a tectonic boundary for the southern colorado plateau abstract a tectonic boundary should be defined by changes in tectonic elements tectonic elements would include such parameters as structural style stress orientations volcanism heat flow seismicity and changes in crustal thickness examination of these tectonic elements for the southern colorado plateau suggests that the southwestern part of the physiographic plateau appears to be tectonically part of the basin and range province i therefore propose a boundary at 112 w longitude the locus of seismicity and recent volcanism and also the site of crustal thickening and a change of structural style the tectonic boundary of the southern colorado plateau is suggested to form part of the eastern boundary of the southern basin and range seismotectonic region this seismotectonic region is bounded on the north by the las vegas shear zone nevada seismic zone and has a different stress orientation than the northern basin and range from which it began to evolve separately 13 m y ago the present principal stress orientation of the southern basin and range of arizona appears to be the result of compound movements of the san andreas transform and garlock las vegas shear zone resulting in a shear couple affecting the crust in arizona and an associated ne sw least principal stress orientation

active seismic deformation in the grabens of northern central america and its relationship to the relative motion of the north america caribbean plate boundary abstract the active seismic deformation along the grabens of northern central america is calculated using a method which relates relative plate velocity with the seismic strain rate tensor the latter is in turn obtained from seismic moment tensors we calculate the typical or average moment tensor from available centroid moment tensors and fault plane solutions this average tensor is then used to obtain the sum of moment tensors of historical and modern earthquakes reported in the literature both historical and modern earthquakes yield an average extension rate of 8 mm yr along the grabens of northern central america while the relative motion between the north america and caribbean plates expressed along the motagua polochic fault system is 20 mm yr this result suggests that part of the seismic deformation related to the plate boundary is taken up as extension along the grabens which play the role of fault termination structures for the motagua polochic system

distribution and genesis of the eastern tibetan plateau geothermal belt western china more than 185 hot springs have been recently discovered in the eastern tibetan plateau geothermal belt also called the kangding litang batang geothermal belt 98 102 e 28 32 n among them more than 60 of springs have temperatures of 40 c and 11 springs have temperature higher than the local water boiling point these hot springs are mostly exposed near the fault or valley areas as bandings in reservoirs of triassic carbonate rocks and clastic quartz sandstone or in fractured granite and intrusive rocks the geothermal belt can be subdivided into the batang xiangcheng geothermal field the ganzi litang geothermal field and the luhuo kangding geothermal field which are controlled by the jinsa fault xiangcheng fault litang fault and xianshuihe fault respectively radiogenic heat from the mesozoic and cenozoic granites possible ductile crustal flow beneath the lower crust and frictional heat generated by active strike slipping along faults are the significant heat resources for the geothermal genesis frictional heat caused by the slipping along the xianshuihe fault is the main thermal source for the luhuo kangding geothermal field whereas magma melting heat is the main source for the batang xiangcheng geothermal field glacier water and river water are the main water supply sources and the fracture serves as the main channel for runoff and hot water flow the activity intensity and magnitude of the kangding litang batang geothermal anomaly were lower than those of the geothermal fields of yangbajing and tengchong in the central and southern tibetan plateau respectively which indicates that the eastern tibetan plateau has a strong heat flow background

microseismicity of the kaibab plateau northern arizona and its tectonic implications abstract a microearthquake investigation of the kaibab plateau in northern arizona revealed swarms of small to very small magnitude earthquakes a 12 station network of portable seismographs recorded 296 events with magnitudes from 0 5 m l t axes from these fault plane solutions yields an average least principal horizontal stress direction of ene wsw the inferred orientation of principal stresses found in this study indicates the kaibab plateau lies within a region of predominantly normal faulting which extends from central arizona northward into southwestern utah although data are sparse in the region surrounding the kaibab plateau evidence for the location of a basin range colorado plateau stress boundary through the kaibab plateau is not supported by the results of this study

attenuation of intensity for the 1887 northern sonora mexico earthquake abstract contouring the intensity data for the northern sonora earthquake of 1887 yields an area of perceptibility defined by the mm iii isoseismal that is greatly elongated to the southeast of the epicenter along the sierra madre occidental north of the epicenter the isoseismals are compressed due to the change in crustal structure between the colorado plateau and the southern basin and range province the higher intensity isoseismals are more symmetric although local structure strongly influences individual intensity values to evaluate the attenuation of intensity with distance three regression curves are calculated as below all data i 12 0 3 2 0 0015 r 1 5 in r 25 500 km i 12 0 0 69 0 0069 r 0 82 in r isoseismal i 12 0 8 1 0 0031 r 2 3 in r where r is the epicentral distance in kilometers the all data curve is derived from a regression computed using all 171 intensity values the 25 500 km curve eliminates the near and far points and the isoseismal curve is a regression on the average radii of the area enclosed by each isoseismal contour the latter two curves are similar to curves for the western united states as a whole anderson 1978 or the cordilleran curve of howell and schultz 1975 for intensities less than or equal to mm x the curve for all data indicates less attenuation at lower isoseismals than the other two 1887 regressions and falls between the cordilleran and eastern united states models of howell and schultz

the 2013 seismic swarm in chihuahua mexico evidence of active extensional deformation in the southern basin and range abstract an earthquake swarm took place from 27 august 2013 to december 2013 in the southern basin and range province of chihuahua mexico during this period the seismological service of mexico located approximately 60 earthquakes in the region the largest earthquake took place on 21 september 2013 m w 5 3 a temporary seismic network was installed in the area for a period of two weeks the hypocenters were relocated using the double difference algorithm the results show a cluster of seismicity along the vallecillo fault where most of the seismicity took place and on the penasco fault these two faults lie within the foothills of the sierras of the same name that bound the el caballo desert basin the seismicity suggests that both faults bounding the el caballo basin slipped during the swarm the main event of 27 august 2013 apparently took place on the vallecillo fault a third cluster of seismicity was located on sierra la mezcalera about 20 km to the south of the vallecillo fault at the western end of the la boquilla dam focal mechanisms of the larger events indicate right lateral slip with extensional deformation on the vallecillo fault with t axes oriented in a northeast southwest direction these source mechanisms reflect a regime of extensional tectonics in the southern basin and range province the vallecillo and penasco fault system is exposed for approximately 12 km along strike scaling relations suggest that earthquakes as large as m w 6 4 may take place on them this magnitude is similar to that of the 1928 parral earthquake that occurred about 125 km to the south of the swarm however segmented faults may rupture sequentially and generate a larger earthquake than the one predicted on the basis of the length of individual mapped faults

structural configuration of the otates fault southern basin and range province and its rupture in the 3 may 1887 mw 7 5 sonora mexico earthquake abstract during the great 3 may 1887 sonoran earthquake surface rupture end to end length 101 8 km m w 7 5 0 3 an array of three north south striking basin and range province faults from north to south pitaycachi teras and otates slipped along the western margin of the sierra madre occidental plateau of northern mexico this detailed field survey of the previously undocumented 1887 earthquake rupture zone along the otates fault includes mapping the rupture scarp and measurements of surface deformation at 25 sites the surface rupture coincides with the mapped trace of the otates fault dips 68 w and has an end point to end point length of 18 2 km the lateral rupture terminations are controlled by cross faults striation measurements and the style of rupture indicate extensional dip slip without significant lateral displacement the average shortening p and extension t kinematic axes inferred from the striations are similar to published composite focal mechanisms of the microseismicity recorded in the epicentral region of the 1887 earthquake based on surface deformation maximum slip along the otates fault in the 1887 earthquake was 270 cm and the average slip was 189 cm a quadratic best fit to the along rupture surface offsets indicates an asymmetric distribution with the maximum offset near the northern end of the rupture segment which can be explained by the mechanical interaction of the teras and otates surface rupture segments through their stress fields the average recurrence interval of 1887 sized earthquakes on the otates fault is 30 42 kyr based on the long term geologic dip slip rate of the fault 0 06 mm yr and its amount of slip in the 1887 earthquake

mmi attenuation and historical earthquakes in the basin and range province of western north america earthquakes in central nevada 1932 1959 were used to develop a modified mercalli intensity mmi attenuation model for estimating moment mag nitude m for earthquakes in the basin and range province of interior western north america m is 7 4 7 5 for the 26 march 1872 owens valley california earthquake in agreement with beanland and clark s 1994 m 7 6 that was estimated from geologic field observations m is 7 5 for the 3 may 1887 sonora mexico earthquake in agreement with natali and sbar s 1982 m 7 4 and suter s 2006 m 7 5 both estimated from geologic field observations mmi at sites in california for earthquakes in the nevada basin and range appar ently are not much affected by the sierra nevada except at sites near the sierra nevada where mmi is reduced this reduction in mmi is consistent with a shadow zone produced by the root of the sierra nevada in contrast mmi assignments for earthquakes located in the eastern sierra nevada near the west margin of the basin and range are greater than predicted at sites in california these higher mmi values may result from critical reflections due to layering near the base of the sierra nevada

frequency and size of quaternary surface ruptures of the pitaycachi fault northeastern sonora mexico movements along the pitaycachi fault since the miocene juxtaposed different alluvial units and created 2 to 45 m high fault scarps downslope from a pedimented mountain front prior to 1887 in 1887 a major earthquake formed a 75 km long 1 2 to 4 m high scarp along the trace of prehistoric surface ruptures diverse evidence from many study sites indicates that about 200 000 yr elapsed between the prior youngest pleistocene event and the 1887 surface rupture cumulative displacements of pliocene to mid pleistocene alluvial fans and stream terraces decrease with decreasing age the trace of the prior rupture was largely buried by sheets of late pleistocene and holocene piedmont alluvium late pleistocene soils are offset about the same amount as the height of the 1887 scarp valleys that are as much as 40 m deep and 0 5 to 0 9 km wide have been eroded since the prior event they contain multiple late pleistocene and holocene stream terraces that were not faulted until 1887 pre 1887 alluvial fault scarps were degraded to 2 to 9 slopes before the 1887 event even in resistant materials such as clay rich soil horizons with unweathered rhyolite cobbles and calcrete scarp height maximum slope regressions and diffusion equation analyses for reconstructed pre 1887 scarp profiles indicate that the prior event occurred more than 100 000 yr ago acceleration of scarp degradation rates during the holocene and or relatively resistant materials exposed in the scarps would increase the age estimates to 200 000 yr or more very long recurrence intervals are the characteristic style of movement on the pitaycachi fault at one site six ages of diverse valley fills were inset into pedimented granodiorite upslope from the fault between the prior and 1887 events only 3 m of relief remained before the 1887 rupture increased the scarp height from 3 to 6 m some hillslopes have triangular talus facets of carbonatecemented colluvium that resulted from infrequent fault movements and intervening periods of erosion smooth hillsides of resistant volcanic rocks between the facets show that virtually all of the prior surface rupture event scarps had been removed by prolonged slope degradation

the seismicity of chihuahua mexico and the 1928 parral earthquake abstract studies of the seismicity of chihuahua mexico and determination of source parameters for the 1928 parral earthquake suggest that the eastern portion of chihuahua is currently undergoing extension the parral earthquake has similar source parameters to other southern basin and range rio grande rift events the focal mechanism for the parral event however indicates northeast southwest oriented extension a direction that is parallel to neither the east west oriented extension seen near the us mexican bordern nor to the physiographic province boundary between the sierra madre occidental and the southern basin and range where the earthquake occurred intensity information for the parral event and the 1931 valentine texas earthquake suggests that attenuation within the region lies somewhere between relationships developed for the eastern and cordilleran portions of the usa

a crustal seismic refraction study in west central arizona a reversed seismic refraction profile was recorded in the southern basin and range province between parker and globe arizona interpretation of both refracted and reflected phases indicates a two layered crust 23 25 km thick and a low pn velocity 7 67 km s pmp pn amplitude analysis on individual traces and synthetic seismogram modeling indicate that a positive velocity gradient may exist in the upper mantle the low pn velocity is indicative of partial melting in the upper mantle and implies that the crust is identical with the lithosphere the heat flow data suggest that the lithosphere was about 40 km thick approximately 5 m y ago on the basis of this and a negative free air gravity anomaly we propose that the lithosphere has been thinned from about 40 to 24 km over the past 5 m y and will probably thin and uplift further in the southern basin and range in arizona

the long lasting aftershock series of the 3 may 1887 mw 7 5 sonora earthquake in the mexican basin and range province we study local and regional body wave arrival times from several seis mic networks to better define the active regional fault pattern in the epicentral region of the 3 may 1887 mw 7 5 sonora mexico southern basin and range province earthquake we determine hypocenter coordinates of earthquakes that originated between 2003 and 2007 from arrival times recorded by the local network resnes red sismica del noreste de sonora and stations of the network of autonomously recording seismographs nars baja array for events between april and december 2007 we also incorporated arrival times from usarray stations located within 150 km of the united states mexico border we first obtained preliminary earthquake loca tions with the hypoinverse program klein 2002 and then relocated these initial hypocenter coordinates with the source specific station term ssst method lin and shearer 2005 most relocated epicenters cluster in the upper crust near the faults that ruptured during the 1887 earthquake and can be interpreted to be part of its long lasting series of aftershocks the region of aftershock activity extends along the same fault zone 40 50 km south of the documented southern tip of the 1887 rupture and includes faults in the epicentral region of the 17 may 1913 imax viii mi 5 0 0 4 and 18 december 1923 imax ix mi 5 7 0 4 granados huasabas sonora earthquakes which themselves are likely to be aftershocks of the 1887 event the long aftershock duration can be explained by the unusually large magnitude of the mainshock and by the low slip rates and long mainshock recurrence times of the faults that ruptured in 1887

the santa rita fault zone evidence for large magnitude earthquakes with very long recurrence intervals basin and range province of southeastern arizona a discontinuous zone of subdued west facing fault scarps offset quaternary alluvium along 58 km of the western piedmont of the santa rita mountains south of tucson arizona scarps trend ne to n s and are 1 to 6 km basinward from the deeply embayed mountain front scarp heights range from 1 to 7 m and maximum scarp slope angles range from 3 to 9 5 a 6 m deep trench excavated in middle pleistocene and younger deposits exposed a high angle fault zone with about 3 5 m of total displacement estimated ages of faulted and unfaulted surfaces extent of degradation of piedmont scarps and stratigraphic relations exposed in the trench suggest an age of about 100 ka for the most recent surface rupture event units having well developed relict soils of late pleistocene age and older are faulted whereas units having weakly to moderately developed soils of latest pleistocene and holocene age are not offset morphologic fault scarp analyses suggest an age of 60 to 100 ka earthquake magnitude estimates derived using minimum and maximum seismic source moment calculations range from 6 4 to 7 3 one or more earlier surface rupture events are implied by significantly high scarp heights on mid pleistocene than on late pleistocene surfaces scarp heights on middle and early pleistocene surfaces are similar restricting faulting to post middle pleistocene time 200 to 300 ka stratigraphic relationships observed in the trench also suggest two fault displacement events tectonic landform analysis of the mountain front piedmont area implies several m y of inactivity along the range bounding fault system prior to these late quaternary displacements extremely long recurrent intervals between displacement events and reactivation of faulting after an interval of tectonic quiescence are typical of late quaternary fault behavior in southeastern arizona

inferred pseudo cryptic speciation in the coccolithophore species braarudosphaera bigelowii gran and braarud during the early paleocene danian abstract pseudo cryptic speciation occurs commonly in living oceanic plankton in the coccolithophores recent genetic studies have revealed that braarudosphaera bigelowii has a number of unique genotypes that correlate well with pentalith size indicating that this coccolithophore species actually contains multiple pseudo cryptic taxa in order to look for evidence of pseudo cryptic speciation in the past we measured the radii of 2800 b bigelowii pentaliths from the braarudosphaera rich limestones that contain the gssp for the lower middle paleocene danian selandian boundary at zumaia spain analysis of the radius measurements using the expectation maximization algorithm yielded two size groups herein termed form x

seismicity focal mechanisms and tectonics in the last four years there has been a tremendous increase in the detail of tectonic processes reported in the typical seismotectonic study new data from many local and regional networks of seismographs established during the previous four year period plus the now routine application of improved hypocentral location procedures long period body wave modelling and moment tensor inversion using digitally recorded data have increased resolution of both the hypocentral location and the nature of the faulting process consequently research emphasis has been on local tectonics or those aspects of regional and global tectonics requiring high resolution i briefly describe below some of the highlights of these studies

the sanfandila earthquake sequence of 1998 queretaro mexico activation of an undocumented fault in the northern edge of central trans mexican volcanic belt abstract a sequence of small earthquakes occurred in central mexico at the northern edge of the trans mexican volcanic belt tmvb in the state of queretaro during the first 3 months of 1998 medium to large events in the continental regime of central mexico are not common but the seismic history of the region demonstrates that faults there are capable of generating destructive events the sequence was analyzed using data from a temporary network with the goals of identifying the causative fault and its relation to regional tectonics employing a waveform inversion scheme adapted from a method used for regional studies we found that the source mechanisms conform to the style of faulting i e extension in the e w direction representative of the taxco san miguel allende fault system this system has been proposed as the southernmost extension of the basin and range br province the spatial distribution of hypocenters and source mechanisms indicate that the seismogenic segment was a fault with an azimuth of approximately 334 with almost pure dip slip since events which occurred just south from this region show features which are consistent with tmvb tectonics i e extension in an n s direction the sequence may mark the boundary between the tmvb and br stress domains

seismicity in the epicentral region of the 1887 northeastern sonoran earthquake mexico the 1887 sonoran earthquake in northeastern sonora mexico has an 80 km rupture length with an average 3 m displacement and an assumed 16 km depth of rupture this corresponds to a seismic moment of 1 27 x 1027 dyne cm and an ms of 7 4 seven to ten portable seismographs with an average spacing of 10 km were operated in a 2800 km 2 region surrounding the 1887 fault scarp thirtythree earthquakes were detected during 30 days of usable recording for all events 1 3 m 2 the most accurate locations horizontal error 5 km define a west dipping normal range bounding fault all events occurred within 15 km of the surface the name pitaycachi fault after the most prominent peak of the horst block is proposed for this zone of active faulting seismicity along the zone terminates abruptly 13 km north of the fault scarp and extends to the south for at least 32 km beyond the southern a composite focal mechanism from events at the southern end of the 1887 scarp indicates a normal fault striking n35 e and dipping 72 to the northwest

present day motion and deformation of the colorado plateau 1 we analyze data from continuous gps stations in the southwestern united states and present the first observations of a systematic motion of the colorado plateau region relative to a north america fixed reference frame westward velocities increase rapidly across the wasatch fault system which comprises the plateau s northwestern margin but increase more gradually between the great plains and the mojave desert province we detect no significant extension across most of the rio grande rift but extension could be as high as 0 5 mm yr 1 along its southernmost portion we suggest that the motion between the plateau and stable continent may partly be accommodated instead across the jemez lineament only when we consider gps velocities within the plateau s center do the data support a rigid body rotation of 0 103 ma 1 around a pole in the northern rocky mountains we conclude that active extension has encroached into the plateau from both the east and west

active tectonics of northeastern sonora mexico southern basin and range province and the 3 may 1887 mw 7 4 earthquake north south striking and west dipping basin and range province normal faults form the western edge of the sierra madre occidental plateau in northeastern sonora these faults and associated half grabens extend over a distance of more than 300 km between the san bernardino basin in the north and the sahuaripa basin in the south an earthquake in 1887 ruptured three neighboring segments of this major fault zone our field mapping in this region indicates that the surface rupture of the 1887 earthquake extends farther to the south and is considerably longer 101 4 km end to end length than previously reported a compilation of the seismicity in the epicentral region of the 1887 earthquake shows the epicenters to be distributed in well defined clusters at the northern end of the 1887 surface rupture in the step overs between the three rupture segments on a neighboring fault in the west fronteras fault and on fault segments farther south along the same fault zone granados region the distribution of seismicity correlates well with calculated changes in coulomb failure stress resulting from the 1887 earthquake

rupture of the pitaycachi fault in the 1887 mw 7 5 sonora mexico earthquake southern basin and range province rupture kinematics and epicenter inferred from rupture branching patterns during the 3 may 1887 mw 7 5 sonora earthquake surface rupture end to end length 101 8 km an array of three north south striking basin and range province faults from north to south pitaycachi teras and otates slipped sequentially along the western margin of the sierra madre occidental plateau this detailed field survey of the 1887 earthquake rupture zone along the pitaycachi fault includes mapping the rupture scarp and measurements of surface deformation the surface rupture has an endpoint to endpoint length of 41 0 km dips 70 w and is characterized by normal left lateral extension the maximum surface offset is 487 cm and the mean offset 260 cm the rupture trace shows a complex pattern of second order segmentation however this segmentation is not expressed in the 1887 along rupture surface offset profile which indicates that the secondary segments are linked at depth into a single coherent fault surface the pitaycachi surface rupture shows a well developed bipolar branching pattern suggesting that the rupture originated in its central part where the polarity of the rupture bifurcations changes most likely the rupture first propagated bilaterally along the pitaycachi fault the southern rupture front likely jumped across a step over to the teras fault and from there across a major relay zone to the otates fault branching probably resulted from the lateral propagation of the rupture after breaching the seismogenic part of the crust given that the much shorter ruptures of the otates and teras segments did not develop branches