rupture process of the 1990 luzon philippines mw 7 7 earthquake the rupture process of the destructive july 16 1990 luzon philippines earthquake is analyzed using a long period surface wave spectral inversion technique to estimate the average source properties and a broadband body wave and surface wave empirical green function technique to investigate the slip distribution the average source model has a seismic moment of 4 2 0 1 1020 n m mw 7 7 a total duration of 30 to 35 s a left lateral strike slip focal mechanism with strike 153 dip 89 and rake 16 and a north northwestward directivity these results are consistent with previous work on the luzon earthquake however the broadband analysis indicates that for periods longer than about 20 s the teleseismic source time function is characterized by a single relatively smooth pulse of energy release with azimuthal variations in duration of 24 to 60 s this contrasts with previous body wave results that inferred two discrete pulses of energy release the simpler source process is inferred as a result of using empirical green functions rather than standard theoretical green functions for a layered crustal model and by considering only the seismic energy with periods longer than 20 s the luzon earthquake began rupturing bilaterally but evolved into a predominantly northwest directed rupture that extended for 75 to 100 km the largest slip 10 15 m occurred about 25 km northwest of the epicenter beyond which the slip decreased gradually as the rupture propagated into a restraining bend the peak slip at depth appears to exceed the surface rupture by a factor of 2 to 3 there is little evidence for significant energy release later than 50 s after the rupture initiated

prompt penetration electric fields ppefs and their ionospheric effects during the great magnetic storm of 30 31 october 2003 1 we explore the ionospheric effects of prompt penetration electric fields ppefs for a variety of interplanetary magnetic field directions we use the great magnetic storm of 30 31 october as an example of ppef effects for intense southward interplanetary magnetic fields imfs inward plasma sheet convection occurs with the result of magnetospheric ring current formation and an intense magnetic storm concurrent with the above positive phase ionospheric storms occur in the dayside and negative phase ionospheric storms occur on the nightside the topics of this paper the dayside ionospheric storms due to ppefs are characterized by transport of near equatorial plasma to higher altitudes and latitudes forming a giant plasma fountain these features are part of what is called the dayside ionospheric superfountain dis for these southward imfs dusk and dawn plasma are predicted to be transported toward the dayside for northward imfs negative phase ionospheric storms are expected on the dayside if the ppefs indeed reach that region of space imf by components are expected to have weak or neglible ionospheric effects on the basis of ppef arguments intervals of imf by should not be related to geomagnetic storms they are not imf by intervals should however cause a shearing of the magnetotail a feature that has been previously reported in the literature

geodetic constraints on postseismic deformation following the 1990 ms 7 8 luzon earthquake and implications for luzon tectonics and philippine sea plate motion 1 we have obtained three epochs of high quality dual frequency gps data at 15 stations in the luzon philippines region since the july 16 1990 ms 7 8 earthquake from which we generate horizontal velocity fields at the earth s surface for the 1993 1996 and 1996 1998 periods we use these velocities plus 1996 1998 gps velocity results reported elsewhere from 13 additional stations to show that present day deformation in luzon is dominated by strike slip motion along the philippine fault system the measured strike slip rate across central luzon is faster than the expected long term slip rate on the fault which we attribute to postseismic deformation following the 1990 earthquake the 1993 1996 and 1996 1998 deformation patterns cannot be statistically distinguished within the 10 uncertainties of the data if the observed deformation is interpreted using an elastic half space model with uniform slip below a subsurface locking depth we find a fault slip rate of 40 mm yr and a locking depth of 15 km this is too fast to be a steady interseismic rate as it disagrees with what is known from paleoseismic and other evidence about earthquake recurrence and long term slip rate on the philippine fault system in central and northern luzon also a 15 km locking depth for steady interseismic slip is probably too shallow compared to the depth of rupture in the 1990 earthquake if the deformation is instead interpreted with two types of viscoelastic model we find that the observed velocities can be fit well for a range of values of lower lithosphere viscosity and long term slip rate using a two dimensional 2 d viscoelastic coupling model the minimum allowable lower lithosphere viscosity is 0 5 1019 pa s with an associated long term slip rate of 15 22 mm yr faster long term slip rates also fit well with correspondingly higher values of viscosity with a possibly more realistic model that includes 3 d viscoelastic effects we find preferred long term velocities in the range 20 35 mm yr and viscosities in the range 2 6 1019 pa s our preferred viscosities correspond to maxwell times on the order of 7 20 of the typical earthquake recurrence interval and are several times higher than values found for a number of californian strike slip earthquakes other implications of our 1993 1998 surface velocities are that the philippine sea eurasia ph eu euler vector of seno et al 1993 is a better description of the ph eu convergence rate than a euler vector recently estimated from gps velocities in the northern ph and that the great majority of the normal component of ph eu plate convergence is taking place west of luzon presumably largely at the manila trench we also find that luzon is rotating counterclockwise relative to ph at 1 2 myr only 25 of the rate recently suggested by other workers on the basis of limited gps data

nighttime vertical plasma drifts and the occurrence of sunrise undulation at the dip equator a study using jicamarca incoherent backscatter radar measurements 1 the absence of photoionization in combination with sustained downward plasma motion at night means that the f region can be severely depleted at the magnetic equator in the morning as a result at sunrise there can be a sudden upward jump in altitude of the f region peak followed by a quick descent in association with the downward motion of the photoionization production peak this constitutes what is known as the equatorial sunrise undulation its anecdotal existence has been reported over jicamarca while it has been seen repeatedly over trivandrum india during equinox conditions by contrast we find that the phenomenon is not as frequent at jicamarca as at trivandrum using incoherent backscatter radar data from jicamarca we show that the differences have an electrodynamical origin the sunrise undulation gets masked when remnant plasma from the previous night does not move down to low enough altitude the nighttime residual ion density and its altitude are found to be strongly influenced by the evening and nighttime electric field there is a strong association between a strong plasma uplift at sunset and the appearance of an undulation at sunrise around the magnetic equator

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

dynamic rupture propagation during the 1891 nobi central japan earthquake a possible extension to the branched faults the dynamic rupture process of the 1891 nobi japan earthquake was closely reinvestigated by using a boundary integral equation method based on currently available observations we discussed mainly a possibility of the rupture propagation on branched faults including a buried fault called the gifu ichinomiya line several numerical simulations were made incorporating the information on the fault geometry based on the active fault traces on the ground surface and the maximum principal strain direction observed by the triangular surveys for the past 100 years the results suggest that the rupture should propagate along the buried fault during the nobi earthquake if a weak geological discontinuity exists along the gifu ichinomiya line and is connected to the neodani fault which is one of the major surface faults appearing during the nobi earthquake

estimating daytime vertical exb drift velocities in the equatorial f region using ground based magnetometer observations 1 the daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100 to 120 km altitude region within 2 latitude of the dip equator a unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the horizontal h component between a magnetometer placed directly on the magnetic equator and one displaced 6 to 9 degrees away the difference between these measured h values provides a direct measure of the daytime electrojet current and in turn the magnitude of the vertical exb drift velocity in the f region ionosphere this paper discusses a recent study that has established the quantitative relationship between the vertical exb drift velocity in the ionospheric f region and the daytime strength of the equatorial electrojet in the south american west coast longitude sector

source mechanism of the luzon philippines earthquake of july 16 1990 the luzon philippines earthquake of july 16 1990 with ms 7 8 was generated by left lateral faulting in the central luzon island ground breakage was observed along a linear trace extending 110 km the maximum horizontal offset as measured on the fault was as much as 6 m a fault area of 120 20 km2 was inferred from a field study and aftershock data this event is one of the largest strike slip earthquakes ever recorded in the world for long period surface waveform analysis we used very broadband records from 14 stations of the gdsn geoscope iris and erios networks the centroid moment tensor cmt solution from surface waves represents almost pure left lateral strike slip faulting on a steep fault with strike 155 dip 88 and rake 7 the seismic moment is 3 9 1020 nm 1027 dyn cm which gives mw 7 7 the average dislocation on the fault is 5 4 m and the stress drop is 5 2 mpa 52 bars teleseismic p and sh waves from 14 stations are used to model the spatiotemporal distribution of subevents five subevents are detected in an interval of 44 sec their sequence indicates a bilateral rupture the mean velocity of rupture toward the north is 2 7 km sec the total seismic moment of the subevents is 3 6 1020 nm the largest aftershock ms 6 6 occurred on july 17 near the recognized northern end of the main fault the cmt solution for the aftershock represents a reverse faulting with moment of 6 4 1019 nm mw 6 5 this aftershock was probably caused by compression produced by block motion of the eastern block of the main fault

earthquake size as a function of fault slip rate abstract estimates of the potential size of earthquakes on mapped active faults are generally based on regressions of earthquake magnitude m w versus length l of fault rupture for historical earthqukes the fault slip rate s has been ignored in formal prediction equations but more accurate predictions of future earthquake magnitudes on mapped faults may be obtained when it is included a least squares regression for a data set of 43 earthquakes occurring on faults for which slip rates are reported shows m w 5 12 1 16 log l 0 20 log s where l is in units of km and s is in units of mm yr the result indicates that the largest earthquakes will occur on the slowest slipping faults if the rupture length is held constant

middle and low latitude ionosphere response to 2015 st patrick s day geomagnetic storm this paper presents a study of the st patrick s day storm of 2015 with its ionospheric response at middle and low latitudes the effects of the storm in each longitudinal sector asian african american and pacific are characterized using global and regional electron content at the beginning of the storm one or two ionospheric positive storm effects are observed depending on the longitudinal zones after the main phase of the storm a strong decrease in ionization is observed at all longitudes lasting several days the american region exhibits the most remarkable increase in vertical total electron content vtec while in the asian sector the largest decrease in vtec is observed at low latitudes using spectral analysis we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field ppef and of the disturbance dynamo electric field ddef on the basis of ground magnetic data concerning the ppef earth s magnetic field oscillations occur simultaneously in the asian african and american sectors during southward magnetization of the b z component of the interplanetary magnetic field concerning the ddef diurnal magnetic oscillations in the horizontal component h of the earth s magnetic field exhibit a behavior that is opposed to the regular one these diurnal oscillations are recognized to last several days in all longitudinal sectors the observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models

interseismic deformation and moment deficit along the manila subduction zone and the philippine fault system we examine interseismic coupling of the manila subduction zone and fault activity in the luzon area using a block model constrained by gps data collected from 1998 to 2015 estimated long term slip rates along the manila subduction zone show a gradual southward decrease from 90 100 mm yr at the northwest tip of luzon to 65 80 mm yr at the southern portion of the manila trench we provide two block models models a and b to illustrate possible realizations of coupling along the manila trench which may be used to infer future earthquake rupture scenarios model a shows a low coupling ratio of 0 34 offshore western luzon and continuous creeping on the plate interface at latitudes 18 19 n model b includes the north luzon trough fault and shows prevalent coupling on the plate interface with a coupling ratio of 0 48 both models fit gps velocities well though they have significantly different tectonic implications the accumulated strain along the manila subduction zone at latitudes 15 19 n could be balanced by earthquakes with composite magnitudes of mw 8 8 9 2 assuming recurrence intervals of 500 1000 years gps observations are consistent with full locking of the majority of active faults in luzon to a depth of 20 km inferred moments of large inland earthquakes in luzon fall in the range of mw 6 9 7 6 assuming a recurrence interval of 100 years

long duration penetration of the interplanetary electric field to the low latitude ionosphere during the main phase of magnetic storms 1 it is well known that the interplanetary electric field can penetrate to the low latitude ionosphere it is generally believed that the penetration of electric fields can last only for 30 min because of the shielding effect in the ring current in this paper we present the observations of the dayside ionospheric electric field enhancements at middle and low latitudes in association with reorientations of the interplanetary magnetic field imf in six cases the eastward electric field in the dayside equatorial ionosphere measured by the jicamarca incoherent scatter radar was enhanced for 2 3 hours after the imf turned southward and remained continuously southward in one case the eastward electric field in the dayside midlatitude ionosphere measured by the millstone hill incoherent scatter radar was continuously enhanced for 10 hours during southward imf since millstone hill is close to the equatorward boundary of the auroral zone during magnetic storms the penetration electric field there may be different from that at the equatorial ionosphere the most striking feature of the measurements is that the enhancements of the ionospheric electric field can last for many hours without significant decay the electric field enhancements in the middle and low latitude ionosphere are closely related to magnetic activity and occur during the main phase of magnetic storms the observations show that the interplanetary electric field can continuously penetrate to the low latitude ionosphere without shielding for many hours as long as the strengthening of the magnetic activity is going on under storm conditions

duskside enhancement of equatorial zonal electric field response to convection electric fields during the st patrick s day storm on 17 march 2015 the equatorial zonal electric field responses to prompt penetration of eastward convection electric fields ppef were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 march 2015 at dusk sector indian longitudes a rapid uplift of equatorial f layer to 550 km and development of intense equatorial plasma bubbles epbs were observed these epbs were found to extend up to 27 13 n and 25 98 s magnetic dip latitudes indicating their altitude development to 1670 km at apex in contrast at few degrees east in the premidnight sector thailand indonesian longitudes no significant height rise and or epb activity has been observed the eastward electric field perturbations due to ppef are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo idd fields whereas they were mostly counter balanced by the idd fields in the premidnight sector in situ observations from swarm a and swarm c and communication navigation outage forecasting system satellites detected a large plasma density depletion near indian equatorial region due to large electrodynamic uplift of f layer to higher than satellite altitudes further this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator this study brings out the significantly enhanced equatorial zonal electric field in response to ppef that is uniquely confined to dusk sector the responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field bz

centroid single force inversion of seismic waves generated by landslides the centroid moment tensor cmt waveform inversion method of dziewonski et al 1981 is modified to analyze long period seismic waves generated by single force events such as the gigantic landslides associated with the 1980 eruption of mount st helens we refer to the method as centroid single force csf inversion as the result of the inversion we obtain the spatio temporal centroid and three components of a vector we call the csf vector which is the seismic point source representation of a landslide and whose direction is the opposite of the direction of sliding the sealer magnitude of the csf vector measures the overall size of the landslide and is given by mcsf md where m is the mass of the sliding object and d is the sliding distance we apply csf inversion to the long period surface waves generated by the 1980 mount st helens event the 1975 kalapana earthquake and the 1974 mantaro landslide using seismograms from the gdsn ida and hglp networks the csf solution for the st helens event is remarkably consistent with the actual geological observations and proves the efficacy of csf inversion the csf solution for the kalapana event does not fit the overall waveforms better than the cmt solution does however because the cmt solution does not explain the observed love wave radiation pattern it may be necessary to invoke a combination of both types of mechanism for this event although the geometry of the csf solution the direction of the force for the mantaro event is consistent with the actual landslide mcsf is about 5 times smaller than that expected from the mass and travel distance of the landslide estimated by geological observations this discrepancy may suggest either the relatively aseismic nature of this landslide or that the total volume of the slide was overestimated by analogy to single station cmt inversion single station csf inversion also appears to be stable and useful

soil formation on the wallagaraugh adamellite southeastern n s w australia abstract soil development on wallagaraugh adamellite has been studied within yambulla state forest southeastern australia twenty five soil profiles have been described and soil chemical and physical properties determined for selected horizons a geomorphological model is described for elucidating processes affecting soil development on this adamellite parent material three main geomorphic environments have been incorporated into this model residual surfaces found on interfluves and broad hillcrests transportational surfaces associated with ridges and hill slopes and depositional surfaces associated with foot slopes and valley floors residual surfaces have developed duplex primary profile forms yellow podzolics with structured b horizons of high clay content where exchangeable al dominates the exchange complex transportational surfaces have soils with shallow uniform to gradational profiles with minimal profile development and highest but most variable concentrations of the exchangeable ca k na and total p depositional surfaces are characterized by a thick accumulation of uniform coarse sandy colluvium alluvium where this surface is stable and well drained podzols have formed in contrast areas of impeded drainage on this depositional surface have humic gley profiles concentrations of total p exchangeable ca and mg are low throughout these aggraded soils the soil landscape units derived from the geomorphological model are discriminated by multivariate analysis using soil chemical and physical properties surface soil chemical properties are shown to be superior in discriminating soil landscape units to subsoil properties the mineralogy geochemistry and texture of the adamellite soil parent material are critical in determining the distinctive geomorphology which in turn affects the development of soils in this forest environment

present day crustal deformation along the philippine fault in luzon philippines abstract the philippine fault results from the oblique convergence between the philippine sea plate and the sunda block eurasian plate the fault exhibits left lateral slip and transects the philippine archipelago from the northwest corner of luzon to the southeast end of mindanao for about 1200 km to better understand fault slip behavior along the philippine fault eight gps surveys were conducted from 1996 to 2008 in the luzon region we combine the 12 yr survey mode gps data in the luzon region and continuous gps data in taiwan along with additional 15 international gnss service sites in the asia pacific region and use the gamit globk software to calculate site coordinates we then estimate the site velocity from position time series by linear regression our results show that the horizontal velocities with respect to the sunda block gradually decrease from north to south along the western luzon at rates of 85 49 mm yr in the west northwest direction this feature also implies a southward decrease of convergence rate along the manila trench significant internal deformation is observed near the philippine fault using a two dimensional elastic dislocation model and gps velocities we invert for fault geometries and back slip rates of the philippine fault the results indicate that the back slip rates on the philippine fault increase from north to south with the rates of 22 37 and 40 mm yr respectively on the northern central and southern segments the inferred long term fault slip rates of 24 40 mm yr are very close to back slip rates on locked fault segments suggesting the philippine fault is fully locked the stress tensor inversions from earthquake focal mechanisms indicate a transpressional regime in the luzon area directions of 1 axes and maximum horizontal compressive axes are between 90 and 110 consistent with major tectonic features in the philippines the high angle between 1 axes and the philippine fault in central luzon suggests a weak fault zone possibly associated with fluid pressure

the impact of the january 15 2010 annular solar eclipse on the equatorial and low latitude ionospheric densities 1 the january 15 2010 solar annular eclipse crossed the magnetic equator in the middle of the day over india in a region instrumented with several magnetometers total electron content stations using gps data and an ionosonde located very near the center of the eclipse with the help of a one dimensional model appropriate for the region of interest we show that the ionosonde data was consistent with a lower f region plasma that was moving upwards with only modest velocities in the morning hours and moving resolutely downwards in the afternoon hours this motion agreed well with the local magnetometer data which revealed a weakened electrojet taking place in the morning hours while a full blown counter electrojet was present in the afternoon hours we show that the unusual solar eclipse induced electrodynamics resulted in a reduction in the total electron content depletion not just at the magnetic equator but also more markedly in the equatorial ionization anomaly eia zone a further 10 degrees to the north this latter point clearly shows that the eclipse led to a cut off in the supply of plasma provided through the equatorial fountain by altering a fundamental aspect of the equatorial electrodynamics

simulation of low latitude ionospheric response to 2015 st patrick s day super geomagnetic storm using ionosonde derived pre vertical drifts over indian region

seasonal differences in the sunrise undulations at the dip equator at solar minimum at two distinct locations and their relation with postsunset electrodynamics a sunrise undulation su is observed by ionosondes when new ionization is produced at sunrise in the upper f region at the geomagnetic equator it creates a very quick upward transition in the f region peak altitude hmf2 which subsequently undergoes a sharp descent at a rate far in excess of any electrodynamic drift the peak density also increases rapidly during the descent however the detection of the new plasma with ionosondes is possible only if plasma from the night before has undergone enough recombination which on average can vary from one location to another and one season to the next with this in mind we have studied seasonal variations in the su occurrence in 2010 at two widely separated geomagnetic equatorial stations in longitude at jicamarca in peru and trivandrum in india noticeable differences were found in the characteristics of undulation observed at the two locations while full undulation both ascend and descend in hmf 2 was observed throughout the year at trivandrum only the descending part of undulation was visible at jicamarca plasma density just before sunrise on average was 2 times larger at jicamarca than at trivandrum the average hmf 2 which peaks during night was also higher at jicamarca by as much as 100 km compared to trivandrum we traced the origin of these differences to the evolution of zonal electric field between sunset and local midnight at the two locations the downward drift during this period was steeper at trivandrum compared to jicamarca particularly during equinox in addition the strength of the downward drifts at jicamarca decreased and even underwent a sign reversal prior to sunrise during equinox and winter months in comparison the downward motion at trivandrum only became stronger during early morning hours the contrast between the vertical drift at the two stations provides a very reasonable qualitative explanation for the differences in the characteristics of su observed at the two stations

global seismicity characteristics of subduction to strike slip transitions there are at least 30 major plate boundary segments worldwide where the plate boundary changes from subduction to strike slip these include six triple junctions and 24 two plate boundaries this study investigates earthquake seismicity in the 24 two plate subduction to strike slip transition ssst regions by utilizing recently published earthquake relocations ternary diagrams of focal mechanisms and moment rate calculations to facilitate cross regional comparisons we categorize the geometry of ssst plate boundaries in terms of 1 their radius of curvature 2 their sense of curvature that is whether they are convex or concave as viewed from the downgoing plate and 3 their tectonic complexity that is the variability of crustal thickness and the segmentation of the plate boundary trace we observe three main trends in ssst regions 1 there is a conspicuous scarcity of strike slip earthquakes along plate boundary segments that plate motion models indicate are strike slip boundaries 2 in these apparent strike slip segments both the rate of occurrence of earthquakes of any kind and the moment release rate are low compared to adjacent subduction segments and 3 there were few observable differences in seismicity between convex and concave boundaries the observation that transform zones exhibit moment rate deficiencies that is have few large magnitude earthquakes in the historical record may have important implications for seismic hazard assessment in ssst regions in particular is motion along these boundaries aseismic with little seismic hazard or is motion expressed in very large magnitude infrequent but potentially devastating earthquakes in at least three such regions new zealand the philippines and the dominican republic paleoseismic evidence and the historical record of seismicity suggest that very large infrequent earthquakes do occur

character and origin of deep arenaceous weathering mantles on the bega batholith southeastern australia summary arenaceous weathering mantles on the bega batholith southeastern australia are similar to those described from europe by millot as in europe they have been formed by hydrothermal alteration of the parent rock and later by chemical weathering of biotites and feldspars but comparisons with nearby torfields shows that their distribution is determined largely by mineralogical variations in the parent rock unlike the examples cited by millot in the bega mantles kaolinite is the dominant clay mineral nonetheless these mantles seem to be contemporary not relict features and apparently formed under a temperate climate

ionospheric electron content within the equatorial f 2 layer anomaly belt this paper describes some new results on the day to day behavior of the location of the equatorial anomaly in the columnar electron content the measurements were made from a unique network of stations covering dip latitudes from 0 n to 25 n during the period in 1975 1976 near sunspot minimum when the ats 6 satellite was visible from india the latitudinal distribution of the total electron content on a particular day was found to depend only on the strength of the electrojet current as determined by the difference of the horizontal magnetic field at stations on the magnetic equator and another outside the equatorial electrojet rather than on the horizontal magnetic field measured only at the equatorial station during magnetically disturbed periods the presence or absence of the anomaly was also found to depend only upon the strength of the electrojet current the varying electrojet current that is the equatorial electric field is very effective in moving the ionization to the anomaly latitudes of 15 20 but the columnar electron content over the magnetic equator remains relatively constant

relation between continental strike slip earthquake segmentation and thickness of the crust 1 high resolution maps of large continental strike slip earthquake surface ruptures show that they are formed of fault segments these segments are bounded by fault bends step overs or combinations of the two the lowest limit in size for such segments may not be relevant in the understanding of earthquake mechanics as it pertains to the granular properties of fault zones the maximum limit in segment length however is important as it is directly relates to the maximum extent of seismic rupture to measure the length of the segments a new quantitative method based on piecewise linear fitting is developed and is used to automatically retrieve segments from earthquake rupture maps next this approach is tested against a set of ten continental strike slip earthquake ruptures derived from similar high quality maps the test suggests that segments have a maximum length of 18 km independent of regional tectonic setting slip inversions for earthquakes based on seismological and or geodetic data most often are not unique and can show some variability even for one particular event some basic characteristics however such as total moment release or general source geometry seem to persist that are relevant to earthquake mechanics measurements of the maximum horizontal extent of individual slip patches derived from seismic source inversion for strike slip ruptures show that their strike dimension does not increase infinitely with magnitude but instead reaches a maximum value of 25 km these two independent lines of observations complemented by earlier data and analog experiments suggest that it is the thickness of the seismogenic crust that controls the structural scaling of the length of seismic segments and that it is independent of the ultimate size of individual earthquakes

deep and intermediate depth non double couple earthquakes interpretation of moment tensor inversions using various passbands of very broadband seismic data summary analysis of moment tensor inversions using various passbands of very broadband seismic data provides clear evidence that some non double couple moment tensors of intermediate depth and deep earthquakes result from the superposition of different double couple sources whose predominant principal axes are aligned with the predominant strain state within the subducting slabs the analyses are performed for three intermediate depth and deep earthquakes 1984 january 1 south of honshu 386 km 1985 april 23 luzon 181 km and 1987 may 7 northern sea of japan 417 km consistent non double couple moment tensors obtained using different sets of seismic waves in various low frequency bands suggest that these three significant non double couple components are not caused by unmodelled propagation errors of seismic waves in the inversion procedure because the various sets of seismic waves traverse very different ray paths for the south of honshu and the luzon events two major arrivals in the broadband p wave diplacement seismograms are observed with varying relative amplitudes or polarities from station to station the different double couple mechanisms which model the two phases combine to produce the significant non double couple moment tensors obtained at long periods the principal axes of the subevents closest in orientation to the predominant strain states within the slabs tend to be quite stable whereas the other two principal axes rotate between subevents this observation may explain the global nature of non double couple components in relation to the strain regime within the slab for the northern sea of japan event two major phases are observed in the p wave displacement waveforms but the variation in mechanism of two subevents that we model is not enough to explain the large non double couple component observed at long periods however since the non double couple component is exceptionally large compared with those for other deep earthquakes changes of focal mechanism with shorter delays than we can resolve appear to explain the overall radiation most simply

day to day variability of equatorial electrojet and its role on the day to day characteristics of the equatorial ionization anomaly over the indian and brazilian sectors the equatorial electrojet eej is a narrow band of current flowing eastward at the ionospheric e region altitudes along the dayside dip equator mutually perpendicular electric and magnetic fields over the equator results in the formation of equatorial ionization anomaly eia which in turn generates large electron density variabilities simultaneous study on the characteristics of eej and eia is necessary to understand the role of eej on the eia variabilities this is helpful for the improved estimation of total electron content tec and range delays required for satellite based communication and navigation applications present study reports simultaneous variations of eej and gps tec over indian and brazilian sectors to understand the role of eej on the day to day characteristics of the eia magnetometer measurements during the low solar activity year 2004 are used to derive the eej values over the two different sectors the characteristics of eia are studied using two different chains of gps receivers along the common meridian of 77 e india and 45 w brazil the diurnal seasonal and day to day variations of eej and tec are described simultaneously variations of eia during different seasons are presented along with the variations of the eej in the two hemispheres the role of eej variations on the characteristic features of the eia such as the strength and temporal extent of the eia crest has also been reported further the time delay between the occurrences of the day maximum eej and the well developed eia is studied and corresponding results are presented in this paper

a dayside ionospheric positive storm phase driven by neutral winds 1 this paper presents observations and numerical simulations of ionospheric and thermospheric disturbances associated with a moderate geomagnetic storm on 10 september 2005 during the event the incoherent radars located in millstone hill and arecibo observed a dayside positive storm phase as manifested by the enhanced electron density in the f region the universal time ut altitude profile of electron density measured by both radars displayed a structure that closely resembles the greek letter a similar structure is also reproduced by the thermosphere ionosphere electrodynamics general circulation model tiegcm this peculiar electron density distribution is found to be associated with vertical ion drift which initially was upward and then became downward using realistic time dependent ionospheric convection and auroral precipitation as inputs the tiegcm reveals that the primary cause of the positive storm response was the enhanced meridional neutral wind rather than the penetration magnetospheric electric field this study reiterates the importance of neutral wind effects on ionospheric disturbance

inversion of surface wave spectra for source parameters of large earthquakes using aspherical earth models abstract amplitude and phase spectra of rayleigh and love waves of periods of 150 to 300 s from eight large earthquakes which occurred between 1990 and 1993 are corrected for wave propagation and then inverted for the source duration rupture directivity and moment tensor of the earthquake source for various propagation anomalies predicted by models of the earth s aspherical elastic and anelastic structure the application of corrections for the focusing and take off azimuth anomaly in addition to conventional corrections for the phase anomaly improves inversions of surface waves rayleigh waves provide better constraints than love waves in the determination of source parameters the data consist of either only rayleigh waves or both love and rayleigh waves whenever the full moment tensor is involved for several earthquakes there is clear discrepancy between source parameters determined from different data sets particularly from rayleigh or love waves the moment tensor solution tends to underpredict observed amplitude spectra for data sets with large amplitude anomalies especially for love waves this study shows that 1 the 1990 sudan earthquake is anomalous for its unusually large non double couple component of the moment tensor 2 the 1990 iran earthquake has a strike slip mechanism with a subvertical nw striking nodal plane which is the fault plane inferred from surface ruptures 3 the 1991 costa rica earthquake may have a seismic moment larger than previously determined from long period surface waves 4 the 1992 nicaragua earthquake involves a predominant rupture parallel to the trench and a large centroid offset up dip to the trench axis and the latter process may be responsible for large tsunami generation 5 the 1993 hokkaido earthquake has a shallow dipping and west plunging nodal plane which is consistent with the p wave first motions but differs from the centroid moment tensor solutions

modelling of earthquake rupturing as a stochastic process and estimation of its distribution function from earthquake observations summary the effect on earthquake rupturing of heterogeneities in tectonic stress and in material strength along a large fault zone is incorporated in the potential dynamic stress drop defined as the difference between the tectonic shear stress and the dynamic frictional strength according to a slip weakening model the distribution of the potential dynamic stress drop az x along the strike of the fault plane is modelled as a 1 d stochastic process using a simple dynamic fracture criterion a relation is established between earthquake rupturing and potential dynamic stress drop by which any earthquake rupture process can be regarded as a segment of a realization of the process at where azd x 0 since dynamic slip varies approximately linearly with dynamic stress drop it has the same distribution function as azd x provided that azd x is a gaussian process three independent earthquake observations i e the average stress drop the gutenberg richter relation and the surface slip along earthquake faults are used to estimate the distribution function of azd x an analytical solution is derived for the distribution function of azd x which shows that among all known distribution models only the fractional brownian motion with index h 0 fractal dimension d 2 in the 1 d case can give rise to the observed approximately constant stress drop independent of earthquake size the probability distribution of the size of zerosets of the fractional brownian motion shows a power law relation with frequency which resembles the frequency seismic moment relation using an average b value of 1 o for small earthquakes an index h o of the fractional brownian motion is obtained the model predicts that the b value for large earthquakes is smaller than that for small earthquakes along the same fault zone which is in agreement with observations the surface slip data of two strike slip dominated earthquake faults with rupture lengths larger than 100 km are inverted using power spectral analysis both data sets display a power law relation between the sample power spectrum and the spatial frequency which implies a fractional brownian distribution the estimated index h is close to zero for both earthquake faults stress drops b values and surface slips all independently suggest that the earthquake rupturing process can be modelled stochastically as a fractional brownian motion with index h 0

a reappraisal of large earthquake scaling abstract twelve years ago i pointed out that observations indicate that the slip in large earthquakes scales with their length rather than their width as expected from the canonical model romanowicz 1992 has recently argued that more recent data show that the opposite is true which has obliged me to re examine the question i point out here a defining flaw in her analysis in that she allowed mo the moment at the cross over from small to large earthquakes to be a free variable in her curve fitting whereas this parameter can be defined independently when this parameter is independently fixed i find that the up dated data set confirms my earlier conclusion that for large crustal earthquakes m0 scales with l 2 a little over a decade ago i pointed out that obser vations indicate that the slip in large earthquakes scales with their rupture length scholz 1982 several sub sequent papers provided additional data supportive of this view chen and molnar 1983 shimazaki 1986 scholz et al 1986 large earthquakes are defined in this con text as those that rupture the entire seismogenic thick ness w0 and are thus constrained to propagate farther in a horizontal direction only for crustal earthquakes w0 is nearly constant 15 km so this scaling conflicts with conventional models of earthquakes such as dislocation models because they predict that slip scales with width which is invariant for these earthquakes i offered two alternative ways to interpret these observations one is that such conventional w models are correct but that stress drop could no longer be regarded as scale invariant but must scale with fault length as an alternative i sug gested the possibility of what i termed an l model in which slip intrinsically scales with fault length this created a minor crisis in seismology which has yet to be resolved it is no exaggeration to say that my l model suggestion has not attracted a noticeable coterie of admirers nor has my other suggestion and there has been no other model proposed in the interim that ex plains the observed l scaling although heaton 1990 has suggested a way in which length may scale with stress drop a variation of my w model scaling alternative in the face of this an alternative is to question the obser vations which is what romanowicz 1992 has recently chosen to do in her interpretation of an updated data set she concluded that seismic moment m0 scales lin early with rupture length l for large earthquakes which is consistent with w models and implies that slip u is scale invariant for large crustal earthquakes this great discrepancy with the earlier result she implies is due to the presence of superior modern measurements in the updated data set this issue has major implications both practical and theoretical and merits some debate here i present my own reappraisal of the data in which the conclusions are very different reappraisal of the data romanowicz s conclusions were based on a log log plot of m0 versus l for a data set of strike slip earth quakes she showed that the data in this figure could be better fit by two straight lines one with slope 3 in the lower scale range and one with slope 1 in the upper scale range than with a single line of slope 2 for small earth quakes which grow in both dimensions with l w m0 should scale with l 3 for large earthquakes where w has saturated at w0 and growth only occurs in the l di rection m0 should scale with l according to conven tional models hence the problem produced by my ob servation that m0 scales with l 2 for those events superficially then it appears that she has resolved the issue the problem however is that she has allowed the cross over length l which separates small from large earthquakes to be a free variable in her curve fitting ex ercise she thus obtains a cross over moment of 0 6 to 0 8 x 1020 n m which is appropriate for a rupture length of 60 to 70 km by adding an additional free parameter to the curve fitting one would expect a much better fit to be achieved the question is whether such a step is justified if small earthquakes grow with l w then the transition to large earthquakes defined as an event that ruptures the entire seismogenic thickness would be l w0 10 to 20 km for the data being studied this may be checked observationally because large earth quakes almost invariably nucleate near the base of the seismogenic layer das and scholz 1983 it follows that the transition to large earthquakes is at the length at which one begins to consistently see surface ruptures inspec tion of the earthquakes in romanowicz s 1992 figure 215

geodetic constraints on coseismic rupture during the 1990 ms 7 8 luzon philippines earthquake 1 we analyze single frequency gps measurements taken before and after the july 16 1990 ms 7 8 luzon earthquake to constrain the faulting parameters of this major strike slip event the geodetic data imply fairly uniform left lateral slip of 5 5 6 5 m along the well mapped part of the fault trace in agreement with field mapping of the rupture and in general accord with seismological estimates of the fault parameters in addition we find that substantial slip of about 4 5 m magnitude continued about 40 50 km northward or northwestward into the cordillera central beyond the end of the mapped rupture this fault segment includes a substantial thrust component in addition to left lateral slip the geodetic data favor a faulting depth of at least 20 km along the central part of the rupture unusually deep for a major continental strike slip earthquake

amplitude anomalies of surface waves from the july 16 1990 philippine islands earthquake love waves from the 1990 philippine islands earthquake show large amplitude anomalies at broadband seismograph stations in japan while rayleigh waves do not we calculate synthetic seismograms using the fully coupled eigensolutions obtained by a variational method to see if this anomalous behavior of surface waves is explained by the laterally heterogeneous earth model m84a of woodhouse and dziewonski we show that the anomalous long period surface wave amplitude behavior can be reproduced relatively well by m84a

on moment length scaling of large strike slip earthquakes and the strength of faults 1 several large strike slip earthquakes have occurred in various tectonic settings in the past 5 years adding well documented data to the global collection of moment and length estimates for such earthquakes based on this augmented dataset we reexamine the controversial issue of scaling of seismic moment with length of rupture we find that the global dataset of large strike slip earthquakes follows a bi modal distribution most oceanic and or intraplate strike slip earthquakes have stress drops that are 5 times larger than interplate continental ones when distinguishing these two classes the scaling is compatible with that predicted by simple dislocation theory

storm time plasma transport at middle and high latitudes associated with the large scale enhancement of the ionospheric convection electric field during disturbed geomagnetic conditions solar produced f region plasma is transported to and through the noontime cleft from a source region at middle and low latitudes in the afternoon sector as a result of the offset between the geomagnetic and geographic poles the afternoon sector region of strong sunward convection is shifted to increasingly lower geographic latitude throughout the interval between 12 ut and 24 ut a snowplow effect occurs in which the convection cell continually encounters fresh corotating ionospheric plasma along its equatorward edge producing a latitudinally narrow region of storm enhanced plasma density sed and increased total electron content which is advected toward higher latitudes in the noon sector the millstone hill incoherent scatter radar regularly observes sed as a spatially continuous large scale feature spanning local times between noon and midnight and at latitudes between the polar cap and its mid or low latitude source region for local times away from noon the latitude of most probable sed occurrence moves equatorward by 6 for an increase of 2 in the kp index during strong disturbances the topside sed is observed to be convecting sunward at 750 m s 1 with a flux of 1014 m 2 s 1 this feature accounts for the pronounced enhancement of ionospheric density near dusk at middle latitudes observed during the early stages of magnetic storms called the dusk effect and constitutes a source for the enhanced f region plasma observed in the polar cap during disturbed conditions

on the historical origins of the cej dp2 and ddyn current systems and their roles in the predictions of ionospheric responses to geomagnetic storms at equatorial latitudes in this short letter we recall the differences between the counter electrojet cej which is a phenomenon observed on the magnetically quiet days and the disturbance dynamo ddyn which can be observed during and after a geomagnetic storm the cej is well known to occur near the geomagnetic dip equator it can be identified by a reversal in the horizontal component h of the geomagnetic field daily regular variations in contrast to equatorial electrojet eej that flows eastward in the daytime the cej is considered to flow westward the magnetic signatures of the reversed solar quiet sq current at the low latitude during magnetic storms are due to the ddyn this disturbance ddyn is produced by current systems that are driven by thermospheric storm winds originating from the joule heating of enhanced high latitude currents the dp2 is the magnetic effect of current systems at high latitudes these currents are associated with the coupling of magnetosphere and ionosphere through geomagnetic field lines they are associated to the magnetospheric convection during intense magnetic storms these high latitude currents are enhanced and their magnetic effects can extend toward the low latitudes this work shows that the study of magnetic perturbations makes it possible to understand the disturbances of the ionospheric electric currents the use of an efficient treatment of the magnetic signals makes it possible to separate the magnetic effects of the different perturbations prompt penetration of the magnetospheric convection electric field and disturbance dynamo electric field this was performed in the paper nava et al 2016

transient composite electric field disturbances near dip equator associated with auroral substorms ionosonde data of kodaikanal geog long 77 29 e dip 3 0 n and huancayo geog long 75 18 w dip 2 0 n are used to show the simultaneous occurrence of a transient disturbance in f region height of composite polarity in day and night sectors near the dip equator during the auroral substorm activity on 20 august 1979 at kodaikanal which is on the nightside at the time of the substorm activity h f first underwent an abrupt and rapid decrease 80km in 1 hr followed by a much larger increase 120km in 1 hr perturbation in hpf2 of exactly opposite polarity was simultaneously seen at huancayo which is on the dayside the decrease in h f at kodaikanal increase in hpf2 at huancayo occurred in association with an increase in polar cap potential drop o estimated from imf parameters and the subsequent increase decrease at huancayo with a decrease in polar cap potential the f region height disturbance is interpreted as the manifestation of a global transient composite disturbance in equatorial zonal electric field caused by the prompt penetration of substorm related high latitude electric fields into the equatorial ionosphere the polarity pattern of the electric field disturbance is consistent with the global convection models which predict westward eastward electric fields at night by day near the geomagnetic equator in response to an increase in polar cap potential drop and fields of opposite signs for a decrease in polar cap potential

on the latitudinal variations of the ionospheric electric field during magnetospheric disturbances a joint alert campaign was organized during the month of october 1980 by the incoherent scatter radars in the american sector namely jicamarca arecibo millstone hill and chatanika the campaign which met with success was designed to study the behavior of the ionospheric electric field as a function of latitude during magnetically active conditions the arecibo data in this campaign support present and previous observations at jicamarca that suggest that when the convection e field suddenly decreases the alfven layer shielding field becomes unbalanced and penetrates the plasmasphere while this type of observation is reasonably convincing others are more difficult to categorize we suggest that beside the high latitude electric fields time varying auroral conductivity models will have to be considered in order to understand the morphology of the low latitude e field disturbances we present the first correlation analysis and determination of the amplitude ratio of the disturbed zonal electric field at 30 geometric latitude arecibo to the field at 0 jicamarca other highlights of the paper are a discussion of dp2 which may help clarify the controversy surrounding it and a discussion of the sensitivity of low and mid latitude radars to disturbances of magnetospheric origin we show that this sensitivity maximizes at the magnetic equator

mineralogical and textural controls on the weathering of granitoid rocks summary the results obtained in several recent studies provide convincing evidence that potassium rich granitoid rocks are relatively more resistant to weathering than their less potassic counterparts this reflects the fact that microcline and orthoclase are more stable in most weathering environments than calcic plagioclase and biotite relatively slight differences in bulk rock chemical composition can lead to differential rates of weathering in areas of inhomogeneous granitoid terrain thereby leading to the development of topographic features such as inselbergs a second major control on the rate of weathering is rock permeability this is largely a function of degree of microfracturing and jointing in most circumstances grain size and other textural differences probably exert a minor influence on rates of chemical weathering although laboratory tests have shown they may profoundly affect physical strength parameters

ionospheric storm of early november 1993 in the indian equatorial region an investigation is made of the response of equatorial ionosphere in the indian 75 e sector to the major magnetic storm of november 3 1993 using data from the ionosonde and magnetometer networks spanning the region 0 3 34 5 n dip some outstanding and new aspects of the storm time ionospheric behaviour are revealed an anomalous and striking positive gradient in 0f2 from the magnetic equator to 34 5 dip developed under counter electrojet cej condition in the morning on november 4 corresponding to the early stage of the storm main phase this storm effect is attributed to plasma transport by a poleward surge in transequatorial winds due to large scale atmospheric gravity waves agws launched by auroral heating remarkable wave like variations in hpf2 and 0f2 immediately followed at locations away from dip equator till local sunset with concomitant disruptions in the development of the equatorial ionization anomaly eia rapid variations in meridional neutral winds due to large scale agws are assessed as the cause of the oscillations in hpf2 and the associated cyclic sequence of development and inhibition of eia as the outcome of the combined effects of plasma transport due to meridional winds and the plasma fountain driven by e b drift just after the onset of the storm recovery phase at 1800 lt a sudden and anomalous drop 54 57 in 0f2 prevailed throughout the anomaly region over the interval 1915 2330 lt with an apparent time delay in occurrence toward the magnetic equator this premidnight collapse of equatorial f region is interpreted in terms of horizontal transport of plasma across the equator toward the opposite hemisphere by an equatorward surge in meridional winds the case study showed that besides disturbances in the zonal electric field due to prompt penetration and ionospheric disturbance dynamo effects perturbations in neutral meridional winds played a prominent role in the ionospheric storm of november 4 1993 in the indian equatorial region

signatures for magnetospheric substorms in the geomagnetic field of dayside equatorial region origin of the ionospheric component 1 an event based study is made of the conditions that lead to the ionospheric current component in the geomagnetic field signature for magnetospheric substorms in the dayside dip equatorial region the substorm activity studied here is characterized by two onsets separated by 40 min the first one occurred during steady southward interplanetary magnetic field imf and steadily increasing cross polar cap potential and enhanced energy input into the magnetosphere while the second one occurred in close association with a northward transition of imf and a rapid reduction of the polar cap potential and energy input into the magnetosphere earlier studies using multispacecraft data as well as ground based optical radar and magnetic recordings ascertained the first onset to be associated with a pseudo breakup and the second onset with a true breakup magnetometer recordings from a meridional network of stations in the indian and pacific sectors revealed the response of daytime equatorial h field to the pseudo breakup to be weak and not readily identifiable in contrast a distinct negative bay like disturbance with an unambiguous dip equator enhancement prevailed in the h field starting with the onset of the expansive phase of the fully developed substorm this behavior indicative of a significant contribution of ionospheric currents to the negative h field bay is seen both in the indian and pacific sectors covering the 1200 1600 lt region the present case study thus suggests that a sudden and prominent reduction in the cross polar cap potential at the substorm expansive phase is responsible for the prevalence of the ionospheric current component in the geomagnetic disturbance in the dayside equatorial region it is also found for the first time that the amplitude of the negative h field disturbance in the afternoon sector exhibits a marked hemisphere asymmetry at midlatitudes it is higher by a factor of about 3 in the summer hemisphere than in the winter hemisphere the equatorial enhancement of the negative h component disturbance is interpreted as the signature of the over shielding effect namely direct penetration of the perturbation component of the large scale electric field associated with the rapid reduction in convection at the onset of the substorm expansion phase the marked summer winter asymmetry of the h field disturbance at midlatitudes is suggested as the outcome of the competing magnetic effects of field aligned currents and polar origin dp2 currents

on the latitudinal changes in ionospheric electrodynamics and composition based on observations over the 76 77 e meridian from both hemispheres during a geomagnetic storm the relative contributions of the composition disturbances and the disturbance electric fields in the redistribution of ionospheric plasma is investigated in detail by taking the case of a long duration positive ionospheric storm that occurred during 18 21 february 2014 gps total electron content tec data from the indian antarctic station bharti 69 4 s 76 2 e geographic the northern midlatitude station hanle 32 8 n 78 9 e geographic northern low latitude station lying in the vicinity of the anomaly crest ahmedabad 23 04 n 72 54 e geographic dip latitude 17 n and the geomagnetic equatorial station trivandrum 8 5 n 77 e geographic dip latitude 0 01 s are used in the study these are the first simultaneous observations of tec from bharti and hanle during a geomagnetic storm the impact of the intense geomagnetic storm dst 130 nt on the southern hemisphere high latitude station was a drastic reduction in the tec negative ionospheric storm starting from around 0330 indian standard time ist on 19 february which continued till 21 february the maximum reduction in tec at bharti being 35 tec units on 19 february in the northern hemisphere midlatitude and equatorial stations a positive ionospheric storm started on 19 february at around 0900 ist and lasted for 3 days the maximum enhancement in tec at hanle was about 25 tecu on 19 february while over trivandrum it was 10 tecu this long duration positive ionospheric storm provided an opportunity to assess the relative contributions of disturbance electric fields and composition changes latitudinally the results indicate that the negative ionospheric storm over bharti and the positive ionospheric storm over hanle are the effect of the changes in the global wind system and the storm induced composition changes at the equatorial latitudes the positive ionospheric storm was due to the interplay of prompt penetration electric field and disturbance dynamo electric field

impact of oscillating imf bz during 17 march 2013 storm on the distribution of plasma over indian low latitude and mid latitude ionospheric regions we show evidence of a positive ionospheric storm occurring simultaneously at the equatorial low and mid latitude ionospheric regions in the indian sector in response to an intense geomagnetic storm on 17 march 2013 the storm had its onset time coinciding with the local noon an on site digisonde at trivandrum dip equator recorded a sharp decrease in the height of f region peak in the afternoon which is a signature of westward electric field associated with a cej coupled with it was a simultaneous increase in tec in the entire indian region the magnitude of increase in tec decreased slowly northward of the dip equator and had almost no change near the anomaly crest further northward of the anomaly crest the tec started increasing again and at shimla a mid latitude station it had a value close to 2 times its monthly mean we surmise that the westward electric field resulting from the cej pushed the f layer at the dip equator down to the altitude regions where recombination and diffusion played minimal roles no loss of plasma due to diffusion while photo production of ions was still taking place led to an enhancement in the electron density near the equatorial low latitude region the joule heating of the thermosphere on the other hand gave rise to the tads which pushed the plasma up in altitude at the equatorial anomaly region it supplemented the loss of plasma at the anomaly crest region resulting in no change in the tec and a marked increase in the tec in the mid latitude ionosphere

analysis of crustal deformation in luzon philippines using geodetic observations and earthquake focal mechanisms we utilize regional gps velocities from luzon philippines with focal mechanism data from the harvard centroid moment tensor cmt catalog to constrain tectonic deformation in the complex plate boundary zone between the philippine sea plate and eurasia the sundaland block processed satellite imagery and digital elevation models are used with existing gravity anomaly seismicity and geologic maps to define a suite of six elastic blocks geodetic and focal mechanism data are inverted simultaneously to estimate plate rotations and fault locking parameters for each of the tectonic blocks and faults comprising luzon major tectonic structures that were found to absorb the plate convergence include the manila trench 20 100 mm yr 1 and east luzon trough 9 15 mm yr 1 philippine trench 29 34 mm yr 1 which accommodate eastward and westward subduction beneath luzon respectively the left lateral strike slip philippine fault 20 40 mm yr 1 and its northward extensions the northern cordillera fault 17 37 mm yr 1 transtension and the digdig fault 17 27 mm yr 1 transpression the macolod corridor a zone of active volcanism crustal thinning extension and extensive normal and strike slip faulting in southwestern luzon is associated with left lateral transtensional slip of 5 10 mm yr 1 the marikina fault which separates the central luzon block from the southwestern luzon block reveals 10 12 mm yr 1 of left lateral transpression our analysis suggests that much of the philippine fault and associated splays are locked to partly coupled while the manila and philippine trenches appear to be poorly coupled luzon is best characterized as a tectonically active plate boundary zone comprising six mobile elastic tectonic blocks between two active subduction zones the philippine fault and associated intra arc faults accommodate much of the trenchparallel component of relative plate motion 2006 elsevier b v all rights reserved

displacement and geometrical characteristics of earthquake surface ruptures issues and implications for seismic hazard analysis and the process of earthquake rupture there now exist about three dozen historical earthquakes for which in vestigators have constructed maps of earthquake rupture traces accompanied by de scriptions of the coseismic slip observed along the fault strike the maps and slip distributions are compiled here to place observational bounds on aspects of seismic hazard analysis and fault mechanics analysis leads to an initial statistical basis to predict the end points of rupture and the amount of surface slip expected at sites along the strike during earthquakes on mapped faults the observations also give support to the ideas that there exists a process zone or volume of about 3 4 km in dimension at the fronts of large laterally propagating earthquake ruptures within which stress changes may be sufficient to trigger slip on adjacent faults and that the ultimate length of earthquake ruptures is controlled primarily by the geometrical complexity of fault traces and variations in accumulated stress levels along faults that arise due to the location of past earthquakes to this may be added the observation that the form of earthquake surface slip distributions is better described by asymmetric rather than symmetric curve forms and that earthquake epicenters do not appear to correlate in any systematic manner to regions of maximum surface slip observed along strike online material maps of surface ruptures digitized values and curve fits to surface slip distributions and notes and references for tables 1 and 2