Magnetic dip

About: Magnetic dip is a research topic. Over the lifetime, 1417 publications have been published within this topic receiving 26530 citations.

Magnetic compass of European robins.

Abstract: The magnetic compass of European robins does not use the polarity of the magnetic field for detecting the north direction. The birds derive their north direction from interpreting the inclination of the axial direction of the magnetic field lines in space, and they take the direction on the magnetic north-south axis for "north" where field lines and gravity vector form the smaller angle.

Shape of the subducted Rivera and Cocos plates in southern Mexico: Seismic and tectonic implications

Abstract: The geometry of the subducted Rivera and Cocos plates beneath the North American plate in southern Mexico was determined based on the accurately located hypocenters of local and teleseismic earthquakes. The hypocenters of the teleseisms were relocated, and the focal depths of 21 events were constrained using a body wave inversion scheme. The suduction in southern Mexico may be approximated as a subhorizontal slab bounded at the edges by the steep subduction geometry of the Cocos plate beneath the Caribbean plate to the east and of the Rivera plate beneath North America to the west. The dip of the interplate contact geometry is constant to a depth of 30 km, and lateral changes in the dip of the subducted plate are only observed once it is decoupled from the overriding plate. On the basis of the seismicity, the focal mechanisms, and the geometry of the downgoing slab, southern Mexico may be segmented into four regions : (1) the Jalisco region to the west, where the Rivera plate subducts at a steep angle that resembles the geometry of the Cocos plate beneath the Caribbean plate in Central America ; (2) the Michoacan region, where the dip angle of the Cocos plate decreases gradually toward the southeast, (3) the Guerrero-Oaxaca region, bounded approximately by the onshore projection of the Orozco and O'Gorman fracture zones, where the subducted slab is almost subhorizontal and underplates the upper continental plate for about 250 km, and (4) the southern Oaxaca and Chiapas region, in southeastern Mexico, where the dip of the subduction gradually increases to a steeper subduction in Central America. These drastic changes in dip do not appear to take place on tear faults, suggesting that smooth contortions accommodate these changes in geometry. The inferred 80 and 100 km depth contours of the subducted slab lie beneath the southern front of the Trans-Mexican Volcanic Belt, suggesting it is directly related to the subduction. Thus the observed nonparallelism with the Middle American Trench is apparently due to the changing geometry of the Rivera and Cocos plates beneath the North American plate in southern Mexico, and not to zones of weakness in the crust of the North American plate as some authors have suggested.

Galileo Magnetometer Measurements: A Stronger Case for a Subsurface Ocean at Europa

Abstract: On 3 January 2000, the Galileo spacecraft passed close to Europa when it was located far south of Jupiter's magnetic equator in a region where the radial component of the magnetospheric magnetic field points inward toward Jupiter. This pass with a previously unexamined orientation of the external forcing field distinguished between an induced and a permanent magnetic dipole moment model of Europa's internal field. The Galileo magnetometer measured changes in the magnetic field predicted if a current-carrying outer shell, such as a planet-scale liquid ocean, is present beneath the icy surface. The evidence that Europa's field varies temporally strengthens the argument that a liquid ocean exists beneath the present-day surface.

Vertical drift velocities and east‐west electric fields at the magnetic equator

Abstract: Incoherent scatter observations of vertical drifts taken at Jicamarca (2° dip) are presented. Vertical drifts are found to be nearly constant as a function of height. These vertical drifts can also be taken as a direct measurement of the east-west electric fields at the magnetic equator. Their daily and seasonal behavior is presented. The effect of geomagnetic activity is discussed.

Nature of seismic coupling along simple plate boundaries of the subduction type

Abstract: The downdip width of the seismogenic zone is defined for 19 subduction zones. This width is measured from the base of the accretionary prism to the maximum depth of nucleation of thrust events along the plate boundary. Those two points are taken to define the upper and lower depth transitions from stable to unstable frictional sliding. The lower depth transition is found to be between 35 and 70 km. The dip angle of the thrust zone is also reevaluated. We find a linear increase in the dip angle as a function of depth, the slope of which varies between 0.2° and 0.6° km−1. The downdip width obtained, which is generally narrower than previously determined by most other authors, varies from about 50 to 150 km. We also determine the ratio of the rate of slip that occurs in earthquakes to the rate of relative plate motion. This ratio is defined as the seismic coupling coefficient (a). We obtain two different estimates of the seismic coupling coefficient: an average value from 90 years of seismicity and a value obtained using the slip-predictable recurrence model for large earthquakes. We find a large variation in the computed values of a along and among subduction zones. For most of the subduction zones a is much less than 1.0; for several it is less than a few percent. Worldwide, we find no significant correlation between either the seismic coupling coefficient or the width of the seismogenic zone and subduction parameters such as the age of the oceanic lithosphere that is being subducted, plate convergence rates or absolute velocity of the upper plate in the hot spot reference frame. Such correlation exists only for a few individual subduction zones where other parameters do not vary as much. The observed variations in seismic coupling could be explained as differences in the frictional behavior of materials at the plate interface. Some of these differences may be attributed to the subduction of large bathymetric features, the roughness of topography, the presence of unstable triple junctions and active-spreading ridges, and sediment composition.