High‐resolution seismic reflection profiles at two different scales were acquired across the transpressional Santa Monica Fault of north Los Angeles as part of an integrated hazard assessment of the fault. The seismic data confirm the location of the fault and related shallow faulting seen in a trench to deeper structures known from regional studies. The trench shows a series of near‐vertical strike‐slip faults beneath a topographic scarp inferred to be caused by thrusting on the Santa Monica fault. Analysis of the disruption of soil horizons in the trench indicates multiple earthquakes have occurred on these strike‐slip faults within the past 50 000 years, with the latest being 1000 to 3000 years ago. A 3.8-km-long, high‐resolution seismic reflection profile shows reflector truncations that constrain the shallow portion of the Santa Monica Fault (upper 300 m) to dip northward between 30° and 55°, most likely 30° to 35°, in contrast to the 60° to 70° dip interpreted for the deeper portion of the fault. Prominent, nearly continuous reflectors on the profile are interpreted to be the erosional unconformity between the 1.2 Ma and older Pico Formation and the base of alluvial fan deposits. The unconformity lies at depths of 30–60 m north of the fault and 110–130 m south of the fault, with about 100 m of vertical displacement (180 m of dip‐slip motion on a 30°–35° dipping fault) across the fault since deposition of the upper Pico Formation. The continuity of the uncomformity on the seismic profile constrains the fault to lie in a relatively narrow (50 m) zone, and to project to the surface beneath Ohio Avenue immediately south of the trench. A very high‐resolution seismic profile adjacent to the trench images reflectors in the 15 to 60 m depth range that are arched slightly by folding just north of the fault. A disrupted zone on the profile beneath the south end of the trench is interpreted as being caused by the deeper portions of the trenched strike‐slip faults where they merge with the thrust fault.

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The Cheyenne belt, a broad mylonitic shear zone, marks a 1.8–1.7 Ga suture between Archean craton to the north and a Proterozoic island arc to the south. A University of Wyoming seismic reflection profile across the Medicine Bow Mountains imaged the steeply dipping Cheyenne belt and crosscutting Laramide faults. By combining surface geology with reflection data from a line that trended oblique to the Cheyenne belt suture and Laramide thrusts, the true subsurface geometry of both could be resolved. The suture zone dips 60° southeast to depths of at least 9 to 14 km. A 5‐ to 10‐km thick zone of reflectors project to the surface near mapped Laramide faults and have a true structural dip of 45°. The imbricate thrusts within this zone cut the Cheyenne belt near 9 km depth. Some weaker events persist throughout the Archean lower crust; however, no clear Moho is observed. The subsurface geometry of the Cheyenne belt suggests that Archean crust is not absent at depth just south of the southernmost splay of the suture as Nd isotope studies might suggest. Alternatively, the Proterozoic hanging wall thickens such that rising plutons may form completely within the hanging wall and show only Proterozoic geochemical signatures. The complex reflectivity pattern observed in the Cheyenne belt line is caused mainly by the multideformational history of the area and the oblique orientation of the line. Ties between reflections and outcrop show that fault‐related lithologic contrasts and deformation within the fault zones generated reflectors at midcrustal depths during the Proterozoic. Later Laramide brittle faulting add to, rather than erased, the reflectivity.

Seismic instruments are highly sensitive and capable of recording a large range of different Earth signals. The high sensitivity of these instruments also makes them prone to various failures. Although many failures are very obvious, such as a dead channel, there are other more subtle failures that easily go unnoticed by both network operators and data users. This work documents several different types of failure modes in which the instrument is no longer faithfully recording ground-motion data. Although some of these failure modes make the data completely unusable, there are also a number of failures in which the data can still be used for certain applications. Of course, the ideal situation is to identify as soon as possible when data become compromised and to have the network operator fix the station. However, knowing how the data became compromised can also help data users to identify if the data can still be used for their particular application. This work in no way attempts to exhaustively document recording failures but rather to communicate examples and equip the reader with ways of identifying failure modes.