• Alaska Earthquake Center Quarterly Technical Report July-September 2024

  Farrell, Alexandra; Grassi, Beth; Holtkamp, Stephen; McFarlin, Heather; Nadin, Elisabeth; Parcheta, Carolyn; Stabs, Angelica; West, Michael (Alaska Earthquake Center, 2024-11)

  This series of technical quarterly reports from the Alaska Earthquake Center (AEC) includes detailed summaries and updates on Alaska seismicity, the AEC seismic network and stations, fieldwork, our online presence, and lists publications and presentations by AEC staff. Multiple AEC staff members contribute to this report. It is issued within 1-2 months after the completion of each quarter Q1: January-March, Q2: April-June, Q3: July-September, and Q4: October-December. The first report was published for January-March, 2021.
• 

  Dynamo action in the ionosphere and motions of the magnetospheric plasma

  DeWitt, Ronald N. (1965-07)

  This thesis presents a study of the dynamic interaction which takes place between the magnetospheric plasma and the underlying neutral atmosphere; it is hoped thus to gain a better understanding of the effects of this interaction upon the steady state configuration of the magnetosphere. The neutral portion of the atmosphere (the neutrosphere) and the overlying ionized regions (the upper atmosphere and magnetosphere) may be regarded as two distinct dynamic domains that interact in a region of transition occurring between 100 and 150 km over the earth. The neutrosphere because of its greater mass will dominate the motion, and the magnetospheric plasma can be expected to undergo motions related to those of the upper neutrosphere and transition region. However, the geomagnetic field restricts the motion of the magnetospheric plasma to a particular class, allowing one to consider the magnetospheric motion to be constrained. Motions in the transition region of the class not permitted the magnetospheric plasma will give rise to forces against the constraint. The reaction of the constraint on the atmosphere of the transition region takes the form of a Lorentz force J x B where J is the current responsible for the well known solar quiet day daily magnetic variation (Sq). The explanation for the production of this current in the transition region has traditionally been presented in terms of a dynamo-like electromotive force generated by motions of the conducting atmosphere through the magnetic field, whence the transition region is aptly named the dynamo region. The Lorentz force represented by this current constitutes a significant term in the equation of motion for the dynamo region. Another important term arises from eddy viscous stresses immediately below the dynamo region. The equation of motion for the dynamo region must thus include such forces as well as the pressure gradient and Coriolis terms. However, our almost total ignorance of the eddy viscous stress field at the lower surface of the dynamo layer at present precludes our deducing the entire dynamo layer winds from the observed Sq magnetic variation. The kinematics of the dynamo layer are discussed and the motion or the dynamo layer is divided into a symmetric and an antisymmetric part. The term symmetric is here used to describe winds in the northern and southern hemisphere that are the mirror images of each other with respect to the equatorial plane. It is demonstrated that the symmetric component gives rise to electrostatic fields transverse to the field lines, but to no currents along the field lines, while the antisymmetric case produces the converse effects. The symmetric and antisymmetric winds are further divided into components according to the horizontal electromotive force they produce. (a) Symmetric Wind. In the case of the symmetric wind, only the portion of the wind producing the solenoidal component of the horizontal dynamo electromotive force is effective in producing ionospheric currents. It is demonstrated that only this current producing wind system acts against the constraints imposed by the geomagnetic field on magnetospheric motions. The motion of the magnetospheric plasma driven by each such wind system is discussed. The earlier treatments of the dynamo theory consider the dynamo region to be a single layer in which the wind system and the electric conductivity are assumed to be uniform in height. A new, more general derivation of the layer's dynamo action is given in which no restrictions are placed upon the vertical distributions. An effective wind is defined which permits the use of the earlier equations relating the current function, the electrostatic field, and the scalar field describing the current producing part of the effective wind. The equation relating the electrostatic field and the current function is essentially that employed by Maeda (1956), allowing his solution for the portion of the electrostatic field associated with the current producing wind to remain unaffected by the stratification of the wind system. Mathematical techniques for solving the dynamo equations for the electrostatic field are developed. These allow for a quite general conductivity distribution over the globe, only requiring that it be expressible in surface harmonics. The effect of undetected zonal currents upon the solution for the electrostatic field is discussed. It is suggested that a considerable diurnal component of electrostatic field and other components as well may be hidden from us by our inability to detect the prevailing magnetic perturbations produced by zonal currents. The electrostatic field associated with the non-current producing components of the symmetric wind is likewise hidden from us. (b) Antisymmetric Wind. The equations for the current driven by the antisymmetric component of wind are derived, and some of the effects of such currents are discussed. It is found that the conduction of current along the field lines from one hemisphere to the other is associated with an interhemispheric stress between geomagnetically conjugate points of order 3 x 10⁻⁷ newtons/meter². In addition it is found that an antisymmetric layer current density of 5 amperes/km into the polar cap region (across the 75° latitude circle) might give rise to a displacement of about 150 km in the relative position of the conjugate points defined by field lines of the magnetospheric tail. It is suggested that the dynamo action in the 100 to 150 km height plays a role in determining the manner in which the magnetosphere divides itself into the corotating region and the magnetospheric tail.
• 

  Summary of noctilucent cloud data from Alaska, Canada, Greenland, Iceland and the southern hemisphere for the years 1885-1966

  Fogle, Benson Tarrant (1967-07)
• 

  Improved contrail forecasting techniques for the subarctic setting of Fairbanks, Alaska

  Wendler, Gerd; Steufer, Martin; Moore, Blake; Boussard, J.; Cole, C.; Curtis, J.; Nakanishi, S.; Robb, M.; Stone, H. (2002-08)

  Jet contrails can be frequently observed in the subarctic setting of Fairbanks, Alaska, much like in the contiguous United States. Since March of 2000, continuous digital imagery of the sky was obtained, supported by FAA flight data and radiosonde ascents at the Fairbanks International Airport. There were a total of 2504 over-flights (March 2000-July 2002) at Fairbanks, but for a great number of these, contrail observations were not possible due to clouds and/or darkness. For 590 cases, the formation of contrails could be confirmed; their life span varied widely from a few seconds to several hours. In general, cold temperatures and high relative humidity at flight level favored the formation of contrails. These conditions are frequently found in the upper troposphere close to the tropopause. Using our substantial database, different existing algorithms were tested and, in part, improved in order to predict contrail formation and lifetime. The best results were obtained with an algorithm described by Schumann (1996) and an aircraft specific contrail factor of 0.036 g/kgK. For contrails within 4 hours of the radiosonde ascents, a combined hit rate for correctly forecasting the occurrence and non-occurrence of contrails of 92% was obtained.
• 

  College step sounding equipment, recording systems, and operating parameters from 1963 to 1965

  Bates, Howard F.; Teas, J. A. (Geophysical Institute at the University of Alaska Fairbanks, 1966-05)
• 

  Maritime Guidance for Distant and Local Source Tsunami Events: Chenega Bay, Alaska

  Nicolsky, Dmitry; Suleimani, Elena; Gardine, Lea (Alaska Earthquake Center, 2020-02-27)

  These documents provide response guidance for Chenega Bay in the event of tsunamis for small vessels such as recreational sailing and motor vessels, and commercial fishing vessels. The developed documents follow the guidance developed by the National Tsunami Hazard Mitigation Program (NTHMP) and are based on anticipated effects of a maximum-considered distant and locally generated tsunami event.
• 

  Manual de observación de las nubes noctilucentes hemisferio sur

  Fogle, Benson (1964-06)
• 

  Telluric current micropulsations at the auroral zone

  Hessler, Victor Peter; Heacock, Richard R. (Geophysical Institute at the University of Alaska Fairbanks, 1967-10)

  This report presents analysis of individual events and statistical results derived from several years of continuous Pc 1 recording at College, using the telluric current technique. Histograms of occurrence distributions versus Kₚ and versus pulse period, together with sonagrams, justify dividing Pc 1 into two main classes. Class 1 activity has pulse periods mainly shorter than 3 sec, is usually structured, has a pronounced mid-day maximum in occurrence, not much seasonal variation in occurrence, and has little occurrence relationship to Kₚ except for a tendency to be absent when Kₚ is large. Class 2 Pc 1 activity has periods usually longer than 2 sec, is usually unstructured, has a very pronounced afternoon maximum in occurrence at College, a seasonal maximum in summer, and has a positive correlation with Kₚ. Class 1 activity may originate mainly in closed field line regions and Class 2 in open field line regions. Class 1 mid-frequencies tend to rise as Kₚ rises and tend to be higher at night than in the daytime. Average Pc 1 amplitudes maximize in daytime at College as do the occurrences. Thus there is an extreme daytime maximum in summed amplitudes, indicating that the Pc 1 incident energy has a pronounced daytime maximum at College. College sonagrams of Pc 1 events show a great variety of frequency-time forms. Rising frequency periodic structures are most common, but falling frequencies are often seen sometimes superimposed on rising events. At times narrow band “necklaces” are clearly seen. Long duration structured events were observed with durations up to 18 hours. The long events tended to occur only at times of rather low Kₚ.
• 

  Sea ice strength

  Peyton, H. R. (Harold R.) (1966-12)

  This report contains the results from a study of the mechanical and structural properties of sea ice; the study commenced in 1958 and was completed in late 1965. Most of the experimental work is based upon stress-strain tests in both direct compression and direct tension. Approximately 3800 of these tests were made. Those parameters anticipated to have significant effect upon strength were measured: temperature, salinity, rate of loading, crystal size, crystallographic orientation, history of the ice and depth in the ice sheet. All of these are found to be significant except that the history factor itself tended to be determined by the other parameters. The analysis was accomplished primarily by the testing of models by linear multiple regression. The models selected yield good results with multiple correlation coefficients between 0.70 and 0.98 over a range of petrofabric types. Sea ice is shown to be complex and its description requires five classifications of petrofabric types, each of which exhibit somewhat different characteristics. The load rate proved to be a highly significant parameter in both strength and stiffness in most cases. Ice failing in tension is somewhat less sensitive to load rate than is ice in compression. The interrelated effects of salinity and temperature were studied using the brine volume concept. This study yielded positive confirmation of the brine volume concept, evidence of solid salt reinforcement, and evidence of failure plane selectivity to bypass strongly reinforced planes. These aspects pertain to both tension and compression failure modes. Depth in the ice sheet is shown to be a strength factor when related to each of three parameters; rate of loading, brine volume and solid salt reinforcement. Additional work accomplished in conjunction with construction of large offshore oil drilling platforms had provided significant information concerning oscillatory failure of sea ice in compression and strength reduction at very high load rates. The ice failure force oscillation is an ice property and is not primarily a function of the response of the structure. The amplitude of oscillation is large and at a frequency in the range of most space frame structures. The failing ice may cause forced resonant vibration in structures, and the forces are large enough to resonantly vibrate structure weighing several thousand tons.
• 

  Geomagnetic influences on thermospheric winds observed in the auroral zone

  Wallis, Donald Douglas James Herbert; Romick, Gerald J. (1974-05)

  A large body of observations of the wind field in the high-latitude thermosphere (140 to 350 km) is examined to characterize the winds and to determine their probably source. Theories and existing models of these winds are first reviewed. The morphologies of auroral particle precipitation, electric fields, and current systems are discussed to elucidate the effects of these factors upon the wind field. Existing models suggest that the effects of auroral electric fields and heating can be separated in a geomagnetic coordinate frame. It is shown, in this study, that the mean temporal dependence of the (geomagnetic) meridional component is similar to that predicted by tidal models except the magnitudes of the observed winds are smaller than predicted (observed peak speeds – 150 m sec⁻¹). Deviations (up to 200 m sec⁻¹) of the observed meridional winds from this mean behavior are probably caused by heating of the thermosphere by Joule dissipation in the auroral electrojets. Zonal winds are shown to be principally driven by collisions of the neutrals with ions drifting under the action of the auroral zone electric field. Zonal speeds from 200 to 400 m sec⁻¹ are typical. The observed zonal winds are correlated with the direction of the auroral electric fields as inferred from magnetometer records. The response time of the observed winds to changes in direction of the electric field (northward to southward) is found to be ≈ 1¹/₂ hours. Tidal winds are of secondary importance for the zonal component (peak speeds ≈ 150 m sec⁻¹). Electric fields and Joule dissipation in the high-latitude thermosphere are concluded to be responsible for the principal observed characteristics of auroral-zone thermospheric winds.
• 

  Polar micropulsations

  Hessler, V. P. (Victor Peter); Troitskai͡a, Valerii͡a Alekseevna; Bolshakova, O. V.; Heacock, Richard R.; Kangas, Jorma; Kivinen, Matti; Olesen, Jens; Sucksdorff, Christian (1972-05)

  Type Pc 1 micropulsation activity at high latitudes: Statistical analyses were made on structured Pc 1 micropulsation data recorded at College (Alaska), Thule (Greenland), and Sodankyla and Nurmijarvi (Finland) from November 1967 through January 1970. Hourly occurrences of Pc 1 were scaled for mid-frequencies, amplitudes, and “sameness” of event as seen at two or more sites. The data give evidence for the existence of a global effect in Pc 1 activity. The effect is thought to be related to drifting trapped solar wind protons, i.e. to some form of proton ring current. The existence of a midday maximum in Pc 1 production at source latitudes is verified. The Pc 1 diurnal variations observed at other latitudes, including Thule (89°), are mainly shaped by characteristics of propagation in the ionosphere horizontal duct. An event occurring on 23 Feb 1967 propagated from the vicinity of Finland, completely over the polar cap, to Alaska, at a time when the disturbance level over the polar cap was minimal. The evidence suggests that E-region electrojets and other ionospheric irregularities are effective in scattering Pc 1 waves which are propagating polewards in the duct. The scattering mechanism explains some of the occurrence characteristics, e.g. the lack of the 2-4 Hz events within the polar cap though these events are fairly common at subauroral and middle latitudes. Main regularities of micropulsations at the geomagnetic poles: Observations of micropulsations in the range from small fractions of an Hz up to several Hz were conducted at the geomagnetic poles, Thule and Vostok, from 1964 to date. Main morphological regularities of different types of pulsations in these regions were investigated. Most typical for the geomagnetic poles in the family of continuous pulsations are types Pc 2 and Pc 3. A distinct seasonal variation was established for the intensity of Pc 3. It is suggested that Pc 2 pulsations penetrate to the polar cap from the far regions of the magnetospheric tail. The deformation in the shape of the Pi 2 pulsations in the region of the geomagnetic pole is stressed. The character of their propagation from the auroral zone where their amplitude is maximum is different towards the pole and towards middle latitudes. The connection of irregular short period magnetic disturbances of the PD* type with disturbances in the interplanetary field was investigated. It was revealed that the delay in PD occurrence is different for day and night hours. Investigation of pulsation behavior at the geomagnetic poles during the growth phase of substorms led to the discovery of precursors having periods equal to several minutes. Bursts of irregular oscillations with periods of 2 to 7 minutes either appear or are intensified approximately one hour before the substorm. It is suggested that these bursts of pulsations correspond to similar oscillations at the boundary of the magnetosphere discovered by direct measurements. Preliminary results of comparison of pulsation behavior at the geomagnetic poles and of aurora development are outlined. Micropulsations associated with polar magnetic substorms: This paper presents a comprehensive study of the irregular type of electromagnetic micropulsations which occur in association with the polar substorm. An extensive review of the literature serves to define the problem and to guide the ensuing scaling, analysis and discussion of results. The study utilizes data recorded on strip chart and magnetic tape over a period of several years from several stations in Alaska and Finland and from Thule, the Danish station near the North geomagnetic pole. The analysis includes extensive statistical studies of the incidence of Pi 1 and 2 at College in relation to magnetic bays and riometer data. Incidence is measured in terms of both spectral and amplitude characteristics. Individual events are studied in detail to determine the temporal and spatial distributions of the micropulsations in relation to the magnetic substorm and electron precipitation. Charts presenting the development of the polar micropulsation substorm are prepared from the above analysis. The results of the analysis are discussed in relation to the properties of the solar wind, velocity, particle densities, and magnetic field, and to the magnetospheric substorm.
• 

  Ionospheric drift measurements in the auroral zone

  Kisabeth, Jerry L. (1970-02)

  An investigation of the apparent horizontal ionospheric drifts in the ’90 km’ region and the E-region is presented. The investigation was made using the spaced-receiver method with a frequency of 3.321 MHz at College, Alaska. The structure and random characteristics of the ionospheric irregularities are described. A comparison between the two different levels shows noticeable differences of these properties. A comparison between the ’90 km’ drift measurements and meteor winds, also obtained at College, is presented. Individual wind and drift measurements were very difficult to compare, because of the lack of meteor events. Instead, average winds and drifts were used for the comparison. The results show that during magnetically quiet periods, the comparison is good, whereas during periods of increased magnetic activity the comparison is poor. Periodic fading events observed at College are also discussed.
• 

  Stratigraphy, petrology, and geochemistry of the Spurr Volcanic Complex, eastern Aleutian Arc, Alaska

  Nye, Christopher J. (1987-12)

  The Spurr Volcanic Complex (SVC) is a calcalkaline, medium-K, sequence of andesites erupted over the last quarter of a million years by the easternmost currently active volcanic center in the Aleutian Arc. The ancestral Mt. Spurr was built mostly of andesites of uniform composition (58-60% SiO₂), although andesite production was episodically interrupted by the introduction of new batches of more mafic magma. Near the end of the Pleistocene the ancestral Mt. Spurr underwent Bezymianny-type avalanche caldera formation, resulting in the production of a volcanic debris avalanche with overlying ashflows. Immediately afterward, a large dome (the present Mt. Spurr) was emplaced in the caldera. Both the ashflows and dome are made of acid andesite more silicic than any analyzed lavas from the ancestral Mt. Spurr (60-63% SiO₂), yet contain olivine and amphibole xenocrysts derived from more mafic magma. The mafic magma (53-57% SiO₂) erupted during and after dome emplacement, forming proto-Crater Peak and Crater Peak. Hybrid pyroclastic flows and lavas were also produced. Proto-Crater Peak underwent glacial dissection prior to the formation of Crater Peak in approximately the same location. The vents for the silicic and mafic lavas are in the center and in the breach of the 5 by 6 km horseshoe shaped caldera, respectively, and are less than 4 km apart. Late Holocene eruptive activity is restricted to Crater Peak, and magmas continue to be relatively mafic and derived from deep within the crust. SVC lavas are plag ± ol + cpx ± opx + mt bearing. All post-caldera units contain small amounts of high AL₂O₃, high alkali pargasite, and Proto-Crater Peak and Crater Peak lavas contain abundant pyroxenite and anorthosite clots presumably derived from an immediately pre-existing magma chamber. Ranges of mineral chemistries within individual samples are often nearly as large as ranges of mineral chemistries throughout the SVC suite, suggesting that magma mixing is common. SVC lavas are unlike experimentally produced cotectic liquids and are thus unlikely to be related to each other by fractional crystallization. Magmatic evolution must instead be controlled in large part by crustal assimilation. Flat Y-SiO₂ and Nb-SiO₂ trends and Rb enrichment beyond that which can be reasonably modeled by fractional crystallization also suggest extensive assimilation of lower crust, bulk upper crust, or partial melts of local batholithic material. Since at least the mid-Holocene there has been no shallow, silicic magma chamber at the SVC. This increases the expectation that the low resistivity layer described by Turner and Wescott (1986) is a highly conductive layer of bedrock, such as a thick, altered tuff.
• 

  The determination of the diurnal variation of the auroral belt by radio means

  Bates, Howard F. (Geophysical Institute at the University of Alaska Fairbanks, 1965-09)

  Backscatter echoes in the high frequency portion of the radio spectrum exhibit a systematic southward movement in the evening and northward in the morning. Typically, the scattering belt lies about 78°N geomagnetic latitude during the day, and moves south to 65 to 70° at night. The extent of the southward movement correlates strongly with geomagnetic activity and, to a lesser degree, local time. No significant difference was found between summer and winter diurnal variations of the scattering belt. The scattering belt has been found to include the optical auroral belt; thus, it is concluded that there is no significant difference in the diurnal variation in the position of the summer and winter auroral belts for given levels of magnetic disturbance. The scattering belt was present on the College magnetic meridian during most of the two and one-half years’ observations. This is interpreted as showing the optical auroral belt existed most of the time somewhere on the College meridian, and hence on others as well. Thus, the auroral belt during the solar activity minimum period existed as a more or less closed curve around the geomagnetic pole. When the latitudinal effects are considered versus local time, the auroral belt takes the form of an oval curve, the northernmost portion approximately on the noon meridian. The size of the oval at any time is proportional to the size of the disturbance. The scattering belts as determined from simultaneous College and Thule backscatter soundings over approximately reciprocal paths generally coincided. This result shows that simultaneous soundings in four to eight directions from the magnetic pole could be used to map the auroral belt completely around the earth at any given time.
• 

  Ice fog studies in Alaska : a survey of past, present and proposed research

  Weller, Gunter E. (Geophysical Institute at the University of Alaska Fairbanks, 1969-03)
• 

  College oblique ionograms

  Bates, Howard F.; Goddard, Arthur (Geophysical Institute at the University of Alaska Fairbanks, 1964-03)

  This report illustrates some of the typical backscatter echoes observed at College, Alaska. Backscatter soundings are being made in five directions—015, 105, 210, 270 and 325 degrees true bearing. The majority of the echoes seen were not groundscatter as usually defined. Many echoes from the northern directions were, in fact, direct scatter echoes from the ionosphere. Groundscatter echoes were regularly observed from the south during this past winter, but only rarely from the north. Sample forward oblique ionograms recorded over the Andöya, Norway, to College, Alaska, path are shown. Preliminary results indicate that the signals were primarily propagated via E or Es layers. Signals with delays of 3 to 10 milliseconds over the great-circle path delay were quite common on all the paths monitored at College. The sample records shown contain signals with delays of 4 to 5 milliseconds.
• 

  Hourly values of the auroral electrojet activity index AE for 1964

  Davis, T. Neil; Wong, Y. S. (Geophysical Institute at the University of Alaska Fairbanks, 1967-09)
• 

  HF/VHF auroral and polar zone forward soundings

  Bates, Howard F. (Howard Francis); Hunsucker, R. D. (Geophysical Institute at the University of Alaska Fairbanks, 1964-05)
• 

  Gravity measurements in the Katmai volcano area, Alaska

  Berg, Eduard; Kienle, Juergen (Geophysical Institute at the University of Alaska Fairbanks, 1966-04)
• 

  The magnetotelluric coast effect near a dyke or long promontory

  Blake, J. R.; Swift, Daniel W. (Geophysical Institute at the University of Alaska Fairbanks, 1967-10)

  The magnetic and telluric fields near a vertical, infinitely deep dyke in an otherwise homogeneous plane medium are calculated. The approximate constancy of the horizontal, surface magnetic field at low frequencies is used as a boundary condition, following Weaver (1963b). Both “polarizations” of the surface electromagnetic field are considered, according to whether the electric or magnetic fields are parallel to the strike. The polarization ellipses of the telluric field and the vertical magnetic field are computed as functions of the conductivity ratio, and dyke thickness, for various observing positions and frequencies, and the fields are compared with similar calculations based on Weaver’s simple fault model. An extension is outlined and the analytical results presented for the case where both ocean and land are underlain by a non-conducting basement. The work of Rankin (1962) is thus extended to cover both polarization orientation of the surface field.

View more