Proceedings of Workshop XIX; Active tectonic and magmatic processes beneath Long Valley Caldera, eastern California; Volumes I and II
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Open-File Report↗
Geology topics
D.P. Hill
Publications and source records attributed to D.P. Hill.
Earthquake swarms and local crustal spreading along major strike-slip faults in California
Earthquake swarms in California are often localized to areas within dextral offsets in the linear trend in active fault strands, suggesting a relation between earthquake swarms and local crustal spreading. Local crustal spereading is required by the geometry of dextral offsets when, as in the San Andreas system, faults have dominantly strike-slip motion with right-lateral displacement. Three clear examples of this relation occur in the Imperial Valley, Coso Hot Springs, and the Danville region, all in California. The first two of these areas are known for their Holocene volcanism and geothermal potential, which is consistent with crustal spreading and magmatic intrusion. The third example, however, shows no evidence for volcanism or geothermal activity at the surface. ?? 1978 Birkha??user Verlag.
Pure and Applied Geophysics PAGEOPH↗
The sound of an earthquake
Historical accounts of earthquakes often include references to sounds which accompany earthquakes.
Earthquake Information Bulletin (USGS)↗
Earthquakes, active faults, and geothermal areas in the Imperial Valley, California
A dense seismograph network in the Imperial Valley recorded a series of earthquake swarms along the Imperial and Brawley faults and a diffuse pattern of earthquakes along the San Jacinto fault. Two known geothermal areas are closely associated with these earthquake swarms. This seismicity pattern demonstrates that seismic slip is occurring along both the Imperial-Brawley and San Jacinto fault systems.
California↗
Point Mugu, California, earthquake of 21 February 1973 and its aftershocks
Seismological investigations show that the Point Mugu earthquake involved north-south crustal shortening deep within the complex fault zone that marks the southern front of the Transverse Ranges province. This earthquake sequence results from the same stress system responsible for the deformation in this province in the Pliocene through Holocene and draws attention to the significant earthquake hazard that the southern frontal fault system poses to the Los Angeles metropolitan area.
California↗
Deformation measurements on Kilauea volcano, Hawaii
Repeated electronic distance measurements across Kilauea Caldera with Tellurometers and Geodimeter show definite horizontal expansion related to the vertical uplift and outward tilting of the summit prior to an eruption, and contraction during and after a flank eruption. Measurements started in October 1964, along a 3098 meter line between Uwekahuna and Keanakakoi, indicate a relatively uniform lengthening of 12 centimeters during the interval October 22, 1964 to March 1, 1965. Rapid shortening of the line by 28 centimeters was measured 4 days after the beginning of a flank eruption which involved emission of approximately 29 million cubic meters of lava during the period March 5 to March 15, 1965. During the expansion, the standard deviation of 10 Tellurometer measurements from a least-squares srtaight line solution is ± 2.0 centimeters (6.5 ppm) whereas 9 Geodimeter measurements have a standard deviation of ± 1.1 (3.6 ppm) centimeters. Absolute distance readings between the two instruments differ by 4 centimeters (13 ppm), but relative changes in distance were the same on both instruments. Changes in distance across Kilauea Caldera can, therefore, be easily measured to accuracies of 4 to 7 parts per million with standard electronic distance measuring systems. On active volcanoes where ground surface deformation exceeds 10–100 parts per million with changes in subsurface magma pressure or volume, repeated horizontal distance measurements can be a most useful technique.
Hawaii↗
Crustal structure in Nevada and southern Idaho from nuclear explosions
The time of first arrival of seismic waves generated by 4 underground nuclear explosions at the Nevada Test Site (NTS) and recorded along a line extending north into southern Idaho is expressed as T 0 = 0. 00 + Δ/3.0 (assumed), T 1 = 0 .40 + Δ/6.03, and T 2 = 6.15 + Δ/7.84, where time is in seconds and the shot-detector distance (Δ) is in km. Assuming constant velocities and horizontal layers, crustal thickness in the vicinity of NTS was determined to be 28 km. Delays in the traveltime segment T 2 , which represents P n , indicate that the crust may thicken to 32 km in northern Nevada. A third phase, expressed as T 3 = 14.48 + Δ/7.84, was also recognized and has arrival times appropriate for SPS. Amplitudes of P n were determined at 7 places from recordings of seismic waves from one underground nuclear explosion (ANTLER).
Nevada;Idaho↗