Donald M. Thomas

Geochemical Precursors to Seismic Activity

Studies of earthquake precursory phenomena during the last several decades have found that significant geophysical and geochemical changes can occur prior to intermediate and large earthquakes. Among the more intensely investigated geochemical phenomena have been: (1) changes in the concentrations of dissolved ions and gases in groundwaters and (2) variations in the concentrations of crustal and mantle volatiles in ground gases. The concentration changes have typically showed no conanomalies trend (either increasing or decreasing), and the spatial and temporal distribution of the observed anomalies have been highly variable. As a result, there is little agreement on the physical or chemical processes responsible for the observed anomalies. Mechanisms proposed to account for precursory groundwater anomalies include ultrasonic vibration, pressure sensitive solubility, pore volume collapse, fracture induced increases in reactive surfaces, and aquifer breaching/fluid mixing. Precursory changes in soil gas composition have been suggested to result from pore volume collapse, micro-fracture induced exposure of fresh reactive silicate surfaces, and breaching of buried gas-rich horizons. An analysis of the available field and laboratory data suggests that the aquifer breaching/fluid mixing (AB/FM) model can best account for many of the reported changes in temperature, dissolved ion and dissolved gas concentrations in groundwater. Ultrasonic vibration and pressure sensitive solubility models cannot reasonably account for the geochemical variations observed and, although the pore collapse model could explain some of the observed chemical changes in groundwater and ground gas, uncertainties remain regarding its ability to generate anomalies of the magnitude observed. Other geochemical anomalies, in particular those associated with hydrogen and radon, seem best accounted for by increases in reactive surface areas (IRSA model) that may accompany precursory deformation around the epicenter of an impending earthquake. Analysis of the probable response of these models to the earthquake preparation process, as well as to other environmental factors, suggests that geochemical monitoring programs can provide information that may be valuable in forecasting the probability of an earthquake; however, because of the complexity of the earthquake preparation process, the absolute prediction of seismic events using geochemical methods alone, does not presently appear to be feasible.

The quality of sea ice velocity estimates

Several aspects of observed and estimated velocities for Arctic sea ice are explored. The long-term mean ice motion field and associated variance are derived using 15 years (over 85,000 observations) of daily buoy motions. The mean field is separated into the part due to long-term currents and internal ice stress and the part due to mean winds. The velocity variance is partitioned into “linear” and “nonlinear” parts. The linear response has no trend over the 15 years examined. For a 5-year subset of the buoy data, an ice-ocean model with constant air-drag parameters is used to estimate daily ice velocities at the buoy locations, and then the linear relationship between the modeled velocities and the geostrophic winds is examined. Compared with buoy velocities, the modeled velocities have a larger variance and larger linear response to the winds. In a parameter study, the effects of seasonally varying air-drag coefficients, increased ice strength, and different ocean currents are examined. Seasonally varying air drag, with smaller average magnitude than the standard value, significantly improves the match of total, linear, and nonlinear variances between observed and modeled velocities. The model simulations with varying air drag also have a smaller root-mean-square daily velocity error. Comparison of daily large-scale deformations shows that the day-to-day deformations are not modeled well but generally have means and standard deviations within ±50% of the observed values. No one version of the model is consistently better than the others at matching the means and standard deviations of the observed daily divergence, vorticity, and shear. Ice thickness is sensitive to the model parameters varied, with 5-year average thicknesses ranging from 2.2 to 3.4 m for the various simulations.

Unspiked K–Ar dating of Pleistocene tholeiitic basalts from the deep core SOH-4, Kilauea, Hawaii

Tholeiitic subaerial lava flows from Kilauea (SOH-4 deep core) were successfully dated by unspiked K–Ar with 40Ar* contents as low as ≈0.1%. Ages between 436 and 42 ka were found on lavas between the depths of 1650 and 468 m. All subaerial ages are consistent with their stratigraphic position and allow us to derive a lava accumulation rate of 3.07±0.44 mm/a, which is within the range of rates determined in high 40Ar* OIBs. Age determinations on dike samples yield ages that are younger than those of the enclosing lavas. The validity of the ages was cross-checked with U-series ages of coral terraces on the northwest flank of Hawaii as determined by Ludwig et al. (1991). Dating problems seem to be restricted to a submarine pillow lava sample from level 1808 m, which gives an apparent age of ≈1 Ma, which is an overestimate with respect both to rate of construction of Kilauea and the Hawaiian plume history.

Geomagnetic field intensity over the last 42,000 years from core SOH‐4, Big Island, Hawaii

A record of the absolute geomagnetic field intensity spanning the last 42 kyr has been obtained from 100 lava flows (187 successful Thellier experiments) recovered in the top 468 m of core from the SOH-4 well on the Island of Hawaii. Assuming a linear extrusion rate between the present and the 42 kyr date obtained with a refined K/Ar technique, this corresponds to an average of one flow every 420 years. Rock magnetic analysis identifies low-Ti content and high-Ti content magnetites in 75% and 25% of the samples, respectively, as the main carriers of magnetization. The low-Ti magnetites are very stable while some transformations occur upon heating in the other samples, but both groups allow reliable paleointensity determinations. The directional record documents inclinations consistent with a geocentric dipole field for the last 16 kyr and between 38 and 42 kyr. Between 16 and 38 kyr shallower and, in some cases, negative inclinations, were observed. Because of the high extrusion rate and the exceptional percentage of reliable intensity determinations, the record of the geomagnetic field intensity over the last 42 kyr has a resolution comparable to the best sedimentary records. The geomagnetic field intensity at Hawaii appears to have varied between 18 and 79 µT and is characterized by large fluctuation with peak-to-peak amplitudes of 20–25 µT. The observed values are quite consistent with other values obtained from Hawaii for the last 31 kyr (Mankinen and Champion, 1993a, b; Tanaka and Kono, 1991; Coe et al., 1978). The mean intensity over the explored time interval, 45 µT, is slightly higher than the present value of the geomagnetic field in Hawaii.

Helium/Carbon Dioxide Ratios as Premonitors of Volcanic Activity

The composition of the gaseous emissions of two fumaroles at the summit of Kilauea Volcano was monitored for m�re than 2 years. Magma was released from the summit reservoir on three occasions during this period; prior to or during each event the ratios of helium to carbon dioxide in the fumarole gases decreased substantially from that observed during periods of quiescence.

Hydrogeology of the Hawaii Scientific Drilling Project borehole KP‐1: 1. Hydraulic conditions adjacent to the well bore

Temperature and formation resistivity logs obtained in borehole KP-1 of the Hawaii Scientific Drilling Project indicate that the adjacent formation is characterized by several zones of distinctly different average temperature and water salinity. A series of hydraulic analyses and water sampling programs were conducted to rule out the possibility of local hydraulic effects associated with the presence of the borehole in the generation of these apparent groundwater zones. Hydraulic tests and sampling with the borehole cased to a depth of 710 m and open below that depth indicate that the deep aquifer contains seawater at a temperature nearly identical to that of the open ocean at the same depth. Various analyses give estimates of aquifer transmissivity of about 10−3 m2/s in the vicinity of the borehole. Isolation of this deeper aquifer from the overlying groundwater zones was investigated by perforating the casing at six locations and then measuring the changes in water level in the borehole, in the salinity of the fluid column, in the temperature profile of the fluid column, and in the rate of flow in the fluid column induced by the perforations. These results positively confirm that the zones of distinctly different formation properties indicated on the temperature and resistivity logs are not caused by flow in or around casing. Flow and fluid column salinity induced by the perforations also confirm significant differences between the hydraulic heads and geochemistry of the different groundwater zones inferred from the well logs.

Geothermal resources assessment in Hawaii

Report prepared for Western States Cooperative Direct Heat Resource Assessment under grant No. DOE DE-ACO3-80SF10819, Feb. 1985.

Geothermal resources assessment in Hawaii. Final report

Final report prepared for Western States Cooperative Direct Heat Resource Assessment under grant no. DOE DE-AC03-80SF10819.

Scientific drilling in hotspot volcanoes

The term “hotspot” describes a small region of intense volcanism that is located far from a plate bo…