A deep earthquake swarm in late 2003 at Lake Tahoe, California (Richter magnitude < 2.2; depth of 29 to 33 kilometers), was coeval with a transient displacement of 6 millimeters horizontally outward from the swarm and 8 millimeters upward measured at global positioning system station Slide Mountain (SLID) 18 kilometers to the northeast. During the first 23 days of the swarm, hypocentral depths migrated at a rate of 2.4 millimeters per second up-dip along a 40-square-kilometer structure striking north 30° west and dipping 50° to the northeast. SLID's transient velocity of 20 millimeters per year implies a lower bound of 200 nanostrains per year (parts per billion per year) on local strain rates, an order of magnitude greater than the 1996 to 2003 regional rate. The geodetic displacement is too large to be explained by the elastic strain from the cumulative seismic moment of the sequence, suggesting an aseismic forcing mechanism. Aspects of the swarm and SLID displacements are consistent with lower-crustal magma injection under Lake Tahoe.

SUMMARY The depth of reflector layers in the Earth's crust is usually estimated using controlled sources or earthquake signals. Ambient seismic noise, however, can also be used for this purpose. We develop and apply a new method, based on continuous waveform analysis, to estimate the two‐way P‐wave reflection component of the Green's function beneath each station. The Green's functions are retrieved from continuous record autocorrelation stacks at broad‐band sensor locations within the USArray EarthScope Transportable Array in the western Great Basin and the Sierra Nevada, in a region with complex crustal and upper‐mantle structure. In this paper, we show evidence of a reflector at the crust–mantle boundary (Moho discontinuity) derived for the first time from ambient noise autocorrelations using short‐period (∼1 s) data. Our results compare well with earthquake and controlled source investigations, and with tomography findings in the region. Moho depth is difficult to resolve seismically because of the lack of favourable spatial distribution of source and receiver geometries. In contrast, our method can be applied at any desired sensor spacing to estimate Earth reflector depth beneath surface‐located sensors, providing unprecedented resolution.

The model of Haskell for explosion source time functions and spectra fails to satisfy data in the short-period band recorded teleseismically from the three Amchitka Island underground nuclear tests: LONG-SHOT, MILROW, and CANNIKIN. A more recent model due to Mueller and Murphy satisfies the data quite well. The difference in the two models is basically in the fall-off at high frequencies. A simple revision of Haskell's model produces waveforms and spectra nearly identical to ones from Mueller and Murphy's model. This revision requires velocity waveforms to have a rise time of extremely short duration at the elastic boundary, a premise validated by actual near-field measurements.Waveforms are derived from the revised Haskell model and the Mueller and Murphy model and illustrated for pressure at the elastic boundary, reduced displacement potential at the elastic boundary, and far-field displacement. Corresponding spectra are derived and illustrated, *