Abstract We focus on movement of magma beneath Kīlauea from the long summit eruption in 1967–1968 through the first historical sustained eruption on the east rift zone (Mauna Ulu 1969–1974), ending with the occurrence of a magnitude 7.2 earthquake beneath Kīlauea's eastern south flank. Magma from the Hawai‘iian hot spot continuously moves upward to summit storage and drives seaward spreading of Kīlauea's south flank on a 10–12 km deep décollement. Spreading creates dilation in Kīlauea's rift zones and provides room to store magma at depths extending to the décollement surface. During the period of study three types of eruptions – normal (short-lived), episodic and sustained – and three types of intrusions – traditional (summit to rift), inflationary and slow – are classified. Rates of sustained eruption are governed by the geometry of the magmatic plumbing. Swarms of earthquakes beneath the south flank signal increased pressure from magma entering Kīlauea's adjacent rift zone. Magma supply rates are obtained by combining the volume of magma transferred to sites of eruption or intrusion with the volume opened by seaward spreading over the same increment of time. In our interpretation the varying character of eruptions and intrusions requires a gradual increase in magma supply rate throughout the period augmented by incremental increases in spreading rate. The three types of eruptions result from different combinations of magma supply and spreading rate.

ABSTRACT The Santa Susana fault extends along the southern edge of the Santa Susana Mountains from the San Fernando Valley in Los Angeles County 28 km west-northwest into Ventura County. It marks an older hinge line between a thick, continuous middle Miocene to Pliocene sequence on the north and a thin, discontinuous sequence of the same age on the south. The Frew reverse-fault system, south-side up, was overridden by the north-side-up Torrey and Roosa faults that formed before deposition of the Saugus Formation and are precursors to the Santa Susana fault. The Santa Susana fault overrides the Saugus and older formations together with alluvial-fan deposits that unconformably overlie the Saugus; younger alluvial-fan deposits overlie the fault trace. The fault is low dipping and lobate near the surface but steepens at depth to a uniform 55°-60° to maximum well control at -1.5 km. Comparisons with aftershocks of the 1971 San Fernando earthquake suggest that the fault maintains this dip to depths greater than 12 km. Minimum separation varies from zero west of Oak Ridge oil field, where the Santa Susana apparently becomes a bedding fault, to more than 4 km near Aliso-Canyon oil field; true displacement is probably much larger. Comparison of separation on the Santa Susana fault and on the older Torrey and Frew systems suggests that fault displacements have been accelerating since the initiation of the Frew fault during deposition of the Pico Formation. Modern seismieity on the fault is relatively low, although the April 4, 1893, Pico Canyon earthquake may have occurred on the fault. The Santa Susana fault trace steps left and steepens in dip at Gillibrand Canyon and at the west end of Sylmar basin; both steps (lateral ramps) are seismically active. The Gillibrand step is outlined by aftershocks of an M = 4.6 event on April 8, 1976, and the Sylmar (San Fernando) step is outlined by aftershocks of the February 9, 1971, earthquake. The Santa Susana fault is part of a discontinuous north-dipping thrust-fault system that extends from the Red Mountain and San Cayetano faults east to the San Fernando, Sierra Madre, and Cucamonga faults, all of which lie on the south-facing margin of the Palmdale uplift

ABSTRACT The Los Angeles basin formed in late Neogene time on a continental margin previously shaped by Cretaceous and early Paleogene subduction, Paleogene terrane accretion, and mid-Miocene rifting and block rotation. During Neogene time, the boundary between the Pacific and North American plates shifted progressively eastward beneath the Los Angeles region, creating the broad San Andreas transform zone. As reviewed in this paper, structures and rocks within the Los Angeles basin document each stage of that Neogene evolution. The Los Angeles basin began to take its present shape in late Miocene time (ca. 7 Ma) by subsidence between the right-oblique Whittier and Palos Verdes fault zones and the left-oblique Santa Monica fault system. The principal phase of basin opening involved early Pliocene extension in a northwest direction, which accompanied the opening of the Gulf of California and the eastward shift of the southern San Andreas fault to its present position. Most of the structural traps that hold the basin's oil fields began to form during this latest Miocene-early Pliocene deformation. Since mid-Pliocene time, many of these traps have been altered and enhanced—and a few have been breached—by Pasadenan deformation, involving southward shortening, the uplift of the Transverse Ranges, and the propagation of blind thrusts beneath the northern Los Angeles basin. The rapid transition from early Pliocene extension to late Pliocene contraction was associated temporally with a change in relative plate motion dated at 3.9- 3.4 Ma. In analyzing Pasadenan deformation, the flake-tectonics model is more appropriate than the fold-and-thrust-belt model, although both models incorporate aseismic detachment at midcrustal depths. The flake-tectonics model is valid for all phases of Neogene deformation, both transtensional and transpressive, in the Los Angeles region. Fields discovered to date in the Los Angeles basin will yield an ultimate 10.4 billion oil-equivalent barrels (GOEB) of petroleum. Of this, approximately 73% is trapped in faulted anticlines, 12% in simple anticlines, 10% in fault traps, and 5% in stratigraphic traps. Folding has been controlled primarily by preexisting structural hingelines and sedimentary wedge belts and secondarily by en echelon folding associated with wrench faults. Oil seeps and Quaternary topographic uplifts led to most of the discoveries prior to 1925 along the Whittier and Newport−Inglewood fault zones and in the Coyote Hills. Most later discoveries, including the 3-billion-barrel Wilmington oil field, were in structures with little or no Quaternary expression.

ABSTRACT The Half Moon Bay oil field was first developed in the 1880’s and further drilling has been done in each “oil boom” of the past 100 years. The field has produced an estimated 58,000 barrels of oil from about 19 wells within a maximum area of 155 acres. Recent peak field production was 11 B0PD in 1985. Efforts to develop new production have been severely limited by Coastal Zone restrictions. The main reservoir in the Half Moon Bay oil field consists of very thin sandstone layers within lower Pliocene (and upper Miocene?) mudstones of the Purisima Formation, at depths of 240 to 3,085 ft (73 to 940 m). Oil is high gravity: 43°-55° API. Petroleum is trapped on two separate structural features. Recent drilling has been concentrated in the Verde area on the northwest-trending Purisima anticline, where the Purisima Formation overlies a thick upper Miocene sequence. The potential for Monterey Shale production on that structure has not been adequately evaluated. Most of the earlier wells and production were located to the northeast in the Purisima Creek area in a fault block on which the Purisima Formation lies unconformably on lower Miocene and Eocene beds. The Eocene Butano Sandstone in that block has produced a very minor amount of oil. The northwest-striking faults which bound that block had significant pre-Pliocene offset. They appear to extend north to join the San Gregorio fault, and south to merge with a previously mapped major fault in the La Honda area. Similarities between the stratigraphic sections in the Half Moon Bay and Point Reyes areas support earlier estimates of about 44 mi (70 km) of right slip along the San Gregorio fault since the end of Miocene time. [Note: this paper is partially excerpted from A. J. Horn ( 1983 ), “The Resurrection of the Half Moon Bay Oil Field, San Mateo County, California”. Because that article emphasized the Purisima Creek area of the oil field, additional sources have been utilized to extend and update its coverage.]