This dissertation investigates earthquake source and nucleation via laboratory earthquakes on a 3-m apparatus at Cornell University and the aftershock sequence of the 3 September 2016 M 5.8 Pawnee, OK earthquake. Chapter 2 presents a broadband calibration method for acoustic emission sensors that is effective from 1 kHz to 1 MHz using generalized ray theory and finite element analysis. This work provided insight into the sensor used to measure earthquake vibrations on the Cornell 3-m apparatus. The Panametrics V103 sensor measures displacement over a broad range from 50 kHz – 0.8 MHz, and behaves like an accelerometer in the 1 – 10 kHz range. Chapter 3 presents observations of slow and fast contained earthquakes on the Cornell 3-m apparatus. The contained ruptures are preferable to conventional “stick-slips” from past studies because the events nucleate, propagate, and arrest before reaching the ends of the sample, thereby avoiding the effects of the loading machine. Slow (0.07 mm/s slip speeds) and fast (0.1 m/s) contained events can occur on the same fault patch. The fastest events have slip speed, stress drop, and apparent stress (0.2 m/s, 0.4 MPa, 1.2 kPa) similar to those of typical M -2.5 earthquakes. The gap between slow and fast events is filled with intermediate events with source spectra depleted near the corner frequency. We propose that this spectrum of events is caused by variations in a ratio p/h*, where h* is the critical nucleation length and p is the length of a fault section with favorable rupture conditions. Chapter 4 investigates earthquake nucleation by examining the spatiotemporal evolution of precursory seismic activity before nine M 2.5 – 3.0 aftershocks of the Pawnee earthquake. Four out of nine study events did not have any detectable precursors within a 2 km radius of their hypocenters in the preceding 16-hour time windows. The remaining five sequences exhibited foreshock sequences, and 70% of our studied events were likely triggered via static stress transfer. All nine sequences are indicative of cascade triggering.