and offer the prospect of making significant advances in the broad related topics of the science, hazard, and policy issues of large continental intraplate earthquakes. Plate tectonics offers little direct insight into the earthquakes beyond the fact that they are consequences of slow deformation within plates and, hence, relatively rare. To alleviate these problems, we use space geodesy to define the slowly deforming interiors of plates away from their boundaries, quantify the associated deformation, and assess its possible causes. For eastern North America, by far the strongest signal is vertical motion due to ice-mass unloading following the last glaciation. Surprisingly, the expected intraplate deformation due to regional stresses from plate driving forces or local stresses are not obvious in the data. Several approaches address difficulties arising from the short history of instrumental seismology compared to the time between major earthquakes, which can bias our views of seismic hazard and earthquake recurrence by focusing attention on presently active features. Comparisons of earthquakes from different areas illustrate cases where earthquakes occur in similar tectonic environments, increasing the data available. Integration of geodetic, seismological, historical, paleoseismic, and other geologic data provides insight into earthquake recurrence and the difficult question of why the earthquakes are where they are. Although most earthquakes can be related to structural features, this explanation alone has little predictive value because continents contain many such features, of which a few are the most active. It appears that continental intra-plate earthquakes are episodic, clustered, and migrate. Thus on short time scales seismicity continues on structures that are active at present, perhaps in part because many events are aftershocks of larger past events. However after periods of activity these structures may become inactive for a long time, so the locus of at least some of the seismicity migrates to other structures. Analysis of the thermomechanical structure of the seismic zones gives insight into their mechanics: whether there is something special about them that results in long-lived weak zones on which intraplate strain release concentrates, or as seems more likely, that they are not that unusual, so seismicity migrates. Accepting our lack of understanding of the underlying causes of the earthquakes, the limitations of the short instrumental record, and the possibility of migrating seismicity helps us to recognize the uncertainties in estimates of seismic hazards. Fortunately, even our limited knowledge can help society develop strategies to mitigate earthquake hazards while balancing resources applied to this goal with those applied to other needs.

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