March Event Research Articles

A Shallow Crustal Earthquake Doublet from the Trans-Mexican Volcanic Belt (Central Mexico)

The Trans-Mexican volcanic belt is an active volcanic arc related to subduction along the Middle America trench and characterized by shallow seismicity and synvolcanic to postvolcanic extensional arc-parallel faulting. The Mezquital graben is a major intra-arc basin of the central Trans-Mexican volcanic belt. A doublet of moderate shallow shocks occurred in March and October 1976 in the region of this graben. These earthquakes were recorded by the Mexican National Seismological network, in particular, by the Bosch-Omori seismograph ( T = 18 sec) at the Tacubaya Observatory in Mexico City. We have carefully relocated the two main shocks and their major aftershocks by reading the original records and using a modified crustal velocity model for this region. A difference of ∼50 km is observed between the locations reported by the Mexican Seismological Service and those obtained in this study, which are additionally supported by the damage distribution of these earthquakes. A first-motion analysis, based on regional and teleseismic records, defines for the March and October shocks normal fault mechanisms, characterized by east–west-striking fault planes, which coincides with the orientation of the master faults of the Mezquital graben. After calculating the instrumental response, the source parameters were obtained from the Bosch-Omori seismograph records by body-wave modeling. For the March earthquake, we estimate a seismic moment of 4.5 × 1023 dyne cm (equivalent to M w 5.0) and a stress drop of 0.7 MPa, assuming a circular rupture model (radius, 3 km). Given the poor quality of the Bosch-Omori record for the October earthquake, we used comparison with the March event of long-period ( T = 20 sec) teleseismic records at two stations to obtain corresponding source parameters for the October event. By assuming a similar stress drop as for the March event, we obtain a M of 5.6 × 1023 dyne cm and M w 5.1 with a rupture length of 6.5 km. According to gravity data, the regional east–west faults are longer than reported. In particular, our detailed measurements indicate that the master fault of the Mezquital graben continue westward in the subsurface below the basin fill. In a more regional context, additional magnetic data suggest that the El Mezquital graben and Aljibes half-graben might be connected at their southern limits by part of the same fault system. This is the first earthquake doublet reported from central Mexico and the biggest seismic event in that zone during the past 50 years. From a physical point of view, it is possible that the seismic energy released by the March event was partially transferred toward the east, triggering the October shock further east on the same fault system. The presence of moderate seismicity in this zone should therefore be taken into account when assessing its seismic hazard.

Towards a physics of dowsing: inverse effects in the northern and southern hemispheres

ABSTRACTIt has been known for some years that parallel horizontal structures separated in a vertical plane produce patterns of equally spaced parallel lines that can be detected and mapped by dowsing detector rods, indicating that the patterns are produced by interaction between the structures and the dowsing field, whatever that is. Consequently the arrangement is called a dowsing interferometer and the lines are referred to as interference fringes. The patterns are produced equally well by electrical insulators as by electrical conductors, and the inference that the field is not electromagnetic was confirmed by experiments carried out in an electromagnetically shielded laboratory. Measurements of interferometer fringe spacings made irregularly from 1991 to 1996, analysed retrospectively, were found to be dependent on time of year, decreasing relatively suddenly by a factor of about three in November and increasing again in April. An isolated rise and fall in early March was also found. These results were confirmed by more frequent measurements in 1997 and published the following year. This paper reports a co-operative programme of interferometry between Scotland and New Zealand from 1997 to 2001. The annual pattern of the fringe spacing is clearly defined, with rapid changes between 2m and 6m in November and in April, and an isolated event in early March; but remarkably the pattern in the southern hemisphere is inverted with respect to that in the north. There are differences of a few days in the timings of the events in the north and south, and the amplitude of the March event is increasing.This paper is a continuation of the work described in Transactions of the Royal Society of Edinburgh: Earth Sciences89 (1998) 1–9.

The Effect of a Large Resuspension Event in Southern Lake Michigan on the Short-term Cycling of Organic Contaminants

In January and March, 1998, a series of intense, northerly wind-driven storms suspended sediment over the entire coastline of the southern basin of Lake Michigan. The effect of large scale resuspension on organic contaminant cycling was investigated using a two-pronged sample collection strategy that included analysis of settling sediment trap material and discrete air and water samples collected before and after a major resuspension event. It was found that major resuspension events result in a large flux of contaminants. For example, 6.2 ng/cm 2 ΣPCB (sum of 89 congener peaks) and 175 ng/cm 2 ΣPAHs (sum of 31 compounds) fell through the water column in the southern basin between November and May but almost half of that occurred in the month of March after a series of intense storms induced a largescale resuspension event in that month. Assuming the concentration of contaminants in settling sediments is similar throughout the basin, the March event brought ∼400 kg of ΣPCBs and ∼13,000 kg ΣPAHs into the water column. Furthermore, the data indicate that concentrations of dissolved phase ΣPCB and ΣPAHs declined significantly (α = 0.05) after the event and after resuspended sediment had settled from the surface waters. As a result of the depressed dissolved concentrations at the surface, the potential for gas-phase input to the lake increases on the southwestern coastal region near Chicago, IL and Gary, IN. The potential input of gas-phase contaminants was 8 kg for ΣPCBs and 2,200 kg for ΣPAHs over the 40-day lifetime of the near-shore event.

Earthquake Doublet in Kagoshima, Japan: Rupture of Asperities in a Stress Shadow

Two shallow moderate ( M ∼ 6) earthquakes occurred in the northwestern part of Kagoshima Prefecture, Kyushu, southern Japan. I discuss the effect of the stress change due to the first earthquake (26 March 1997) on the occurrence of the second earthquake (13 May 1997). The rupture characteristics of the two earthquakes are inferred in two steps to form the basis of the discussion. I first invert strong ground motion data to construct kinematic source models and then estimate the distribution of static stress drop from the derived dislocation distributions. The rupture process of the March event is simple and well described with rupture of a single asperity (patch of high stress drop). On the other hand, multiple asperities on conjugate faults ruptured during the May event. The maximum value of static stress drop for both earthquakes is about 4 MPa, and seems lower than those of other Japanese intraplate earthquakes. The hypocenter and the largest asperity of the May earthquake are located in a stress shadow caused by the March earthquake. Thus the rupture history of the May earthquake is difficult to explain with a static stress change model. Other mechanisms such as fluid migration and dynamic stresses were also investigated, but failed to explain the triggering. I propose the coupled effect of static change in shear stress and normal stress under the rate- and state-dependent friction law as a possible mechanism.

Hydrological and hydrochemical response of a small canadian shield catchment to late winter rain‐on‐snow events

AbstractA study was undertaken during the winter of 1990–1991 in a small (3.7 ha) Canadian Shield catchment to examine the hydrological and hydrochemical response during rain‐on‐snow events. The results are presented of two large (37.9 and 34.6 mm) rain‐on‐snow events occurring in early and late March 1991. Peak and total runoff and the groundwater response from the two events are significantly different. Hydrological data indicate that these differences can be attributed to a combination of meteorological (temperature) and physical conditions (antecedent snowpack ripeness, soil moisture and groundwater levels). An immature snowpack (low temperature and density) combined with low antecedent soil moisture conditions significantly reduced the magnitude of the net hydrological input and runoff from the catchment during the early March event, whereas a more mature snowpack and high antecedent soil moisture conditions led to a large runoff event during late March.During both rain‐on‐snow events a significant portion of the pre‐event snowpack chemical load was lost. Based on the maximum snowpack chemical load measured before the events, the two large rain‐on‐snow events and a brief mid‐March warm period during which there were two much smaller rain‐on‐snow events removed 78% of the hydrogen ion and 63% of the sulphate and nitrate load from the snowpack, while only reducing snowpack water equivalence by 7%. A two‐component (rain and snowmelt) isotopic (δ18O SMOW %0) separation of snowmelt lysimeter water during the two events indicated that snowmelt was an important (50 and 65%, respectively) water source available for infiltration and runoff at the snow‐soil interface. Considering the high hydrogen ion loadings to the catchment during these two events (3.3 and 3.0 mequiv.m−2, respectively) streamflow pH was not significantly reduced due to an increase in the discharge of well‐buffered groundwater. A two‐component isotopic hydrograph separation of peak stream discharge during the 2–3 March event indicated that 75% of the total flow was groundwater. In mid‐latitude acid‐sensitive catchments, winter rain‐on‐snow events are an important hydrological occurrence due to their ability to elute much of the chemical load (H+, SO4, NO3) from the snowpack before the onset of spring melt when the maximum annual hydrological input typically occurs.

Preliminary comparison of dose measurements on CRRES to NASA model predictions

Measurements of proton and electron dose from the space radiation dosimeter on the CRRES satellite, in a 18.1 degrees , 350 km by 33000 km orbit, are compared to the NASA models for solar maximum conditions. Up to the time of the large, solar-initiated particle events near the end of March 1991, the results are similar to those previously reported for solar minimum at low altitudes. That is, prior to the March event, there is excellent agreement between model and measured values for protons and poor agreement for electrons. During the event period a second proton belt was formed at higher altitudes which is not contained in the proton models, and the electrons increased over an order of magnitude for the CRRES orbit. This resulted in poorer agreement between model and measured values for protons during and after the solar proton event and better agreement for electrons during the electron enhancement period. What the data show is that, depending on orbit, both the existing proton and electron models can give large errors in dose that can compromise space system performance and lifetime.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Horizontal and vertical structure of the major sporadic sodium layer events observed during ALOHA‐90

Sporadic Na (Nas) layers have been observed frequently at low‐ and high‐altitude sites primarily in the Northern Hemisphere. Nas layers are very dense and very thin (∼1 km FWHM) and can form over periods ranging from a few minutes to several hours. Radar and lidar observations by our group at Arecibo have shown conclusively that Nas layers are linked to the formation of sporadic E (Es) layers. Large Nas events were observed on several flights during ALOHA‐90 to extend over horizontal distances of approximately 1800 km. Atmospheric tides and gravity waves were observed to have an effect on the vertical motion of these layers. We describe the 22 March event which was observed from Maui (21°N) to near the equator (5°N) and the 27 March event which was observed from Maui (156°W) to almost the International Date Line (∼172°W).

Effects of absorption on high‐latitude meteor scatter communication systems

Data acquired with the Geophysics Laboratory's high‐latitude meteor scatter test‐bed between Sondrestrom Air Base (AB) and Thule AB, Greenland, during the solar disturbances of March and August 1989 are presented. These disturbances provided a unique opportunity to observe a number of naturally occurring disturbance effects on meteor scatter links operated in the frequency range (35 to 147 MHz) covered by the test‐bed. The disturbances range from signal absorption to system noise variations. The properties of ionospheric absorption in general are discussed and illustrated with computations using electron density profiles from the September 1978 solar proton event (SPE). It has been found that accurate measurements of high levels of ionospheric absorption with riometers pose special problems. These problems are identified and discussed. The data acquired during the March and August 1989 solar disturbances are then related to the zenith absorption measured at Thule, and the influence of absorption as well as system noise variations are discussed. The two events presented are very different. The August event was dominated by ionospheric absorption which affected meteor arrival rates and duty cycles primarily at the lower frequencies (35 and 45 MHz), although some effects could also be seen at the higher frequencies (65 to 147 MHz). The March event combined weak ionospheric absorption with large solar noise bursts. The effects of this event on the test‐bed were dominated by increased solar noise at all frequencies. The relative influence of solar noise and ionospheric absorption during SPE events is discussed along with speculation as to the validity of frequency dependence conclusions based on testing of the JANET system.

Activity of the 5 March 1979 event source

The time structure and energy spectra obtained in the pulsating stage of the gamma-ray burst on 5 March 1979 and in a series of recurrent bursts from the same source permit a conclusion that their nature is related with nonstationary accretion and the intense initial pulse of the 5 March event is of thermonuclear nature.

Temperatures and meridional winds in the vicinity of the SAR-arc as observed from Albany, New York

Photometric and interferometric data obtained from a field station near Albany (42.68°N, 73.82°W), New York during two SAR-arc events of 6 March 1981 (U.T.) and 9 May 1981 (U.T.) are presented and the thermospheric response to the SAR-arc is discussed here. The maximum intensities of the arcs were 2.2 and 0.7 kR, respectively. While no visible aurora was sighted from Albany during the March event, a very intense aurora was observed in the northern sky during the less intense SAR-arc event in May. The neutral gas temperatures within the SAR-arc were quite stable when the arc was intense (2.2 kR) and there were large temperature gradients on either side of the arc. The meridional wind pattern was such that the winds were blowing away from the main heating region of the arc. More specifically, the winds to the South of the arc were equatorward and the winds to the North of the arc were poleward. However, when the intensity of the arc started decreasing and the arc moved farther out to the South on 6 March 1981, the poleward winds diminished in speed and became equatorward after midnight under the influence of general circulation. During the less intense arc of 9 May 1981, the temperature gradient to the North of the arc was considerably greater than that in the southern side and, in spite of the presence of a visible aurora far out to the North, the winds to the North of the arc were always poleward. In general, the thermospheric meridional wind pattern strongly responded to the maximum heating effects within the SAR-arc.

Characteristics of energetic particle events associated with interplanetary shocks

We present observations of the 35‐ to 1600‐keV proton intensity‐time profiles and the three‐dimensional 35‐ to 56‐keV anisotropy distributions recorded during two interplanetary shock events on ISEE 3, and discuss these in the light of current particle acceleration models. The large April 5, 1979, event associated with a quasi‐parallel shock shows an extended foreshock region with a strong increase of the upstream proton flux, a downstream plateaulike profile, upstream flow from the shock, and downstream isotropy in the solar wind frame of reference. The small March 9, 1979, event has a structured intensity‐time profile, a narrow shock spike, and anisotropic angular distributions both upstream and downstream, the anisotropies immediately behind the shock exhibiting an intensity peak at pitch angles around 90°. The April event, representative for a class of large energetic storm particle events, shows many observational features which are in agreement with predictions made by diffusive shock acceleration models. The March event, representative for a class of events with irregular profiles and mainly associated with quasi‐perpendicular shocks, exhibits features which are characteristic of shock drift acceleration. We conclude that both acceleration models are operative in association with interplanetary shocks.