Refinement of the modified time-to-failure method for intermediate-term earthquake prediction

The modified time-to-failure method for intermediate-term earthquake prediction utilizes empirical relationships to reduce the number of unknown parameters providing a stable and unique solution set. The only unknown parameters in the modified time-to-failure method are the time and size of the impending main shock. The modified time-to-failure equation is used to model the precursory events and a prediction contour diagram is constructed with the magnitude and time-of-failure as the axes of the diagram. The root-mean-square (rms) is calculated for each set of time and magnitude on the prediction diagram representing the difference between the model (calculated) acceleration and the actual accelerated energy release of the precursory events. A small region, corresponding to the low rms region on the diagram, defines the prediction. The prediction has been shown to consistently under-estimate the magnitude and over-estimate the time-of-failure. These shortcomings are caused by an underestimation in energy release of the modified time-to-failure equation at the very end of the sequence. An empirical correction can be applied to the predicted results to minimize this problem. A main shock location search technique has been developed for use with the modified time-to-failure method. The location technique is used to systematically search an earthquake catalog and identify locations corresponding to precursory sequences that display accelerated energy releases. It has shown good results when applied in retrospective predictions, and is essential for the practical application of the modified time-to-failure method. In addition, an observed linear characteristic in long-term energy release can be used to minimize false predictions. The refined empirical relationships that eliminate or constrain unknown constants used in the modified time-to-failure method and the main shock location search technique are used in a practical application in the New Madrid Seismic Zone (NMSZ). The NMSZ, which is over due for a magnitude 6 event according to recurrence rates (Johnston and Nava, 1985), makes this region ideal for testing the method. One location was identified in the NMSZ as a high risk area for an event in the magnitude 4.5 range. The prediction, if accurate, is of scientific interest only because of the relatively small size of the main shock.     

A Holocene record of climate change,fire ecology and human activity from montane Flat Top Bog,Maui

A sediment core from a high-elevation bog on Maui in the Hawaiian Islands contains evidence for drier conditions between 9.4–5.8 kyr BP, followed by a wetter interval between 5.8–2.2 kyr BP, and a variable late Holocene. These precipitation changes may be a reflection of vertical displacements of the upper boundary of the mid-Pacific Trade Wind Inversion (TWI) cloud layer. Fires, probably volcanically ignited, occurred in the forests prior to human arrival. Polynesian activity in this high-elevation, remote site was apparently limited, with no pollen, charcoal, or sedimentological evidence for local anthropogenic disturbance. After European contact, grass fires increased and introduced plant species invaded the site. Values for Cd, Cu, Pb, and Zn in sediments throughout the Holocene indicate low trace-metal deposition from atmospheric particulates at the site, even in the twentieth century.This paper is one of a series of papers guest edited by Dr. Mark Brenner on tropical paleolimnology     

Further investigations of the fog in the photo-electric condensation nucleus counter

Summary The effect on extinction of isothermal distillation, shrinking of the droplets by evaporation without recondensation of the liberated water vapour, coagulation and differential settling of the fog droplets which take place in the fog of a photo-electric nucleus counter and which can produce a small additional extinction («creep») in the first seconds after its formation, were numerically examined. The relative contribution of each process to the total creep observed is assessed. It is found that isothermal distillation can produce amounts of creep (up to 1.70%) which exceed considerably those caused by evaporation or coagulation. The results of these computations explain the occurrence of creep with concentrations greater than approx. 25 000 nuclei/cm³ in fog-tubes of 3.85 cm air-column diameter.That the disappearance of creep in fog-tubes of diameters 2.5 cm and less is due to the accelerated heat-flow from the walls of the narrow fog-tube was previously proved by reducing appropriately the diameter of the light pencil through the fog. In order to meet the objection that by restricting the cross section of the light pencil the fine structure of the fog comes into play, the increase in the travel time of the heat from the walls was achieved this time by using a photo-electric counter with a fog-tube of 8 cm diameter and a light beam of 2.8 cm diameter as in the «Standard Counter 1946». As expected, creep was found in every single measurement up to readings of 53%. Typical examples of the galvanometer pointer-movement and photographic records of the extinction during fog formation in such a wide fog-tube for readings between approx. 10 and 76% are given and their peculiarities discussed.The extinction over the range from 175 000 to 20 000 nuclei/cm³ was also measured with a red and a blue monochromatic interference filter and the results contrasted against the computed extinctions for these two wave lengths. It was ascertained that for the same number of nuclei the extinction for red light is in general larger than that for blue; the difference between the observed extinctions varies considerably, becoming zero or even negative. The most striking feature, however, is the different course of the extinction for the two wave lengths as a function of the number or size of the droplets.The size of the fog droplets in the counter was deduced from the extinction measurements for these two wave lengths and by collecting the falling droplets on coated slides. The radius of the droplets obtained by the optical method varies from 1.81 to 3.19 when the extinction decreases from 86 to 56%. The radius of the droplets as deduced from gelatine coated slides dyed with Naphtol Green B increases from 1.44 at 67.4% extinction (42 400 nuclei/cm³) to 6.30 at 15.6% (858 nuclei/cm³).

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Zusammenfassung Der Einflus der isothermalen Destillation, des Einschrumpfens der Tröpfchen durch Verdunstung ohne Wiederkondensation des freiwerdenden Wasserdampfes, des Zusammenfliessens und Absetzens der Nebeltröpfchen auf die Extinktion, welche im Nebel des photo-elektrischen Kernzählers stattfinden und die in den ersten Sekunden nach seiner Bildung eine kleine zusätzliche Extinktion (im folgenden Kriechen genannt) erzeugen können, wurde numerisch geprüft. Der entsprechende Beitrag jedes einzelnen der oben genannten Prozesse zum Gesamtbetrag des beobachteten Kriechens wurde abgeschätzt. Es wurde gefunden, dass isothermale Destillation zusätzliche Extinktions-Beträge (bis zu 1.70%) erzeugen kann, welche jene durch Verdunstung oder Zusammenfliessen der Tröpfchen verursachten, beträchtlich übersteigen. Die Resultate dieser Berechnungen erklären das Auftreten des Kriechens bei Konzentrationen grösser als ca. 25 000 Kerne per cm³ in Nebelrohren von 3.85 cm Luftsäulen-Durchmesser.Dass das Verschwinden des Kriechens in Nebelrohren mit einem Durchmesser von 2.5 cm und weniger dem beschleunigten Wärmefluss von den Wänden des engen Nebelrohres zuzuschreiben ist, wurde früher durch eine entsprechende Verengung des Lichtbündels, welches zur Durchleuchtung des Nebels verwendet wird, bewiesen. Um dem Einwand zu begegnen, dass bei so starker Verkleinerung des Querschnittes des Lichtbündels, wie sie benützt wurde, schon die Feinstruktur des Nebels eine Rolle spielt, wurde diesmal die Verlängerung der Laufzeit der Wärme von den Wänden durch Erweiterung des Nebelrohres auf 8 cm Durchmesser erzielt, während der Durchmesser des Lichtbündels mit 2.8 cm — wie im «Standard photo-elektrischen Kernzähler 1946» — unverändert belassen wurde. Entsprechend den Erwartungen wurde bei jeder einzelnen Messung bis zu Lesungen von 53% Kriechen festgestellt. Typische Beispiele der Bewegung des Galvanometer-Zeigers und photographische Aufzeichnungen der Extinktion während der Nebelbildung in einem solchen weiten Nebelrohr werden für Lesungen zsischen ca. 10 und 76% gegeben und ihre Eigentümlichkeiten besprochen.Die Extinktion für Konzentrationen zwischen 175 000 und 20 000 Kernen per cm³ wurde auch mit einem roten und blauen Interferenz-Filter gemessen und die Resultate den für diese zwei Wellenlängen berechneten Extinktionen gegenübergestellt. Es wurde festgestellt, dass bei der gleichen Kernzahl die Extinktion für rotes Licht im allgemeinen grösser ist als jene für blaues; die Differenz zwischen den beobachteten Extinktionen schwankt beträchtlich, wird null oder sogar negativ. Am auffallendsten ist jedoch der verschiedene Verlauf der Extinktion für die zwei Wellenlängen als Funktion der Zahl oder Grösse der Tröpfchen.Die Grösse der Nebeltröpfchen im Nebelrohr des photo-elektrischen Kernzählers wurde aus den Extinktions-Messungen in diesen zwei Wellenlängen und durch Auffangen der fallenden Tröpfchen auf Mikroskop-Objektträgern und Deckgläsern, welche mit gefärbter Gelatine überzogen waren, bestimmt. Der Radius der Tröpfchen, welcher mittels der optischen Methode ermittelt wurde, liegt zwischen 1.81 und 3.19 , wenn die Extinktion von 86 auf 56% abnimmt.Der Tröpfchenradius, wie er aus den Flecken auf den Mikroskopgläschen, deren Gelatineüberzug mit Naphtol Grün B eingefärbt war, bestimmt wurde, wächst von 1.44 bei 67.4% Extinktion (42 400 Kerne per cm³) auf 6.30 bei 15.6% (858 Kerne per cm³).

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The research reported in this article has been sponsored and supported in part by the Geophysics Research Directorate of the Air Force Cambridge Research Center, Air Research and Development Command, United States Air Force, under Contract AF 61(052)-26, through the European Office, ARDC in Brussels.     

Enigmatic Efflorescence in Kärkevagge, Swedish Lapland: The Key to Chemical Weathering?

The second marvel to catch the eye of the visitor to Kärkevagge, after the impressive boulder deposit on the floor of the valley, is the series of prominent white stripes running down the valley's dark cliffs. Streams and springs descending the eastern flank of Kärkevagge are marked by the presence of whitish coatings on the black rock surfaces and on cobbles lining ephemeral waterways. These were referred to as 'lime crusts' by early investigators, but they are not reactive to HCl. We believe that they are a precipitate resulting from acid attack on the local rocks. Pyrite is common in many of the rocks in the valley and its oxidation produces sulfuric acid. As the dissolved mineral elements are carried in the drainage water, efflorescence forms on the surfaces where the water flows due to evaporation or to changes in temperature. The exact mineralogy of the white crusts is unknown, but the crusts are dominated by Al, S, and O, and in some cases by Ca, depending on the substrate and local conditions. Gypsum, illite, and chlorite have been identified by X–ray diffraction of some scrapings of white–coated rocks. However, we believe that some unidentified oxy–hydroxy aluminum sulfates make up the bulk of the precipitates.     

Nature and significance of the Neoproterozoic Sturtian–Marinoan Boundary,Northern Adelaide Geosyncline,South Australia

The Cryogenian succession of the Northern Flinders Ranges reveals a complex sedimentary record between the Sturtian and Marinoan glacial deposits. A major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a subaerial erosion surface with terrestrial and marginal marine infill directly above the Angepena and Balcanoona Formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with thepreviously defined Sturtian–Marinoan Time Series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta ReefComplex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow-water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation.     

Recovering magnetic susceptibility from electromagnetic data over a one-dimensional earth

While the inversion of electromagnetic data to recover electrical conductivity has received much attention, the inversion of those data to recover magnetic susceptibility has not been fully studied. In this paper we invert frequency-domain electromagnetic (EM) data from a horizontal coplanar system to recover a 1-D distribution of magnetic susceptibility under the assumption that the electrical conductivity is known. The inversion is carried out by dividing the earth into layers of constant susceptibility and minimizing an objective function of the susceptibility subject to fitting the data. An adjoint Green's function solution is used in the calculation of sensitivities, and it is apparent that the sensitivity problem is driven by three sources. One of the sources is the scaled electric field in the layer of interest, and the other two, related to effective magnetic charges, are located at the upper and lower boundaries of the layer. These charges give rise to a frequency-independent term in the sensitivities. Because different frequencies penetrate to different depths in the earth, the EM data contain inherent information about the depth distribution of susceptibility. This contrasts with static field measurements, which can be reproduced by a surface layer of magnetization. We illustrate the effectiveness of the inversion algorithm on synthetic and field data and show also the importance of knowing the background conductivity. In practical circumstances, where there is no a priori information about conductivity distribution, a simultaneous inversion of EM data to recover both electrical conductivity and susceptibility will be required.