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Michael Lisowski

Publications and source records attributed to Michael Lisowski.

48 records · Page 3Linked to original sources
USGS2008

Instrumentation in remote and dangerous settings; examples using data from GPS “spider” deployments during the 2004-2005 eruption of Mount St. Helens, Washington

Self-contained, single-frequency GPS instruments fitted on lightweight stations suitable for helicopter-sling payloads became a critical part of volcano monitoring during the September 2004 unrest and subsequent eruption of Mount St. Helens. Known as “spiders” because of their spindly frames, the stations were slung into the crater 29 times from September 2004 to December 2005 when conditions at the volcano were too dangerous for crews to install conventional equipment. Data were transmitted in near-real time to the Cascades Volcano Observatory in Vancouver, Washington. Each fully equipped unit cost about $2,500 in materials and, if not destroyed by natural events, was retrieved and redeployed as needed. The GPS spiders have been used to track the growth and decay of extruding dacite lava (meters per day), thickening and accelerated flow of Crater Glacier (meters per month), and movement of the 1980-86 dome from pressure and relaxation of the newly extruding lava dome (centimeters per day).

Washington↗
USGS2007

Analytical volcano deformation source models

Primary volcanic landforms are created by the ascent and eruption of magma. The ascending magma displaces and interacts with surrounding rock and fluids as it creates new pathways, flows through cracks or conduits, vesiculates, and accumulates in underground reservoirs. The formation of new pathways and pressure changes within existing conduits and reservoirs stress and deform the surrounding rock. Eruption products load the crust. The pattern and rate of surface deformation around volcanoes reflect the tectonic and volcanic processes transmitted to the surface through the mechanical properties of the crust.

Book chapter↗
USGS2006

Constraints on the mechanism of long-term, steady subsidence at Medicine Lake volcano, northern California, from GPS, leveling, and InSAR

Leveling surveys across Medicine Lake volcano (MLV) have documented subsidence that is centered on the summit caldera and decays symmetrically on the flanks of the edifice. Possible mechanisms for this deformation include fluid withdrawal from a subsurface reservoir, cooling/crystallization of subsurface magma, loading by the volcano and dense intrusions, and crustal thinning due to tectonic extension (Dzurisin et al., 1991 [Dzurisin, D., Donnelly-Nolan, J.M., Evans, J.R., Walter, S.R., 1991. Crustal subsidence, seismicity, and structure near Medicine Lake Volcano, California. Journal of Geophysical Research 96, 16, 319-16, 333.]; Dzurisin et al., 2002 [Dzurisin, D., Poland, M.P., Bürgmann, R., 2002. Steady subsidence of Medicine Lake Volcano, Northern California, revealed by repeated leveling surveys. Journal of Geophysical Research 107, 2372, doi:10.1029/2001JB000893.]). InSAR data that approximate vertical displacements are similar to the leveling results; however, vertical deformation data alone are not sufficient to distinguish between source mechanisms. Horizontal displacements from GPS were collected in the Mt. Shasta/MLV region in 1996, 1999, 2000, 2003, and 2004. These results suggest that the region is part of the western Oregon block that is rotating about an Euler pole in eastern Oregon. With this rotation removed, most sites in the network have negligible velocities except for those near MLV caldera. There, measured horizontal velocities are less than predicted from ∼10 km deep point and dislocation sources of volume loss based on the leveling data; therefore volumetric losses simulated by these sources are probably not causing the observed subsidence at MLV. This result demonstrates that elastic models of subsurface volume change can provide misleading results where additional geophysical and geological constraints are unavailable, or if only vertical deformation is known. The deformation source must be capable of causing broad vertical deformation with comparatively smaller horizontal displacements. Thermoelastic contraction of a column of hot rock beneath the volcano cannot reproduce the observed ratio of vertical to horizontal surface displacements. Models that determine deformation due to loading by the volcano and dense intrusions can be made to fit the pattern of vertical displacements by assuming a weak upper crust beneath MLV, though the subsidence rates due to surface loading must be lower than the observed displacements. Tectonic extension is almost certainly occurring based on fault orientations and focal mechanisms, but does not appear to be a major contributor to the observed deformation. We favor a model that includes a combination of sources, including extension and loading of a hot weak crust with thermal contraction of a cooling mass of rock beneath MLV, which are processes that are probably occurring at MLV. Future microgravity surveys and the planned deployment of an array of continuous GPS stations as part of a Plate Boundary Observatory volcano cluster will help to refine this model.

California↗
USGS2006

Geodetic observations and modeling of magmatic inflation at the Three Sisters volcanic center, central Oregon Cascade Range, USA

Tumescence at the Three Sisters volcanic center began sometime between summer 1996 and summer 1998 and was discovered in April 2001 using interferometric synthetic aperture radar (InSAR). Swelling is centered about 5 km west of the summit of South Sister, a composite basaltic-andesite to rhyolite volcano that last erupted between 2200 and 2000 yr ago, and it affects an area ∼20 km in diameter within the Three Sisters Wilderness. Yearly InSAR observations show that the average maximum displacement rate was 3–5 cm/yr through summer 2001, and the velocity of a continuous GPS station within the deforming area was essentially constant from June 2001 to June 2004. The background level of seismic activity has been low, suggesting that temperatures in the source region are high enough or the strain rate has been low enough to favor plastic deformation over brittle failure. A swarm of about 300 small earthquakes ( M max = 1.9) in the northeast quadrant of the deforming area on March 23–26, 2004, was the first notable seismicity in the area for at least two decades. The U.S. Geological Survey (USGS) established tilt-leveling and EDM networks at South Sister in 1985–1986, resurveyed them in 2001, the latter with GPS, and extended them to cover more of the deforming area. The 2001 tilt-leveling results are consistent with the inference drawn from InSAR that the current deformation episode did not start before 1996, i.e., the amount of deformation during 1995–2001 from InSAR fully accounts for the net tilt at South Sister during 1985–2001 from tilt-leveling. Subsequent InSAR, GPS, and leveling observations constrain the source location, geometry, and inflation rate as a function of time. A best-fit source model derived from simultaneous inversion of all three datasets is a dipping sill located 6.5 ± 2.5 km below the surface with a volume increase of 5.0 × 10 6 ± 1.5 × 10 6 m 3 /yr (95% confidence limits). The most likely cause of tumescence is a pulse of basaltic magma intruding the upper crust along the brittle–ductile interface — a process that must occur episodically beneath the Cascade Range but in the past would have escaped detection in the absence of unusual seismicity. We speculate that such intrusive episodes last from days to years and are separated by quiescent periods of decades to centuries. The likelihood that the current episode at Three Sisters will culminate in an eruption is judged to be low, but the impact of an eruption could be great. The USGS has updated its volcano hazards assessment for the Three Sisters region, notified appropriate agencies and the public, and is helping to prepare an emergency coordination and communication plan.

Central Oregon Cascade Range, Three Sisters volcan↗
USGS2005

Global Positioning System measurements on the island of Hawai`i: 1997 through 2004

This report summarizes GPS data and observations collected between 1997 and 2004 on the island of Hawai‘i with static surveying and continuously recording instruments. On Kīlauea, the long-term deformation field is dominated by steady southeastern velocities of more than 6 cm/year and uplift of about 2 cm/yr at stations on the south flank (with respect to a fixed Pacific Plate). Superimposed on this steady signal are transient displacements associated with magmatic intrusions, earthquakes, and aseismic slip events. The largest of these was the January 30, 1997 dike intrusion and eruption. GPS instruments near Kīlauea’s summit also record numerous additional short-term fluctuations associated with variations in magma reservoir pressure and geometry. From mid-1997 through 2001, the dominant signal at the summit was deflationary, with maximum subsidence of ~5 cm/yr south of Kīlauea caldera. However, inflation of the magma system was observed from late 2001 to May 2002, and from mid-2003 through 2004. The east rift zone eruption continued at the Pu‘u ‘O‘o vent during the entire period of this report. Mauna Loa Volcano, which most recently erupted in 1984, showed low rates of contraction across the summit caldera and southeasterly motion of the southeast flank from 1997 until May 2002. Reinflation started abruptly in May 2002. Inflation contin ued through 2004, but at highly variable rates. Extension rates on a baseline across the summit caldera slowed in October 2002 and increased again starting in mid-2003. The most dramatic change during the inflation period, however, was a significant increase in extension rate on longer baselines, from the northwest to southeast flanks, in July 2004. GPS measurements on Hualalai volcano show no significant motion relative to the Pacific Plate.

Hawai'i↗
USGS1997

The Loma Prieta, California, earthquake of October 17, 1989: Aftershocks and postseismic effects

While the damaging effects of the earthquake represent a significant social setback and economic loss, the geophysical effects have produced a wealth of data that have provided important insights into the structure and mechanics of the San Andreas Fault system. Generally, the period after a large earthquake is vitally important to monitor. During this part of the seismic cycle, the primary fault and the surrounding faults, rock bodies, and crustal fluids rapidly readjust in response to the earthquake's sudden movement. Geophysical measurements made at this time can provide unique information about fundamental properties of the fault zone, including its state of stress and the geometry and frictional/rheological properties of the faults within it. Because postseismic readjustments are rapid compared with corresponding changes occurring in the preseismic period, the amount and rate of information that is available during the postseismic period is relatively high. From a geophysical viewpoint, the occurrence of the Loma Prieta earthquake in a section of the San Andreas fault zone that is surrounded by multiple and extensive geophysical monitoring networks has produced nothing less than a scientific bonanza. The reports assembled in this chapter collectively examine available geophysical observations made before and after the earthquake and model the earthquake's principal postseismic effects. The chapter covers four broad categories of postseismic effect: (1) aftershocks; (2) postseismic fault movements; (3) postseismic surface deformation; and (4) changes in electrical conductivity and crustal fluids.

California↗
USGS1996

The Loma Prieta, California, Earthquake of October 17, 1989: Main shock characteristics

The October 17, 1989, Loma Prieta, Calif., earthquake (0004:15.2 G.m.t. October 18; lat 37.036º N., long 121.883º W.; 19-km depth) had a local magnitude (M L ) of about 6.7, a surface-wave magnitude (M S ) of 7.1, a seismic moment of 2.2x10 19 N-m to 3.5x10 19 N-m, a source duration of 6 to 15 s, and an average stress drop of at least 50 bars. Slip occurred on a dipping fault surface about 35 km long and was largely confined to a depth of about 7 to 20 km. The slip vector had a large vertical component, and slip was distributed in two main regions situated northwest and southeast of the hypocenter. This slip distribution caused about half of the earthquake's energy to be focused toward the urbanized San Francisco Bay region, while the other half was focused toward the southeast. Had the rupture initiated at the southeast end of the aftershock zone, shaking in the bay region would have been both longer and stronger. These source parameters suggest that the earthquake was not a typical shallow San Andreas-type event but a deeper event on a different fault with a recurrence interval of many hundreds of years. Therefore, the potential for a damaging shallow event on the San Andreas fault in the Santa Cruz Mountains may still exist.

California↗
USGS1995

Strain accumulation in Owens Valley, California, 1974 to 1988

Strain accumulation observed over the 1974 to 1988 interval in a 25 by 100 km aperture trilateration network spanning Owens Valley is adequately described by a strain rate that is uniform in space and time. The tensor strain-rate components referred to a coordinate system with the 2 axis directed N18°W (parallel to the trend of the valley) and the 1 axis N72°E are ∈˙11′ = 0.042 ± 0.014 μstrain/yr, ∈˙12′ = -0.058 ± 0.007 μstrain/yr, and ∈˙22′ = 0.002 ± 0.014 μstrain/yr; quoted uncertainties are standard deviations and extension is reckoned positive. Across the 25-km breadth of the network, this amounts to 1.0 ± 0.3 mm/yr extension normal to the axis of the valley, 2.9 ± 0.4 mm/yr right-lateral shear across the axis, and no extension parallel to the axis. If the measured strain accumulation is attributed to slip on the deeper section of the Owens Valley fault with the uppermost 10 km of the fault locked, the observed right-lateral deformation would imply about 7 mm/yr right-lateral slip on the buried fault, much greater than the geologic estimate of 2 ± 0.5 mm/yr right-lateral secular slip (Beanland and Clark, 1994). Nor is the observed uplift profile across the valley consistent with continuing normal slip on just the deep segment of the Owens Valley fault; normal slip at depth on the Sierra frontal fault also seems to be required. The observed deformation across Owens Valley apparently implies processes more complicated than those represented by the conventional model of strain accumulation along a throughgoing fault.

California↗
USGS1993

The Loma Prieta, California, earthquake of October 17, 1989: Preseismic observations

The October 17, 1989, Loma Prieta, Calif., Ms=7.1 earthquake provided the first opportunity in the history of fault monitoring in the United States to gather multidisciplinary preearthquake data in the near field of an M=7 earthquake. The data obtained include observations on seismicity, continuous strain, long-term ground displacement, magnetic field, and hydrology. The papers in this chapter describe these data, their implications for fault-failure mechanisms, the scale of prerupture nucleation, and earthquake prediction in general. Of the 10 papers presented here, about half identify preearthquake anomalies in the data, but some of these results are equivocal. Seismicity in the Loma Prieta region during the 20 years leading up to the earthquake was unremarkable. In retrospect, however, it is apparent that the principal southwest-dipping segment of the subsequent Loma Prieta rupture was virtually aseismic during this period. Two M=5 earthquakes did occur near Lake Elsman near the junction of the Sargent and San Andreas faults within 2.5 and 15 months of, and 10 km to the north of, the Loma Prieta epicenter. Although these earthquakes were not on the subsequent rupture plane of the Loma Prieta earthquake and other M=5 earthquakes occurred in the preceding 25 years, it is now generally accepted that these events were, in some way, foreshocks to the main event.

California↗
USGS1990

Surface displacements in the 1906 San Francisco and 1989 Loma Prieta earthquakes

The horizontal displacements accompanying the 1906 San Francisco earthquake and the 1989 Loma Prieta earthquake are computed from geodetic survey measurements. The 1906 earthquake displacement field is entirely consistent with right-lateral strike slip on the San Andreas fault. In contrast, the 1989 Loma Prieta earthquake exhibited subequal components of strike slip and reverse faulting. This result, together with other seismic and geologic data, may indicate that the two earthquakes occurred on two different fault planes.

California↗