unveiling the sources of the catastrophic 1456 multiple earthquake hints to an unexplored tectonic mechanism in southern italy we revisited data related to the 1456 seismic crisis the largest earthquake to have ever occurred in peninsular italy in search of its causative source s data about this earthquake consist solely of historical reports and their intensity assessment because of the age of this multiple earthquake the scarcity and sparseness of the data and the unusually large damage area no previous studies have attempted to attribute the 1456 events to specific faults existing analytical methods to identify a likely source from intensity data also proved inappropriate for such a sparse dataset since historical evidence suggests that the cumulative damage pattern contains at least three widely separated events we subdivided the 1456 damage pattern into three independent mesoseismal areas each of these areas falls onto east west tectonic trends previously identified and marked by deep 10 km right lateral slip earthquakes based on this evidence we propose 1 that the 1456 events were generated by individual segments of regional east west structures and are evidence of a seismogenic style that involves oblique dextral reactivation of east west lower crustal faults 2 that each event may have triggered subsequent but relatively distant events in a cascade fashion as suggested by historical accounts hence 3 that the 1456 sequence reveals a fundamental but unexplored mechanism of tectonic deformation and seismic release in southern italy this style dominates the region that lies between the northwest southeast system of large extensional faults straddling the crest of the southern apennines and the buried outer front of the chain although the quality of the available information concerning the 1456 earthquake is naturally limited we show that the overlap of the damage distribution the orientation and characteristics of regional tectonic structures the seismicity patterns and the focal mechanisms all concur with our interpretations and would be difficult to justify otherwise

ground motion modeling of the 1906 san francisco earthquake part ii ground motion estimates for the 1906 earthquake and scenario events abstract we estimate the ground motions produced by the 1906 san francisco earthquake making use of the recently developed song et al 2008 source model that combines the available geodetic and seismic observations and recently constructed 3d geologic and seismic velocity models our estimates of the ground motions for the 1906 earthquake are consistent across five ground motion modeling groups employing different wave propagation codes and simulation domains the simulations successfully reproduce the main features of the boatwright and bundock 2005 shakemap but tend to over predict the intensity of shaking by 0 1 0 5 modified mercalli intensity mmi units velocity waveforms at sites throughout the san francisco bay area exhibit characteristics consistent with rupture directivity local geologic conditions e g sedimentary basins and the large size of the event e g durations of strong shaking lasting tens of seconds we also compute ground motions for seven hypothetical scenarios rupturing the same extent of the northern san andreas fault considering three additional hypocenters and an additional random distribution of slip rupture directivity exerts the strongest influence on the variations in shaking although sedimentary basins do consistently contribute to the response in some locations such as santa rosa livermore and san jose these scenarios suggest that future large earthquakes on the northern san andreas fault may subject the current san francisco bay urban area to stronger shaking than a repeat of the 1906 earthquake ruptures propagating southward towards san francisco appear to expose more of the urban area to a given intensity level than do ruptures propagating northward

geochronological constraints on paleoarchean thrust nappe and neoarchean accretionary tectonics in southern west greenland abstract major regional deformation and metamorphic events in the godthabsfjord region southern west greenland occurred at 3650 and 2820 2720 ma e g precambrian res 78 1996 1 new geochronological constraints u pb zircon sensitive high resolution ion microprobe shrimp and thermal ionisation mass spectrometry tims have been obtained from a stack of mylonitic crystalline thrust nappes in the footwall of the western part of the paleoarchean 3 8 3 7 ga isua greenstone belt isukasia a mylonitic tonalite sheet interpreted to have intruded synkinematically with respect to mylonitisation yields a magmatic crystallisation age of 3640 3 ma a cross cutting pegmatite and a post kinematic tonalite pluton yield magmatic crystallisation ages of 2948 8 and 2991 2 ma respectively accordingly we interpret the thrust nappe stack to have formed during the paleoarchean 3640 ma making it the oldest example known on earth the similarity of this structural regime to that of modern mountain belts suggests that paleoarchean and modern continental crust were comparable in terms of mechanical strength and constitution southern west greenland has been interpreted in terms of neoarchean accretion comparable with modern plate tectonics e g earth planet sci lett 142 1996 353 isukasia lies just east of a purported neoarchean accretionary boundary between the akia terrane to the northwest and the akulleq terrane to the southeast the akia terrane was previously considered to overthrust the akulleq terrane at 2820 2720 ma our geochronological and geological data indicate i that the two terranes as presently defined were stitched at 2991 2 ma and ii that thrusting across the boundary was directed toward the akia terrane therefore we suggest that the akia akulleq interface was not a fundamental tectonic structure during the neoarchean and we question its identification as an accretionary boundary

do moderate magnitude earthquakes generate seismically induced ground effects the case study of the m w 5 16 29th december 2013 matese earthquake southern apennines italy seismically induced ground effects characterize moderate to high magnitude seismic events whereas they are not so common during seismic sequences of low to moderate magnitude a low to moderate magnitude seismic sequence with a m w 5 16 0 07 main event occurred from december 2013 to february 2014 in the matese ridge area in the southern apennines mountain chain in the epicentral area of the m w 5 16 main event which happened on december 29th 2013 in the southeastern part of the matese ridge field surveys combined with information from local people and reports allowed the recognition of several earthquake induced ground effects such ground effects include landslides hydrological variations in local springs gas flux and a flame that was observed around the main shock epicentre a coseismic rupture was identified in the sw fault scarp of a small sized intermontane basin mt airola basin to detect the nature of the coseismic rupture detail scale geological and geomorphological investigations combined with geoelectrical and soil gas prospections were carried out such a multidisciplinary study besides allowing reconstruction of the surface and subsurface architecture of the mt airola basin and suggesting the occurrence of an active fault at the sw boundary of such basin points to the gravitational nature of the coseismic ground rupture based on typology and spatial distribution of the ground effects an intensity i vii viii is estimated for the m w 5 16 earthquake according to the esi 07 scale which affected an area of at least 90 km2

late archaean terrane accretion in the godthab region southern west greenland tectono stratigraphic terranes fault bounded blocks of the earth s crust characterized by a geological history distinct from that of adjacent terranes1 are now widely recognized in phanerozoic and proterozoic orogenic belts and their present configurations are thought to result from plate tectonic processes similar to those in operation today2 4 there has been much debate about whether such processes operated in archaean times5 6 here we present new data from the archaean high grade gneiss complex of the godthab now nuuk region of southern west greenland which show that discrete tectonic units recognized in the south of the region7 can be more widely identified at least four terranes are recognized each of which evolved separately until their juxtaposition in the late archaean this suggests that at least some archaean high grade gneiss complexes may resemble more recent orogenic belts formed by plate tectonic processes

earthquake swarms in the southern apennines chain italy the 1997 seismic sequence in the sannio matese mountains abstract in this paper we analyze a seismic sequence that occurred in the sannio matese mountains southern apennines italy one of the most dangerous seismic areas of the italian peninsula on 19 march 1997 at 23 10 utc a seismic event of md 4 1 hit a zone near the border between the campania and the molise regions swarm type earthquake activity followed the main event and lasted for more than six months with alternation of intense activity and relative quiescence periods evolution of the seismic sequence both in time and space has allowed us to divide it into three stages with rather similar characteristics the seismic energy release process of this sequence exhibits the typical swarm pattern of the minor seismic sequences occurring in the southern apennines and involving relatively minor faults located in the marginal border of the chain such pattern unlike the main shock aftershock model consists of low energy events closely clustered in time and space without a single main shock about 2800 micro earthquakes were recorded from march to september 1997 by the seismic networks of the istituto nazionale di geofisica and of the osservatorio vesuviano among them only 20 events had md 3 0 a selection of 370 earthquakes recorded at a minimum of five stations with at least three s phase readings have been located between latitudes 41 20 and 41 30 and longitudes 14 36 and 14 42 the events are clustered along a nearly vertical plane striking nne ssw and dipping towards the east their hypocentral depths range from 5 to 15 km the focal mechanisms of 67 events show a variety of different solutions even if a prevalence of normal dip slip solutions with a strike component is observed the t axes distribution of all mechanisms show two trends the prevalent one is aligned along a nnw sse direction whereas the other one is along a nne ssw direction the hypocentral distribution the prevalence of focal mechanisms with fault planes striking about ne sw as well as the t axes distribution suggest that earthquakes relative to this sequence took place along nne ssw oriented faults and that the local stress field acting in this sector of the southern apennines is prevalently transtensional and is strongly controlled by local faults heterogeneities

stratigraphic and geochemical evidence for the depositional environment of the early archaean isua supracrustal belt southern west greenland the highly deformed c 3800 ma isua supracrustal belt is a fragment of a more extensive early archaean sedimentary and volcanic succession intruded by and tectonically intercalated with tonalitic and granitic amftsoq gneisses in the period 3800 3600 ma the supracrustal rocks recrystallised under amphibolite facies conditions between 3800 and 3600 ma in the late archaean and locally at c 1800 ma layered sequences of rock of sedimentary and probable volcanic origin form over 50 of the belt bodies of high mg al basic rocks and ultramafic rocks were intruded into the layered sequences prior to isoclinal folding and intrusion of amitsoq gneisses the layered rocks which are 1 km thick are divided into two sequences that are in faulted contact with each other the way up of these sequences has been determined from facing directions of locally preserved graded layering in felsic metasediments at several localities the overall upwards change in sedimentary succession is interpreted as showing change from dominantly basic to dominantly felsic volcanism which provided the major clastic component of the sediments clastic sedimentation took place against a background of chemical sedimentation shown by interlayers of banded iron formation metachert and calc silicate rocks throughout the sequences the felsic rocks locally preserve graded bedding and possible conglomerate structures indicating deposition from turbidite flows and possibly as debris flows nodules in the felsic rocks contain structures interpreted as fiamme there is an irregular enrichment in k2o na2o in many of the felsic rocks at constant sio2 and al2o3 content interpreted as owing to alteration of original andesitic to dacitic volcanic rocks banded iron formations locally contain conglomeratic structures suggesting sedimentary reworking possibly under shallow water conditions lithological and geochemical characters of the clastic components of the supracrustal sequences are consistent with derivation from felsic and basic volcanic rocks and do not require a continental source

seismic evidence of longitudinal extension in the southern apennines chain italy the 1997 1998 sannio matese seismic sequence 1 we present evidence of longitudinal extension in the apennines based on data from the 1997 1998 sannio matese seismic sequence the earthquakes occurred between the nw se faults responsible for larger historical earthquakes inversion of focal mechanisms indicates a stress field with a prevailing normal stress characterized by a nnw sse sub horizontal 3 this stress regime is consistent with normal movements along ne sw faults these features suggest that the ne sw faults located in between the nw se faults cannot be interpreted as transfer faults or old faults reactivated during the eastward migration of the chain we propose that the deformation due to the eastward chain migration concentrates along nw se normal faults which are responsible for the largest earthquakes whereas the deformation related to the chain curvature concentrates along ne sw normal faults which are responsible for the lower energy seismic sequences

fault plane solutions and seismicity of the italian peninsula abstract a new fault plane solution map of the italian peninsula is presented in this paper the earthquakes analyzed are included in the period 1905 1980 with magnitudes ranging 4 7 75 earthquakes are located in the crust while 31 are related to the deep and intermediate zone of the calabrian arc the large seismic events of the italian peninsula are generally associated with normal faulting while strike slip motion is mostly related to small earthquakes located along lateral segments of the mountain chain the deep and intermediate earthquakes of the tyrrhenian sea indicate predominant down dip compression and strike slip motion at the boundaries of this benioff zone this last is interpreted as a remnant of a subduction zone active since oligocene extending to 500 km depth with a very small lateral size about 300 km the present tectonics of this benioff zone is strongly conditioned by the lateral bending more so than the gravitational sinking process the coexistence of thrust and normal faulting motion associated to the earthquakes within a few tens of kilometers of each other seems to be explained by the strong lateral inhomogeneities of the crustal rocks present in this region more so than to the depth of the seismogenetic zone and the nature of the faulting process

seismic activity of the san francisco bay region moment magnitude m with objective confidence level uncertainties are estimated for felt san francisco bay region earthquakes using bakun and went worth s 1997 analysis strategy for seismic intensity observations the frequency magnitude distribution is well described for m 5 5 events since 1850 by a gutenberg richter relation with a b value of 0 90 the seismic moment rate m yr since 1836 is 2 68 1018 n m yr 95 confidence range 1 29 1018 n m yr to 4 07 1018 n m yr the seismic moment rate since 1850 is nearly the same m yr in the 56 years before 1906 is about 10 times that in the 70 years after 1906 in contrast m yr since 1977 is about equal that in the 56 years before 1906 80 1 14 of the plate motion moment accumulation rate is available for release in earthquakes the historical m yr and the portion of the plate motion moment accumulation rate available for release in earthquakes are used in a seismic cycle model to estimate the rate of seismic activity in the twenty first century high and low rates of future seismic activity are both permissible given the range of possible seismic cycle recurrence times t and the uncertainties in the historical m and in the percentage of plate motion available for release in earthquakes if the historical seismic moment rate is not greater than the estimated 2 68 1018 n m yr and the percentage of the plate motion moment accumulation available for release in earthquakes is not less than the estimated 80 then for all t the rate of seismic moment release from now until the next 1906 sized shock will be comparable to the rate from 1836 to 1905 when m 6 1 2 shocks occurred every 15 to 20 years

continental collision and basin opening in southern italy a new plate subduction in the tyrrhenian sea an analysis of the spatial distribution of the seismicity of the southern tyrrhenian sea is presented with the aim of putting constraints on the geometry of the complex benioff zone of this area by relocating the earthquakes that occurred in the period 1985 1990 the data set used in this analysis is based on information from ing isc and neis databases in order to ensure the quality of epi hypocentral locations we based our selection of earthquakes on both the available number of p and s readings at least eight p and two s pickings and the epicentral distances of the stations reporting the event 5 such a selection enabled us to obtain a catalogue of 450 well located events with focal depths of up to 500 km the seismogenetic volumes estimated from the distribution of hypocentres of the whole seismicity analysed were interpreted according to a recent geodynamic model proposed for this area this has led us to the hypothesis of an active nw se oriented subduction of the lithosphere generated and stressed by the opening of the tyrrhenian basin

segmentation pattern and structural complexities in seismogenic extensional settings the north matese fault system central italy abstract we investigated the northern slope of the matese mts molise central italy with the aim of characterizing the n to ne dipping active normal fault system in the bojano basin a sector of primary importance from a seismic hazard perspective we collected field data to define the geometry and segmentation pattern of two sub systems patalecchia colle di mezzo and bojano campochiaro new evidence of late quaternary faulting was obtained by exploiting well log interpretations kinematic analysis revealed the interaction of pre quaternary inherited mainly e w striking and newly formed nw se striking normal faults slip accommodation through linkage was clearly noted in the case of the patalecchia colle di mezzo sub system detailed topographic profiles across the active fault segments provided post lgm 15 3 kyr slip rates up to 2 mm yr which agree with the high deformation rates based on different approaches in the literature finally the instrumental seismicity analysis constrained the bottom of the seismogenic layer to depths of 13 14 km and the gathered information allowed us to reconstruct the north matese seismogenic source its 3d geometry and dimensions agree with both the dimension magnitude relationships and macroseismic information available for the 1805 earthquake mw 6 6 the main historical earthquake to have struck the bojano basin

large scale crustal structure of the northwestern yilgarn craton western australia evidence from nd isotopic data and zircon geochronology u pb zircon geochronology and nd isotope geochemistry have been used in the northwestern yilgarn craton region of western australia to map gneiss units of different ages and to provide a model for late archean crustal evolution despite the inherent difficulties of minimal exposure and variations in the appearance of units brought about by heterogeneous strain the 3300 3730 ma gneisses and intercalated metasedimentary units crop out in a 100 km wide tract bounded on both sides by areas containing 2920 3000 ma gneisses between 2750 and 2620 ma several generations of granitoids were emplaced throughout the region regardless of whether the granitoids intruded the 3300 3730 ma or 2920 3000 ma gneisses modeling of their initial nd isotopic compositions shows that they were most likely formed by partial melting of predominantly 2920 3000 ma gneisses only a minor input from early archean sources is indicated for granitoids cutting the 3300 3730 ma gneisses and intercalated metasediments some of the granitoids that intrude the 3300 3730 ma gneisses contain 2920 ma inherited zircons supporting the nd evidence that their source is dominated by 2920 3000 ma gneisses the 3300 3730 ma gneisses are interpreted as belonging to an allochthonous terrain emplaced over a younger terrain comprising the 2920 3000 ma gneisses subsequently partial melting concentrated in the underlying 2920 3000 ma terrain gave rise to the late archean granitoids

an estimate of hypocentre location accuracy in a large network possible implications for tectonic studies in italy summary data recorded by the italian telemetered seismic network itsn of the istituto nazionale di geofisica ing have been widely used in recent years to image slab structures and to find evidence for active processes along the italian peninsula however the use of seismic data for geostructural purposes may be affected by the well known trade off between earthquake location and seismic velocity parameters furthermore the confidence ellipse predicted by standard procedures may be inadequate for the representation of the probable error of a computed localization this paper evaluates the probable errors on the hypocentre determinations of the seismic events recorded by the itsn using a monte carlo method we compute synthetic arrival times using a 1 d velocity model appropriate as an average for the italian area the hypocentres used are ail those recorded by the itsn during the period january 1992 to march 1994 1972 events station locations are those of the current itsn configuration the synthetic arrival times are perturbed with a gaussian distribution of errors and input to ings standard hypocentral location procedure but using crustal velocities differing by 10 per cent from those used to generate them each simulation is repeated at least 30 times average absolute shifts of hypocentres are assessed in grid cells of linear dimension 33 km covering the whole italian region for regions within the itsn shifts are typically 5 10 km in location and up to 20 km in depth however for offshore and coastal regions they are much greater 50 km or more in both location and depth far exceeding the equivalent uncertainties quoted by ing bulletins possible consequences of this are highlighted by producing a cross section of subcrustal hypocentres from the adriatic to the tyrrhenian sea where the large uncertainty in depth precludes any confident interpretation of dipping tectonic features

ion probe u th pb zircon dating of polymetamorphic orthogneisses from northern labrador canada rounded zircons included within igneous zircons from the uivak i gneisses northern labrador have ages of up to 3863 12 ma 2 showing the former existence of rocks that predate the uivak gneisses by more than 100 ma the igneous zircons themselves have experienced varying amounts of early pb loss but age estimates based on maximum 207pb 206pb from three separate gneiss samples agree to within error at 3732 6 ma 2 which is taken as the age of emplacement of the igneous precursor to the dominant component of the uivak gneisses a new generation of zircons was formed during migmatization at ca 3620 ma the volumetrically less important lister gneiss was emplaced at 3235 8 ma 2 in the late archaean different parts of the gneiss complex were subjected to different grades of metamorphic overprinting the zircon chronology of gneisses affected by granulite facies metamorphism suggests a rapid sequence of events with simultaneous recrystallization of old zircons and growth of new u poor zi

nature of the crust below the southern granulite terrain sgt of peninsular india across the bavali shear zone based on analysis of gravity data abstract the bavali shear zone is a major proterozoic structure in the southern granulite terrain sgt of peninsular india a detailed gravity survey has been carried out in order to delineate the crustal structure and tectonics of the shear zone and adjacent areas the bouguer anomaly map of the region shows a number of features i an e w gravity gradient zone with an average gradient of 3 0 mgal km in the west and 0 4 mgal km in the east across the shear ii a broad gravity low with a relief of 20 mgal in the wynad plateau se of the shear iii a series of gravity lows in the southern part of the shear between kannur and vayittiri iv a broad gravity high of 30 40 mgal encircling the charnockite province in the nw part of the shear and v a sharp localised gravity high closure of 40 50 mgal towards coast at nileswaram spatially filtered gravity anomaly maps clearly exhibit contrasting gravity signatures on either side of the shear zone with relatively higher gravity values within the northern block crustal thickness estimates in general vary from 36 to 41 km with a thinning of 2 to 3 km towards the north below the shear zone using two dimensional crustal models determined from gravity anomaly profiles across the bavali shear zone it is interpreted that the shear zone extends downward close to a plane separating blocks of different crustal densities the shear zone dips steeply towards the south and its downward extension meets with a slight moho rise suggesting that the bavali shear zone is a crustal scale structure eastwards below the wynad plateau however the shear zone becomes less prominent suggesting local variations in its geometry the models also point out the presence of a thick high density body 2 98 g cc in the lower part of the crust below the northern charnockite province which narrows towards the wynad plateau region in the east the presence of such a high density body could be due to factors such as evolution together with the protoliths of overlying charnockitic rocks a dense lower crustal residual fraction during anorthosite genesis or emplacement during pan african later anorogenic events the models also indicate that the wynad plateau region is characterised by a relatively homogeneous crust

the early archaean itsaq gneiss complex of southern west greenland the importance of field observations in interpreting age and isotopic constraints for early terrestrial evolution geochemical and isotopic studies of small volumes of variably preserved 3600 ma rocks in gneiss complexes are crucial for documenting early earth history in the itsaq gneiss complex of the nuuk region west greenland there is dispute whether the granitic sensu lato orthogneisses dominating it are mainly products of a single ca 3650 ma crust formation super event or whether they formed in several unrelated events between ca 3850 and 3560 ma which of these interpretations of the dates is correct has major implications regarding what the whole rock radiogenic isotopic record pb pb sm nd rb sr reveals about continental crust formation and early terrestrial differentiation there is also debate whether some west greenland metasedimentary rocks with 12c 13c data interpreted as evidence for life are 3850 ma or only 3650 ma old establishing the correct age for these rocks is important for debates concerning early surficial environments and origin of life controversies have arisen because of different approaches taken by different workers specifically with respect to how much emphasis is placed on field geology in interpreting dates and isotopic data in this paper field observations and sampling from low strain zones where the origin and geological context of the rocks are best preserved and understood are closely integrated with u pb zircon dates and cathodoluminescence cl imagery of the zircons this approach shows that most single phase well preserved meta granitoid samples have simple zircon populations dominated by oscillatory zoned prismatic grains formed when their host magmas crystallized on the other hand migmatites and some strongly deformed banded gneisses have much more complex zircon populations the combined field evidence and zircon geochronology on the itsaq gneiss complex demonstrate that 1 some areas contain exposed orthogneisses formed during multiple magmatic thermal events between ca 3850 and 3560 ma and are not as suggested by kamber and moorbath 1998 dominated by ca 3650 ma granitoids containing abundant 3650 ma zircons inherited from cryptic unexposed older rocks 2 abundant 3750 ma granitoids are present which are locally well preserved 3 some water lain sediments reported as showing c isotope evidence for life were deposited as early as 3850 ma 4 the whole rock sm nd isochron approach fails to distinguish with any confidence 3650 ma from 3800 ma rocks 5 however it reinforces previous indications for markedly depleted 2 5 nd domains in the pre 3750 ma mantle

new pieces to the archaean terrane jigsaw puzzle in the nuuk region southern west greenland steps in transforming a simple insight into a complex regional tectonothermal model in the south of the nuuk region of west greenland our 1980s mapping recognized four archaean gneiss terranes f ringehavn tre brodre tasiusarsuaq and akia terranes with different protolith ages and separate early tectonothermal histories later in the archaean these were juxtaposed and then experienced the same 2700 2500 ma tectonothermal events here we abandon extrapolation of only these four terranes across the whole region and distinguish two new terranes in the ne the northernmost isukasia terrane previously regarded as the northernmost exposure of the f ringehavn terrane consists of palaeoarchaean rocks 3600 ma tectonically bounded on its south by the 3075 2960 ma kapisilik terrane these were juxtaposed and metamorphosed together by 2950 ma the previously recognized f ringehavn terrane to the sw is another separate entity of palaeoarchaean rocks that was juxtaposed with adjacent terranes only after c 2800 ma hence in an increasingly complex regional model there were several mid to neoarchaean terrane assembly events with superimposed orogenies from c 2950 ma until after 2700 ma although the f ringehavn and isukasia terranes were incorporated into the later archaean terrane collage at different times they might be fragments from a larger palaeoarchaean complex rifted apart from c 3500 ma onwards

a new fragment of the early earth crust the aasivik terrane of west greenland abstract the aasivik terrane is a 1500 km 2 complex of gneisses dominated by 3600 ma components which has been discovered in the archaean craton of west greenland 20 50 km south of the paleoproterozoic nagssugtoqidian orogen the aasivik terrain comprises granulite facies tonalitic to granitic gneisses with bands of mafic granulite which include disrupted mafic dykes four gneiss samples of the aasivik terrain have given imprecise shrimp u pb zircon ages of 3550 3780 ma with strong loss of radiogenic lead and new growth of zircon probably associated with a granulite facies metamorphic event s at 2800 2700 ma to the southeast the aasivik terrane is in tectonic contact with a late archaean complex of granitic and metapelitic gneisses with apparently randomly distributed mafic and ultramafic units here named the ukaleq gneiss complex two granitic samples from the ukaleq gneiss complex have u pb zircon ages of 2817 10 and 2820 12 ma and t zircon e nd values of 2 3 5 4 given their composition and positive e nd values they probably represent melts of only slightly older juvenile crust a reconnaissance shrimp u pb study of a sample of metasedimentary rock from the ukaleq gneiss complex found 2750 2900 ma zircons of probable detrital origin and that two or more generations of 2700 2500 ma metamorphic zircons are present this gneiss complex is provisionally interpreted as a late archaean accretionary wedge a sample of banded granulite facies gneiss from a complex of banded gneisses south of the aasivik terrain here named the tasersiaq gneiss complex has yielded two zircon populations of 3212 11 and 3127 12 ma contacts between the three gneiss complexes are mylonites which are locally cut by late post kinematic granite veins with shrimp u pb zircon ages of 2700 ma the isotopic character and the relationships between the lithologies from the different gneiss complexes suggest the assembly of unrelated rocks along shear zones between 2800 and 2700 ma the collage of archaean gneiss complexes were intruded by a type granites here named the umiatsiaasat granites at 2700 ma later than the tectonic intercalation of the gneiss complexes

san andreas fault zone california m 5 5 earthquake history the san andreas fault zone has been a very significant source of major california earthquakes from 1812 to 1906 it generated four major earthquakes of m 7 or larger in two pairs on two major portions of the fault a pair of major earthquakes occurred on the central to southern region where the 1857 faulting overlapped the 1812 earthquake faulting a pair of major earthquakes occurred on the northern region where the 1906 faulting overlapped the 1838 earthquake faulting also earthquakes of m 7 occurred in the san francisco bay area on the hayward fault in 1868 and the santa cruz mountains near loma prieta in 1989 and on the imperial fault near the border with mexico in 1940 the 1838 earthquake s damage effects throughout the bay area from san francisco to santa clara valley and monterey were unequalled by any historical earthquake other than the 1906 event this and numerous strong possible aftershocks during the following 3 years in the san juan bautista vicinity suggest 1838 faulting from san francisco to san juan bautista cycles of seismicity and quiescence were associated with the bay area earthquakes of 1868 1906 and 1989 the 1868 earthquake on the hayward fault was preceded by 12 earthquakes of m 5 5 from 1855 to 1866 within 60 km of the hayward fault and was followed by 13 quiet years the 1906 san andreas fault event was preceded from 1881 to 1903 by 18 earthquakes of m 5 5 and was followed by quiescence with only three earthquakes of m 5 5 until 1954 the bay area has been seismically quiet at the m 5 5 level since the 1989 loma prieta earthquake and its 1990 aftershocks which contrasts with the 10 years before 1989 when five m 5 5 6 2 events occurred the loma prieta earthquake is of similar magnitude to the 1868 hayward event and could be followed by a similarly short quiet period the 1857 earthquake had immediate foreshocks in the lonoak bitterwater region 50 km northwest of parkfield in the northern end zone of the 1857 rupture extending southeast from bitterwater 70 km to parkfield the rate of seismic moment release has decreased with time since 1857 this may reflect the decay with time of the stress loading due to the 9 m 1857 fault displacements 80 km southeast of parkfield and explain why the predicted earthquake which was based on the assumption of regular recurrence of parkfield earthquakes has not yet occurred the extent of the 1812 earthquake fault rupture is not well defined jacoby et al 1988 estimated that it extended 170 km from cajon pass to tejon pass based on this estimate we present the hypothesis that the rupture occurred in two segments in december 1812 the eastern segment generated the 8 december earthquake that damaged san juan capistrano san gabriel san fernando and san buenaventura thirteen days later the western segment ruptured generating the earthquake that damaged san fernando and san buenaventura again as well as santa barbara santa ynez and purisima concepcion

the distribution of modified mercalli intensity in the 18 april 1906 san francisco earthquake we analyze boatwright and bundock s 2005 modified mercalli intensity mmi map for the 18 april 1906 san francisco earthquake reviewing their interpretation of the mmi scale and testing their correlation of 1906 cemetery damage with mmi intensity we consider in detail four areas of the intensity map where boatwright and bundock 2005 added significantly to the intensity descriptions compiled by lawson 1908 we show that the distribution of off fault damage in sonoma county suggests that the rupture velocity approached the p wave velocity along tomales bay in contrast the falloff of intensity with distance from the fault appears approximately constant throughout mendocino county the intensity in humboldt county appears somewhat higher than the intensity in mendocino county suggesting that the rupture process at the northern end of the rupture was relatively energetic and that there was directivity consistent with a subsonic rupture velocity on the section of the fault south of shelter cove finally we show that the intensity sites added in santa cruz county change the intensity distribution so that it decreases gradually along the southeastern section of rupture from corralitos to san juan bautista and implies that the stress release on this section of rupture was relatively low

northern san andreas fault near shelter cove california the location of the san andreas fault in the shelter cove area of northern california has been the subject of long standing debate within the geological community although surface ruptures were reported near shelter cove in 1906 several subsequent workers questioned whether these ruptures represented true fault slip or shaking related gravity driven deformation this study involving geologic and geomorphic mapping historical research and excavation across the 1906 rupture zone concludes that the surface ruptures reported in 1906 were the result of strike slip faulting and that a significant quaternary fault is located onshore near shelter cove geomorphic arguments suggest that the holocene slip rate of this fault is greater than about 14 mm yr indicating that it plays an important role within the modern plate boundary system the onshore trace of the fault zone is well expressed as far north as telegraph hill north of telegraph hill its location is less well constrained but we propose that a splay of the fault may continue onshore northward for at least 9 km to the vicinity of saddle mountain

fault geometries from the space distribution of the 1990 1997 sannio benevento earthquakes inferences on the active deformation in southern apennines in this study we analyze the recent 1990 1997 seismicity that affected the northern sector sannio benevento area of the southern apennines chain we applied the best estimate method bem which collapses hypocentral clouds to the events of low energy md max 4 1 seismic sequences in order to constrain the location and geometry of the seismogenetic structures the results indicate that earthquakes aligned along three main structures two sub parallel structures striking nw se 1990 1992 benevento sequence and one structure striking ne sw 1997 sannio sequence the southernmost nw se structure which dips towards ne overlies the fault that is likely to be responsible for a larger historical earthquake io max xi mcs 1688 earthquake the northernmost nw se striking structure dips towards sw the ne sw striking structure is sub vertical and it is located at the northern tip of the fault segment supposed to be responsible for the 1688 earthquake the spatio temporal evolution of the 1990 1997 seismicity indicates a progressive migration from se benevento to nw sannio associated to a deepening of hypocenters i e from about 5 to 12 km hypocenters cluster at the interface between the major structural discontinuities e g pre existing thrust surfaces or within higher rigidity layers e g the apulia carbonates available focal mechanisms from earthquakes occurred on the recognized nw se and ne sw faults are consistent with dip slip normal solutions this evidences the occurrence of coexisting nw se and ne sw extensions in southern apennines

crustal growth through successive arc magmatism reconnaissance u pb shrimp data from the northeastern superior province canada abstract north of the la grande subprovince in northern quebec the superior province is dominated by plutonic rocks of the bienville subprovince and minto block which have been further subdivided into domains on the basis of reconnaissance geological mapping and geochronology and projected along strike using aeromagnetic anomalies to test the validity of the extrapolations u pb ages were obtained through shrimp analyses of zircon from 18 small archival samples selected from a suite of 2000 specimens collected during a helicopter reconnaissance survey conducted in the 1960s the results reveal a history of successive arc magmatism between 3 07 and 2 70 ga followed by metamorphism emplacement of crustally derived granites 2 702 2 685 ga and late hydrothermal events ca 2 65 ga in the northeastern minto block the douglas harbour domain previously extrapolated from dated localities to the northeast is substantiated through an age of 2 87 ga the older tonalitic crust is punctured by 2 734 2 725 ga granodioritic plutons of the leaf river suite that locally carry 3 01 ga inherited zircon the northern utsalik domain is made up of pyroxene and hornblende bearing leaf river plutons with consistent 2 725 2 723 ga ages and local inheritance of 2 82 and 2 77 ga however the southern extension of utsalik domain contains pyroxene bearing granodiorites both older 2 762 ga and younger 2 692 ga than the leaf river suite a tonalitic rock from the southern goudalie domain with an age of 2 833 ga supports a linkage to 2 84 2 83 ga units of the qalluviartuuq domain along strike to the north tikkerutuk domain represents a north trending 50 km wide calc alkaline magmatic arc with ages between 2 71 and 2 70 ga that extends southward into the bienville subprovince on the basis of aeromagnetic anomalies and geochronology zircon inheritance ages indicate that the tikkerutuk arc was built upon antecedent arcs of 2 84 2 77 and 2 725 ga the inukjuak domain in the west consists mainly of granite dated in one locality at 2 72 ga

the age and pb loss behaviour of zircons from the isua supracrustal belt as determined by ion microprobe ion microprobe uthpb analyses of zircons from a conglomeratic metavolcanic unit in the isua supracrustal belt of west greenland show that their magmatic age is3807 1ma and failed to detect any older zircon cores or xenocrysts low u areas within zircons at a 30 m scale lost only small amounts of radiogenic pb and only in the recent past whereas high u areas within grains lost much greater proportions of their pb both recently and as early as the archaean some areas in the zircons have concordant upb and thpb ages the ion probe results agree with earlier determinations for the isua supracrustals and clarify minor discrepancies between previous multigrain and single crystal analyses

the 2001 seismic activity near isernia italy implications for the seismotectonics of the central southern apennines abstract we analyze the seismic activity that occurred in 2001 near the city of isernia southern apennines with the aim to add information on the seismotectonics of the transition zone between central and southern apennines seismic activity lasted for 9 months showing the typical behaviour of swarms a large number of events of low magnitude without a distinct main shock and clustered in space and time the maximum magnitude md of the events was 3 3 comparable with the magnitude md of the background seismicity of the area hypocentral distribution of the events maximum depth 15 km suggests that seismic activity took place along a best fitting plane striking n33 e and steeply dipping eastward the results of the strain analysis performed on selected well constrained focal mechanisms indicate that most of the ruptures associated to the 2001 seismic sequence occurred along n s to ne sw striking faults characterized by strike slip to normal movements this kinematics is consistent with a prevailing nw se extension this direction of extension already observed in the 1997 98 seismic sequence which occurred at about 35 km toward se from the 2001 epicentral area is not consistent with that one assumed at regional scale on the basis of the analysis of focal mechanisms of stronger earthquakes the results of the 1997 98 and 2001 seismic sequences discussed in light of the available geological and geophysical data evidence that i in this portion of the apennine chain low magnitude seismic sequences cluster along ne sw striking faults that move in response to a nw se extension and ii the ne sw striking faults along which the 1997 98 and the 2001 seismic sequences occurred mark the southeastern and northwestern tips of the nw se fault segment responsible for the 1805 earthquake

resolution of fault slip along the 470 km long rupture of the great 1906 san francisco earthquake and its implications data from all available triangulation networks affected by the 1906 earthquake have been combined to assess the trade off between slip resolution and its uncertainty and to construct a conservative image of coseismic slip along the rupture because of varying network aperture and station density slip resolution is very uneven although slip is determined within uncertainties of 1 0 m along 60 of the fault constraints are poor on the remaining mostly offshore portions of the rupture slip decreases from maxima of 8 6 and 7 5 m at shelter cove and tomales bay to 4 5 m near mount tamalpais and 2 7 m at loma prieta the geodetically derived slip distribution is in poor agreement with estimates based on analysis of s wave seismograms probably because these waves register only 20 30 of the total seismic moment obtained from longer period surface waves consideration of a range of fault geometries for 1906 slip near loma prieta indicates right lateral motions lie between 2 3 and 3 1 m these values are considerably greater than the 1 5 m of measured surface slip on which several assessments of high earthquake hazard for this fault segment were based this factor along with the absence of 1989 slippage where 1906 surface slip was used to make the forecasts casts doubt on some claims of success in predicting the 1989 m 6 9 loma prieta earthquake

re evaluation of 1906 surface faulting geomorphic expression and seismic hazard along the san andreas fault in the southern santa cruz mountains the lack of through going right lateral surface rupture accompanying the loma prieta earthquake has raised questions about the behavior of the san andreas fault in the southern santa cruz mountains we re evaluated previously published reports of ground deformation due to the 1906 earthquake in this region to determine if san andreas fault surface rupture accompanied this event and whether any of the reported values of offset are reliable in addition our search for historical data has brought to light new information about the 1906 earthquake in the southern santa cruz mountains none of the reports provides indisputable evidence for 1906 san andreas fault surface rupture however taken together with a study of the geomorphology of the fault zone and relationships exposed in excavations across the fault they do provide a basis for believing that surface rupture extended through the region in 1906 none of the reported values for 1906 offset is a reliable measurement however calling into question current and pre 1989 seismic hazard assessments for the loma prieta area the geologic and geomorphic relationships indicate that shallow right lateral crustal strain is typically expressed as surface rupture across a narrow san andreas fault zone in contrast to the 1989 loma prieta earthquake

three dimensional earthquake locations and upper crustal structure of the sannio matese region southern italy abstract the sannio matese region is one of the most seismically active regions of italy and has been struck by large historical earthquakes at present the area is characterized by low magnitude background seismicity and small seismic sequences following m 4 main events in this paper we show vp and vp vs models and 3d locations for a complete set of earthquakes occurring in the period 1991 2001 we observe a significant crustal heterogeneity with large scale east verging high vp fault related folds stacked by the pliocene compression the relocated earthquakes cluster along a 70 east dipping nw striking plane located at the border of the high vp thrust units normal fault earthquakes related to the young and active extension occur within these high vp zones interpreted as high strength material we expect large future earthquakes to occur within these high vp zones actually characterized by low magnitude seismicity at their borders

the september 27 2012 ml 4 1 benevento earthquake a case of strike slip faulting in southern apennines italy abstract on september 27 2012 at 01 08 utc a m l 4 1 earthquake started a seismic sequence approximately 10 km east of the city of benevento in southern apennines italy during the following four days about 40 events with m l ranging between 1 3 and 4 1 were detected in the same area where the seismic hazard is one of the largest of the italian peninsula and where several historical and destructive events took place in order to investigate the seismicity spatio temporal pattern and to identify the seismogenic source geometry a detailed analysis was performed integrating data recorded at three different seismic networks the earthquakes were relocated using the double difference technique and focal mechanism solutions were obtained by the moment tensor inversion also to better understand the rupture process seismic source parameters were estimated and apparent source time functions were inverted to retrieve the slip distribution for the largest magnitude event our results show the existence in the study area of roughly e w striking fault plane with a right lateral strike slip kinematics seated at mid crustal depths 10 20 km revealing a characteristic seismicity quite different from that typically associated to the outcropping nw se striking active normal faults that are responsible of moderate to large earthquakes in the southern apennines axial sector in this work we address questions concerning i the presence in the benevento area of a mid crust seismogenic strike slip fault previously unrecognized ii its link to the regional seismotectonic setting and iii the existence of a strike slip tectonic regime that uniformly extends in the footwall of the apennines thrust at relevant depth not only in the apulian foreland as demonstrated to date but also under the mountain chain axial zone

concurrent deformation processes in the matese massif area central southern apennines italy abstract we investigated the interseismic gps velocity field across the transition zone between central and southern apennine comprising the meta mainarde venafro and alto molise sannio matese mounts the kinematic field obtained by combining gps network solutions is based on data collected by the unpublished episodic campaigns carried out on southern apennine geodetic network sagnet from 2000 to 2013 igm95 network giuliani et al 2009 from 1994 to 2007 and continuous gps stations the data collected after the 29 december 2013 earthquake mw 5 0 until early 2014 allowed estimating displacements at 15 sagnet stations the extension rate computed across the matese massif along an anti apennine profile is 2 0 0 2 mm yr the interseismic velocities projected along the profile show that the maximum extension does not follow the topographic high of the apennines but is shifted toward the eastern outer belt no significant gps deformation corresponding to inner faults systems of the matese massif is detected taking into account our results and other geophysical data we propose a conceptual model which identifies the 2013 2014 seismic sequence as not due to an extensional deformation style usual along the apennine chain in fact we have measured too large coseismic displacements that could be explained as the result of tectonic regional stress co2 rich fluid migration and elastic loading of water in the karst matese massif we recognized a tensile source as model of dislocation of 2013 2014 earthquakes it represents a simplification of a main fault system and fracture zone affecting the matese massif the dislocation along ne dipping north matese fault system nmfs could be the driving mechanism of the recent seismic sequences moreover to the first time the sagnet gps data collected from 1994 to 2014 are share and available to the scientific community in the open access data archive

early archaean amitsoq tonalites and granites of the isukasia area southern west greenland development of the oldest known sial amphibolite facies early archaean amitsoq gneisses envelop and intrude the c 3 800 ma isua supracrustal belt isukasia area southern west greenland most of these gneisses are strongly deformed but in a c 75 km2 augen of lower deformation the amitsoq gneisses are seen to comprise predominantly 3 750 3 700 ma tonalitic grey gneisses that were intruded first by thin bodies of mafic to dioritic composition known collectively as the inaluk dykes and then by c 3 600 ma white gneisses and finally by sporadic c 3 400 ma pegmatitic gneiss sheets the grey gneisses could have formed by partial melting of crust consisting predominantly of basic rocks the inaluk dykes are interpreted as strongly fractionated basic melts of mantle origin contaminated by crustal material the white gneisses consist mostly of medium grained granite and occur as lenses and anastomosing sheets throughout their host of grey gneisses with subordinate inclusions of supracrustal rocks the white gneisses have chemistry compatible with formation by partial melting at depth of a source dominated by grey gneisses the igneous chemistry including ree abundances of the grey gneisses and white gneisses has been modified to varying degrees by metasomatism and assimilation reactions during the crystallisation of the white gneisses and also during subsequent tectonometamorphic events the white gneisses are evidence for considerable reworking by anatexis of sialic crust in the early archaean 150 to 100 ma after its formation the white gneisses and the pegmatitic gneisses show that granitic rocks s s were important in the earliest archaean and are further evidence of the diversity of the oldest known sial

the seismogenic structure of the 2013 2014 matese seismic sequence southern italy implication for the geometry of the apennines active extensional belt

a low magnitude seismic sequence near isernia molise central italy in january 1986 following the increase in seismic activity which occurred near isernia molise central italy in january 1986 a digital seismic network of four stations with three component short period seismometers was installed in the area by the osservatorio vesuviano the temporary network had an average station spacing of about 8 10 km and in combination with permanent local seismic stations allowed the accurate determination of earthquake locations during an operating period of about one month among the 1517 detected earthquakes 170 events were selected with standard errors on epicentre and depth not greater than respectively 0 5 and 1 5 km the most frequent focal depths ranged between 4 and 8 km while the epicentres distribution covered a small area ne of isernia of about 10 km2 a main rupture zone could not be clearly identified from the spatial distribution of the earthquakes suggesting a rupture mechanism involving heterogeneous materials the activity was characterized by low energy levels the largest earthquake on january 18 1986 havingmd 4 0 the time sequence of events and pattern of seismic energy release revealed a strong temporal clustering of events similar to the behaviour commonly associated with seismic swarms

magnitude distribution of linear morphogenic earthquakes in the mediterranean region insights from palaeoseismological and historical data we analyse the earthquake magnitude distribution of linear morphogenic earthquakes that reactivated dip slip normal faults within the mediterranean region information on past events is obtained following two distinct methodological approaches the geological one morphotectonic investigations and palaeoseismological excavations and the historical one contemporaneous descriptions and surveys of coseismic ruptures in order to homogenize the different data sets and therefore enabling a comparison we calculate moment magnitudes m w starting from seismic moments m 0 estimates the cumulative distributions thus obtained for the two data sets show differences that a series of non parametric tests suggests to be statistically significant coseismic displacements are systematically overestimated for strong m w 6 5 historically based earthquakes and for moderate 5 0 6 0 palaeoseismologically observed events also concerning the rupture length the geological information generally provides larger values for moderate earthquakes the possible causes of this discrepancy and the consequences in using the two data sets for seismic hazard assessment analyses are also discussed

a regional view of urban sedimentary basins in northern california based on oil industry compressional wave velocity and density logs compressional wave sonic and density logs from 119 oil test wells provide knowledge of the physical properties and impedance contrasts within urban sedimentary basins in northern california which is needed to better understand basin amplification these wire line logs provide estimates of sonic velocities and densities for primarily upper cretaceous to pliocene clastic rocks between 0 1 and 5 6 km depth to an average depth of 1 8 km regional differences in the sonic velocities and densities in these basins largely 1reflect variations in the lithology depth of burial porosity and grain size of the strata but not necessarily formation age for example miocene basin filling strata west of the calaveras fault exhibit higher sonic velocities and densities than older but finer grained and or higher porosity rocks of the upper cretaceous great valley sequence as another example hard eocene sandstones west of the san andreas fault have much higher impedances than eocene strata mainly higher porosity sandstones and shales located to the east of this fault and approach those expected for franciscan complex basement rocks basement penetrations define large impedence contrasts at the sediment basement contact along the margins of several basins where quaternary pliocene and even miocene deposits directly overlie franciscan or salinian basement rocks at depths as much as 1 7 km in contrast in the deepest geographic centers of the basins such logs exhibit only a modest impedance contrast at the sediment basement contact at depths exceeding 2 km prominent up to 1 km sec and thick up to several hundred meters velocity and density reversals in the logs refute the common assumption that velocities and densities increase monotonically with depth online material borehole log regression parameters and metadata

upper crustal structure of the benevento area southern italy fault heterogeneities and potential for large earthquakes summary the benevento region is part of the southern apennines seismogenic belt which experienced large destructive seismic events both in historical and in recent times the study area lies at the northern end of the irpinia fault which ruptured in 1980 with a ms 6 9 normal faulting event which caused about 3000 casualties the aims of this paper are to image lateral heterogeneities in the upper crust of the benevento region and to try to identify the fault segments that are expected to generate such large earthquakes this work is motivated by the recognition that lithological heterogeneities along major fault zones inferred from velocity anomalies reflect the presence of fault patches that behave differently during large rupture episodes in this paper we define the crustal structure of the benevento region by using the background seismicity recorded during 1991 and 1992 by a local seismic array these data offer a unique opportunity to investigate the presence of structural discontinuities of a major seismogenic zone before the occurrence of the next large earthquake the main result that we obtained is the delineation of two nw trending high velocity zones hvzs in the upper crust beneath the matese limestone massif these high velocities are interpreted as high strength regions that extend for 30 40 km down to at least 12 km depth the correspondence of these hvzs with the maximum intensity regions of historical earthquakes 1688 ad 1805 ad suggests that these anomalies delineate the extent of two fault segments of the southern apenninic belt capable of generating m 6 5 7 earthquakes the lateral offset observed between the two segments from tomographic results and isoseismal areas is possibly related to transverse right lateral faults

a transitional volume beneath the sannio irpinia border region southern apennines different tectonic styles at different depths abstract in this paper we investigate the border between the sannio and irpinia seismogenic regions a sector of the southern apennine chain considered among the most active seismic areas of the italian peninsula to shed further light on its complex seismotectonic setting we integrated recent seismicity with literature data a detailed analysis of the seismicity that occurred in the 2013 2016 time interval was performed the events were relocated after manual re picking using different approaches to retrieve information about the stress field active in the area inversion of fault plane solutions was also carried out hypocentral distribution of the relocated events ml 3 5 whose depth is included between 5 and 25 km with the deepest ones located in the nw sector of the study area shows a different pattern between the northern sector and the southern one the computed fault plane solutions can be grouped in three depth ranges 18 km dominated by strike slip kinematics stress field inversion across the whole area shows that we are dealing with an heterogeneous set of data apparently governed by distinct stress fields we built an upper crustal model profile through integration of geological data well logs and seismic tomographic profiles our results suggest the co existence of different tectonic styles at distinct crustal depths the upper crust seems to be affected mostly by normal faulting whereas strike slip faulting prevails in the intermediate and lower crust we infer about the existence of a transitional volume located between 12 and 18 km depth between the sannio and irpinia regions acting as a vertical transfer zone

the influence of critical moho reflections on strong ground motions recorded in san francisco and oakland during the 1989 loma prieta earthquake the amplitudes of strong ground motions from the loma prieta earthquake recorded in the san francisco and oakland areas exceeded the levels predicted by standard empirical attenuation relations preliminary analysis of accelerograms having known trigger times strongly suggests that the elevation of ground motion amplitudes in the distance range of approximately 40 to 100 km was due to critical reflections from the base of the crust these reflections which are identified on the basis of their arrival times and phase velocity and by comparison with simulated accelerograms were large and occurred at relatively close range because of the deep focal depth of the earthquake and the strong velocity gradient at the base of the crust these motions were further amplified presumably by impedance contrast effects at soft soil sites in san francisco and oakland the effect of the critical reflections in amplifying peak accelerations of the loma prieta earthquake in the san francisco and oakland regions was as large as the effect of soft soil site conditions focal depth has an important influence on strong motion attenuation at distances beyond about 40 km and empirical attenuation relations derived from shallow crustal earthquakes may underpredict the ground motions of deeper crustal events in this distance range further analyses using an expanded data base that includes recordings of aftershocks are required to rigorously test the proposed explanation of the ground motions recorded in san francisco and oakland and the conclusions drawn from that explanation

timing of late archaean terrane assembly crustal thickening and granite emplacement in the nuuk region southern west greenland abstract a breakthrough in understanding the structural and metamorphic evolution of archaean gneiss complexes occurred with the recognition that the nuuk region of southern west greenland comprised separate terranes assembled in the late archaean from northwest to southeast these are the akia 3220 2970 ma akulleq 3870 3600 and 2820 ma and tasiusarsuaq 2920 2860 ma terranes the minimum time of assembly is recorded by the first event common to all component terranes using shrimp u pb zircon geochronology the oldest events common to all terranes including emplacement of crustally derived granites contemporaneous metamorphism and anatexis have been dated at 2710 2725 ma in the akulleq terrane areas where in situ diatexite formed abundant granitoid sheets were intruded and common growth of metamorphic zircon mostly low th u in most lithologies occurred in the akia and tasiusarsuaq terranes there was only intrusion of a lesser number of 2720 ma granitoid sheets because metamorphic zircons of that age have not been found the 2720 ma event is interpreted as marking or shortly following terrane assembly when the diverse components of the akulleq terrane were tectonically juxtaposed with the other two this new documentation of metamorphic and associated igneous events within an accreting cratonic region is an illustration that the stabilisation of extensive areas of archaean gneisses can be due to accretionary tectonics long after the individual components were first formed

contrasting styles of tectonism and magmatism in the late archaean crustal evolution of the northeastern part of the ivisârtoq region inner godthabsfjord southern west greenland abstract varieties of late archaean gneisses recognized on the basis of field petrographic and chemical data include multiphase tonalitic granitic gneisses with abundant enclaves of amphibolite granodioritic gneisses largely devoid of enclaves leucocratic schlieric gneisses with pods of amphibolite and hornblendite and grey granitic gneisses with locally abundant enclaves of amphibolite the bulk of the gneisses are correlated with the nuk gneisses c 3000 2900 ma of outer godthabsfjord most of the gneisses were emplaced during a period of horizontal tectonic interleaving of thick slices of amitsoq gneisses c 3700 ma and younger malene supracrustal rocks mainly amphibolites older than c 2900 ma interleaving took place on tectonic slides during regional horizontal heterogeneous simple shear movements flattening strains modified ameralik amphibolite dykes in the amitsoq gneisses and gave rise to s fabrics banding and schistosity in the malene rocks the s fabrics facilitating emplacement of voluminous nuk gneisses mainly as broadly concordant sheets potash feldspar blastesis and localized partial melting occurred in some of the earlier phases of nuk gneisses and possibly the amitsoq gneisses but the timing of these processes in relation to this period of emplacement is uncertain high temperatures appear to have been sustained into the second period of deformation when large mainly upright domes and synforms some cuspate were superimposed on the broadly horizontal pile of amitsoq gneisses malene rocks and nuk gneisses tectonic fabrics are dominated by mineral and ribbing lineations coaxial with folds of this second period magmatic emplacement of sheets of granitic gneisses and pegmatites continued many of the sheets being injected coplanar with the second phase parasitic folds pegmatites and schlieric gneisses were generated by syntectonic and younger feldspar blastesis and partial melting the close of late archaean magmatism is marked by the post tectonic qorqut granite and pegmatite complex c 2500 ma the horizontal tectonic movements emplacement of gneisses generation of domes and synforms and syntectonic injection of younger granitic gneisses appear to have taken place in the interval between c 3000 2600 ma ago similar relations between late archaean tectonism and magmatism have been recognized elsewhere in the archaean block of greenland but syntectonic injection of granitic gneisses and transformation of older gneisses to schlieric types appear to be more widespread in this part of the archaean block in ivis rtoq

the 1906 san francisco earthquake a century later introduction to the special section the great 1906 san francisco earthquake is perhaps the landmark event in the history of earthquake science it began with a foreshock at 5 12 a m local time in the morning of 18 april 1906 some 30 sec later the main event initiated on the san andreas fault just off the san francisco coast lawson 1908 within 90 sec nearly 480 km of the san andreas fault ruptured see fig 1 extending south to the northern end of the creeping section near san juan bautista and north to the terminus of the fault at the triple junction near cape mendocino song et al 2008 as it ruptured it generated powerful seismic waves over the entire rupture length and set in motion a chain of events that led to the destruction of most of san francisco the largest city of the western united states at the time the earthquake occurred in the early days of instrumental seismology which renders the data difficult to analyze but our best estimate is that the moment magnitude was 7 9 song et al 2008 about 26 times the size of the 1989 magnitude 6 9 loma prieta earthquake as measured by seismic moment hanks and krawinkler 1991 song et al 2008 figure 1 the thick dark line shows the extent of rupture along the san andreas fault in the 1906 earthquake and the star denotes the epicenter the strong shaking caused widespread damage along the entire length of the rupture see figs 2 4 masonry walls were reduced to rubble houses were knocked off their foundations chimneys fell down and pipes were severed lawson 1908 ground failures in the form of landslides and liquefaction were also prevalent especially in the man made fill along the san francisco waterfront lawson 1908 the city of san francisco a bustling city of 400 000 suffered

the 1952 kern county california earthquake a case study of issues in the analysis of historical intensity data for estimation of source parameters abstract seismic intensity data based on first hand accounts of shaking give valuable insight into historical and early instrumental earthquakes comparing an observed intensity distribution to intensity prediction models based on modern calibration events allows the magnitude to be estimated for many historic earthquakes magnitude estimates can also potentially be refined for earthquakes for which limited instrumental data are available however the complicated nature of macroseismic data and the methods used to collect and interpret the data introduce significant uncertainties in this paper we illustrate these challenges and possible solutions using the 1952 kern county california earthquake as a case study published estimates of its magnitude vary from mw 7 2 7 5 making it possibly the second largest in california during the 20th century we considered over 1100 first hand reports of shaking supplemented with other data and inferred the magnitude in several ways using intensity prediction equations yielding a preferred intensity magnitude mi 7 2 0 2 where the uncertainty reflects our judgement the revised intensity distribution reveals stronger shaking on the hanging wall south of the surface expression of the white wolf fault than on the footwall characterizing the magnitude and shaking distribution of this early instrumental earthquake can help improve estimation of the seismic hazard of the region such reinterpreted intensities for historic earthquakes combined with u s geological survey usgs did you feel it data for more recent events can be used to produce a uniform shaking dataset with which earthquake hazard map performance can be assessed

petrogenesis of archaean malene supracrustal rocks nw buksefjorden region west greenland geochemical evidence for highly evolved archaean crust abstract we report new data for major minor and trace elements in forty nine samples of malene supracrustal rocks nw buksefjorden region west greenland the samples consist principally of quartz cordierite biotite garnet anthophyllite gedrite sillimanite with abundant accessory zircon and minor rutile allanite and monazite plagioclase is rare to absent while muscovite occurs in only a few cases thus the malene paragneisses closely resemble cordierite orthoamphibole rocks found in other metamorphic complexes the nw buksefjorden malene paragneisses have on average high sio2 moderate al2o3 fe2o3 t and mgo and low k2o na2o and especially cao distinctive trace element characteristics include 1 low sc co cr ni and sr 2 high y zr nb hf ta th u and ree with prominent negative eu anomalies in nearly every case and 3 high ga up to 65 ppm with ga al ratios significantly higher than average crustal material on the basis of afm assemblage type the paragneisses can be divided into distinct groups which preserve the field distinctions noted by previous workers however these groupings primarily reflect variations in mg total range from 0 26 0 89 with no meaningful distinctions appearing among trace elements except possibly cu the trace element characteristics of the nw buksefjorden malene paragneisses are identical to those of the malene quartz cordierite gneisses found throughout the greater godthabsfjord region these gneisses are different from the malene quartzite psammite pelite group of clastic metasediments the trace element data of the quartz cordierite gneisses are compatible with a protolith dominated by material derived from felsic igneous precursors an interpretation supported by immobile element discriminant plots and ternary la th sc and th co hf plots however negative eu anomalies and low sr and ca suggest that plagioclase was lost from the protolith or from the precursor lithology or both the high concentrations of ga indicate either that the source rocks for the paragneisses were unusually ga rich or that assembly of the protolith was accompanied by a major fractionation of al from ga we propose that the protolith for most of the nw buksefjorden malene paragneisses was a quartz chlorite sericite schist derived from felsic volcaniclastic sediment hydrothermally altered by seawater prior to metamorphism this alteration resulted in gain of mg and possibly fe and loss of lime and alkalis and possibly sr and eu this hypothesis contrasts with earlier proposals that the protolith included mg rich clay palygorskite that precipitated directly from seawater but it is more consistent with the new data there is a remarkably close correspondence between the element enrichments and depletions shown by the malene paragneisses and those found in a type granitic rocks and their volcanic equivalents consequently we suggest a comparable source for the paragneisses the petrogenesis of a type granites is associated typically with thickened stable continental crust this implies that the protolith for the malene paragneisses formed after or in conjunction with a major event of archaean crustal thickening

a unified source model for the 1906 san francisco earthquake abstract we reconcile two previously discordant source models of the 1906 san francisco earthquake and obtain a model that satisfies both triangulation and seismic data by allowing the rupture velocity to exceed the shear wave velocity employing a projection method to remove the dependence on initial station positions allowed us to make use of a more stable triangulation network including nonrepeated angle observations along the northern san andreas fault this strengthens the case for significant slip over the entire northern segment of the san andreas fault from san juan bautista to cape mendocino during the 1906 earthquake we also found that the teleseismic body wave data can be reconciled with the geodetically derived slip model by allowing supershear rupture this resolves a longstanding conflict between the two previous slip models geodetic and seismic of this earthquake supershear rupture has long been recognized as a theoretical possibility for strike slip faulting and it has been observed in several recent large strike slip earthquakes which raises the prospect that it might be typical for such events supershear rupture leads to substantially different strong ground motion and as a result may need to be taken into account when developing ground motion prediction relations for large strike slip earthquakes our final slip model has a seismic moment of 7 9 10 20 n m which corresponds to a moment magnitude of m w 7 9

very early archean crustal accretion complexes preserved in the north atlantic craton the north atlantic craton contains very early archean supracrustal rocks orthogneisses and massive ultramafic rocks most units of supracrustal rocks are dominated by mafic volcanic rocks layered gabbros and banded iron formations bust some also contain abundant felsic volcanic sedimentary rocks quartzites and marbles some quartzites contain detrital zircons derived from rocks identical in age to felsic volcanic sedimentary rocks in these sequences ca 3800 ma and also from older ca 3850 ma sources the presence of the ca 3850 ma detrital zircons suggests that the supracrustal units containing them were deposited on or close to ca 3850 ma sialic crust the massive ultramafic rocks have chemical affinities to upper mantle rocks the voluminous suites of tonalitic gneisses are dominated by 3700 3730 ma bodies that intrude the supracrustal sequences but they also locally contain components with ages between 3820 and 3920 ma the diverse supracrustal units upper mantle rocks and ge 3820 ma components in the gneisses were tectonically interleaved in very early archean convergent plate boundaries giving rise to accretion complexes in the period 3700 3730 ma voluminous tonalitic magmas produced by partial melting of predominantly mafic rocks in the base of the accretion complexes were emplaced at higher levels forming juvenilemore continental crust and leaving behind a refractory lower crustal to upper mantle substrate less

basin structure beneath the santa rosa plain northern california implications for damage caused by the 1969 santa rosa and 1906 san francisco earthquakes regional gravity data in the northern san francisco bay region reflect a complex basin configuration beneath the santa rosa plain that likely contributed to the significant damage to the city of santa rosa caused by the 1969 m 5 6 5 7 santa rosa earthquakes and the 1906 m 7 9 san francisco earthquake inversion of these data indicates that the santa rosa plain is underlain by two sedimentary basins about 2 km deep separated by the trenton ridge a shallow west northwest striking bedrock ridge west of santa rosa the city of santa rosa is situated above the 2 km wide protruding northeast corner of the southern basin where damage from both the 1969 and 1906 earthquakes was concentrated ground motion simulations of the 1969 and 1906 earthquakes two events with opposing azimuths using the gravity defined basin surface show enhanced ground motions along the northeastern edge of this corner suggesting that basin edge effects contributed to the concentration of shaking damage in this area in the past and may also contribute to strong shaking during future earthquakes

the 1906 earthquake on california s north coast humboldt county on california s north coast was the furthest region from the 1906 epicenter to suffer significant damage in the 1906 earthquake this study reassesses the impacts described in the state earthquake investigation commission report lawson 1908 and subsequent intensity studies by examining reports from local newspapers weather service logs and the large collection of photographs journals and letters collected by local historical societies and museums the highest intensity modified mercalli mmi ix occurred in the petrolia and upper mattole valley the entire coastal region from shelter cove to the eel river valley experienced intensities of at least viii the most detailed damage descriptions come from ferndale where newspaper reports detail the damage to over 40 structures in the downtown area fewer than 2 of chimneys survived both brick buildings were severely damaged and about 25 of the commercial wood buildings were twisted by the ground shaking liquefaction was observed in the mattole valley throughout the eel river valley and as far north as fields landing on humboldt bay which exceeded the aerial extent and scale of any other historic event including the 1992 cape mendocino earthquake m w 7 2 in contrast to the isoseismal map published in the lawson report damage in eureka and the humboldt bay region was less than in ferndale based on the severity of damage and scale of liquefaction the 1906 earthquake was humboldt county s strongest historic event peak intensities likely exceeded the cape mendocino earthquake the intensity vii or larger isoseismal was about twice as large and peak ground velocity values likely exceeded 50 cm sec in much of southern humboldt county the strong shaking in humboldt county supports models showing significant slip along the northern segment of the 1906 rupture zone