Modelling of near-surface seismic structure beneath Hawaii using reverberations     

Yingping Li  Clifford H. Thurber 《Geophysical Journal International》1995,122(2):441-456

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Comparison of a complex rupture model with the precursor asperities of the 1975 HawaiiM s-7.2 earthquake     

D. Harvey  M. Wyss 《Pure and Applied Geophysics》1986,124(4-5):957-973

A simplified multiple source model was constructed for the 1975 HawaiiM _s=7.2 earthquake by matching synthetic signals with three component accelerograms at two stations located approximately 45 km from the epicenter. Six major subevents were identified and located approximately. The signals of these are larger by factors of 1.4 to 3.2 than that of theM _L=5.9 foreshock which occurred 70 minutes before the main rupture and also triggered the SAM-1 recorders at the two stations. Dividing the rupture length (40 km) by the duration of strong ground shaking ( 50 sec) an, average rupture velocity of 0.8 km/sec (about 25% of S-velocity) is obtained. Thus it is likely that the rupture stopped between subevents. The approximate epicenters of the 6 major subevents, and of the foreshock, support the hypothesis that they were located in high stress asperities which rupture during the main shock, except for the last events which is interpreted as a stopping phase generated at a barrier. These asperities have been previously defined on the basis of differences in the precursor pattern before the mainshock. Thus, it appears that both the details of the precursors and of the main rupture depended critically on the heterogeneous tress distribution in the source volume. This suggests that main rupture initiation points and locations of high rupture accelerations may be identified before the mainshock occurs, based on precursor anomaly patterns. A satisfactory match of synthetic signals with the observations could be obtained only if the aximuth of the fault plane of subevents was rotated from N60°E to N90°E and back to N30°E. These orientations are approximately parallel to the nearest Kilauea rift segments. Hence the slip directions and greatest principal stresses were oriented perpendicular to the rifts everywhere. From this analysis and other work, it is concluded that this fault surface consisted of three types of segments with different strength: hard asperities (radius 5 km), soft but brittle segments between the asperities (radius 5 km), and a viscous half (10×40 km) which slipped during the mainshock, but where microearthquakes and aftershocks are not common.  相似文献   

Factors controlling the lengths of channel-fed lava flows     

Harry Pinkerton  Lionel Wilson 《Bulletin of Volcanology》1994,56(2):108-120

Factors which control lava flow length are still not fully understood. The assumption that flow length as mainly influenced by viscosity was contested by Walker (1973) who proposed that the length of a lava flow was dependent on the mean effusion rate, and by Malin (1980) who concluded that flow length was dependent on erupted volume. Our reanalysis of Malin's data shows that, if short duration and tube-fed flows are eliminated, Malin's Hawaiian flow data are consistent with Walker's assertion. However, the length of a flow can vary, for a given effusion rate, by a factor of 7, and by up to 10 for a given volume. Factors other than effusion rate and volume are therefore clearly important in controlling the lengths of lava flows. We establish the relative importance of the other factors by performing a multivariate analysis of data for recent Hawaiian lava flows. In addition to generating empirical equations relating flow length to other variables, we have developed a non-isothermal Bingham flow model. This computes the channel and levee width of a flow and hence permits the advance rates of flows and their maximum cooling-limited lengths for different gradients and effusion rates to be calculated. Changing rheological properties are taken into account using the ratio of yield strength to viscosity; available field measurements show that this varies systematically from the vent to the front of a lava flow. The model gives reasonable agreement with data from the 1983–1986 Pu'u Oo eruptions and the 1984 eruption of Mauna Loa. The method has also been applied to andesitic and rhyolitic lava flows. It predicts that, while the more silicic lava flows advance at generally slower rates than basaltic flows, their maximum flow lengths, for a given effusion rate, will be greater than for basaltic lava flows.  相似文献   

A detailed palaeointensity and inclination record from drill core SOH1 on Hawaii   总被引：1，自引：0，他引：1  

Nicholas Teanby  Carlo LajDavid Gubbins  Malcolm Pringle 《Physics of the Earth and Planetary Interiors》2002,131(2):101-140

A new record of absolute palaeointensity was obtained from drill core Scientific Observation Hole 1 (SOH1) on Kilauea volcano, Hawaii. Kilauea’s high eruption rate resulted in a relatively continuous record and stratigraphic constraints preserved the chronological order. Three hundred and sixty samples were studied with the Thellier-Thellier technique, which gave 195 successful palaeointensity and 271 successful inclination determinations. Three geomagnetic excursions were observed, which exhibited intensity reductions of about 50%. Initial age control from K-Ar and Ar/Ar dating only constrained the total age between 20 and 120 ka. The final age model was obtained by stretching the SOH1 record relative to other Hawaiian palaeomagnetic data. This gave an age range of 0-45 ka for the flows and identified the excursions as the Hilina Pali, Mono Lake and Laschamp events. The SOH1 record of the Hilina Pali event is the most detailed ever, incorporating data from around 40 flows. This age model suggests that Kilauea had a burst of activity at the SOH1 site around 20 ka. All available data was combined to form a composite record of palaeointensity and inclination on Hawaii for 0-45 ka.  相似文献   

Carbon dioxide dynamics in rivers and coastal waters of the “big island” of Hawaii,USA, during baseline and heavy rain conditions     

François S. Paquay  Fred T. Mackenzie  Alberto V. Borges 《Aquatic Geochemistry》2007,13(1):1-18

The distributions of the partial pressure of carbon dioxide (pCO₂) and total alkalinity (TA) were examined for a 6-month period in the Wailuku and Wailoa rivers and coastal waters of Hilo Bay on the west coast of the Island of Hawaii, USA. Main results for the largest and turbulent Wailuku River show in the watershed an oversaturation in CO₂ with respect to atmospheric equilibrium and a CO₂ undersaturation in the estuary. In the Wailoa river-estuary system, extremely high pCO₂ values ranging from 1500 to 10500 ppm were measured with significant shifts in pCO₂ from drought to flood period. In the two rivers, water residence time, groundwater inputs and occasional flood events are the predominant drivers of the spatial and temporal patterns in the distribution of pCO₂. In Hilo Bay, CO₂ oversaturation dominates and the bay was a source of CO₂ to the atmosphere during the study period. TA is conservative along the salinity gradient, indicating calcification in the bay is not a significant source of CO₂ to the atmosphere.  相似文献   

Temporal variability in SO<Subscript>2</Subscript> exposures at Hawai’i Volcanoes National Park,USA     

Jene D. Michaud  Jon-Pierre Michaud  Dmitry Krupitsky 《Environmental Geology》2007,52(1):81-92

Sulfur dioxide measured at the Visitor’s Center of Hawai’i Volcanoes National Park, USA exhibits seasonal and diurnal patterns and is sensitive to rainfall, but the relationship between wind direction and SO₂ is too inconsistent to support deterministic predictions of hourly SO₂ based on hourly wind direction. Although SO₂ at the Visitor Center has usually been below regulatory levels, high SO₂ levels and adverse health effects remain a concern. This investigation identified patterns in hourly SO₂ based on wind direction, time of day, month, and rainfall occurrence using 4 years of hourly data. Empirical probabilities were investigated using a Bayesian approach. Winds from the volcanic vents were rare, but when they did occur SO₂ was elevated about half of the time. Conversely, half of the hours with elevated SO₂ occurred when volcanic vents were not directly upwind. Episodes of elevated SO₂ tended to occur during the months of November–March and between 8:00 a.m. and 5:00 p.m. Rainfall was associated with a marked reduction in SO₂ (29–81% depending on wind direction). Individuals that wish to avoid exposure to volcanic fumes can take these patterns into account.  相似文献   

Surface alteration of basalt due to cation-migration     

Dorothee J. M. Burkhard  Hiltrud Müller-Sigmund 《Bulletin of Volcanology》2007,69(3):319-328

Basaltic lava from Kilauea, Hawaii may have a red-brown surface, indicative of Fe-(hydr)oxides. This surface is not found where exposed to weathering, but at the interface between lava lobes, or in the interior of lava channels. We use several analytical techniques to determine how these Fe-(hydr)oxide surfaces may have developed. WDS-elemental distribution line profiles from the lava surface towards the lava′s interior detect an Fe-rich film of less than 5 μm thickness. Heat treatment of quenched, fresh lava samples of the same chemical composition between 600–1,090°C helps to replicate temperatures under which such an Fe-rich film might have formed. These experiments suggest that Fe-enrichment occurs above 1,020°C, whereas at lower temperatures Ca is enriched relative to Fe. One sample was treated below the glass transition temperature, at 600°C for 164 h. A depth profile with secondary neutral mass spectrometry shows an enrichment of Mg at the outer 50 nm of the glass surface. The formation of films requires cation migration, which is driven by an oxygen chemical potential between air and the reduced basalt (Fe²⁺/Fe³⁺ ratio of 13.3). The change of surface alteration from Mg to Ca film at lower temperatures, to predominantly Fe at high temperatures, is determined by a change of cation availability, largely controlled by crystallization that already occurs below 850°C, and volume crystallization that occurs above 925°C.  相似文献   

SCUBA observations of Hawaii 167     

Geraint F. Lewis  S. C. Chapman 《Monthly notices of the Royal Astronomical Society》2000,318(3):L31-L33

We present the first submillimetre observations of the z =2.36 broad absorption line system Hawaii 167. Our observations confirm the hypothesis that Hawaii 167 contains a massive quantity of dust, the optical depth of which is sufficient to extinguish completely our ultraviolet view of a central, buried quasar. The submillimetre luminosity and associated dust mass of Hawaii 167 are similar to those of the ultraluminous class of infrared galaxies, supporting the existence of an evolutionary link between these and the active galaxy population. Hawaii 167 appears to be a young quasar that is emerging from its dusty cocoon.  相似文献   

Base flow‐driven shifts in tropical stream temperature regimes across a mean annual rainfall gradient          下载免费PDF全文

Ayron M. Strauch  Richard A. MacKenzie  Ralph W. Tingley III 《水文研究》2017,31(9):1678-1689

Climate change is expected to affect air temperature and watershed hydrology, but the degree to which these concurrent changes affect stream temperature is not well documented in the tropics. How stream temperature varies over time under changing hydrologic conditions is difficult to isolate from seasonal changes in air temperature. Groundwater and bank storage contributions to stream flow (i.e., base flow [BF]) buffer water temperatures against seasonal and daily fluctuations in solar radiation and air temperature, whereas rainfall‐driven runoff produces flooding events that also influence stream temperature. We used a space‐for‐time substitution to examine how shifts in BF and runoff alter thermal regimes in streams by analyzing hydrological and temperature data collected from similar elevations (400–510 m above sea level) across a 3,500‐mm mean annual rainfall gradient on Hawai'i Island. Sub‐daily water temperature and stream flow gathered for 3 years were analyzed for daily, monthly, and seasonal trends and compared with air temperature measured at multiple elevations. Results indicate that decreases in median BF increased mean, maximum, and minimum water temperatures as well as daily temperature range. Monthly and daily trends in stream temperature among watersheds were more pronounced than air temperature, driven by differences in groundwater inputs and runoff. Stream temperature was strongly negatively correlated to BF during the dry season but not during the wet season due to frequent wet season runoff events contributing to total flow. In addition to projected increases in global air temperature, climate driven shifts in rainfall and runoff are likely to affect stream flow and groundwater recharge, with concurrent influences on BF resulting in shifts in water temperature that are likely to affect aquatic ecosystems.  相似文献   

Lithospheric heating by mantle plumes     

Norman H. Sleep 《Geophysical Journal International》1987,91(1):1-11

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