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Asta Miklius

Publications and source records attributed to Asta Miklius.

26 records · Page 2Linked to original sources
USGS2009

Kilauea slow slip events: Identification, source inversions, and relation to seismicity

Several slow slip events beneath the south flank of Kilauea Volcano, Hawaii, have been inferred from transient displacements in daily GPS positions. To search for smaller events that may be close to the noise level in the GPS time series, we compare displacement fields on Kilauea's south flank with displacement patterns in previously identified slow slip events. Matching displacement patterns are found for several new candidate events, although displacements are much smaller than previously identified events. One of the candidates, 29 May 2000, is coincident with a microearthquake swarm, as are all of the previously identified slow slip events. The microearthquakes follow the onset of slow slip, implying that they are triggered by stress changes during slip. The new slow slip event brings the total number of events on Kilauea, between 1997 and 2007, to eight, the smallest having M W = 5.3, and the largest having M W = 6.0. While the recurrence time between the four largest events is 2.11 ± 0.01 years, the repeat time for all eight events is 0.9 ± 0.6 years. We invert for the fault geometry and distribution of slip during the slow slip events. The optimal source depths of 5 km, assuming uniform slip dislocations in an elastic half‐space, are considerably shallower than the accompanying swarm earthquakes (6.5–8.5 km), which would place the earthquakes in a zone of decreased Coulomb stress. Inversions including the effects of topography and layered elastic structure in the forward models favor depths comparable to microearthquake depths, such that the earthquakes are located in a region of increased Coulomb stress. We also invert for time‐dependent fault slip directly from the 30 s GPS phase observations, constraining the source to the optimal uniform slip geometry. On the basis of these inversions, the larger events last between 1.5–2.2 days. The data are unable to resolve migration of slip along the fault. The temporal pattern of accompanying microearthquakes is consistent with the fault slip history assuming a seismicity rate theory based on rate and state‐friction, making the swarm earthquakes coshocks and aftershocks of the slow slip events.

Hawaii↗
USGS2009

Surface deformation analysis of the Mauna Loa and Kīlauea volcanoes, Hawai‘i, based on InSAR displacement time series

We investigate the deformation of Mauna Loa and Kilauea volcanoes, Hawai`i, by exploiting the advanced differential Synthetic Aperture Radar Interferometry (InSAR) technique referred to as the Small BAseline Subset (SBAS) algorithm. In particular, we present time series of line-of-sight (LOS) displacements derived from SAR data acquired by the ASAR instrument, on board the ENVISAT satellite, from the ascending (track 93) and descending (track 429) orbits between 2003 and 2008. For each coherent pixel of the radar images we compute time-dependent surface displacements as well as the average LOS deformation rate. Our results quantify, in space and time, the complex deformation of Mauna Loa and Kilauea volcanoes. The derived InSAR measurements are compared to continuous GPS data to asses the quality of the SBAS-InSAR products.

Hawaii↗
USGS2008

Evolution of deformation studies on active Hawaiian volcanoes

Everything responds to pressure, even rocks. Deformation studies involve measuring and interpreting the changes in elevations and horizontal positions of the land surface or sea floor. These studies are variously referred to as geodetic changes or ground-surface deformations and are sometimes indexed under the general heading of geodesy. Deformation studies have been particularly useful on active volcanoes and in active tectonic areas. A great amount of time and energy has been spent on measuring geodetic changes on Kilauea and Mauna Loa Volcanoes in Hawai`i. These changes include the build-up of the surface by the piling up and ponding of lava flows, the changes in the surface caused by erosion, and the uplift, subsidence, and horizontal displacements of the surface caused by internal processes acting beneath the surface. It is these latter changes that are the principal concern of this review. A complete and objective review of deformation studies on active Hawaiian volcanoes would take many volumes. Instead, we attempt to follow the evolution of the most significant observations and interpretations in a roughly chronological way. It is correct to say that this is a subjective review. We have spent years measuring and recording deformation changes on these great volcanoes and more years trying to understand what makes these changes occur. We attempt to make this a balanced as well as a subjective review; the references are also selective rather than exhaustive. Geodetic changes caused by internal geologic processes vary in magnitude from the nearly infinitesimal - one micron or less, to the very large - hundreds of meters. Their apparent causes also are varied and include changes in material properties and composition, atmospheric pressure, tidal stress, thermal stress, subsurface-fluid pressure (including magma pressure, magma intrusion, or magma removal), gravity, and tectonic stress. Deformation is measured in units of strain or displacement. For example, tilt of the ground surface on the rim of Kilauea Caldera is measured in microradians, a strain unit that gives the change in angle from some reference. The direction in which the tilt is measured must be defined - north or south, or some direction normal to the maximum changes. For displacements related to surface faulting, the changes are normally given in linear measures of offset. Changes in the diameter of a caldera can be given in either displacements or strain units. In the later case, the displacement divided by the 'original' diameter gives the strain ratio. Strains are dimensionless numbers; displacements have the dimensions of length. Vectors commonly are used to show the direction and amount of displacements in plan view. Strain results from stress. It can be elastic strain, when the strain is linearly related to stress and is recoverable; it can be viscous strain, where the rate of strain is proportional to the stress and is not recoverable; or it can be plastic strain that is often some complex stress-strain relationship, for example, elastic up to some yield strength and viscous beyond. Volcanic rocks are brittle when cold and under near-surface pressures but plastic to viscous under higher temperature and pressure regimes. It is important in deformation studies to try to define the nature of the strain and the rheology of the rocks being deformed. A good text on rheology is 'The Structure and Rheology of Complex Fluids' by R.G. Larson, 1999. Under changing tensional or compressional stresses, tiny cracks in brittle rocks may open or close, causing a quasielastic strain response. If the stresses exceed the breaking strength of the rock, brittle failure occurs, and the stress-strain relationship breaks down.

Scientific Investigations Report↗
USGS2006

Corrigendum: Earthquakes triggered by silent slip events on Kīlauea volcano, Hawaii

There was a plotting error in Fig. 1 that inadvertently displays earthquakes for the incorrect time interval. The location of earthquakes during the two-day-long slow-slip event of January 2005 are shown here in the corrected Fig. 1 . Because the incorrect locations were also used in the Coulomb stress-change (CSC) calculation, the error could potentially have biased our interpretation of the depth of the slow-slip event, although in fact it did not. Because nearly all of the earthquakes, both background and triggered, are landward of the slow-slip event and at similar depths (6.5–8.5 km), the impact on the CSC calculations is negligible ( Fig. 2 ; compare with Fig. 4 in original paper). The error does not alter our conclusion that the triggered events during the January 2005 slow-slip event were located on a subhorizontal plane at a depth of 7.5 1 km. This is therefore the most likely depth of the slow-slip events. We thank Cecily J. Wolfe for pointing out the error in the original Fig. 1 .

Hawai'i↗
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↗
USGS1990

Deep magma body beneath the summit and rift zones of Kilauea Volcano, Hawaii

A magnitude 7.2 earthquake in 1975 caused the south flank of Kilauea Volcano, Hawaii, to move seaward in response to slippage along a deep fault. Since then, a large part of the volcano's edifice has been adjusting to this perturbation. The summit of Kilauea extended at a rate of 0.26 meter per year until 1983, the south flank uplifted more than 0.5 meter, and the axes of both the volcano's rift zones extended and subsided; the summit continues to subside. These ground-surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones. Kilauea's magmatic system is, therefore, probably deeper and more extensive than previously thought; the summit and both rift zones may be underlain by a thick, near vertical dike-like magma system at a depth of 3 to 9 kilometers.

Hawaii↗