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Sample records for aftershock focal mechanisms

  1. Aftershocks of the 2014 M6 South Napa Earthquake: Detection, Location, and Focal Mechanisms

    NASA Astrophysics Data System (ADS)

    Hardebeck, J.; Shelly, D. R.

    2014-12-01

    The aftershock sequence of the South Napa earthquake is notable both for its low productivity and for its geometric complexity. The aftershocks do not clearly define a fault plane consistent with the NNW-striking vertical plane implied by the mainshock moment tensor and the mapped surface rupture, but instead seem to delineate multiple secondary structures at depth. We investigate this unusual sequence by identifying additional aftershocks that do not appear in the network catalog, relocating the combined aftershock catalog using waveform cross-correlation arrival times and double-difference techniques, and determining focal mechanisms for individual events and event clusters. Additional aftershocks are detected by applying a matched filter approach to the continuous seismic data at nearby stations, with the catalog earthquakes serving as the waveform templates. In tandem with new event detections, we measure precise differential arrival times between events, which we then use in double-difference event location. We detect about 4 times as many well-located aftershocks as in the network catalog. We relocate the events using double-difference in both a 1D and a 3D velocity model. Most of the aftershocks occur between 8 and 11 km depth, similar depth to the mainshock hypocenter and deeper than most of the slip imaged seismically and geodetically. The aftershocks form a diffuse NNW-trending structure, primarily to the north of the mainshock hypocenter and on the west side of the main surface rupture. Within this diffuse trend there are clusters of aftershocks, some suggesting a N-S strike, and some that appear to dip to the east or west. Preliminary single-event and composite focal mechanisms also imply N-S striking strike-slip structures. The mainshock hypocenter and many of the aftershocks occur near the intersection of a sharply defined NE-dipping seismicity structure and the probable location of the West Napa fault, suggesting that stress is concentrated at a

  2. The impact of static stress change, dynamic stress change, and the background stress on aftershock focal mechanisms

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2014-01-01

    The focal mechanisms of earthquakes in Southern California before and after four M ≥ 6.7 main shocks provide insight into how fault systems respond to stress and changes in stress. The main shock static stress changes have two observed impacts on the seismicity: changing the focal mechanisms in a given location to favor those aligned with the static stress change and changing the spatial distribution of seismicity to favor locations where the static stress change aligns with the background stress. The aftershock focal mechanisms are significantly aligned with the static stress changes for absolute stress changes of ≥ 0.02 MPa, for up to ~20 years following the main shock. The dynamic stress changes have similar, although smaller, effects on the local focal mechanisms and the spatial seismicity distribution. Dynamic stress effects are best observed at long periods (30–60 s) and for metrics based on repeated stress cycling in the same direction. This implies that dynamic triggering operates, at least in part, through cyclic shear stress loading in the direction of fault slip. The background stress also strongly controls both the preshock and aftershock mechanisms. While most aftershock mechanisms are well oriented in the background stress field, 10% of aftershocks are identified as poorly oriented outliers, which may indicate limited heterogeneity in the postmain shock stress field. The fault plane orientations of the outliers are well oriented in the background stress, while their slip directions are not, implying that the background stress restricts the distribution of available fault planes.

  3. High-Resolution Locations and Focal Mechanisms of Aftershocks of the September 5, 2012 Mw=7.6 Nicoya, Costa Rica Earthquake

    NASA Astrophysics Data System (ADS)

    Laure, Duboeuf; Susan, Schwartz

    2015-04-01

    Subduction beneath the Nicoya Peninsula, Costa Rica generates the largest underthrusting earthquakes in the country with a recurrence interval of about 50 years. The most recent of these events occurred on September 5th 2012 (Mw 7.6). A vigorous aftershock sequence of more than 6400 earthquakes was recorded by a local seismic network within the first 4 months of the mainshock. We identify those aftershocks occurring on the mainshock fault plane and compare their locations to the 2012 mainshock slip distribution, the location of past interplate seismicity, and slow slip phenomena to better understand the mechanical behavior of this plate interface. Our focal mechanism determination includes all aftershocks occurring within the first nine days after the mainshock and aftershocks with magnitude greater than four occurring through the end of December 2012. We use the HASH (Hardebeck and Shearer, 2002) software package, based on first motion polarities, to obtain aftershock focal mechanisms. We are able to determine reliable focal mechanisms for 583 of the aftershocks and identify 264 of them as occurring on the plate interface. All of these are relocated using HypoDD (Waldhauser and Ellsworth, 2000) and their locations are compared with other plate boundary activity. We find no significant seismicity patterns as a function of time or magnitude, but confirm that deeper underthrusting events occur in the north compared to the south as revealed by previous studies (Newman et al., 2002). Most of the aftershocks occur in and around the updip part of the coseismic rupture zone. This suggests that the Nicoya mainshock released all of the accumulated strain in the deeper part of the plate interface, leaving none to occur as aftershocks. Previous interface seismicity in this region reveals a similar distribution to the aftershocks, however it extends to deeper depth and defines the entire seismogenic zone. The coseismic slip occurs even deeper than the background interface

  4. Mechanical origin of aftershocks.

    PubMed

    Lippiello, E; Giacco, F; Marzocchi, W; Godano, C; de Arcangelis, L

    2015-01-01

    Aftershocks are the most striking evidence of earthquake interactions and the physical mechanisms at the origin of their occurrence are still intensively debated. Novel insights stem from recent results on the influence of the faulting style on the aftershock organisation in magnitude and time. Our study shows that the size of the aftershock zone depends on the fault geometry. We find that positive correlations among parameters controlling aftershock occurrence in time, energy and space are a stable feature of seismicity independently of magnitude range and geographic areas. We explain the ensemble of experimental findings by means of a description of the Earth Crust as an heterogeneous elastic medium coupled with a Maxwell viscoelastic asthenosphere. Our results show that heterogeneous stress distribution in an elastic layer combined with a coupling to a viscous flow are sufficient ingredients to describe the physics of aftershock triggering. PMID:26497720

  5. Mechanical origin of aftershocks

    NASA Astrophysics Data System (ADS)

    Lippiello, E.; Giacco, F.; Marzocchi, W.; Godano, C.; de Arcangelis, L.

    2015-10-01

    Aftershocks are the most striking evidence of earthquake interactions and the physical mechanisms at the origin of their occurrence are still intensively debated. Novel insights stem from recent results on the influence of the faulting style on the aftershock organisation in magnitude and time. Our study shows that the size of the aftershock zone depends on the fault geometry. We find that positive correlations among parameters controlling aftershock occurrence in time, energy and space are a stable feature of seismicity independently of magnitude range and geographic areas. We explain the ensemble of experimental findings by means of a description of the Earth Crust as an heterogeneous elastic medium coupled with a Maxwell viscoelastic asthenosphere. Our results show that heterogeneous stress distribution in an elastic layer combined with a coupling to a viscous flow are sufficient ingredients to describe the physics of aftershock triggering.

  6. Mechanical origin of aftershocks

    PubMed Central

    Lippiello, E.; Giacco, F.; Marzocchi, W.; Godano, C.; de Arcangelis, L.

    2015-01-01

    Aftershocks are the most striking evidence of earthquake interactions and the physical mechanisms at the origin of their occurrence are still intensively debated. Novel insights stem from recent results on the influence of the faulting style on the aftershock organisation in magnitude and time. Our study shows that the size of the aftershock zone depends on the fault geometry. We find that positive correlations among parameters controlling aftershock occurrence in time, energy and space are a stable feature of seismicity independently of magnitude range and geographic areas. We explain the ensemble of experimental findings by means of a description of the Earth Crust as an heterogeneous elastic medium coupled with a Maxwell viscoelastic asthenosphere. Our results show that heterogeneous stress distribution in an elastic layer combined with a coupling to a viscous flow are sufficient ingredients to describe the physics of aftershock triggering. PMID:26497720

  7. Seismic amplitude measurements suggest foreshocks have different focal mechanisms than aftershocks.

    PubMed

    Lindh, A; Fuis, G; Mantis, C

    1978-07-01

    The ratio of the amplitudes of P and S waves from the foreshocks and aftershocks to three recent California earthquakes show a characteristic change at the time of the main events. As this ratio is extremely sensitive to small changes in the orientation of the fault plane, a small systematic change in stress or fault configuration in the source region may be inferred. These results suggest an approach to the recognition of foreshocks based on simple measurements of the amplitudes of seismic waves. PMID:17777756

  8. The 7.9 Denali Fault, Alaska Earthquake of November 3, 2002: Aftershock Locations, Moment Tensors and Focal Mechanisms from the Regional Seismic Network Data

    NASA Astrophysics Data System (ADS)

    Ratchkovski, N. A.; Hansen, R. A.; Kore, K. R.

    2003-04-01

    The largest earthquake ever recorded on the Denali fault system (magnitude 7.9) struck central Alaska on November 3, 2002. It was preceded by a magnitude 6.7 earthquake on October 23. This earlier earthquake and its zone of aftershocks were located ~20 km to the west of the 7.9 quake. Aftershock locations and surface slip observations from the 7.9 quake indicate that the rupture was predominately unilateral in the eastward direction. The geologists mapped a ~300-km-long rupture and measured maximum offsets of 8.8 meters. The 7.9 event ruptured three different faults. The rupture began on the northeast trending Susitna Glacier Thrust fault, a splay fault south of the Denali fault. Then the rupture transferred to the Denali fault and propagated eastward for 220 km. At about 143W the rupture moved onto the adjacent southeast-trending Totschunda fault and propagated for another 55 km. The cumulative length of the 6.7 and 7.9 aftershock zones along the Denali and Totschunda faults is about 380 km. The earthquakes were recorded and processed by the Alaska Earthquake Information Center (AEIC). The AEIC acquires and processes data from the Alaska Seismic Network, consisting of over 350 seismograph stations. Nearly 40 of these sites are equipped with the broad-band sensors, some of which also have strong motion sensors. The rest of the stations are either 1 or 3-component short-period instruments. The data from these stations are collected, processed and archived at the AEIC. The AEIC staff installed a temporary seismic network of 6 instruments following the 6.7 earthquake and an additional 20 stations following the 7.9 earthquake. Prior to the 7.9 Denali Fault event, the AEIC was locating 35 to 50 events per day. After the event, the processing load increased to over 300 events per day during the first week following the event. In this presentation, we will present and interpret the aftershock location patterns, first motion focal mechanism solutions, and regional seismic

  9. Focal Depth of the WenChuan Earthquake Aftershocks from modeling of Seismic Depth Phases

    NASA Astrophysics Data System (ADS)

    Luo, Y.; Zeng, X.; Chong, J.; Ni, S.; Chen, Y.

    2008-12-01

    After the 05/12/2008 great WenChuan earthquake in Sichuan Province of China, tens of thousands earthquakes occurred with hundreds of them stronger than M4. Those aftershocks provide valuable information about seismotectonics and rupture processes for the mainshock, particularly accurate spatial distribution of aftershocks is very informational for determining rupture fault planes. However focal depth can not be well resolved just with first arrivals recorded by relatively sparse network in Sichuan Province, therefore 3D seismicity distribution is difficult to obtain though horizontal location can be located with accuracy of 5km. Instead local/regional depth phases such as sPmP, sPn, sPL and teleseismic pP,sP are very sensitive to depth, and be readily modeled to determine depth with accuracy of 2km. With reference 1D velocity structure resolved from receiver functions and seismic refraction studies, local/regional depth phases such as sPmP, sPn and sPL are identified by comparing observed waveform with synthetic seismograms by generalized ray theory and reflectivity methods. For teleseismic depth phases well observed for M5.5 and stronger events, we developed an algorithm in inverting both depth and focal mechanism from P and SH waveforms. Also we employed the Cut and Paste (CAP) method developed by Zhao and Helmberger in modeling mechanism and depth with local waveforms, which constrains depth by fitting Pnl waveforms and the relative weight between surface wave and Pnl. After modeling all the depth phases for hundreds of events , we find that most of the M4 earthquakes occur between 2-18km depth, with aftershocks depth ranging 4-12km in the southern half of Longmenshan fault while aftershocks in the northern half featuring large depth range up to 18km. Therefore seismogenic zone in the northern segment is deeper as compared to the southern segment. All the aftershocks occur in upper crust, given that the Moho is deeper than 40km, or even 60km west of the

  10. Analyzing the characteristics of focal mechanism solutions of Wenchuan earthquake sequence

    NASA Astrophysics Data System (ADS)

    Cui, X.; Hu, X.; Xie, F.; Yu, C.; Wang, Y.

    2009-12-01

    We firstly read out initial P wave polarity from the digital wave form data given by Chinese national seismic networks, regional seismic networks, temporary seismic networks as well as some IRIS stations. Then employing improved grid point test method we obtain focal mechanism solutions of the strong aftershocks (M≥4.0) and composite fault plane solutions of the moderate and small aftershocks of Wenchuan earthquake sequence. In order to improve the reliability of focal mechanism solutions, we precisely locate the hypocenter location of aftershocks during the determining of focal mechanism solutions. Most of the aftershocks are thrust faulting or strike slip faulting except few ones. Thrust and predominately thrust aftershocks are distributed along the whole rapture zone except the southwest section, while strike slip aftershocks are distributed mainly in the southwest and the northeast sections. In the section from Beichuan to Pingwu, there are hardly any strike slip aftershocks but thrust and predominately thrust aftershocks. In terms of the azimuths of P axes of the focal mechanism solutions of the aftershocks, we find that the ones of the aftershocks with magnitude above 5.0 show good homogeneity, mainly concentrate on the orientation of NWW-SEE, which is consistent with that of Wenchuan mainshock, while as for aftershocks with magnitude below 4.9, they have two dominant distributions of NWW-SEE (azimuth 280°-310°) and NE-SW (azimuth 40°-70°). It shows that the focal mechanism solutions and their distribution characteristics of Wenchuan earthquake sequence are both complex. From the types and the azimuths of P axes of the focal mechanism solutions of the aftershocks, we can obtain the characteristics of segmentation, which is important to realize the dynamic mechanism of the Wenchuan earthquake sequence.

  11. On the origin of diverse aftershock mechanisms following the 1989 Loma Prieta earthquake

    USGS Publications Warehouse

    Kilb, Debi; Ellis, M.; Gomberg, J.; Davis, S.

    1997-01-01

    We test the hypothesis that the origin of the diverse suite of aftershock mechanisms following the 1989 M 7.1 Loma Prieta, California, earthquake is related to the post-main-shock static stress field. We use a 3-D boundary-element algorithm to calculate static stresses, combined with a Coulomb failure criterion to calculate conjugate failure planes at aftershock locations. The post-main-shock static stress field is taken as the sum of a pre-existing stress field and changes in stress due to the heterogeneous slip across the Loma Prieta rupture plane. The background stress field is assumed to be either a simple shear parallel to the regional trend of the San Andreas fault or approximately fault-normal compression. A suite of synthetic aftershock mechanisms from the conjugate failure planes is generated and quantitatively compared (allowing for uncertainties in both mechanism parameters and earthquake locations) to well-constrained mechanisms reported in the US Geological Survey Northern California Seismic Network catalogue. We also compare calculated rakes with those observed by resolving the calculated stress tensor onto observed focal mechanism nodal planes, assuming either plane to be a likely rupture plane. Various permutations of the assumed background stress field, frictional coefficients of aftershock fault planes, methods of comparisons, etc. explain between 52 and 92 per cent of the aftershock mechanisms. We can explain a similar proportion of mechanisms however by comparing a randomly reordered catalogue with the various suites of synthetic aftershocks. The inability to duplicate aftershock mechanisms reliably on a one-to-one basis is probably a function of the combined uncertainties in models of main-shock slip distribution, the background stress field, and aftershock locations. In particular we show theoretically that any specific main-shock slip distribution and a reasonable background stress field are able to generate a highly variable suite of failure

  12. High-resolution relocation and mechanism of aftershocks of the 2007 Tocopilla (Chile) earthquake

    NASA Astrophysics Data System (ADS)

    Fuenzalida, A.; Schurr, B.; Lancieri, M.; Sobiesiak, M.; Madariaga, R.

    2013-08-01

    event. We also studied the focal mechanisms of the aftershocks, most of them were thrust events like the mainshock. As the aftershock activity was significantly reduced, on 2007 December 13, an ML 6.1 event occurred offshore of the Mejillones peninsula reactivating the seismicity. Three days later the Michilla intraslab earthquake of Mw 6.8 ruptured an almost vertical fault with slab-push mechanism. The aftershocks locations of this event define a planar zone about 11 km in depth, situated right bellow the subduction interface.

  13. Nonlinear Viscoelastic Stress Transfer As a Possible Aftershock Triggering Mechanism

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Shcherbakov, R.

    2014-12-01

    The earthquake dynamics can be modelled by employing the spring-block system [Burridge and Knopoff, 1967]. In this approach the earthquake fault is modelled by an array of blocks coupling the loading plate and the lower plate. The dynamics of the system is governed by the system of equations of motion for each block. It is possible to map this system into a cellular automata model, where the stress acting on each block is increased in each time step, and the failing process (frictional slip) is described by stress transfer rules [Olami et al, 1992]. The OFC model produces a power-law distribution for avalanche statistics but it is not capable of producing robust aftershock sequences which follow Omori's law.We propose a nonlinear viscoelastic stress transfer mechanism in the aftershock triggering. In a basic spring-block model setting, we introduce the nonlinear viscoelastic stress transfer between neighbouring blocks, as well as between blocks and the top loading plate. The shear stress of the viscous component is a power-law function of the velocity gradient with an exponent smaller or greater than 1 for the nonlinear viscoelasticity, or 1 for the linear case. The stress transfer function of this nonlinear viscoelastic model has a power-law time-dependent form. It features an instantaneous stress transmission triggering an instantaneous avalanche, which is the same as the original spring-block model; and a power-law relaxation term, which could trigger further aftershocks. We incorporate this nonlinear viscoelasticity mechanism in a lattice cellular automata model. The model could exhibit both the Gutenberg-Richter scaling for the frequency-magnitude distribution and a power-law time decay of aftershocks, which is in accordance with Omori's law. Our study suggests that the stress transfer function may play an important role in the aftershock triggering. We have found that the time decay curve of aftershocks is affected by the shape of the stress transfer function

  14. Statistical Earthquake Focal Mechanism Forecasts

    NASA Astrophysics Data System (ADS)

    Kagan, Y. Y.; Jackson, D. D.

    2013-12-01

    The new whole Earth focal mechanism forecast, based on the GCMT catalog, has been created. In the present forecast, the sum of normalized seismic moment tensors within 1000 km radius is calculated and the P- and T-axes for the focal mechanism are evaluated on the basis of the sum. Simultaneously we calculate an average rotation angle between the forecasted mechanism and all the surrounding mechanisms. This average angle shows tectonic complexity of a region and indicates the accuracy of the prediction. The method was originally proposed by Kagan and Jackson (1994, JGR). Recent interest by CSEP and GEM has motivated some improvements, particularly to extend the previous forecast to polar and near-polar regions. The major problem in extending the forecast is the focal mechanism calculation on a spherical surface. In the previous forecast as our average focal mechanism was computed, it was assumed that longitude lines are approximately parallel within 1000 km radius. This is largely accurate in the equatorial and near-equatorial areas. However, when one approaches the 75 degree latitude, the longitude lines are no longer parallel: the bearing (azimuthal) difference at points separated by 1000 km reach about 35 degrees. In most situations a forecast point where we calculate an average focal mechanism is surrounded by earthquakes, so a bias should not be strong due to the difference effect cancellation. But if we move into polar regions, the bearing difference could approach 180 degrees. In a modified program focal mechanisms have been projected on a plane tangent to a sphere at a forecast point. New longitude axes which are parallel in the tangent plane are corrected for the bearing difference. A comparison with the old 75S-75N forecast shows that in equatorial regions the forecasted focal mechanisms are almost the same, and the difference in the forecasted focal mechanisms rotation angle is close to zero. However, though the forecasted focal mechanisms are similar

  15. Statistical earthquake focal mechanism forecasts

    NASA Astrophysics Data System (ADS)

    Kagan, Yan Y.; Jackson, David D.

    2014-04-01

    Forecasts of the focal mechanisms of future shallow (depth 0-70 km) earthquakes are important for seismic hazard estimates and Coulomb stress, and other models of earthquake occurrence. Here we report on a high-resolution global forecast of earthquake rate density as a function of location, magnitude and focal mechanism. In previous publications we reported forecasts of 0.5° spatial resolution, covering the latitude range from -75° to +75°, based on the Global Central Moment Tensor earthquake catalogue. In the new forecasts we have improved the spatial resolution to 0.1° and the latitude range from pole to pole. Our focal mechanism estimates require distance-weighted combinations of observed focal mechanisms within 1000 km of each gridpoint. Simultaneously, we calculate an average rotation angle between the forecasted mechanism and all the surrounding mechanisms, using the method of Kagan & Jackson proposed in 1994. This average angle reveals the level of tectonic complexity of a region and indicates the accuracy of the prediction. The procedure becomes problematical where longitude lines are not approximately parallel, and where shallow earthquakes are so sparse that an adequate sample spans very large distances. North or south of 75°, the azimuths of points 1000 km away may vary by about 35°. We solved this problem by calculating focal mechanisms on a plane tangent to the Earth's surface at each forecast point, correcting for the rotation of the longitude lines at the locations of earthquakes included in the averaging. The corrections are negligible between -30° and +30° latitude, but outside that band uncorrected rotations can be significantly off. Improved forecasts at 0.5° and 0.1° resolution are posted at http://eq.ess.ucla.edu/kagan/glob_gcmt_index.html.

  16. Focal Mechanisms and Stress Environment of the 12 May 2008 Wenchuan, China, Earthquake Sequence

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Luo, Y.; Ni, S.

    2012-12-01

    The 12 May 2008 Wenchuan earthquake (Mw=7.9) was the largest earthquake in China ever recorded by modern seismic instruments. It generated numerous moderate sized aftershocks that were well recorded by both permanent stations as well as portable instruments deployed after the mainshock. These waveform records yield high-quality data for the determination of focal mechanisms of aftershocks, which in turn provide important information for the investigation of regional stress field and the seismogenic environment in the Wenchuan earthquake source region. In this study, we determine the focal mechanisms, depths and moment magnitudes of moderate-sized (Mw ≥ 4.0) Wenchuan aftershocks using broadband waveform records. The focal mechanism results are then used to obtain the orientation and ratio of the principle stresses by the damped linear stress inversion method of Hardebeck & Michael (2006). Our results show that the majority of the moderate aftershocks occur at a depth range of 10-20 km and outside of the major rupture zones of the mainshock. The Wenchuan source region remains under a nearly horizontal compression with mostly thrust and occasional strike-slip faulting, especially towards the two ends of the rupture of the main shock. There is also clearly local variations in the orientation of the principle stresses.

  17. A possible mechanism for aftershocks: time-dependent stress relaxation in a slider-block model

    NASA Astrophysics Data System (ADS)

    Gran, Joseph D.; Rundle, John B.; Turcotte, Donald L.

    2012-08-01

    We propose a time-dependent slider-block model which incorporates a time-to-failure function for each block dependent on the stress. We associate this new time-to-failure mechanism with the property of stress fatigue. We test two failure time functions including a power law and an exponential. Failure times are assigned to 'damaged' blocks with stress above a damage threshold, σW and below a static failure threshold, σF. If the stress of a block is below the damage threshold the failure time is infinite. During the aftershock sequence the loader-plate remains fixed and all aftershocks are triggered by stress transfer from previous events. This differs from standard slider-block models which initiate each event by moving the loader-plate. We show the resulting behaviour of the model produces both the Gutenberg-Richter scaling law for event sizes and the Omori's scaling law for the rate of aftershocks when we use the power-law failure time function. The exponential function has limited success in producing Omori's law for the rate of aftershocks. We conclude the shape of the failure time function is key to producing Omori's law.

  18. Focal Mechanism determination of local M

    NASA Astrophysics Data System (ADS)

    Vales, Dina; Custório, Susana; Carrilho, Fernando

    2015-04-01

    We determine the focal mechanisms of local small (ML<3.9) earthquakes that occurred between 2013 and 2014 in mainland Portugal. These low magnitude events were recorded by several stations that provide first-motion polarity solutions. However, only few stations are located near the epicenter and record a waveform with a signal-to-noise ratio (SNR) high enough to allow full waveform modelling. To overcome this limitation, we used a new approach called cyclic scanning of the polarity solutions (CSPS) (Fojtíková and Zahradnik, 2014), which performs a joint inversion of full waveform and first motion polarities to retrieve the focal mechanism. This methodology has the advantage of yielding reliable focal mechanism solutions, even when high SNR waveforms are available from only a few near field stations (or in the limiting case, only with one single station). To apply the CSPS method one needs to: i) run the the FOCal MEChanism (FOCMEC) code (Snoke, 2003) to obtain a suite of the DC solutions corresponding to the first motion polarities, and then ii) perform the waveform modelling in order to decrease the uncertainty. The ISOLated Asperities (ISOLA) software (Sokos and Zahradník, 2008, 2013) is used in this second step. We applied this method to weak events recorded by a network of 30 broadband seismic stations that transmit data in real-time to Instituto Português do Mar e da Atmosfera (IPMA), the institution responsible for seismic monitoring in Portugal. We interpret the obtained fault plane solutions in light of active faults and regional tectonics, and in comparison with focal mechanisms previously inferred for events in the region. The focal mechanisms obtained for small earthquakes allow us to significantly expand the database of available focal mechanisms in mainland Portugal, contributing to the understanding of active deformation in the region.

  19. The dynamic implication of focal mechanism solutions of Wenchuan earthquake sequence

    NASA Astrophysics Data System (ADS)

    Hu, X.; Cui, X.; Chen, L.

    2010-12-01

    At 14:28 CST on May 12, 2008, the disastrous MS8.0 Wenchuan earthquake took place in Sichuan province of China, followed by tens of thousands of aftershocks. It occurred on the Longmenshan fault zone which is a high-angle inland over-thrust fault. What is the corresponding tectonic implication behind the focal mechanism is an important issue to realize the dynamic mechanism of Wenchuan earthquake sequence. In order to reveal it, our research as following is carried out. 1) We extensively collected digital waveform records, seriously and strictly read out P wave first motion, used more accurate locating results, employed the improved grid point test method, computed the focal mechanism solutions of Wenchuan earthquake sequence, and gave out 125 reliable focal mechanism solutions (M≥4.0,including a M3.9 earthquake result). The result shows that most of the earthquakes are thrust or strike-slip. The focal mechanism solutions have characteristic of subsection distribution. The P axis mainly distribute in direction of E-W within a certain range. 2) According to the main faults information and fine medium parameters, using ANSYS software, we established a three-dimensional elastic finite element model of the Longmenshan fault zone and its surrounding areas. According to Global Position System observations, considering three representative patterns of tectonic deformation velocity varying with depth, we loaded three different boundary conditions and got each numerical simulation result of the tectonic stress field in this region. The simulation results of the three patterns consistently show that the orientation of the principal compressive stress is almost E-W in Longmenshan fault zone and its surrounding area. And from north to south, there is a clockwise rotation within a narrow range. The result is consistent with the previous research in these areas. 3) Based on the numerical simulation results of tectonic stress field of three structural deformation patterns

  20. Estimating the similarity of earthquake focal mechanisms from waveform cross-correlation in regions of minimal local azimuthal station coverage

    NASA Astrophysics Data System (ADS)

    Kilb, D. L.; Martynov, V.; Bowen, J.; Vernon, F.; Eakins, J.

    2002-12-01

    In the Xinjiang province of China, ~2000 earthquakes were recorded by the Tien Shan network during 1997-1999 that exhibit a clear spatial progression of seismicity. This progression, which is confined to a 50 km diameter region, is undetectable in other data catalogs, both global (e.g., REB, PDE, CMT) and local (KIS). The two largest earthquakes in this sequence were the M6.1 August 2, 1998, and the M6.2 August 27, 1998, earthquakes. According to the Harvard moment tensor solutions, both events ruptured faults that trend parallel to the geologic structures in the region (~N55W). However, the August 27 event was a vertical strike slip event while the August 2 event ruptured a dipping fault and had a normal component of slip. These slip directions are counter to what we expect for this fold-and-thrust-belt, which typically has earthquakes with thrust mechanisms. Often seismological researchers make the assumption that aftershocks have the same focal mechanism as their associated mainshocks and/or assume all aftershock fault planes are similarly oriented. We test this assumption by examining the similarity of aftershock mechanisms from the August 2nd and 27th mainshocks. It is difficult to determine focal mechanisms from inversions of full seismic waveforms because the velocity model in the Tien Shan region is so complicated a 3D velocity model would be required. Also, the azimuthal station coverage is poor. Alternative, it impossible to determine accurate focal mechanisms from first motion data because the closest seismic stations have weak and complicated first arrivals. Our approach more easily determines the similarity of earthquake focal mechanisms using waveform cross-correlation. In this way information from the full waveform is utilized, and there is no need to make estimates of the complicated velocity structure. In general, we find there is minimal correlation between pairs of event waveforms (filter 1-8 Hz) within each aftershock sequence. For example, at

  1. The Mechanisms and Spatiotemporal Behavior of the 2011 Mw7.1 Van, Eastern Turkey Earthquake Aftershocks

    NASA Astrophysics Data System (ADS)

    Ezgi Guvercin Isik, Sezim; Ozgun Konca, A.; Karabulut, Hayrullah

    2016-04-01

    We studied the mechanisms and spatiotemporal distribution of the aftershocks of the Mw7.1 Van Earthquake, in Eastern Turkey. The 2011 Van Earthquake occurred on a E-W trending blind thrust fault in Eastern Turkey which is under N-S compression due to convergence of the Arabian plate toward the Eurasia. In this study, we relocated and studied the mechanisms of the M3.5-5.5 aftershocks from regional Pnl and surface waves using the "Cut and Paste" algorithm of Zhu and Helmberger (1996). Our results reveal that the aftershocks in the first day following the mainshock are in the vicinity of the co-seismic slip and have mostly thrust mechanism consistent with the mainshock. In the following day, a second cluster of activity at the northeast termination of the fault ( North of Lake Erçek) has started. These aftershocks have approximately N-S lineation and left lateral source mechanisms. The aftershocks surrounding the mainshock rupture are deeper (>20 km) than the aftershocks triggered on the north (<15km). We also observe strike slip earthquakes on the south of the mainshock. Both of delayed activities (north of the mainshock and south of the mainshock) are consistent with the Coulomb stress increase due to slip on the mainshock. We propose that the Van Fault is truncated by two strike-slip faults at each end, which has determined the along-strike rupture extent of the 2011 mainshock.

  2. Incorporating fault mechanics into inversions of aftershock data for the regional remote stress, with application to the 1992 Landers, California earthquake

    NASA Astrophysics Data System (ADS)

    Maerten, Frantz; Madden, Elizabeth H.; Pollard, David D.; Maerten, Laurent

    2016-04-01

    We present a new stress inversion algorithm that accounts for the physics relating the remote stress, slip along complex faults, and aftershock focal mechanisms, in a linear-elastic, heterogeneous, isotropic whole- or half-space. For each new remote stress, the solution of the simulation is obtained by the superposition of three pre-calculated solutions, leading to a constant time evaluation. Consequently, the full three-dimensional boundary element method model need not be recomputed and is independent of the structural complexity of the underlying model. Using a synthetic model, we evaluate several different measures of fit, or cost functions, between aftershocks and model results. Cost functions that account for aftershock slip direction provide good constraint on the remote stress, while functions that evaluate only nodal plane orientations do not. Inversion results are stable for values of friction ≤ 0.5 on mainshock faults. We demonstrate the technique by recovering the remote stress regime at the time of the 1992 M 7.3 Landers, California earthquake from its aftershocks and find that the algorithm performs well relative to methods that invert earthquakes occurring prior to the Landers mainshock. In the mechanical inversion, incorporating fault structures is necessary, but small differences in fault geometries do not impact these inversion results. Each inversion provides a complete solution for an earthquake as output, including fault slip and the stress and deformation fields around the fault(s). This allows for many additional datasets to be used as input, including fault surface slip, GPS data, InSAR data, and/or secondary fracture orientations.

  3. Focal adhesions, stress fibers and mechanical tension

    PubMed Central

    Burridge, Keith; Guilluy, Christophe

    2016-01-01

    Stress fibers and focal adhesions are complex protein arrays that produce, transmit and sense mechanical tension. Evidence accumulated over many years led to the conclusion that mechanical tension generated within stress fibers contributes to the assembly of both stress fibers themselves and their associated focal adhesions. However, several lines of evidence have recently been presented against this model. Here we discuss the evidence for and against the role of mechanical tension in driving the assembly of these structures. We also consider how their assembly is influenced by the rigidity of the substratum to which cells are adhering. Finally, we discuss the recently identified connections between stress fibers and the nucleus, and the roles that these may play, both in cell migration and regulating nuclear function. PMID:26519907

  4. Friction coefficient of faults inferred from earthquake focal mechanisms

    NASA Astrophysics Data System (ADS)

    Viganò, Alfio; Ranalli, Giorgio; Andreis, Daniele; Martin, Silvana; Rigon, Riccardo

    2013-04-01

    In earthquake mechanics and structural geology the static friction coefficient is usually assumed to have the laboratory value (μ = 0.6-0.8) according to the Coulomb-Byerlee's law. Estimates from deep boreholes and/or natural faults generally confirm this hypothesis but in some cases friction coefficients can be significantly lower, suggesting the existence of weak faults able to be activated by lower effective stress than theoretically expected. We apply a modified version of the method proposed by Yin and Ranalli (1995, Journal of Structural Geology, vol. 17, pp. 1327-1335), where the average friction coefficient of a set of n faults is estimated. This method is based on minimization of the sum of squares of the misfit ratios, where the misfit ratio of each fault is given dividing the misfit stress difference (i.e. the misfit between normalized stress difference and average normalized stress difference) by the average normalized stress difference. The normalized stress difference is defined as the critical stress difference divided by the effective overburden pressure, while the average stress difference is obtained considering the entire fault dataset. Input data are (i) the orientation of faults, (ii) the stress field orientation, and (iii) the stress ratio. The latter two must be independently estimated. A uniform stress field and a similar normalized critical stress difference for the fault dataset are assumed. The procedure has been extended to apply to fault plane solutions by considering both nodal planes of a set of n focal mechanisms and estimating the range of acceptable average friction coefficients from all possible combination of planes (2n number of combinations). The amount of calculation can be considerably reduced if independent information makes it possible to select which one of the nodal planes of each focal mechanism is the true fault plane (for example when aftershocks delineate the fault geometry at depth), resulting in only n combinations

  5. Mechanism of Focal Adhesion Kinase Mechanosensing.

    PubMed

    Zhou, Jing; Aponte-Santamaría, Camilo; Sturm, Sebastian; Bullerjahn, Jakob Tómas; Bronowska, Agnieszka; Gräter, Frauke

    2015-11-01

    Mechanosensing at focal adhesions regulates vital cellular processes. Here, we present results from molecular dynamics (MD) and mechano-biochemical network simulations that suggest a direct role of Focal Adhesion Kinase (FAK) as a mechano-sensor. Tensile forces, propagating from the membrane through the PIP2 binding site of the FERM domain and from the cytoskeleton-anchored FAT domain, activate FAK by unlocking its central phosphorylation site (Tyr576/577) from the autoinhibitory FERM domain. Varying loading rates, pulling directions, and membrane PIP2 concentrations corroborate the specific opening of the FERM-kinase domain interface, due to its remarkably lower mechanical stability compared to the individual alpha-helical domains and the PIP2-FERM link. Analyzing downstream signaling networks provides further evidence for an intrinsic mechano-signaling role of FAK in broadcasting force signals through Ras to the nucleus. This distinguishes FAK from hitherto identified focal adhesion mechano-responsive molecules, allowing a new interpretation of cell stretching experiments. PMID:26544178

  6. Mechanism of Focal Adhesion Kinase Mechanosensing

    PubMed Central

    Sturm, Sebastian; Bullerjahn, Jakob Tómas; Bronowska, Agnieszka; Gräter, Frauke

    2015-01-01

    Mechanosensing at focal adhesions regulates vital cellular processes. Here, we present results from molecular dynamics (MD) and mechano-biochemical network simulations that suggest a direct role of Focal Adhesion Kinase (FAK) as a mechano-sensor. Tensile forces, propagating from the membrane through the PIP2 binding site of the FERM domain and from the cytoskeleton-anchored FAT domain, activate FAK by unlocking its central phosphorylation site (Tyr576/577) from the autoinhibitory FERM domain. Varying loading rates, pulling directions, and membrane PIP2 concentrations corroborate the specific opening of the FERM-kinase domain interface, due to its remarkably lower mechanical stability compared to the individual alpha-helical domains and the PIP2-FERM link. Analyzing downstream signaling networks provides further evidence for an intrinsic mechano-signaling role of FAK in broadcasting force signals through Ras to the nucleus. This distinguishes FAK from hitherto identified focal adhesion mechano-responsive molecules, allowing a new interpretation of cell stretching experiments. PMID:26544178

  7. Deep Moonquake Focal Mechanisms: Recovery and Implications

    NASA Technical Reports Server (NTRS)

    Knapmeyer, Martin; Weber, Renee C.

    2011-01-01

    A defining characteristic of deep moonquakes is their tendency to occur with tidal periodicity, prompting previous studies to infer that they are related to the buildup and release of tidal stress within the Moon. In studies of tidal forcing, a key constraint is the focal mechanism: the fault parameters describing the type of failure moonquakes represent. The quality of the lunar seismic data and the limited source/receiver geometries of the Apollo seismic network prohibit the determination of deep moonquake fault parameters using first-motion polarities, as is typically done in terrestrial seismology. Without being able to resolve tidal stress onto a known failure plane, we can examine only gross qualities of the tidal stress tensor with respect to moonquake occurrence, so we cannot fully address the role of tidal stress in moonquake generation. We will examine the extent to which shear (S) and compression (P) wave amplitude ratios can constrain moonquake fault geometry by determining whether, for a given cluster, there exists a focal mechanism that can produce a radiation pattern consistent with the amplitudes measured by the Apollo instruments. Amplitudes are read in the ray coordinate frame, directly from seismograms for which the P and S arrivals are clearly identifiable on all long-period channels of the four Apollo stations. We apply an empirical station correction to account for site effects and the differences between P- and S-wave attenuation. Instead of focusing on the best fitting solution only, we formulate the inverse problem using a falsification criterion: all source orientations that do not reproduce the observed SV/P ratios within an error margin derived from the uncertainty of amplitude readings are rejected. All others are accepted as possible solutions. The inversion is carried out using an exhaustive grid search on a regular grid with predefined step size, encompassing all possible combinations of strike, dip and slip. To assess the

  8. Multispectral linear array (MLA) focal plane mechanical and thermal design

    NASA Technical Reports Server (NTRS)

    Mitchell, A. S.; Kaminski, E. F.

    1982-01-01

    The mechanical and thermal design of an integrated focal plane subsystem of a Multispectral Linear Array (MLA) instrument is discussed in terms of focal-plane alignment, thermoelastic performance, and thermal requirements. The modular construction and thermal control of the focal plane array are discussed.

  9. Deep Moonquake Focal Mechanisms: Recovery and Implications

    NASA Technical Reports Server (NTRS)

    Weber, Renee C.; Knapmeyer, Martin

    2012-01-01

    A defining characteristic of deep moonquakes is their tendency to occur with tidal periodicity, prompting previous studies to infer that they are related to the buildup and release of tidal stress within the Moon [refs]. In studies of tidal forcing, a key constraint is the focal mechanism: the fault parameters describing the type of failure moonquakes represent. The quality of the lunar seismic data and the limited source/receiver geometries of the Apollo seismic network prohibit the determination of deep moonquake fault parameters using first-motion polarities, as is typically done in terrestrial seismology [ref]. Without being able to resolve tidal stress onto a known failure plane, we can examine only gross qualities of the tidal stress tensor with respect to moonquake occurrence, so we cannot fully address the role of tidal stress in moonquake generation.

  10. Aftershocks triggered by fluid intrusion: Evidence for the aftershock sequence occurred 2014 in West Bohemia/Vogtland

    NASA Astrophysics Data System (ADS)

    Hainzl, S.; Fischer, T.; Čermáková, H.; Bachura, M.; Vlček, J.

    2016-04-01

    The West Bohemia/Vogtland region, central Europe, is well known for its repeating swarm activity. However, the latest activity in 2014, although spatially overlapping with previous swarm activity, consisted of three classical aftershock sequences triggered by ML3.5, 4.4, and 3.5 events. To decode the apparent system change from swarm-type to mainshock-aftershock characteristics, we have analyzed the details of the major ML4.4 sequence based on focal mechanisms and relocated earthquake data. Our analysis shows that the mainshock occurred with rotated mechanism in a step over region of the fault plane, unfavorably oriented to the regional stress field. Most of its intense aftershock activity occurred in-plane with classical characteristics such as (i) the maximum magnitude of the aftershocks is significantly less than the mainshock magnitude and (ii) the decay can be well fitted by the Omori-Utsu law. However, the absolute number of aftershocks and the fitted Omori-Utsu c and p parameters are much larger than for typical sequences. By means of the epidemic-type aftershock sequence model, we show that an additional aseismic source with an exponentially decaying strength triggered a large fraction of the aftershocks. Corresponding pore pressure simulations with an exponentially decreasing flow rate of the fluid source show a good agreement with the observed spatial migration front of the aftershocks extending approximately with log(t). Thus, we conclude that the mainshock opened fluid pathways from a finite fluid source into the fault plane explaining the unusual high rate of aftershocks, the migration patterns, and the exponential decrease of the aseismic signal.

  11. Analysis of the 2012 Oct 27 Haida Gwaii Aftershock Sequence

    NASA Astrophysics Data System (ADS)

    Mulder, T.; Brillon, C.; Bentkowski, W.; White, M.; Rosenberger, A.; Rogers, G. C.; Vernon, F.; Kao, H.

    2013-12-01

    The magnitude 7.7 thrust earthquake that occurred on 2012 Oct 28 offshore of Haida Gwaii (formerly the Queen Charlotte Islands), in British Columbia, Canada, produced a rich and on-going aftershock sequence. Ten months of aftershock events are determined from analyst reviewed solutions and automatic detectors and locators. For automated solutions, rotating the waveforms and running P and S wave filters (Rosenberger, 2010) over them produced phase arrivals for an improved catalogue of aftershocks compared to using a traditional signal to noise ratio detector on standard vertical and horizontal component seismograms. The automated aftershock locations from the rotated waveforms are compared to the automated locations from the standard vertical and horizontal waveforms and to analyst locations (which are generally M>2.5). The best of the automated solutions are comparable in quality to analyst solutions and much more numerous making this a viable method of processing extensive aftershock sequences. They outline a region approximately 50 km wide and 100 km long, with the aftershocks in two parallel bands. Most of the aftershocks are not on the rupture surface but are in the overlying or underlying plates. It is thought that this earthquake represents the Pacific plate thrusting underneath the North America plate with the rupture surface lying beneath the sedimentary Queen Charlotte terrace and terminating to the east in the vicinity of the Queen Charlotte fault. Due to the one-sided station distribution on land, depth trades off with distance offshore, resulting in poor depth determinations. However, using ocean bottom seismometers deployed early in the aftershock sequence, depth resolution was significantly improved. First motion focal North America plate with the rupture surface lying beneath the sedimentary Queen Charlotte terrace and terminating to the east in the vicinity of the Queen Charlotte fault.mechanisms for a portion of the aftershock sequence are compared

  12. PATHOGENETIC MECHANISMS OF FOCAL CORTICAL DYSPLASIA

    PubMed Central

    Marin-Valencia, Isaac; Guerrini, Renzo; Gleeson, Joseph G.

    2014-01-01

    SUMMARY Objective Focal cortical dysplasias (FCDs) constitute a prevalent cause of intractable epilepsy in children, and one of the leading conditions requiring epilepsy surgery. Despite the recent advances on the cellular and molecular biology of these conditions, the pathogenetic mechanisms of FCDs remain largely unknown. The purpose if this work is to review the molecular underpinnings of FCDs and to highlight potential therapeutic targets. Methods A systematic review of the literature regarding the histological, molecular, and electrophysiological aspects of FCDs was conducted. Results Disruption of the mTOR signaling comprises a common pathway underlying the structural and electrical disturbances of some FCDs. Other mechanisms such as viral infections, prematurity, head trauma, and brain tumors are also posited. mTOR inhibitors (i.e., rapamycin) have shown positive results on seizure management in animal models and in a small cohort of patients with FCD. Significance Encouraging progresses have been achieved on the molecular and electrophysiological basis of constitutive cells in the dysplastic tissue. Despite the promising results of mTOR inhibitors, large-scale randomized trials are in need to evaluate their efficacy and side effects, along with additional mechanistic studies for the development of novel, molecular-based diagnostic and therapeutic approaches. PMID:24861491

  13. Aftershock mechanisms from the 2010 Mw 8.8 Maule, Chile earthquake: detailed analysis using full waveform inversion

    NASA Astrophysics Data System (ADS)

    Rietbrock, A.; Hicks, S. P.; Chagas, B.; Detzel, H. A.

    2014-12-01

    Since the earthquake rupture process is extremely heterogeneous, it is vital to understand how structural variations in the overriding plate and downgoing slab may control slip style along the subduction megathrust. The large-scale 3-D geometry of subduction plate boundaries is rapidly becoming well understood; however, the nature of any finer-scale structure along the plate interface remains elusive. A detailed study of earthquake source mechanisms along a megathrust region can shed light on the nature of fine-scale structures along the megathrust. The Mw 8.8 Maule earthquake that struck central Chile in 2010 is the sixth largest earthquake ever recorded. Following the earthquake, there was an international deployment of seismic stations in the rupture area, making this one of the best datasets of an aftershock sequence following a large earthquake. This dataset provides a unique opportunity to perform a detailed study of megathrust earthquake source mechanisms. Based on a high-resolution 3-D velocity model and robust earthquake locations [Hicks et al., 2014], we calculate regional moment tensors using the ISOLA software package [Sokos & Zahradnik, 2008]. We incorporate accelerometer recordings, important for constraining solutions of large earthquakes in the overriding plate. We also validate the robustness of our solutions by assessing the consistency of mechanisms with P-wave polarities observed at both onshore and offshore seismic stations, and compare them to already published solutions. We find that accurate earthquake locations are vital for the fine-scale interpretation of focal mechanisms, particularly for offshore events. Our results show that most moment tensor solutions with thrusting mechanisms have a nodal plane dipping parallel to the subducting plate interface. Interestingly, we also find earthquakes with normal faulting mechanisms lying along to the megathrust plate interface in the south of the rupture area. This finding suggests that megathrust

  14. Investigating Fault Zone Damage Processes Using Waveform Relocated Seismicity and High Precision Focal Mechanisms

    NASA Astrophysics Data System (ADS)

    Hauksson, E.; Yang, W.

    2011-12-01

    We analyze waveform relocated seismicity and focal mechanisms located near the principal slip zones (PSZs) of the late Quaternary fault zones in southern California to address questions such as: 1) Do mainshocks, aftershocks, and interseismic seismicity occur in the same place? 2) Is there evidence for fault normal compression along strike-slip faults? 3) Does seismicity in the near-field (±2km) of PSZs respond strongly to stress changes from nearby large earthquakes? 4) Is there other evidence for weak faults? We show that major earthquakes that can slip more than several meters, aftershocks, and near-fault relocated background seismicity mostly rupture different surfaces within late Quaternary fault zones. Major earthquakes rupture along the mapped traces of the late Quaternary faults, called the PSZs. Aftershocks illuminate damage zones in the immediate vicinity of the PSZs, typically ±2 km wide. In contrast, the near-fault background seismicity is mostly accommodated on a secondary heterogeneous network of small slip surfaces, and forms spatially decaying distributions extending out to distances of ±10 km away from the PSZs. As part of our efforts to address these questions, we have completed waveform relocations of more than 500,000 earthquakes. We have also determined a new focal mechanism catalog of more than 150,000 events, applying the latest techniques that include using S/P amplitude ratios for additional constraints, and taking advantage of the new waveform based relocations. We use the data set of focal mechanisms to analyze the style of faulting and the stress field next to PSZs of major faults. For detailed analysis we select all the events located within ±10 km of major PSZs as defined in the SCEC Community Fault Model. There is a difference in the depth distribution as well as in the rake distribution on each side of the PSZs. The events may be deeper on one side of the PSZ as compared to the other. Further, the focal mechanisms often have a

  15. Analysis of Mw 7.2 2014 Molucca Sea earthquake and its aftershocks

    NASA Astrophysics Data System (ADS)

    Shiddiqi, Hasbi Ash; Widiyantoro, Sri; Nugraha, Andri Dian; Ramdhan, Mohamad; Wiyono, Samsul Hadi; Wandono, Wandono

    2016-05-01

    A Mw 7.2 earthquake struck an area in the Molucca Sea region on November 15, 2014, and was followed by more than 300 aftershocks until the end of December 2014. This earthquake was the second largest event in the Molucca Sea during the last decade and was well recorded by local networks. Although the seismicity rate of the aftershocks was declining at the end of 2014, several significant earthquakes with magnitude (Mw) larger than five still occurred from January to May 2015 within the vicinity of the mainshock location. In this study, we investigated the earthquake process and its relation to the increasing seismicity in the Molucca Sea within six months after the earthquake. We utilized teleseismic double-difference hypocenter relocation method using local, regional, and teleseismic direct body-wave arrival times of 514 earthquakes from the time of mainshock occurrence to May 2015. Furthermore, we analyzed the focal mechanism solutions from the National Research Institute for Earth Science and Disaster Prevention (NIED), Japan. From our results, we observed that aftershocks propagated along the NNE-SSW direction within a 100 km fault segment length of the Mayu Ridge. The highest number of the aftershocks was located in the SSW direction of the main event. The aftershocks were terminated at around 60 km depth, which may represent the location of the top of the Molucca Sea Plate (MSP). Between January and May 2015, several significant earthquakes propagated westward and were extended to the Molucca Sea slab. From focal mechanism catalog, we found that the mainshock mechanism was reverse with strike 192o and dip 55o. While most of the large aftershock mechanisms were consistent with the main event, several aftershocks had reverse, oblique mechanisms. Stress inversion result from focal mechanism data revealed that the maximum stress direction was SE and was not perpendicular with fault direction. We suggest that the non-perpendicular maximum stress caused several

  16. Aftershocks of the 2014 South Napa, California, Earthquake: Complex faulting on secondary faults

    USGS Publications Warehouse

    Hardebeck, Jeanne L.; Shelly, David R.

    2016-01-01

    We investigate the aftershock sequence of the 2014 MW6.0 South Napa, California, earthquake. Low-magnitude aftershocks missing from the network catalog are detected by applying a matched-filter approach to continuous seismic data, with the catalog earthquakes serving as the waveform templates. We measure precise differential arrival times between events, which we use for double-difference event relocation in a 3D seismic velocity model. Most aftershocks are deeper than the mainshock slip, and most occur west of the mapped surface rupture. While the mainshock coseismic and postseismic slip appears to have occurred on the near-vertical, strike-slip West Napa fault, many of the aftershocks occur in a complex zone of secondary faulting. Earthquake locations in the main aftershock zone, near the mainshock hypocenter, delineate multiple dipping secondary faults. Composite focal mechanisms indicate strike-slip and oblique-reverse faulting on the secondary features. The secondary faults were moved towards failure by Coulomb stress changes from the mainshock slip. Clusters of aftershocks north and south of the main aftershock zone exhibit vertical strike-slip faulting more consistent with the West Napa Fault. The northern aftershocks correspond to the area of largest mainshock coseismic slip, while the main aftershock zone is adjacent to the fault area that has primarily slipped postseismically. Unlike most creeping faults, the zone of postseismic slip does not appear to contain embedded stick-slip patches that would have produced on-fault aftershocks. The lack of stick-slip patches along this portion of the fault may contribute to the low productivity of the South Napa aftershock sequence.

  17. High resolution earthquake source mechanisms in a subduction zone: 3-D waveform simulations of aftershocks from the 2010 Mw 8.8 Chile rupture

    NASA Astrophysics Data System (ADS)

    Hicks, Stephen; Rietbrock, Andreas

    2015-04-01

    The earthquake rupture process is extremely heterogeneous. For subduction zone earthquakes in particular, it is vital to understand how structural variations in the overriding plate and downgoing slab may control slip style. The large-scale 3-D geometry of subduction plate boundaries is rapidly becoming well understood (e.g. Hayes et al., 2012); however, the nature of slip style along any finer-scale structures remains elusive. Regional earthquake moment tensor (RMT) inversion can shed light on faulting mechanisms. However, many traditional regional moment tensor inversions use simplified (1-D) Earth models (e.g. Agurto et al., 2012; Hayes et al., 2013) that only use the lowest frequency parts of the waveform, which may mask source complexity. As a result, we may have to take care when making small-scale interpretations about the causative fault and its slip style. This situation is compounded further by strong lateral variations in subsurface geology, as well as poor station coverage for recording offshore subduction earthquakes. A formal assessment of the resolving capability of RMT inversions in subduction zones is challenging and the application of 3-D waveform simulation techniques in highly heterogeneous media is needed. We generate 3-D waveform simulations of aftershocks from a large earthquake that struck Chile in 2010. The Mw 8.8 Maule earthquake is the sixth largest earthquake ever recorded. Following the earthquake, there was an international deployment of seismic stations in the rupture area, making this one of the best observed aftershock sequences to date. We therefore have a unique opportunity to compare recorded waveforms with simulated waveforms for many earthquakes, shedding light on the effect of 3-D heterogeneity on source imaging. We perform forward simulations using the spectral element wave propagation code, SPEFEM3D (e.g. Komatitsch et al., 2010) for a set of moderate-sized aftershocks (Mw 4.0-5.5). A detailed knowledge of velocity structure

  18. A damage mechanics model for power-law creep and earthquake aftershock and foreshock sequences

    NASA Astrophysics Data System (ADS)

    Main, Ian G.

    2000-07-01

    It is common practice to refer to three independent stages of creep under static loading conditions in the laboratory: namely transient, steady-state, and accelerating. Here we suggest a simple damage mechanics model for the apparently trimodal behaviour of the strain and event rate dependence, by invoking two local mechanisms of positive and negative feedback applied to constitutive rules for time-dependent subcritical crack growth. In both phases, the individual constitutive rule for measured strain ɛ takes the form ɛ(t)=ɛ0[1+t/mτ]m, where τ is the ratio of initial crack length to rupture velocity. For a local hardening mechanism (negative feedback), we find that transient creep dominates, with 0mechanism (positive feedback), m<0, and crack growth is unstable and accelerating. In this case a quasi-static instability criterion ɛ->∞ can be defined at a finite failure time, resulting in the localization of damage and the formation of a throughgoing fracture. In the hybrid model, transient creep dominates in the early stages of damage and accelerating creep in the latter stages. At intermediate times the linear superposition of the two mechanisms spontaneously produces an apparent steady-state phase of relatively constant strain rate, with a power-law rheology, as observed in laboratory creep test data. The predicted acoustic emission event rates in the transient and accelerating phases are identical to the modified Omori laws for aftershocks and foreshocks, respectively, and provide a physical meaning for the empirical constants measured. At intermediate times, the event rate tends to a relatively constant background rate. The requirement for a finite event rate at the time of the main shock can be satisfied by modifying the instability criterion to having a finite crack velocity at the dynamic failure time, dx/dt->VR, where VR is the dynamic rupture velocity. The same hybrid

  19. Use of focal mechanisms to determine stress: a control study.

    USGS Publications Warehouse

    Michael, A.J.

    1987-01-01

    The results of this control study show that focal mechanisms can be inverted to find the best stress tensor, but the resolution is decreased unless the fault planes can be picked a priori. The resolution can also be increased by including constraints on the magnitude of the tangential traction on the fault plane.-from Author

  20. Thrust-faulting earthquake induced many normal-faulting aftershocks, in northeastern Chiba Prefecture, Japan

    NASA Astrophysics Data System (ADS)

    Sakai, S.; Kato, A.; Hirata, N.; Nakagawa, S.; Kasahara, K.; Sato, H.; Kurashimo, E.; Nanjo, K.; Panayotopoulos, Y.; Obara, K.; Aketagawa, T.; Kimura, H.

    2010-12-01

    A thrust faulting type earthquake of a local body wave magnitude (MJMA) of 4.9 occurred near the upper interface of the subducting Philippine Sea Plate (PHS) in northeastern Chiba Prefecture on July 22, 2010. We have been developing a dense seismic net work call the MeSO-net in the Tokyo Metropolitan area. So far, 249 stations are available for the study of a large felt earthquakes and small event as low as M=1.5. We also deployed a temporary seismic array 24 of which were used for the analysis of the aftershocks. We locate the July 22 earthquake(MJMA=4.9) and its 19 aftershocks (M>1.5) by the double difference location algorithm. We also determine focal mechanisms for the main- and after-shocks. The locations of the main shock and three aftershocks are closely distributed near the upper interface of PHS, which is consistent with the idea that the event occurred on the plate interface. However, most aftershocks whose focal mechanism is normal-fault type with a T-axis directing NE-SW are located off the upper interface indicating that intra-slab events are also generated by the event. Acknowledgement: The present study is supported by Special Project for Earthquake Disaster Mitigation in Tokyo Metropolitan Area from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

  1. Stress tensor and focal mechanisms in the Dead Sea basin

    NASA Astrophysics Data System (ADS)

    Hofstetter, A.; Dorbath, C.; Dorbath, L.; Braeuer, B.; Weber, M.

    2016-04-01

    We use the recorded seismicity, confined to the Dead Sea basin and its boundaries, by the Dead Sea Integrated Research (DESIRE) portable seismic network and the Israel and Jordan permanent seismic networks for studying the mechanisms of earthquakes in the Dead Sea basin. The observed seismicity in the Dead Sea basin is divided into nine regions according to the spatial distribution of the earthquakes and the known tectonic features. The large number of recording stations and the adequate station distribution allowed the reliable determinations of 494 earthquake focal mechanisms. For each region, based on the inversion of the observed polarities of the earthquakes, we determine the focal mechanisms and the associated stress tensor. For 159 earthquakes, out of the 494 focal mechanisms, we could determine compatible fault planes. On the eastern side, the focal mechanisms are mainly strike-slip mechanism with nodal planes in the N-S and E-W directions. The azimuths of the stress axes are well constrained presenting minimal variability in the inversion of the data, which is in agreement with the Eastern Boundary fault on the east side of the Dead Sea basin and what we had expected from the regional geodynamics. However, larger variabilities of the azimuthal and dip angles are observed on the western side of the basin. Due to the wider range of azimuths of the fault planes, we observe the switching of σ1 and σ2 or the switching of σ2 and σ3 as major horizontal stress directions. This observed switching of stress axes allows having dip-slip and normal mechanisms in a region that is dominated by strike-slip motion.

  2. Crustal stress state inferred from earthquake focal mechanisms: Recognition of a non-uniform stress state, slip plane selection criteria, and implications for the mechanics of faulting

    NASA Astrophysics Data System (ADS)

    Magee, Marian Eileen

    Populations of earthquake focal mechanisms that are characterized by diverse styles of faulting require some degree of heterogeneity in the causative stress field or variable fault strength. Methods for finding a stress tensor compatible with a set of focal mechanisms are based on methods which determine paleostress tensors from fault slip data. Although slip on any specific fault plane places a different constraint on the causative stress tensor, this is only directly measured for fault slip data. The actual slip plane and direction are rarely known for most earthquakes. The capability of published methods to determine the degree of heterogeneity required by inversion of diverse earthquake focal mechanisms is examined through a comparison of several fault plane selection criteria on synthetic focal mechanisms where the fault planes are constrained to be in agreement with specific stress tensors. My approach is to use a modified published stress inversion method to quantify the range of allowable model stress tensors, then the likelihood and degree of stress heterogeneity. To examine the fault strength variability requires that the earthquakes have occurred in a region characterized by a uniform stress field and that fault planes be identified. A new stress inversion method is developed which uses the P-wave first motion polarity readings that constrain focal mechanisms to select probable fault planes and constrain the stress tensor for a population of earthquakes. This method is applied to two problematic data sets: small earthquakes in the New Madrid seismic zone and aftershocks to the 1989 Loma Prieta earthquake. A uniform reverse faulting stress state can be constrained using the observed polarities for most of the New Madrid area, but not for the entire seismic zone due to errors in velocity structure. A uniform reverse faulting tensor with an SsbHmax direction that acts approximately normal to the mainshock plane is well constrained by the P-wave polarity

  3. Aftershocks are well aligned with the background stress field, contradicting the hypothesis of highly-heterogeneous crustal stress

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2010-01-01

    It has been proposed that the crustal stress field contains small-length-scale heterogeneity of much larger amplitude than the uniform background stress. This model predicts that earthquake focal mechanisms should reflect the loading stress rather than the uniform background stress. So, if the heterogeneous stress hypothesis is correct, focal mechanisms before and after a large earthquake should align with the tectonic loading and the earthquake-induced static stress perturbation, respectively. However, I show that the off-fault triggered aftershocks of the 1992 M7.3 Landers, California, earthquake align with the same stress field as the pre-Landers mechanisms. The aftershocks occurred on faults that were well oriented for failure in the pre-Landers stress field and then loaded by the Landers-induced static stress change. Aftershocks in regions experiencing a 0.05 to 5 MPa coseismic differential stress change align with the modeled Landers-induced static stress change, implying that they were triggered by the stress perturbation. Contrary to the heterogeneous stress hypothesis, these triggered aftershocks are also well aligned with the pre-Landers stress field obtained from inverting the pre-Landers focal mechanisms. Therefore, the inverted pre-Landers stress must represent the persistent background stress field. Earthquake focal mechanisms provide an unbiased sample of the spatially coherent background stress field, which is large relative to any small-scale stress heterogeneity. The counterexample provided by the Landers earthquake is strong evidence that the heterogeneous stress model is not widely applicable.

  4. Hypocentral Relocations of the 2008 Mt. Carmel, Illinois Aftershock Sequence

    NASA Astrophysics Data System (ADS)

    Shoemaker, K.; Hamburger, M. W.; Pavlis, G. L.; Horton, S. P.; Withers, M. M.

    2009-12-01

    On April 18, 2008, a moderate sized earthquake (Mw 5.2, hypocentral depth of 16 km) occurred near the Indiana-Illinois state border within 3 km of the Mt. Carmel-New Harmony fault at the northern termination of the Wabash Valley Fault System. A total of 257 aftershocks were recorded over the next month by a fourteen-station temporary network deployed by Indiana University and University of Memphis/Center of Earthquake Research and Information (CERI). The number of recorded aftershocks is greater than aftershocks recorded from previous earthquakes in the WVFS of similar magnitude within the last 50 years. The number and density of local stations allowed the generation of precise hypocentral relocations with the combination of waveform cross-correlation and joint hypocentral techniques. The relocated hypocenters indicate a well-defined near-vertical fault plane striking east-west. The fault orientation is consistent with the focal mechanism of the main shock and nearly orthogonal with respect to the trace of the neighboring Mt. Carmel-New Harmony fault. The interpreted ruptured fault orientation suggests the aftershock sequence occurred on a transfer structure at the fault termination. The structure may be related to the change in deformation styles suggested by the transition from the northeast-trending WVFS to the northwest-trending La Salle anticlinorium.

  5. Focal mechanisms of recent earthquakes in the Southern Korean Peninsula

    NASA Astrophysics Data System (ADS)

    Park, Jong-Chan; Kim, Woohan; Chung, Tae Woong; Baag, Chang-Eob; Ree, Jin-Han

    2007-06-01

    We evaluate the stress field in and around the southern Korean Peninsula with focal mechanism solutions, using the data collected from 71 earthquakes (ML = 1.9-5.2) between 1999 and 2004. For this, the hypocentres were relocated and well-constrained fault plane solutions were obtained from the data set of 1270 clear P-wave polarities and 46 SH/P amplitude ratios. The focal mechanism solutions indicate that the prevailing faulting types in South Korea are strike-slip-dominant-oblique-slip faultings with minor reverse-slip component. The maximum principal stresses (σ1) estimated from fault-slip inversion analysis of the focal mechanism solutions show a similar orientation with E-W trend (269° -275°) and low-angle plunge (10° -25°) for all tectonic provinces in South Korea, consistent with the E-W trending maximum horizontal stress (σHmax) of the Amurian microplate reported from in situ stress measurements and earthquake focal mechanisms. The directions of the intermediate (σ2) and minimum (σ3) principal stresses of the Gyeongsang Basin are, however, about 90 deg off from those of the other tectonic provinces on a common σ2-σ3 plane, suggesting a permutation of σ2 and σ3. Our results incorporated with those from the kinematic studies of the Quaternary faults imply that NNW- to NE-striking faults (dextral strike-slip or oblique-slip with a reverse-slip component) are highly likely to generate earthquakes in South Korea.

  6. Internal tectonic structure of the Central American Wadati-Benioff zone based on analysis of aftershock sequences

    NASA Astrophysics Data System (ADS)

    Špičák, Aleš; Hanuš, Václav; Vaněk, Jiří; Běhounková, Marie

    2007-09-01

    Relocated Engdahl et al. (1998) global seismological data for 10 aftershock sequences were used to analyze the internal tectonic structure of the Central American subduction zone; the main shocks of several of these were the most destructive and often referenced earthquakes in the region (e.g., the 1970 Chiapas, 1983 Osa, 1992 Nicaragua, 1999 Quepos, 2001 El Salvador earthquakes). The spatial analysis of aftershock foci distribution was performed in a rotated Cartesian coordinate system (x, y, z) related to the Wadati-Benioff zone, and not in a standard coordinate system ($\\varphi$, λ, h are latitude, longitude, focal depth, respectively). Available fault plane solutions were also transformed into the plane approximating the Wadati-Benioff zone. The spatial distribution of earthquakes in each aftershock sequence was modeled as either a plane fit using a least squares approximation or a volume fit with a minimum thickness rectangular box. The analysis points to a quasi-planar distribution of earthquake foci in all aftershock sequences, manifesting the appurtenance of aftershocks to fracture zones. Geometrical parameters of fracture zones (strike, dip, and dimensions) hosting individual sequences were calculated and compared with the seafloor morphology of the Cocos Plate. The smooth character of the seafloor correlates with the aftershock fracture zones oriented parallel to the trench and commonly subparallel to the subducting slab, whereas subduction of the Cocos Ridge and seamounts around the Quepos Plateau coincides with steeply dipping fracture zones. Transformed focal mechanisms are almost exclusively (>90%) of normal character.

  7. Internal tectonic structure of the Central American Wadati-Benioff zone based on analysis of aftershock sequences

    NASA Astrophysics Data System (ADS)

    Å PičáK, Aleš; Hanuš, VáClav; VaněK, JiřÃ.­; BěHounková, Marie

    2007-09-01

    Relocated Engdahl et al. (1998) global seismological data for 10 aftershock sequences were used to analyze the internal tectonic structure of the Central American subduction zone; the main shocks of several of these were the most destructive and often referenced earthquakes in the region (e.g., the 1970 Chiapas, 1983 Osa, 1992 Nicaragua, 1999 Quepos, 2001 El Salvador earthquakes). The spatial analysis of aftershock foci distribution was performed in a rotated Cartesian coordinate system (x, y, z) related to the Wadati-Benioff zone, and not in a standard coordinate system (ϕ, λ, h are latitude, longitude, focal depth, respectively). Available fault plane solutions were also transformed into the plane approximating the Wadati-Benioff zone. The spatial distribution of earthquakes in each aftershock sequence was modeled as either a plane fit using a least squares approximation or a volume fit with a minimum thickness rectangular box. The analysis points to a quasi-planar distribution of earthquake foci in all aftershock sequences, manifesting the appurtenance of aftershocks to fracture zones. Geometrical parameters of fracture zones (strike, dip, and dimensions) hosting individual sequences were calculated and compared with the seafloor morphology of the Cocos Plate. The smooth character of the seafloor correlates with the aftershock fracture zones oriented parallel to the trench and commonly subparallel to the subducting slab, whereas subduction of the Cocos Ridge and seamounts around the Quepos Plateau coincides with steeply dipping fracture zones. Transformed focal mechanisms are almost exclusively (>90%) of normal character.

  8. Aftershocks of the june 20, 1978, Greece earthquake: A multimode faulting sequence

    USGS Publications Warehouse

    Carver, D.; Bollinger, G.A.

    1981-01-01

    A 10-station portable seismograph network was deployed in northern Greece to study aftershocks of the magnitude (mb) 6.4 earthquake of June 20, 1978. The main shock occurred (in a graben) about 25 km northeast of the city of Thessaloniki and caused an east-west zone of surface rupturing 14 km long that splayed to 7 km wide at the west end. The hypocenters for 116 aftershocks in the magnitude range from 2.5 to 4.5 were determined. The epicenters for these events cover an area 30 km (east-west) by 18 km (north-south), and focal depths ranges from 4 to 12 km. Most of the aftershocks in the east half of the aftershock zone are north of the surface rupture and north of the graben. Those in the west half are located within the boundaries of the graben. Composite focalmechanism solutions for selected aftershocks indicate reactivation of geologically mapped normal faults in the area. Also, strike-slip and dip-slip faults that splay off the western end of the zone of surface ruptures may have been activated. The epicenters for four large (M ??? 4.8) foreshocks and the main shock were relocated using the method of joint epicenter determination. Collectively, those five epicenters form an arcuate pattern convex southward, that is north of and 5 km distant from the surface rupturing. The 5-km separation, along with a focal depth of 8 km (average aftershock depth) or 16 km (NEIS main-shock depth), implies that the fault plane dips northward 58?? or 73??, respectively. A preferred nodal-plane dip of 36?? was determined by B.C. Papazachos and his colleagues in 1979 from a focal-mechanism solution for the main shock. If this dip is valid for the causal fault and that fault projects to the zone of surface rupturing, a decrease of dip with depth is required. ?? 1981.

  9. Aftershock seismicity of the 2010 Maule Mw=8.8 Chile, earthquake: Correlation between co-seismic slip models and aftershock distribution?

    USGS Publications Warehouse

    Rietbrock, A.; Ryder, I.; Hayes, G.; Haberland, C.; Comte, D.; Roecker, S.

    2012-01-01

    The 27 February 2010 Maule, Chile (Mw=8.8) earthquake is one of the best instrumentally observed subduction zone megathrust events. Here we present locations, magnitudes and cumulative equivalent moment of the first -2 months of aftershocks, recorded on a temporary network deployed within 2 weeks of the occurrence of the mainshock. Using automatically-determined onset times and a back projection approach for event association, we are able to detect over 30,000 events in the time period analyzed. To further increase the location accuracy, we systematically searched for potential S-wave arrivals and events were located in a regional 2D velocity model. Additionally, we calculated regional moment tensors to gain insight into the deformation history of the aftershock sequence. We find that the aftershock seismicity is concentrated between 40 and 140 km distance from the trench over a depth range of 10 to 35 km. Focal mechanisms indicate a predominance of thrust faulting, with occasional normal faulting events. Increased activity is seen in the outer-rise region of the Nazca plate, predominantly in the northern part of the rupture area. Further down-dip, a second band of clustered seismicity, showing mainly thrust motion, is located at depths of 40–45 km. By comparing recent published mainshock source inversions with our aftershock distribution, we discriminate slip models based on the assumption that aftershocks occur in areas of rapid transition between high and low slip, surrounding high-slip regions of the mainshock.

  10. Thermal and mechanical architecture for the SAFARI focal plane assembly

    NASA Astrophysics Data System (ADS)

    Martignac, J.

    2010-07-01

    The very challenging SPICA/SAFARI scientific goals imply to cool most detector solutions below 100 mK. This implies to find reliable solutions providing not only very efficient thermal insulation between the different temperature stages, but also keeping the stray light level well below the foreseen astronomical background (20 aW/pixel !). The main constraint is the available power budget (1-2μW) this value includes optical, electrical and parasitic power loads. This poster describes how the Herschel/PACS Bolometer Focal Plane thermo-mechanical design can be adapted to the new thermal and optical needs, while keeping a sufficiently stiff structure to withstand launch vibrations. We give the first results on the thermal and mechanical behaviour obtained with a prototype.

  11. Mechanotransduction at focal adhesions: integrating cytoskeletal mechanics in migrating cells

    PubMed Central

    Kuo, Jean-Cheng

    2013-01-01

    Focal adhesions (FAs) are complex plasma membrane-associated macromolecular assemblies that serve to physically connect the actin cytoskeleton to integrins that engage with the surrounding extracellular matrix (ECM). FAs undergo maturation wherein they grow and change composition differentially to provide traction and to transduce the signals that drive cell migration, which is crucial to various biological processes, including development, wound healing and cancer metastasis. FA-related signalling networks dynamically modulate the strength of the linkage between integrin and actin and control the organization of the actin cytoskeleton. In this review, we have summarized a number of recent investigations exploring how FA composition is affected by the mechanical forces that transduce signalling networks to modulate cellular function and drive cell migration. Understanding the fundamental mechanisms of how force governs adhesion signalling provides insights that will allow the manipulation of cell migration and help to control migration-related human diseases. PMID:23551528

  12. Full waveform modelling of aftershock seismicity in the Chilean subduction zone using the VERCE platform

    NASA Astrophysics Data System (ADS)

    Garth, T.; Hicks, S. P.; Fuenzalida Velasco, A. J.; Casarotti, E.; Spinuso, A.; Rietbrock, A.

    2014-12-01

    The VERCE platform allows high resolution waveforms to be simulated through an interactive web-based portal. The platform runs on a variety of HPC clusters, and waveforms are calculated using SPECFEM3D. We use the full waveform modelling techniques supported on the VERCE platform to test the validity of a number of subduction zone velocity models from the Chilean subduction zone. Waveforms are calculated for aftershocks of the 2010 Mw 8.8 Maule (central Chile) and the Mw 8.1 2014 Pisagua (Northern Chile) earthquakes. For the Maule region, we use a 2D tomographic model of the rupture area (Hicks et al., 2012), and the focal mechanisms of Agurto et al., (2012). For the Pisagua earthquake, we use a 2.5D composite velocity model based on tomographic studies of the region (e.g. Husen et al., 2000, Contreras-Reyes et al., 2012) and Slab1.0 (Hayes et al., 2012). Focal mechanisms for the Pisagua aftershock sequence are produced from waveforms recorded on the IPOC network using the program ISOLA (Sokos and Zahradnik, 2008). We also test a number of synthetic velocity models. The simulated waveforms are directly compared to waveforms recorded on the temporary deployment for the Maule earthquake aftershocks, and waveforms recorded on the IPOC network for the Pisagua earthquake aftershocks. The waveforms produced by the 3D full waveform simulations are also compared to the waveforms produced by the focal mechanism inversion, which assume a 1D velocity model. The VERCE platform allows waveforms from the full 3D model to be produced easily, and allows us to quantifiably assess the validity of both the velocity model and the source mechanisms. In particular the dependence of the dip of the focal mechanism on the velocity model used is explored, in order to assess the reliability of current models of the plate interface geometry in the Chilean subduction zone.

  13. Basic mechanisms leading to focal emphysema in coal workers' pneumoconiosis

    SciTech Connect

    Rom, W.N. )

    1990-10-01

    Coal miners develop focal emphysema characterized by dilatation of second- and third-order respiratory bronchioles with coal mine dust-laden macrophages infiltrating the wall. A reticulin network with small amounts of collagen and atrophy of smooth muscle occurs. To evaluate the mechanisms of lung injury associated with this lesion, 17 long-term non- or ex-smoking West Virginia underground coal miners underwent bronchoalveolar lavage (BAL) and were compared to healthy nonsmoker and smoker controls. The coal miners had evidence of an alveolar macrophage-neutrophil alveolitis with a significant increase in neutrophils/microliter of epithelial lining fluid and an increased gallium lung scan index (206 +/- 26 units). Alveolar macrophages lavaged from coal miners spontaneously released exaggerated amounts of superoxide anion and hydrogen peroxide in vitro compared to nonsmoking controls. Coal workers had significantly elevated levels of neutrophil elastase in BAL fluid complexed with alpha 1-antitrypsin (P less than 0.01) and normal levels of alpha 1-antitrypsin. An accumulation of activated, dust-laden inflammatory cells with increased release of oxidants and elastase may contribute to the development of focal emphysema identified at postmortem in miners with coal workers' pneumoconiosis.

  14. Stress evolution following the 1999 Chi-Chi, Taiwan, earthquake: Consequences for afterslip, relaxation, aftershocks and departures from Omori decay

    USGS Publications Warehouse

    Chan, C.-H.; Stein, R.S.

    2009-01-01

    We explore how Coulomb stress transfer and viscoelastic relaxation control afterslip and aftershocks in a continental thrust fault system. The 1999 September 21 Mw = 7.6 Chi-Chi shock is typical of continental ramp-d??collement systems throughout the world, and so inferences drawn from this uniquely well-recorded event may be widely applicable. First, we find that the spatial and depth distribution of aftershocks and their focal mechanisms are consistent with the calculated Coulomb stress changes imparted by the coseismic rupture. Some 61 per cent of the M ??? 2 aftershocks and 83 per cent of the M ??? 4 aftershocks lie in regions for which the Coulomb stress increased by ???0.1 bars, and there is a 11-12 per cent gain in the percentage of aftershocks nodal planes on which the shear stress increased over the pre-Chi Chi control period. Second, we find that afterslip occurred where the calculated coseismic stress increased on the fault ramp and d??collement, subject to the condition that friction is high on the ramp and low on the d??collement. Third, viscoelastic relaxation is evident from the fit of the post-seismic GPS data on the footwall. Fourth, we find that the rate of seismicity began to increase during the post-seismic period in an annulus extending east of the main rupture. The spatial extent of the seismicity annulus resembles the calculated ???0.05-bar Coulomb stress increase caused by viscoelastic relaxation and afterslip, and we find a 9-12 per cent gain in the percentage of focal mechanisms with >0.01-bar shear stress increases imparted by the post-seismic afterslip and relaxation in comparison to the control period. Thus, we argue that post-seismic stress changes can for the first time be shown to alter the production of aftershocks, as judged by their rate, spatial distribution, and focal mechanisms. ?? Journal compilation ?? 2009 RAS.

  15. Spectral scaling of the aftershocks of the Tocopilla 2007 earthquake in northern Chile

    NASA Astrophysics Data System (ADS)

    Lancieri, M.; Madariaga, R.; Bonilla, F.

    2012-04-01

    We study the scaling of spectral properties of a set of 68 aftershocks of the 2007 November 14 Tocopilla (M 7.8) earthquake in northern Chile. These are all subduction events with similar reverse faulting focal mechanism that were recorded by a homogenous network of continuously recording strong motion instruments. The seismic moment and the corner frequency are obtained assuming that the aftershocks satisfy an inverse omega-square spectral decay; radiated energy is computed integrating the square velocity spectrum corrected for attenuation at high frequencies and for the finite bandwidth effect. Using a graphical approach, we test the scaling of seismic spectrum, and the scale invariance of the apparent stress drop with the earthquake size. To test whether the Tocopilla aftershocks scale with a single parameter, we introduce a non-dimensional number, ?, that should be constant if earthquakes are self-similar. For the Tocopilla aftershocks, Cr varies by a factor of 2. More interestingly, Cr for the aftershocks is close to 2, the value that is expected for events that are approximately modelled by a circular crack. Thus, in spite of obvious differences in waveforms, the aftershocks of the Tocopilla earthquake are self-similar. The main shock is different because its records contain large near-field waves. Finally, we investigate the scaling of energy release rate, Gc, with the slip. We estimated Gc from our previous estimates of the source parameters, assuming a simple circular crack model. We find that Gc values scale with the slip, and are in good agreement with those found by Abercrombie and Rice for the Northridge aftershocks.

  16. Direct simulation Monte Carlo method with a focal mechanism algorithm

    NASA Astrophysics Data System (ADS)

    Rachman, Asep Nur; Chung, Tae Woong; Yoshimoto, Kazuo; Yun, Sukyoung

    2015-01-01

    To simulate the observation of the radiation pattern of an earthquake, the direct simulation Monte Carlo (DSMC) method is modified by implanting a focal mechanism algorithm. We compare the results of the modified DSMC method (DSMC-2) with those of the original DSMC method (DSMC-1). DSMC-2 shows more or similarly reliable results compared to those of DSMC-1, for events with 12 or more recorded stations, by weighting twice for hypocentral distance of less than 80 km. Not only the number of stations, but also other factors such as rough topography, magnitude of event, and the analysis method influence the reliability of DSMC-2. The most reliable result by DSMC-2 is obtained by the best azimuthal coverage by the largest number of stations. The DSMC-2 method requires shorter time steps and a larger number of particles than those of DSMC-1 to capture a sufficient number of arrived particles in the small-sized receiver.

  17. Inversions for earthquake focal mechanisms and regional stress in the Kachchh Rift Basin, western India: Tectonic implications

    NASA Astrophysics Data System (ADS)

    Singh, A. P.; Zhao, L.; Kumar, Santsoh; Mishra, Smita

    2016-03-01

    More than a decade after the 2001 MW 7.7 Bhuj earthquake in western India, aftershocks up to MW 5.0 are still continuing around the rupture zone in the Kachchh Rift Basin. Over the years, some surrounding faults in the region have been activated, and a transverse fault generated an MW 5.1 earthquake in 2012. Most of the earthquakes occur in the lower crust at depths between 15 and 35 km. We have determined focal mechanism solutions of 47 earthquakes (MW 3.2-5.1) that were recorded by a 60-station broadband network during 2007-2014 within an area of 50 km radius of the 2001 main shock. South dipping nodal planes in most of the solutions correlate well with the active faults. The earthquakes near the epicenter of the 2001 main shock primarily show reverse-faulting mechanisms. The surrounding earthquakes in the area, however, show predominantly strike-slip mechanisms. The P axes of the earthquakes mostly oriented in north-south, and the T axes in east-west. However, the orientations of the P and T axes exhibit more complexity near the source area of the main shock. Stress field inversion of the solutions yields a dominant north-south compression, which is consistent with the ambient tectonic stress field owing to the northward movement of the Indian Plate with respect to the Eurasian Plate. The geodetic measurements are in reasonable agreement with our results.

  18. Comparative Study Of Focal Mechanisms In South Central Chile Before And After The 2010 Maule Earthquake

    NASA Astrophysics Data System (ADS)

    Agurto, H.; Rietbrock, A.; Ryder, I. M.; Haberland, C. A.

    2011-12-01

    On 27 February 2010, a Mw=8.8 earthquake occurred off the coast of south central Chile rupturing nearly 500 km of the subduction zone plate interface. The earthquake also generated a tsunami and caused more than 500 fatalities. The largest earthquakes recorded have taken place along subduction margins (e.g. Chile 1960, 2010, Andaman-Sumatra 2004, Japan 2011) and understanding their rupture mechanisms and deformation regimes is therefore of vital importance. From November 2004 to October 2005, the TIPTEQ project ("From The Incoming Plate to megaThrust EarthQuake"; Rietbrock et al., 2007; Haberland et al., 2009) maintained a network of 120 seismic stations inland and 10 stations at sea between 37 and 39° lat. S., continuously-recording and monitoring the seismicity occurring in the area before the 2010 Maule earthquake. By using first motion polarities and moment tensor inversion we have computed and analyzed focal mechanisms for a subset of data from these records. We found thrust faulting along the subduction interface down to a depth of ~30 km, followed by a gap in the seismicity and then deeper earthquakes showing diverse faulting mechanisms more sparsely distributed within the subducting plate. We also see strike-slip crustal faulting occurring down to ~12 km depth within the area of the Lanalhue fault. The most striking observation is the presence of deep (40 km) normal faulting seismicity in the fore-arc, close to the trench. We have now started to analyze the International Maule Aftershocks Dataset (IMAD) of the 2010 earthquake in the southern rupture region. Again we observe thrust faulting in the subduction interface and a seismic gap between an upper and lower zone of seismicity along the interface. By comparison of the pre- and post-earthquake datasets we are investigating whether the Maule earthquake caused any changes in the style of deformation in this part of Chile. References Haberland, C., A. Rietbrock, D. Lange, K. Bataille, and T. Dahm (2009

  19. The Importance of Small Aftershocks for Earthquake Triggering

    NASA Astrophysics Data System (ADS)

    Woessner, Jochen; Meier, Men-Andrin; Werner, Max; Wiemer, Stefan

    2013-04-01

    Earthquakes occur in response to changes in the crust's stress state, however, the full picture of the causative process for earthquake triggering remains unclear. Many researchers have employed Coulomb stress change theory, which quantifies the changes in static Coulomb stress from nearby ruptures. This theory seems to at least partly explain the spatial patterns of triggered earthquakes, in particular during aftershock sequences and along faults. Several assumptions are needed to facilitate the calculation of stress changes. Here, we challenge the typical neglect of stress changes induced by the small but numerous and strongly clustered aftershocks during the evolution of the sequence. Both empirical observations and a simple scaling law suggest that this neglect may not be justified. We estimate the evolution of Coulomb stress changes during the 1992 Mw 7.3 Landers earthquake sequence by including the effect of the detected aftershocks using the focal mechanisms from the recently updated Southern California catalog. This estimation is hampered by that only 62% of located events from our study window have a focal mechanism, by the neglect of events that are too small to be detected and by the unreliability of near-field stress change estimations. As a consequence, we are limited to analyzing only a part of the full stress change signal imparted by small events. Despite these shortcomings, our calculations suggest that small to moderate events strongly dominate static stress redistribution in dense secondary aftershock clusters. However, their relative importance varies over space and is, on average, smaller than the main shock contribution. Furthermore, we find that aftershocks - with their reported relative orientations and positions - impose more often positive than negative stress changes, which is what would be expected if they were actively involved in triggering processes. However, this effect appears to be limited to event pairs with inter-event distances

  20. Aftershock activity of the 2015 Gorkha, Nepal, earthquake determined using the Kathmandu strong motion seismographic array

    NASA Astrophysics Data System (ADS)

    Ichiyanagi, Masayoshi; Takai, Nobuo; Shigefuji, Michiko; Bijukchhen, Subeg; Sasatani, Tsutomu; Rajaure, Sudhir; Dhital, Megh Raj; Takahashi, Hiroaki

    2016-02-01

    The characteristics of aftershock activity of the 2015 Gorkha, Nepal, earthquake (Mw 7.8) were evaluated. The mainshock and aftershocks were recorded continuously by the international Kathmandu strong motion seismographic array operated by Hokkaido University and Tribhuvan University. Full waveform data without saturation for all events enabled us to clarify aftershock locations and decay characteristics. The aftershock distribution was determined using the estimated local velocity structure. The hypocenter distribution in the Kathmandu metropolitan region was well determined and indicated earthquakes located shallower than 12 km depth, suggesting that aftershocks occurred at depths shallower than the Himalayan main thrust fault. Although numerical investigation suggested less resolution for the depth component, the regional aftershock epicentral distribution of the entire focal region clearly indicated earthquakes concentrated in the eastern margin of the major slip region of the mainshock. The calculated modified Omori law's p value of 1.35 suggests rapid aftershock decay and a possible high temperature structure in the aftershock region.

  1. Tsunami potential assessment based on rupture zones, focal mechanisms and repeat times of strong earthquakes in the major Atlantic-Mediterranean seismic fracture zone

    NASA Astrophysics Data System (ADS)

    Agalos, Apostolos; Papadopoulos, Gerassimos A.; Kijko, Andrzej; Papageorgiou, Antonia; Smit, Ansie; Triantafyllou, Ioanna

    2016-04-01

    In the major Atlantic-Mediterranean seismic fracture zone, extended from Azores islands in the west to the easternmost Mediterranean Sea in the east, including the Marmara and Black Seas, a number of 22 tsunamigenic zones have been determined from historical and instrumental tsunami documentation. Although some tsunamis were produced by volcanic activity or landslides, the majority of them was generated by strong earthquakes. Since the generation of seismic tsunamis depends on several factors, like the earthquake size, focal depth and focal mechanism, the study of such parameters is of particular importance for the assessment of the potential for the generation of future tsunamis. However, one may not rule out the possibility for tsunami generation in areas outside of the 22 zones determined so far. For the Atlantic-Mediterranean seismic fracture zone we have compiled a catalogue of strong, potentially tsunamigenic (focal depth less than 100 km) historical earthquakes from various data bases and other sources. The lateral areas of rupture zones of these earthquakes were determined. Rupture zone is the area where the strain after the earthquake has dropped substantially with respect the strain before the earthquake. Aftershock areas were assumed to determine areas of rupture zones for instrumental earthquakes. For historical earthquakes macroseismic criteria were used such as spots of higher-degree seismic intensity and of important ground failures. For the period of instrumental seismicity, focal mechanism solutions from CMT, EMMA and other data bases were selected for strong earthquakes. From the geographical distribution of seismic rupture zones and the corresponding focal mechanisms in the entire Atlantic-Mediterranean seismic fracture zone we determined potentially tsunamigenic zones regardless they are known to have produced seismic tsunamis in the past or not. An attempt has been made to calculate in each one of such zones the repeat times of strong

  2. Focal contacts as mechanosensors: externally applied local mechanical force induces growth of focal contacts by an mDia1-dependent and ROCK-independent mechanism.

    PubMed

    Riveline, D; Zamir, E; Balaban, N Q; Schwarz, U S; Ishizaki, T; Narumiya, S; Kam, Z; Geiger, B; Bershadsky, A D

    2001-06-11

    The transition of cell-matrix adhesions from the initial punctate focal complexes into the mature elongated form, known as focal contacts, requires GTPase Rho activity. In particular, activation of myosin II-driven contractility by a Rho target known as Rho-associated kinase (ROCK) was shown to be essential for focal contact formation. To dissect the mechanism of Rho-dependent induction of focal contacts and to elucidate the role of cell contractility, we applied mechanical force to vinculin-containing dot-like adhesions at the cell edge using a micropipette. Local centripetal pulling led to local assembly and elongation of these structures and to their development into streak-like focal contacts, as revealed by the dynamics of green fluorescent protein-tagged vinculin or paxillin and interference reflection microscopy. Inhibition of Rho activity by C3 transferase suppressed this force-induced focal contact formation. However, constitutively active mutants of another Rho target, the formin homology protein mDia1 (Watanabe, N., T. Kato, A. Fujita, T. Ishizaki, and S. Narumiya. 1999. Nat. Cell Biol. 1:136-143), were sufficient to restore force-induced focal contact formation in C3 transferase-treated cells. Force-induced formation of the focal contacts still occurred in cells subjected to myosin II and ROCK inhibition. Thus, as long as mDia1 is active, external tension force bypasses the requirement for ROCK-mediated myosin II contractility in the induction of focal contacts. Our experiments show that integrin-containing focal complexes behave as individual mechanosensors exhibiting directional assembly in response to local force. PMID:11402062

  3. Full waveform modelling using the VERCE platform - application to aftershock seismicity in the Chile subduction zone

    NASA Astrophysics Data System (ADS)

    Garth, Thomas; Rietbrock, Andreas; Hicks, Steve; Fuenzalida Velasco, Amaya; Casarotti, Emanuele; Spinuso, Alessandro

    2015-04-01

    The VERCE platform is an online portal that allows full waveform simulations to be run for any region where a suitable velocity model exists. We use this facility to simulate the waveforms from aftershock earthquakes from the 2014 Pisagua earthquake, and 2010 Maule earthquake that occurred at the subduction zone mega thrust in Northern and Central Chile respectively. Simulations are performed using focal mechanisms from both global earthquake catalogues, and regional earthquake catalogues. The VERCE platform supports specFEM Cartesian, and simulations are run using meshes produced by CUBIT. The full waveform modelling techniques supported on the VERCE platform are used to test the validity of a number of subduction zone velocity models from the Chilean subduction zone. For the Maule earthquake we use a 2D and 3D travel time tomography model of the rupture area (Hicks et al. 2011; 2014). For the Pisagua earthquake we test a 2D/3D composite velocity model based on tomographic studies of the region (e.g. Husen et al. 2000, Contreyes-Reyes et al. 2012) and slab1.0 (Hayes et al. 2012). Focal mechanisms from the cGMT catalogue and local focal mechanisms calculated using ISOLA (e.g. Agurto et al. 2012) are used in the simulations. The waveforms produced are directly compared to waveforms recorded on the temporary deployment for the Maule earthquake aftershocks, and waveforms recorded on the IPOC network for the Pisagua earthquake aftershocks. This work demonstrates how the VERCE platform allows waveforms from the full 3D simulations to be easily produced, allowing us to quantify the validity of both the velocity model and the source mechanisms. These simulations therefore provide an independent test of the velocity models produced synthetically and by travel time tomography studies. Initial results show that the waveform is reasonably well reproduced in the 0.05 - 0.25 frequency band using a refined 3D travel time tomography, and locally calculated focal mechanisms.

  4. Seismotectonic model of the MITIDJA basin using gravity data and aftershock sequence of the BOUMERDES (may 21, 2003; ALGERIA) earthquake

    NASA Astrophysics Data System (ADS)

    Ouyed, Merzouk; Idres, Mouloud; Salah Boughacha, Mohame; Bourmatte, Amar; Samai, Saddek

    2010-05-01

    The present study relates to the interpretation of gravity and seismological data in the Boumerdes area (Eastern part of the Mitidja Basin, Algeria), in relation to the earthquake of May 21, 2003 (Mw=6.8). The residual anomaly and the horizontal gradient maps made it possible to obtain the basement shape and gravity discontinuities. The seismological data processing of the aftershock sequence recorded by 16 tri-component seismological stations allowed the location of 1987 events during the period of May 23 to June 30, 2003. A seismotectonic model obtained from the aftershocks distribution and gravity data is proposed. This model consists of three active faults; one lying offshore and two other onshore faults highlighted in this study. The offshore fault striking NE-SW is consistent with the USGS focal mechanism of the main event; the onshore faults strike NW-SE. This configuration emphasizes the failure mode complexity during the main shock. The geometry and location of the onshore faults are obtained from the spatial distribution of seismicity and focal solutions, supported by the results of gravity, but also by the coastal uplift and the Algiers canyon close to one of these faults. The topography of the basement obtained by 3D gravity inversion shows that all the aftershocks located onshore occurred in the basement. The 3D model of the basement also shows that the area between the two onshore faults was raised by their movement. Keywords: Aftershock sequence, Algeria, Basement, Boumerdes earthquake, Gravity

  5. Composite focal mechanism for microearthquakes along the northeastern border of the Caribbean plate

    SciTech Connect

    Frankel, A.

    1982-05-01

    Seismograms from a local seismic network in the Virgin Islands portion of the northeastern Caribbean are used to determine a composite focal mechanism for 26 microearthquakes along the North America--Caribbean plate boundary. Only one nodal plane of the focal mechanism could be constrained from P-wave first motion data alone. P/SV amplitude ratios observed for these events were compared to theoretical amplitude ratios calculated for different focal mechanisms. This procedure constrained the dip of the second nodal plane to be shallower than about 50/sup 0/, ruling out the possibility of a transform fault in this portion of the plate boundary. The resulting focal mechanism indicates that oblique underthrusting of the North American plate beneath the Caribbean plate occurs in the area. This oblique motion is accommodated along a thrust plane that dips at a relatively shallow angle beneath the Virgin Islands platform.

  6. Static stress triggering explains the empirical aftershock distance decay

    NASA Astrophysics Data System (ADS)

    Hainzl, Sebastian; Moradpour, Javad; Davidsen, Jörn

    2014-12-01

    The shape of the spatial aftershock decay is sensitive to the triggering mechanism and thus particularly useful for discriminating between static and dynamic stress triggering. For California seismicity, it has been recently recognized that its form is more complicated than typically assumed consisting of three different regimes with transitions at the scale of the rupture length and the thickness of the crust. The intermediate distance range is characterized by a relative small decay exponent of 1.35 previously declared to relate to dynamic stress triggering. We perform comprehensive simulations of a simple clock-advance model, in which the number of aftershocks is just proportional to the Coulomb-stress change, to test whether the empirical result can be explained by static stress triggering. Similarly to the observations, the results show three scaling regimes. For simulations adapted to the depths and focal mechanisms observed in California, we find a remarkable agreement with the observation over the whole distance range for a fault distribution with fractal dimension of 1.8, which is shown to be in good agreement with an independent analysis of California seismicity.

  7. A New Set of Focal Mechanisms and a Geodynamic Model for the Eastern Tennessee Seismic Zone

    NASA Astrophysics Data System (ADS)

    Cooley, M. T.; Powell, C. A.; Choi, E.

    2014-12-01

    We present a new set of 26 focal mechanisms for the eastern Tennessee seismic zone (ETSZ) and discuss the implications for regional uplift. The mechanisms are for earthquakes with magnitudes 2.5 and greater occurring after 1999. The ETSZ is the second largest seismic zone in the central and eastern US and the seismicity is attributed to reactivation of a major Grenville-age shear zone. P- and S- wave velocity models, the distribution of hypocenters, focal mechanisms, and potential field anomalies suggest the presence of a basement shear zone. The new focal mechanism solutions supplement and are consistent with a previously calculated set of 26 focal mechanisms for the period 1983-1993. Focal mechanisms fall into two groups. The first group shows strike-slip motion on steeply dipping nodal planes striking N-S/E-W and NE-SW/NW-SE. Mechanisms in the second group display primarily dip-slip motion and are constrained geographically to the southern portion of the seismic zone. Events in the second group are among the shallowest in the dataset (8-12 km). We are developing a geodynamic model of the regional structure to examine the stress regime, which may be changing with depth. This model will be used to determine a possible relationship between the localized normal faulting and previously established recent regional uplift.

  8. Comparison of Early Aftershocks for the 2004 Mid-Niigata and 2007 Noto Hanto Earthquakes in Japan

    NASA Astrophysics Data System (ADS)

    Mori, J.; Kano, Y.; Enescu, B.

    2007-12-01

    We compared the aftershock sequences of the similar 2004 Mid-Niigata (Mw6.6) and 2007 Noto Hanto (Mw6.7) earthquakes in central Japan. Although the two mainshocks had similar size, depth, and focal mechanisms, the numbers of aftershocks were quite different, with the Niigata mainshock producing a much stronger sequence. We examined the continuously recorded data from nearby Hi-Net stations operated by the National Institute for Earth Science and Disaster Prevention (NIED), to identify the early aftershocks following both mainshocks. A 5 hz high-pass filter was chosen to facilitate identification of the high-frequency arrivals from individual aftershocks. We used 6 stations distributed at distances within about 30 km. Aftershocks were identified by looking at large printouts of the continuous records for the six stations and peak amplitudes were measured to calculate the magnitude. The magnitude determination using these high-pass filtered records was calibrated by using a set of 30 earthquakes that were also listed in the catalog of the Japan Meteorological Agency (JMA). We estimate that the completeness level of small aftershocks is about Mj3.5. The event counts show that the aftershock sequences of the two earthquakes were quite similar for about the first 7 minutes. Following that time, the Niigata aftershocks clearly continue at a much higher rate which is about 3 times the rate of the Noto earthquake. The time where the rates diverge corresponds to the occurrence of a Mj6.3 earthquake in the Niigata sequence. This pattern can be seen in both the plots for the Mj¡Ý3.5 and Mj¡Ý4.0 events. Since there are more earthquakes for the Mj¡Ý3.5 data set, the time resolution is better. These results show an enhanced triggering of aftershocks for the Niigata sequence several minutes after the mainshock. The Niigata region is an area of hydrocarbon production with regions of high pressure fluids, and Sibson (2007) proposes that the swarm-like behavior is due to

  9. Retrograde Fluxes of Focal Adhesion Proteins in Response to Cell Migration and Mechanical Signals

    PubMed Central

    Guo, Wei-hui

    2007-01-01

    Recent studies suggest that mechanical signals mediated by the extracellular matrix play an essential role in various physiological and pathological processes; yet, how cells respond to mechanical stimuli remains elusive. Using live cell fluorescence imaging, we found that actin filaments, in association with a number of focal adhesion proteins, including zyxin and vasodilator-stimulated phosphoprotein, undergo retrograde fluxes at focal adhesions in the lamella region. This flux is inversely related to cell migration, such that it is amplified in fibroblasts immobilized on micropatterned islands. In addition, the flux is regulated by mechanical signals, including stretching forces applied to flexible substrates and substrate stiffness. Conditions favoring the flux share the common feature of causing large retrograde displacements of the interior actin cytoskeleton relative to the substrate anchorage site, which may function as a switch translating mechanical input into chemical signals, such as tyrosine phosphorylation. In turn, the stimulation of actin flux at focal adhesions may function as part of a feedback mechanism, regulating structural assembly and force production in relation to cell migration and mechanical load. The retrograde transport of associated focal adhesion proteins may play additional roles in delivering signals from focal adhesions to the interior of the cell. PMID:17804814

  10. Local near instantaneously dynamically triggered aftershocks of large earthquakes.

    PubMed

    Fan, Wenyuan; Shearer, Peter M

    2016-09-01

    Aftershocks are often triggered by static- and/or dynamic-stress changes caused by mainshocks. The relative importance of the two triggering mechanisms is controversial at near-to-intermediate distances. We detected and located 48 previously unidentified large early aftershocks triggered by earthquakes with magnitudes between ≥7 and 8 within a few fault lengths (approximately 300 kilometers), during times that high-amplitude surface waves arrive from the mainshock (less than 200 seconds). The observations indicate that near-to-intermediate-field dynamic triggering commonly exists and fundamentally promotes aftershock occurrence. The mainshocks and their nearby early aftershocks are located at major subduction zones and continental boundaries, and mainshocks with all types of faulting-mechanisms (normal, reverse, and strike-slip) can trigger early aftershocks. PMID:27609887

  11. Early aftershock statistics

    NASA Astrophysics Data System (ADS)

    Narteau, C.; Shebalin, P.; Holschneider, M.; Schorlemmer, D.

    2009-04-01

    In the Limited Power Law model (LPL) we consider that after a triggering event - the so-called mainshock - rocks subject to sufficiently large differential stress can fail spontaneously by static fatigue. Then, earlier aftershocks occur in zones of highest stress and the c-value, i.e. the delay before the onset of the power-law aftershock decay rate, depends on the amplitude of the stress perturbation in the aftershock zone. If we assume that this stress perturbation is proportional to the absolute level of stress in the area, the model also predicts that shorter delay occur in zones of higher stress. Here, we present two analyses that support such a prediction. In these analyses, we use only aftershocks of 2.5 < M < 4.5 earthquakes to avoid well-known artifacts resulting from overlapping records. First, we analyze the c-value across different types of faulting in southern California to compare with the differential shear stress predicted by a Mohr-Coulomb failure criterion. As expected, we find that the c-value is on average shorter for thrust earthquakes (high stress) than for normal ones (low stress), taking intermediate values for strike-slip earthquakes (intermediate stress). Second, we test the hypothesis that large earthquakes occur in zones where the level of stress is abnormally high. Instead of the c-value we use the < t >-value, the geometric average of early aftershock times. One more time, we observed that M > 5 earthquakes occur where and when the < t >-value is small. This effect is even stronger for M > 6 earthquakes.

  12. Focal mechanisms of small earthquakes and the stress field in the western Quebec Adirondack region

    NASA Astrophysics Data System (ADS)

    Mareschal, Jean-Claude; Zhu, Pei-Ding

    1989-09-01

    Focal mechanisms were determined for 42 small earthquakes (1.4 < M < 3.4) that occurred in the Adirondacks-western Quebec seismic region. The analysis demonstrates the variability of the focal mechanisms and suggests that the region can be divided into two subprovinces with distinctive seismotectonic regimes: (1) in the Adirondacks, the focal mechanisms are mostly strike-slip with a comparatively smaller thrust component and indicate NNE compression: (2) in the western Quebec seismic region, the stress field is more heterogeneous and is dominated by two directions (NE and NW) of horizontal compression. This variable pattern suggests that the seismicity and stress field are controlled by regional plate stresses but are affected by local structures and/or by the predominant orientation of preexisting faults.

  13. Focal mechanisms and the stress regime in NE and SW Tanzania, East Africa

    NASA Astrophysics Data System (ADS)

    Brazier, Richard A.; Nyblade, Andrew A.; Florentin, Juliette

    2005-07-01

    We report 12 new focal mechanisms from earthquakes in NE and SW Tanzania where the stress regime within the East African rift system is not well constrained. Focal mechanisms for events at the intersection of the Lake Tanganyika and Rukwa rifts in SW Tanzania indicate a complicated stress pattern with possible dextral strike-slip motion on some faults but oblique motion on others (either sinistral on NW striking faults or dextral on NE striking faults). Within the Rukwa rift, focal mechanisms indicate normal dip-slip motion with NE-SW opening. In NE Tanzania where the Eastern rift impinges on the margin of the Tanzania Craton, fault motions are consistent with a zone of distributed block faults and sub E-W extension. All twelve earthquakes likely nucleated within the crust.

  14. The Mw 8.1 2014 Iquique, Chile, seismic sequence: a tale of foreshocks and aftershocks

    NASA Astrophysics Data System (ADS)

    Cesca, S.; Grigoli, F.; Heimann, S.; Dahm, T.; Kriegerowski, M.; Sobiesiak, M.; Tassara, C.; Olcay, M.

    2016-03-01

    The 2014 April 1, Mw 8.1 Iquique (Chile) earthquake struck in the Northern Chile seismic gap. With a rupture length of less than 200 km, it left unbroken large segments of the former gap. Early studies were able to model the main rupture features but results are ambiguous with respect to the role of aseismic slip and left open questions on the remaining hazard at the Northern Chile gap. A striking observation of the 2014 earthquake has been its extensive preparation phase, with more than 1300 events with magnitude above ML 3, occurring during the 15 months preceding the main shock. Increasing seismicity rates and observed peak magnitudes accompanied the last three weeks before the main shock. Thanks to the large data sets of regional recordings, we assess the precursor activity, compare foreshocks and aftershocks and model rupture preparation and rupture effects. To tackle inversion challenges for moderate events with an asymmetric network geometry, we use full waveforms techniques to locate events, map the seismicity rate and derive source parameters, obtaining moment tensors for more than 300 events (magnitudes Mw 4.0-8.1) in the period 2013 January 1-2014 April 30. This unique data set of fore- and aftershocks is investigated to distinguish rupture process models and models of strain and stress rotation during an earthquake. Results indicate that the spatial distributions of foreshocks delineated the shallower part of the rupture areas of the main shock and its largest aftershock, well matching the spatial extension of the aftershocks cloud. Most moment tensors correspond to almost pure double couple thrust mechanisms, consistent with the slab orientation. Whereas no significant differences are observed among thrust mechanisms in different areas, nor among thrust foreshocks and aftershocks, the early aftershock sequence is characterized by the presence of normal fault mechanisms, striking parallel to the trench but dipping westward. These events likely occurred

  15. Analysis of rupture area of aftershocks caused by twin earthquakes (Case study: 11 April 2012 earthquakes of Aceh-North Sumatra)

    NASA Astrophysics Data System (ADS)

    Diansari, Angga Vertika; Purwana, Ibnu; Subakti, Hendri

    2015-04-01

    The 11 April 2012 earthquakes off-shore Aceh-North Sumatra are unique events for the history of Indonesian earthquake. It is unique because that they have similar magnitude, 8.5 Mw and 8.1 Mw; close to epicenter distance, similar strike-slip focal mechanism, and occuring in outer rise area. The purposes of this research are: (1) comparing area of earthquakes base on models and that of calculation, (2) fitting the shape and the area of earthquake rupture zones, (3) analyzing the relationship between rupture area and magnitude of the earthquakes. Rupture area of the earthquake fault are determined by using 4 different formulas, i.e. Utsu and Seki (1954), Wells and Coppersmith (1994), Ellsworth (2003), and Christophersen and Smith (2000). The earthquakes aftershock parameters are taken from PGN (PusatGempabumiNasional or National Earthquake Information Center) of BMKG (Indonesia Agency Meteorology Climatology and Geophysics). The aftershock epicenters are plotted by GMT's software. After that, ellipse and rectangular models of aftershock spreading are made. The results show that: (1) rupture areas were calculated using magnitude relationship which are larger than the the aftershock distributions model, (2) the best fitting model for that earthquake aftershock distribution is rectangular associated with Utsu and Seki (1954) formula, (3) the larger the magnitude of the earthquake, the larger area of the fault.

  16. Analysis of rupture area of aftershocks caused by twin earthquakes (Case study: 11 April 2012 earthquakes of Aceh-North Sumatra)

    SciTech Connect

    Diansari, Angga Vertika Purwana, Ibnu; Subakti, Hendri

    2015-04-24

    The 11 April 2012 earthquakes off-shore Aceh-North Sumatra are unique events for the history of Indonesian earthquake. It is unique because that they have similar magnitude, 8.5 Mw and 8.1 Mw; close to epicenter distance, similar strike-slip focal mechanism, and occuring in outer rise area. The purposes of this research are: (1) comparing area of earthquakes base on models and that of calculation, (2) fitting the shape and the area of earthquake rupture zones, (3) analyzing the relationship between rupture area and magnitude of the earthquakes. Rupture area of the earthquake fault are determined by using 4 different formulas, i.e. Utsu and Seki (1954), Wells and Coppersmith (1994), Ellsworth (2003), and Christophersen and Smith (2000). The earthquakes aftershock parameters are taken from PGN (PusatGempabumiNasional or National Earthquake Information Center) of BMKG (Indonesia Agency Meteorology Climatology and Geophysics). The aftershock epicenters are plotted by GMT’s software. After that, ellipse and rectangular models of aftershock spreading are made. The results show that: (1) rupture areas were calculated using magnitude relationship which are larger than the the aftershock distributions model, (2) the best fitting model for that earthquake aftershock distribution is rectangular associated with Utsu and Seki (1954) formula, (3) the larger the magnitude of the earthquake, the larger area of the fault.

  17. Aftershock relocation and frequency-size distribution, stress inversion and seismotectonic setting of the 7 August 2013 M = 5.4 earthquake in Kallidromon Mountain, central Greece

    NASA Astrophysics Data System (ADS)

    Ganas, Athanassios; Karastathis, Vassilios; Moshou, Alexandra; Valkaniotis, Sotirios; Mouzakiotis, Evangelos; Papathanassiou, George

    2014-03-01

    On August 7, 2013 a moderate earthquake (NOA ML = 5.1, NOA Mw = 5.4) occurred in central Kallidromon Mountain, in the Pthiotis region of central Greece. 2270 aftershocks were relocated using a modified 1-D velocity model for this area. The b-value of the aftershock sequence was b = 0.85 for a completeness magnitude of Mc = 1.7. The rate of aftershock decay was determined at p = 0.63. The spatial distribution of the aftershock sequence points towards the reactivation of a N70° ± 10°E striking normal fault at crustal depths between 8 and 13 km. A NNW-SSE cross-section imaged the activation of a steep, south dipping normal fault. A stress inversion analysis of 12 focal mechanisms showed that the minimum horizontal stress is extensional at N173°E. No primary surface ruptures were observed in the field; however, the earthquake caused severe damage in the villages of the Kallidromon area. The imaged fault strike and the orientation of the long-axis of the aftershock sequence distribution are both at a high-angle to the strike of known active faults in this area of central Greece. We interpret the Kallidromon seismic sequence as release of extensional seismic strain on secondary, steep faults inside the Fokida-Viotia crustal block.

  18. Types Of The Focal Mechanisms Of Seismic Events In The Khibiny Massif

    NASA Astrophysics Data System (ADS)

    Fedotova, I. V.; Yunga, S. L.

    The stress-strain state of Khibiny massif and the focal mechanisms of microseismic events (magnitudes as many M=1) were investigated. This analysis was based on seis- mical data registered by automized monitoring system of in the ore mines "Apatite" as well as on the catalogue of earthquakes registered by Kola regional seismological centre. The main goal of this study is the estimation of applicability of methods of quantitative seismology for a solution of local tasks of prognosis of the dynamic phe- nomena in the ore mines of Khibiny massif during widescale mining operations. On the basis of the existing methods original computer programs were developed. Taking into account features of local monitoring systems of seismicity and collection of the obtained data on focal mechanisms, calculations of matrix of mean "composite" focal mechanisms of the registered seismic events were carried out. The process of grouping of events was based on revealing of similar focal mechanisms. Eigen value analysis of average matrix was performed and the directions of main stresses and tendency of principal deformation directions in the massif are revealed. Thus schema of relative blocks movements is created. As a result of this study 5 basic groups with different types of focal mechanisms of seismic events are selected: normal fault; strike-slip fault (with contraction along the strike of ore bodies), thrust fault, and two interme- diate types - strike-slip with normal movement and strike-slip with upthrust move- ment. Specific structural blocks are revealed on the basis of schema of fault zones and zones of tectonic weakness and analysis of seismic events with the particular focal mechanisms. The directions of main stresses based on the composite focal mecha- nisms well correlates with the directions obtained by other methods. Composite focal mechanisms determined for low magnitude seismic events may be effectively used to control stress-strain state in rock massif, to select

  19. Attempt to identify seismic sources in the eastern Mitidja basin using gravity data and aftershock sequence of the Boumerdes (May 21, 2003; Algeria) earthquake

    NASA Astrophysics Data System (ADS)

    Ouyed, Merzouk; Idres, Mouloud; Bourmatte, Amar; Boughacha, Mohamed Salah; Samai, Sadek; Yelles, Abdelkrim; Haned, Abderrahmene; Aidi, Chafik

    2011-04-01

    In order to try to identify the seismogenic sources in the epicentral area, we interpreted data collected from gravity and aftershocks in the eastern part of the Mitidja basin after the occurrence of the 21 May 2003 Boumerdes earthquake (Mw = 6.8). The residual gravity anomaly and the horizontal gradient maps revealed the basement shape and density discontinuities. A seismotectonic model obtained from the aftershocks distribution and gravity data is proposed. This model highlights three active faults: one offshore and two onshore. The offshore reverse fault striking NE-SW, parallel to the coast, is consistent with the USGS focal mechanism of the main event, which is assumed to have the most moment release. The two onshore dipping blind active faults are postulated at crossing angles near the SW tip of the main fault. The interpretation is based mainly on the re-location and distribution of aftershocks, and their focal solutions. It is also supported by the basin structures obtained from the inversion and interpretation of residual gravity anomalies, as well as by additional compiled information such as the pattern of coastal co-seismic uplift. This configuration puts forward the failure mode complexity during the main shock. The topography of the basement obtained from 3D gravity inversion shows that all the onshore located aftershocks occurred in the basement, and the area between the two onshore faults rose as a consequence of their sliding.

  20. Insights on earthquake triggering processes from early aftershocks of repeating microearthquakes

    NASA Astrophysics Data System (ADS)

    Lengliné, O.; Ampuero, J.-P.

    2015-10-01

    Characterizing the evolution of seismicity rate of early aftershocks can yield important information about earthquake nucleation and triggering. However, this task is challenging because early aftershock seismic signals are obscured by those of the mainshock. Previous studies of early aftershocks employed high-pass filtering and template matching but had limited performance and completeness at very short times. Here we take advantage of repeating events previously identified on the San Andreas Fault at Parkfield and apply empirical Green's function deconvolution techniques. Both Landweber and sparse deconvolution methods reveal the occurrence of aftershocks as early as few tenths of a second after the mainshock. These events occur close to their mainshock, within one to two rupture lengths away. The aftershock rate derived from this enhanced catalog is consistent with Omori's law, with no flattening of the aftershock rate down to the shortest resolvable timescale ˜0.3 s. The early aftershock rate decay determined here matches seamlessly the decay at later times derived from the original earthquake catalog, yielding a continuous aftershock decay over timescales spanning nearly 8 orders of magnitude. Aftershocks of repeating microearthquakes may hence be governed by the same mechanisms from the earliest time resolved here, up to the end of the aftershock sequence. Our results suggest that these early aftershocks are triggered by relatively large stress perturbations, possibly induced by aseismic afterslip with very short characteristic time. Consistent with previous observations on bimaterial faults, the relative location of early aftershocks shows asymmetry along strike, persistent over long periods.

  1. Surface-Wave Focal Mechanism of the 23 July 2002 Yellow-Sea Earthquake Event

    NASA Astrophysics Data System (ADS)

    Nguyen, B. V.; Hsu, V.

    2002-12-01

    The Yellow-Sea earthquake event of 23 July 2002 was reported by the USGS as follows: mb=4.7, Origin Time=12:48:08.23, Latitude = 35.563N, Longitude = 122.183E. In this study, we will present the focal mechanism of this event. Corrected Love-wave and Rayleigh-wave amplitude data from six CDSN stations and INCN station were used in the search for focal mechanism employing the technique of Nguyen and Herrmann (1992, SRL). Eigenfunctions were computed from the average crustal model that was obtained by inversion from surface-wave group velocities of these stations. Surface-wave attenuation coefficients were obtained using the technique of Tsai and Aki (1969). The result for surface-wave focal mechanism is much less as a strike-slip source than a more strike-slip one of the 4.8-mb Yellow-Sea 03 November 1992, as reported by Nguyen (1994 AGU Spring Meeting). The focal mechanism of this event has a nodal plane with dip= 65 deg., slip = 140 deg., and rake = 10 deg. The seismic moment obtained is 1.9E+23 dyne-cm. The source depth is 9 km.

  2. Implications of mainshock-aftershocks interactions during the 2013 Ebreichsdorf sequence, Austria

    NASA Astrophysics Data System (ADS)

    Tary, Jean-Baptiste; Apoloner, Maria-Theresia; Bokelmann, Götz

    2015-04-01

    The Vienna basin is a pull-apart basin located at the contact between the Alpine arc and the Eurasian plate, with the Eastern Alps to the West, the Western Carpathian to the East, the Bohemian massif to the North, and the Pannonian basin to the South. The southern border of this basin, called the Vienna Basin Fault System (VBFS), is accommodating part of the extrusion of the Pannonian basin (~1-2 mm/yr) due to the convergence between the Adriatic microplate and the Eurasian plate. The VBFS is a sinistral strike-slip fault and one of the most active fault in Austria. Along the VBFS, the seismicity is mainly concentrated in separate clusters with a spacing of approximately 20 km. In 2000 and 2013, two sequences constituted by two main shocks and 20-30 aftershocks occurred in one of these clusters located close to Ebreichsdorf, approximately 30 km south of Vienna. We focus here on the sequence of 2013 whose earthquakes were relocated using the double-difference method. The two main shocks, with local magnitudes of 4.2 and very similar focal mechanisms (N63, sinistral strike-slip), seem to be almost collocated. The aftershocks are located mainly to the northwest and at shallower depths compared with the main shocks. In order to better understand the relationships between the two main shocks and their aftershocks, we use two simple models of Coulomb failure stress to investigate possible coseismic static stress transfer between the main shocks and the aftershocks: the constant apparent friction model and the isotropic poroelastic model. The Coulomb failure stress change at the location of most aftershocks is positive but under 0.01 MPa. Aftershock triggering due to coseismic static stress is then unlikely. On the other hand, two other mechanisms could drive this sequence i.e., rapid non-linear pore pressure diffusion along the fault plane or aseismic slip. Given inter-event distances and times of ~0.5-1 km and hours to days, respectively, a high hydraulic diffusivity of

  3. FMC: a one-liner Python program to manage, classify and plot focal mechanisms

    NASA Astrophysics Data System (ADS)

    Álvarez-Gómez, José A.

    2014-05-01

    The analysis of earthquake focal mechanisms (or Seismic Moment Tensor, SMT) is a key tool on seismotectonics research. Each focal mechanism is characterized by several location parameters of the earthquake hypocenter, the earthquake size (magnitude and scalar moment tensor) and some geometrical characteristics of the rupture (nodal planes orientations, SMT components and/or SMT main axes orientations). The aim of FMC is to provide a simple but powerful tool to manage focal mechanism data. The data should be input to the program formatted as one of two of the focal mechanisms formatting options of the GMT (Generic Mapping Tools) package (Wessel and Smith, 1998): the Harvard CMT convention and the single nodal plane Aki and Richards (1980) convention. The former is a SMT format that can be downloaded directly from the Global CMT site (http://www.globalcmt.org/), while the later is the simplest way to describe earthquake rupture data. FMC is programmed in Python language, which is distributed as Open Source GPL-compatible, and therefore can be used to develop Free Software. Python runs on almost any machine, and has a wide support and presence in any operative system. The program has been conceived with the modularity and versatility of the classical UNIX-like tools. Is called from the command line and can be easily integrated into shell scripts (*NIX systems) or batch files (DOS/Windows systems). The program input and outputs can be done by means of ASCII files or using standard input (or redirection "<"), standard output (screen or redirection ">") and pipes ("|"). By default FMC will read the input and write the output as a Harvard CMT (psmeca formatted) ASCII file, although other formats can be used. Optionally FMC will produce a classification diagram representing the rupture type of the focal mechanisms processed. In order to count with a detailed classification of the focal mechanisms I decided to classify the focal mechanism in a series of fields that include

  4. Theory of the mechanical response of focal adhesions to shear flow

    NASA Astrophysics Data System (ADS)

    Biton, Y. Y.; Safran, S. A.

    2010-05-01

    The response of cells to shear flow is primarily determined by the asymmetry of the external forces and moments that are sensed by each member of a focal adhesion pair connected by a contractile stress fiber. In the theory presented here, we suggest a physical model in which each member of such a pair of focal adhesions is treated as an elastic body subject to both a myosin-activated contractile force and the shear stress induced by the external flow. The elastic response of a focal adhesion complex is much faster than the active cellular processes that determine the size of the associated focal adhesions and the direction of the complex relative to the imposed flow. Therefore, the complex attains its mechanical equilibrium configuration which may change because of the cellular activity. Our theory is based on the experimental observation that focal adhesions modulate their cross-sectional area in order to attain an optimal shear. Using this assumption, our elastic model shows that such a complex can passively change its orientation to align parallel to the direction of the flow.

  5. Focal Plane Array Shutter Mechanism of the JWST NIRSpec Detector System

    NASA Technical Reports Server (NTRS)

    Hale, Kathleen; Sharma, Rajeev

    2006-01-01

    This viewgraph presentation reviews the requirements, chamber location, shutter system design, stepper motor specifications, dry lubrication, control system, the environmental cryogenic function testing and the test results of the Focal Plane Array Shutter mechanism for the James Webb Space Telescope Near Infrared Spectrum Detector system. Included are design views of the location for the Shutter Mechanism, lubricant (lubricated with Molybdenum Di Sulfide) thickness, and information gained from the cryogenic testing.

  6. Identification of a major segment boundary between two megathrust subduction zone earthquakes from aftershock seismicity

    NASA Astrophysics Data System (ADS)

    Sobiesiak, M.; Victor, P.; Eggert, S.

    2009-04-01

    Aftershock seismicity is commonly used to characterize the extent of rupture planes of megathrust earthquakes. From unique datasets, covering the two adjacent fault planes of the Mw 8.0, 1995, Antofagasta and the Mw 7.7, 2007, Tocopilla earthquakes, we were able to identify a segment boundary (SB), located beneath Mejillones Peninsula. This segment boundary hosted the onset of the Antofagasta rupture and constituted the end of the Tocopilla rupture plane. The data recorded during the mission of the German Task Force for Earthquakes after the 2007 Tocopilla earthquake is supporting our observations regarding the northern part of the SB. 34 seismological stations registered the aftershocks from November 2007 until May 2008. First hypocenter determinations show that the aftershock sequences of both events meet along this E-W oriented segment boundary. The segment boundary is furthermore conformed by the historic record of megathrust events. Evidence for long term persistency of this SB comes from geological observations as differential uplift rates across the boundary and different fault patterns. Geomorpholocical analysis defines a topographic anomaly ~ 20 km wide and oriented along strike the SB..The main shock hypocenter determinations (NEIC, local network, ISC) which are related to the start of the rupture are all located in this zone. The SB is further characterized by intermediate b-values derived from a spatial b-value study of the Antofagasta fault plane and hosts several elongated clusters of aftershock seismicity. A detailed study of the focal mechanism solutions in one of these clusters showed a number of aligned strike slip events with one E-W striking nodal plane having a strike angle which is similar to the angle of subduction obliquity of the oceanic Nazca plate in this area. In further investigations we will search for detailed information on the nature and dynamics of processes along such a segment boundary, their meaning for the initiation of large

  7. Earthquakes focal mechanism and stress field pattern in the northeastern part of Egypt

    NASA Astrophysics Data System (ADS)

    Mohamed, Emad K.; Hassoup, A.; Abou Elenean, K. M.; Othman, Adel A. A.; Hamed, Diaa-Eldin M. K.

    2015-12-01

    Egypt is characterized by moderate size seismicity where earthquakes are distributed within several active regions. In the present study, we investigated the source mechanism of earthquakes using the digital waveform data recorded by the Egyptian National Seismic Network (ENSN) during the period from 2004 to 2008. The focal mechanisms are constructed with high reliability based on the polarity of the first motion of P-wave. These solutions are used to examine the mode of tectonic deformation and the present-day stress field pattern affecting on different tectonic provinces in the northern part of Egypt. The results demonstrate mainly a normal faulting mechanism with minor strike slip component generally trending parallel to the northern Red Sea, the Suez rift, Aqaba rift with their connection with the great rift system of the Red Sea and the Gulf of Suez and Cairo-Alexandria trend. The inversion technique scheme is used also in the present study for determining the regional stress field parameters for earthquake focal mechanism solutions based on the grid search method of Gephart and Forsyth (1984). The Results of the stress tensor using focal mechanisms of recent earthquakes show a prevailed tension stress field in N52°E, N41°E and N52°E for the northern Red Sea, Gulf of Suez and Gulf of Aqaba zone respectively.

  8. Comparing the mechanical influence of vinculin, focal adhesion kinase and p53 in mouse embryonic fibroblasts

    SciTech Connect

    Klemm, Anna H.; Diez, Gerold; Alonso, Jose-Luis

    2009-02-13

    Cytoskeletal reorganization is an ongoing process when cells adhere, move or invade extracellular substrates. The cellular force generation and transmission are determined by the intactness of the actomyosin-(focal adhesion complex)-integrin connection. We investigated the intracellular course of action in mouse embryonic fibroblasts deficient in the focal adhesion proteins vinculin and focal adhesion kinase (FAK) and the nuclear matrix protein p53 using magnetic tweezer and nanoparticle tracking techniques. Results show that the lack of these proteins decrease cellular stiffness and affect cell rheological behavior. The decrease in cellular binding strength was higher in FAK- to vinculin-deficient cells, whilst p53-deficient cells showed no effect compared to wildtype cells. The intracellular cytoskeletal activity was lowest in wildtype cells, but increased in the following order when cells lacked FAK+p53 > p53 > vinculin. In summary, cell mechanical processes are differently affected by the focal adhesion proteins vinculin and FAK than by the nuclear matrix protein, p53.

  9. Stress field in central Japan estimated by multiple inverse method from focal mechanisms

    NASA Astrophysics Data System (ADS)

    Kubo, A.; Otsubo, M.; Ishi, T.

    2008-12-01

    In central Japan, active faults with strike-slip type are dominated. In addition small fractions of reverse faults are observed in Nigata Kobe Tectonic Zone (NKTZ) and other places. However large part of focal mechanism solutions in this region shows reverse fault type. Thus relation between existent fault and stress field are essentially important problem. To obtain precise heterogeneous stress field, we apply multiple inverse method (Otsubo et al., in press) and K-means clustering (Otsubo el al., 2006) to the shallower focal mechanism solutions (NIED F-net focal mechanisms catalogue: depth <30km) in this region. The multiple inverse method can treat heterogeneous stress field and have no requirement for strict a priori data selection which can be assumed under homogeneous stress field. First we extract two stress solutions within each 1° × 1° (lat, lon) region. Most of the stress solutions show strike-slip or reverse fault type with stress ratio (φ) between 0 and 0.66. Then we divide input fault parameters into four groups using misfit angles between the observed and computed slip directions for detected stress solutions in each region. The misfit angle is 30°. We estimated the spatial changes of stress field from the focal mechanisms of which observed slip directions are consistent with only one stress solution. These selected dataset are useful to map spatial heterogeneity of the stress field. Solutions with medium stress ratio (φ = 0.33 to 0.66) and strike-slip regime appear in central Japan enclosed by Itoigawa Shizuoka Tectonic Line and Median Tectonic Line. Stress solution with reverse fault regime and medium stress ratio are seen in northeast region and Japan Sea side. In contrast, solutions with low stress ratio (φ) between 0.00 and 0.33 (s1 >> s2=s3) appears along high strain rate zone (NKTZ). It may show that the high strain rate zone correspond to stress concentrated region toward Shmax direction.

  10. Relocation of Early and Late Aftershocks of the 2001 Bhuj Earthquake Using Joint Hypocentral Determination (JHD) Technique: Implication toward the Continued Aftershock Activity for more than Four Years

    NASA Astrophysics Data System (ADS)

    Mandal, Prantik; Narsaiah, R.; Sairam, B.; Satyamurty, C.; Raju, I. P.

    2006-08-01

    We employed layered model joint hypocentral determination (JHD) with station corrections to improve location identification for the 26 January, 2001 Mw 7.7 Bhuj early and late aftershock sequence. We relocated 999 early aftershocks using the data from a close combined network (National Geophysical Research Institute, India and Center for Earthquake Research Institute, USA) of 8 18 digital seismographs during 12 28 February, 2001. Additionally, 350 late aftershocks were also relocated using the data from 4 10 digital seismographs/accelerographs during August 2002 to December 2004. These precisely relocated aftershocks (error in the epicentral location<30 meter, error in the focal depth estimation < 50 meter) delineate an east-west trending blind thrust (North Wagad Fault, NWF) dipping (~ 45°) southward, about 25 km north of Kachchh main land fault (KMF), as the causative fault for the 2001 Bhuj earthquake. The aftershock zone is confined to a 60-km long and 40-km wide region lying between the KMF to the south and NWF to the north, extending from 2 to 45 km depth. Estimated focal depths suggest that the aftershock zone became deeper with the passage of time. The P- and S-wave station corrections determined from the JHD technique indicate that the larger values (both +ve and -ve) characterize the central aftershock zone, which is surrounded by the zones of smaller values. The station corrections vary from -0.9 to +1.1 sec for the P waves and from -0.7 to +1.4 sec for the S waves. The b-value and p-value of the whole aftershock (2001 2004) sequences of Mw ≥ 3 are estimated to be 0.77 ± 0.02 and 0.99 ± 0.02, respectively. The p-value indicates a smaller value than the global median of 1.1, suggesting a relatively slow decay of aftershocks, whereas, the relatively lower b-value (less than the average b-value of 1.0 for stable continental region earthquakes of India) suggests a relatively higher probability for larger earthquakes in Kachchh in comparison to other

  11. Improved understanding of aftershock triggering by waveform detection of aftershocks with GPU computing

    NASA Astrophysics Data System (ADS)

    Peng, Z.; Meng, X.; Hong, B.; Yu, X.

    2012-12-01

    Large shallow earthquakes are generally followed by increased seismic activities around the mainshock rupture zone, known as "aftershocks". Whether static or dynamic triggering is responsible for triggering aftershocks is still in debate. However, aftershocks listed in standard earthquake catalogs are generally incomplete immediately after the mainshock, which may result in inaccurate estimation of seismic rate changes. Recent studies have used waveforms of existing earthquakes as templates to scan through continuous waveforms to detect potential missing aftershocks, which is termed 'matched filter technique'. However, this kind of data mining is computationally intensive, which raises new challenges when applying to large data sets with tens of thousands of templates, hundreds of seismic stations and years of continuous waveforms. The waveform matched filter technique exhibits parallelism at multiple levels, which allows us to use GPU-based computation to achieve significant acceleration. By dividing the procedure into several routines and processing them in parallel, we have achieved ~40 times speedup for one Nvidia GPU card compared to sequential CPU code, and further scaled the code to multiple GPUs. We apply this paralleled code to detect potential missing aftershocks around the 2003 Mw 6.5 San Simeon and 2004 Mw6.0 Parkfield earthquakes in Central California, and around the 2010 Mw 7.2 El Mayor-Cucapah earthquake in southern California. In all these cases, we can detect several tens of times more earthquakes immediately after the mainshocks as compared with those listed in the catalogs. These newly identified earthquakes are revealing new information about the physical mechanisms responsible for triggering aftershocks in the near field. We plan to improve our code so that it can be executed in large-scale GPU clusters. Our work has the long-term goal of developing scalable methods for seismic data analysis in the context of "Big Data" challenges.

  12. The 24 May 2014 Mw 6.9 Gokceada, North Aegean Sea Earthquake and Its Aftershocks

    NASA Astrophysics Data System (ADS)

    Baydar Gorgun, B.; Gorgun, E.

    2014-12-01

    On 2014 May 24, the Gokceada Island in northern Aegean Sea region was hit by an Mw = 6.9 earthquake. The Gokceada earthquake occurred 43 km SW of Gokceada Island. Centroid moment tensors for 42 events with Mw between 3.5 and 6.9 are computed by applying a waveform inversion method. The time span of data covers the period between 2014 May 24 - June 26. The mainshock is a shallow focus strike-slip event at a depth of 15 km. Focal depths of aftershocks range from 5 to 25 km. The seismic moment (M0) of the mainshock is estimated 2.53 × 1019 Nm. The focal mechanisms of the aftershocks are mainly strike-slip faulting with a variable and sometimes significant normal component. This geometry indicates a strike-slip faulting regime with NE-SW trending direction of T-axis in the entire activated region. A Stress tensor inversion of focal mechanism data is performed to obtain a more accurate picture of the Gokceada earthquake stress field. The stress tensor inversion results show a predominant strike-slip stress regime with a NW-SE to NNE-SSW oriented maximum horizontal compressive stress (SH). The secondary fault system striking mostly E-W is activated generally with normal faulting in the east of the mainshock. This difference in mechanism suggests that towards the east, a different fault system is activated with respect to the NE-SW trending strike-slip faults beneath Gokceada Island and more to the west. Thus, to first order, the Gokceada Island earthquake region is characterized by a homogeneous intraplate stress field.

  13. The role of focal adhesion kinase in the regulation of cellular mechanical properties

    NASA Astrophysics Data System (ADS)

    Mierke, Claudia Tanja

    2013-12-01

    The regulation of mechanical properties is necessary for cell invasion into connective tissue or intra- and extravasation through the endothelium of blood or lymph vessels. Cell invasion is important for the regulation of many healthy processes such as immune response reactions and wound healing. In addition, cell invasion plays a role in disease-related processes such as tumor metastasis and autoimmune responses. Until now the role of focal adhesion kinase (FAK) in regulating mechanical properties of cells and its impact on cell invasion efficiency is still not well known. Thus, this review focuses on mechanical properties regulated by FAK in comparison to the mechano-regulating protein vinculin. Moreover, it points out the connection between cancer cell invasion and metastasis and FAK by showing that FAK regulates cellular mechanical properties required for cellular motility. Furthermore, it sheds light on the indirect interaction of FAK with vinculin by binding to paxillin, which then impairs the binding of paxillin to vinculin. In addition, this review emphasizes whether FAK fulfills regulatory functions similar to vinculin. In particular, it discusses the differences and the similarities between FAK and vinculin in regulating the biomechanical properties of cells. Finally, this paper highlights that both focal adhesion proteins, vinculin and FAK, synergize their functions to regulate the mechanical properties of cells such as stiffness and contractile forces. Subsequently, these mechanical properties determine cellular invasiveness into tissues and provide a source sink for future drug developments to inhibit excessive cell invasion and hence, metastases formation.

  14. Aftershock Triggering and Estimation of the Coulomb Stress Changes with Approach of Optimally Oriented Fault Planes: Examples of Some Contemporary Earthquakes in Turkey

    NASA Astrophysics Data System (ADS)

    Demirci, Alper

    2013-04-01

    The Coulomb Stress changes due to the some moderate and large earthquakes are shaped according to the orientations of reciever faults or weakness zones along the corresponding seismogenic zones. In some cases, the determination of the fault plane parameters (e.g. length, width, strike, dip) of the receiver faults are more difficult due to the tectonical complexity of the region. Therefore, in order to understand the aftershock distrubition in such areas Coulomb stress changes can be calculated under the assumption of optimally oriented fault planes which increases the spatial correlation between stress changes and aftershock distribution. In the scope of the present sutdy, aftershock distrubiton of some contemporary earthquakes in Turkey (Simav (Mw 5.8), May 2011; Van (Mw 7.0), Oct 2011 and Gulf of Fethiye (Mw 6.1), June 2012) and their coulomb stress changes were correlated. Fault plane parameters of these earthquakes which suggest three different types of focal mechanism were calculated using moment tensor inversion technique and aftershock location data in a period of 30 days for each corresponding events were taken from Kandilli Observatory and Earthquake Research Institute (KOERI) catalog. The focal mechanisms of the selected earthquakes represent normal, strike slip and thrust faulting for the earthquakes of Simav, Gulf of Fethite and Van, respectively. Coulomb Stress Changes were calculated using the open source Matlab based (Coulomb 3.3) codes. The calculations were performed by assuming Poisson's ratio and apparent friction coefficient to be 0.25 and 0.4, respectively. The coulomb stress variations were calculated at fixed depths for each event and aftershocks were selected as ±4 km for corresponding depths. Keeping in mind that the increase of static stress more than 0.5 bar can cause the triggered events in an area, the accordance rates of Coulomb stress changes and aftershock distribution under different tectonic regimes were disscussed. The accordance

  15. Decay of aftershock density with distance indicates triggering by dynamic stress.

    PubMed

    Felzer, K R; Brodsky, E E

    2006-06-01

    The majority of earthquakes are aftershocks, yet aftershock physics is not well understood. Many studies suggest that static stress changes trigger aftershocks, but recent work suggests that shaking (dynamic stresses) may also play a role. Here we measure the decay of aftershocks as a function of distance from magnitude 2-6 mainshocks in order to clarify the aftershock triggering process. We find that for short times after the mainshock, when low background seismicity rates allow for good aftershock detection, the decay is well fitted by a single inverse power law over distances of 0.2-50 km. The consistency of the trend indicates that the same triggering mechanism is working over the entire range. As static stress changes at the more distant aftershocks are negligible, this suggests that dynamic stresses may be triggering all of these aftershocks. We infer that the observed aftershock density is consistent with the probability of triggering aftershocks being nearly proportional to seismic wave amplitude. The data are not fitted well by models that combine static stress change with the evolution of frictionally locked faults. PMID:16760974

  16. Decay of aftershock density with distance indicates triggering by dynamic stress

    USGS Publications Warehouse

    Felzer, K.R.; Brodsky, E.E.

    2006-01-01

    The majority of earthquakes are aftershocks, yet aftershock physics is not well understood. Many studies suggest that static stress changes trigger aftershocks, but recent work suggests that shaking (dynamic stresses) may also play a role. Here we measure the decay of aftershocks as a function of distance from magnitude 2-6 mainshocks in order to clarify the aftershock triggering process. We find that for short times after the mainshock, when low background seismicity rates allow for good aftershock detection, the decay is well fitted by a single inverse power law over distances of 0.2-50 km. The consistency of the trend indicates that the same triggering mechanism is working over the entire range. As static stress changes at the more distant aftershocks are negligible, this suggests that dynamic stresses may be triggering all of these aftershocks. We infer that the observed aftershock density is consistent with the probability of triggering aftershocks being nearly proportional to seismic wave amplitude. The data are not fitted well by models that combine static stress change with the evolution of frictionally locked faults. ?? 2006 Nature Publishing Group.

  17. Focal mechanism of the seismic series prior to the 2011 El Hierro eruption

    NASA Astrophysics Data System (ADS)

    del Fresno, C.; Buforn, E.; Cesca, S.; Domínguez Cerdeña, I.

    2015-12-01

    The onset of the submarine eruption of El Hierro (10-Oct-2011) was preceded by three months of low-magnitude seismicity (Mw<4.0) characterized by a well documented hypocenter migration from the center to the south of the island. Seismic sources of this series have been studied in order to understand the physical process of magma migration. Different methodologies were used to obtain focal mechanisms of largest shocks. Firstly, we have estimated the joint fault plane solutions for 727 shocks using first motion P polarities to infer the stress pattern of the sequence and to determine the time evolution of principle axes orientation. Results show almost vertical T-axes during the first two months of the series and horizontal P-axes on N-S direction coinciding with the migration. Secondly, a point source MT inversion was performed with data of the largest 21 earthquakes of the series (M>3.5). Amplitude spectra was fitted at local distances (<20km). Reliability and stability of the results were evaluated with synthetic data. Results show a change in the focal mechanism pattern within the first days of October, varying from complex sources of higher non-double-couple components before that date to a simpler strike-slip mechanism with horizontal tension axes on E-W direction the week prior to the eruption onset. A detailed study was carried out for the 8 October 2011 earthquake (Mw=4.0). Focal mechanism was retrieved using a MT inversion at regional and local distances. Results indicate an important component of strike-slip fault and null isotropic component. The stress pattern obtained corresponds to horizontal compression in a NNW-SSE direction, parallel to the southern ridge of the island, and a quasi-horizontal extension in an EW direction. Finally, a simple source time function of 0.3s has been estimated for this shock using the Empirical Green function methodology.

  18. Characteristics of Focal Mechanisms and the Stress Field in the Southeastern Margin of the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Luo, Jun; Zhao, Cui-ping; Lü, Jian; Zhou, Lian-qing; Zheng, Si-hua

    2016-08-01

    Crustal earthquake focal mechanisms are investigated in the southeastern margin of the Tibetan Plateau, where the Tibetan Plateau and stable South China Block merge. An updated database of focal mechanisms has been compiled by selecting 132 Global Centroid Moment Tensor solutions and by adding the 173 new solutions (3.5 ≤ Ms ≤ 7.4) estimated by waveform inversion in this study. A total of 305 mechanisms are included in this database. These solutions show regionally specific distributions with dominant strike-slip faulting and some normal and reverse faulting. Focal mechanism solutions have also been inverted for the stress tensor orientation to obtain the principal stress axes over the study region. Results show that the horizontal maximum principal σ 1 axes rotate clockwise with a wider range than the geodetically measured surface motion in the east, which is not limited to the Xianshuihe-Xiaojiang fault, but has some overlap with the Zhaotong-Lianfeng fault. Localized normal faulting stress regimes are observed in the Jinshajiang-Litang fault areas and the Baoshan sub-block. The minimum principal axes are oriented with a gradually changing trend from north-south to northwest-southeast, from north to south, indicating diverse compression stress patterns. Significant changes in the crustal stress field after the Wenchuan earthquake are preliminarily observed in the Baoshan sub-block where orientations of two principal axes have changed, and in the Jinggu-Ximeng sub-block areas where the strike-slip faulting stress pattern has transformed to normal faulting.

  19. Stress changes, focal mechanisms, and earthquake scaling laws for the 2000 dike at Miyakejima (Japan)

    NASA Astrophysics Data System (ADS)

    Passarelli, Luigi; Rivalta, Eleonora; Cesca, Simone; Aoki, Yosuke

    2015-06-01

    Faulting processes in volcanic areas result from a complex interaction of pressurized fluid-filled cracks and conduits with the host rock and local and regional tectonic setting. Often, volcanic seismicity is difficult to decipher in terms of the physical processes involved, and there is a need for models relating the mechanics of volcanic sources to observations. Here we use focal mechanism data of the energetic swarm induced by the 2000 dike intrusion at Miyakejima (Izu Archipelago, Japan), to study the relation between the 3-D dike-induced stresses and the characteristics of the seismicity. We perform a clustering analysis on the focal mechanism (FM) solutions and relate them to the dike stress field and to the scaling relationships of the earthquakes. We find that the strike and rake angles of the FMs are strongly correlated and cluster on bands in a strike-rake plot. We suggest that this is consistent with optimally oriented faults according to the expected pattern of Coulomb stress changes. We calculate the frequency-size distribution of the clustered sets finding that focal mechanisms with a large strike-slip component are consistent with the Gutenberg-Richter relation with a b value of about 1. Conversely, events with large normal faulting components deviate from the Gutenberg-Richter distribution with a marked roll-off on its right-hand tail, suggesting a lack of large-magnitude events (Mw > 5.5). This may result from the interplay of the limited thickness and lower rock strength of the layer of rock above the dike, where normal faulting is expected, and lower stress levels linked to the faulting style and low confining pressure.

  20. Stress Field in Brazil with Focal Mechanism: Regional and Local Patterns

    NASA Astrophysics Data System (ADS)

    Dias, F.; Assumpcao, M.

    2013-05-01

    The knowledge of stress field is fundamental not only to understand driving forces and plate deformation but also in the study of intraplate seismicity. The stress field in Brazil has been determined mainly using focal mechanisms and a few breakout data and in-situ measurements. However the stress field still is poorly known in Brazil. The focal mechanisms of recent earthquakes (magnitude lower than 5 mb) were studied using waveform modeling. We stacked the record of several teleseismic stations ( delta > 30°) stacked groups of stations separated according to distance and azimuth. Every record was visually inspected and those with a good signal/noise ratio (SNR) were grouped in windows of ten degrees distance and stacked. The teleseismic P-wave of the stacked signals was modeled using the hudson96 program of Herrmann seismology package (Herrmann, 2002) and the consistency of focal mechanism with the first-motion was checked. Some events in central Brazil were recorded by closer stations (~ 1000 km) and the moment tensor was determined with the ISOLA code (Sokos & Zahradnik, 2008). With the focal mechanisms available in literature and those obtained in this work, we were able to identify some patterns: the central region shows a purely compressional pattern (E-W SHmax), which is predicted by regional theoretical models (Richardson & Coblentz, 1996 and the TD0 model of Lithgow & Bertelloni, 2004). Meanwhile in the Amazon we find an indication of SHmax oriented in the SE-NW direction, probably caused by the Caribbean plate interaction (Meijer, 1995). In northern coastal region, the compression rotates following the coastline, which indicates an important local component related to spreading effects at the continental/oceanic transition (Assumpção, 1998) and flexural stresses caused by sedimentary load in Amazon Fan. We determine the focal mechanism of several events in Brazil using different techniques according to the available data. The major difficulty is to

  1. High-Resolution Uitra Low Power, Intergrated Aftershock and Microzonation System

    NASA Astrophysics Data System (ADS)

    Passmore, P.; Zimakov, L. G.

    2012-12-01

    Rapid Aftershock Mobilization plays an essential role in the understanding of both focal mechanism and rupture propagation caused by strong earthquakes. A quick assessment of the data provides a unique opportunity to study the dynamics of the entire earthquake process in-situ. Aftershock study also provides practical information for local authorities regarding the post earthquake activity, which is very important in order to conduct the necessary actions for public safety in the area affected by the strong earthquake. Refraction Technology, Inc. has developed a self-contained, fully integrated Aftershock System, model 160-03, providing the customer simple and quick deployment during aftershock emergency mobilization and microzonation studies. The 160-03 has no external cables or peripheral equipment for command/control and operation in the field. The 160-03 contains three major components integrated in one case: a) 24-bit resolution state-of-the art low power ADC with CPU and Lid interconnect boards; b) power source; and c) three component 2 Hz sensors (two horizontals and one vertical), and built-in ±4g accelerometer. Optionally, the 1 Hz sensors can be built-in the 160-03 system at the customer's request. The self-contained rechargeable battery pack provides power autonomy up to 7 days during data acquisition at 200 sps on continuous three weak motion and triggered three strong motion recording channels. For longer power autonomy, the 160-03 Aftershock System battery pack can be charged from an external source (solar power system). The data in the field is recorded to a built-in swappable USB flash drive. The 160-03 configuration is fixed based on a configuration file stored on the system, so no external command/control interface is required for parameter setup in the field. For visual control of the system performance in the field, the 160-03 has a built-in LED display which indicates the systems recording status as well as a hot swappable USB drive and battery

  2. Focal Mechanism Solutions of the 2008 Wenchuan earthquake sequence from P-wave polarities and SH/P amplitude ratios: new results and implications

    NASA Astrophysics Data System (ADS)

    Tian, Yuan; Ning, Jieyuan; Yu, Chunquan; Cai, Chen; Tao, Kai

    2013-12-01

    The 2008 Wenchuan earthquake, a major intraplate earthquake with M w 7.9, occurred on the slowly deforming Longmenshan fault. To better understand the causes of this devastating earthquake, we need knowledge of the regional stress field and the underlying geodynamic processes. Here, we determine focal mechanism solutions (FMSs) of the 2008 Wenchuan earthquake sequence (WES) using both P-wave first-motion polarity data and SH/P amplitude ratio (AR) data. As P-wave polarities are more reliable information, they are given priority over SH/P AR, the latter of which are used only when the former has loose constraint on the FMSs. We collect data from three categories: (1) permanent stations deployed by the China Earthquake Administration (CEA); (2) the Western Sichuan Passive Seismic Array (WSPSA) deployed by Institute of Geology, CEA; (3) global stations from Incorporated Research Institutions for Seismology. Finally, 129 events with magnitude over M s 4.0 in the 2008 WES are identified to have well-constrained FMSs. Among them, 83 are well constrained by P-wave polarities only as shown by Cai et al. (Earthq Sci 24(1):115-125, 2011), and the rest of which are newly constrained by incorporating SH/P AR. Based on the spatial distribution and FMSs of the WES, we draw following conclusions: (1) the principle compressional directions of most FMSs of the WES are subhorizontal, generally in agreement with the conclusion given by Cai et al. (2011) but with a few modifications that the compressional directions are WNW-ESE around Wenchuan and ENE-WSW around Qingchuan, respectively. The subhorizontal compressional direction along the Longmenshan fault from SW to NE seems to have a left-lateral rotation, which agrees well with regional stress field inverted by former researchers (e.g., Xu et al., Acta Seismol Sin 30(5), 1987; Acta Geophys Sin 32(6), 1989; Cui et al., Seismol Geol 27(2):234-242, 2005); (2) the FMSs of the events not only reflected the regional stress state of the

  3. Present-day Tectonic Stress Regimes in Northern Iraq and Surrounding Regions from Focal Mechanism Data

    NASA Astrophysics Data System (ADS)

    Mahdi, H. H.; Abdulnaby, W.; Al-Shukri, H. J.; Numan, N.

    2013-12-01

    The collision zone between the Arabian and the Eurasian plates is one of the most seismically active regions. Northern Iraq represents the northeastern part of the Arabian plate that has a suture zone with the Turkish and Iranian plates named Bitlis-Zagros suture zone. The present-day tectonic stress regimes can be estimated from focal mechanism data. The waveform moment tensor inversion method was used to derive the focal mechanism solution of 65 earthquakes with magnitudes of ≥3.5. Green's functions for the local and regional seismograms were generated in order to perform the moment tensor inversion using complete seismograms. From focal mechanism solutions, the direction of slip and the orientations of the moment tensor axes (P, N, and T) on the fault surface during an earthquake were determined. The tectonic stress regime of each focal mechanism was estimated based on Zoback (1992). The results show that all six categories of the stress regimes, which are normal faulting (NF), normal faulting with strike-slip component (NS), strike-slip faulting (SS), thrust faulting with strike-slip component (TS), thrust faulting (TF), and unknown or oblique faulting (UF), exist. However, the most common tectonic regimes in the study area are the SS (43.94%), UF (27.27%), and TF (13.64%). In most cases, the strike-slip movement on the fault surfaces consists of left-lateral movement. The NF regime, which is located in one small area near Diyala city at the Iraq-Iran border, might be a local tensional stress regime. The directions of the compressional stress axes show that the stress regime at the Zagros suture zone has two directions. One is perpendicular to the suture near the Iraq-Iran border, and the second is parallel to the suture near the Iraq-Turkey border. In addition, the compressional stress axes at the city of Sinjar, near the Iraq-Syria border, have E-W direction. These results are compatible with the tectonic setting of the Arabain-Eurasian continental

  4. Triggering of earthquake aftershocks by dynamic stresses.

    PubMed

    Kilb, D; Gomberg, J; Bodin, P

    2000-11-30

    It is thought that small 'static' stress changes due to permanent fault displacement can alter the likelihood of, or trigger, earthquakes on nearby faults. Many studies of triggering in the near-field, particularly of aftershocks, rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault. Here we report a comparison of the aftershock pattern of the moment magnitude Mw = 7.3 Landers earthquake, not only with static stress changes but also with transient, oscillatory stress changes transmitted as seismic waves (that is, 'dynamic' stresses). Dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone. These dynamically weakened faults may fail after the seismic waves have passed by, and might even cause earthquakes that would not otherwise have occurred. We find similar asymmetries in the aftershock and dynamic stress patterns, the latter being due to rupture propagation, whereas the static stress changes lack this asymmetry. Previous studies have shown that dynamic stresses can promote failure at remote distances, but here we show that they can also do so nearby. PMID:11117741

  5. Deterministic model of earthquake clustering shows reduced stress drops for nearby aftershocks

    NASA Astrophysics Data System (ADS)

    Shaw, Bruce E.; Richards-Dinger, Keith; Dieterich, James H.

    2015-11-01

    While a number of viable physical mechanisms have been offered to explain the temporal clustering of aftershocks, the spatial clustering of aftershocks, in particular the concentrated productivity of aftershocks very near the mainshock rupture area, has been difficult to reproduce with physical models. Here we present a new deterministic physical model capable of reproducing both the spatial and temporal clustering. We apply this new model to a longstanding puzzling question raised by ground motion observations, which suggest that nearby aftershocks show reduced ground motions relative to similar magnitude mainshocks. In the model, the physical basis for these observations is reduced stress drops for nearby aftershocks compared to similar magnitude mainshocks. These reduced stress drops are due to nearby aftershocks rerupturing incompletely healed parts of the fault which ruptured in the mainshock.

  6. Tomographic images and focal mechanisms beneath the Tatun volcano group, northern Taiwan

    NASA Astrophysics Data System (ADS)

    Pu, H.; Lin, C.; Chang, T.; Konstantinou, K.; Wen, K.

    2010-12-01

    The Tatun volcano group (TVG) is just located nearby the Taipei metropolis, where is the major economic and political center of Taiwan. To improve the understanding of the volcanic structures and their properties, we have deployed a dense seismic network at the TVG for monitoring the volcanic earthquakes since 2004. This network is composed of 18 seismic stations in the area about 10km by 10km. We detected a great quantity of local earthquakes (over 5,000). Over 3,000 events provide useful observations to invert detailed subsurface structures by using tomography method. Our tomographic images show that both variations of Vp and Vs might be likely related to the volcanic activity in some area. We also determined over 600 focal mechanisms of micro-earthquakes by using the first-motion polarization. Most of focal mechanisms are the normal faulting and indicating that the extensional stress predominate the micro-earthquakes beneath the TVG. These dense normal mechanisms may be caused by volcanic activity beneath the TVG area.

  7. Focal Depths and Mechanisms of Earthquakes in the Himalayan-Tibetan Region

    NASA Astrophysics Data System (ADS)

    Bai, L.; Li, G.; Khan, N.; Zhao, J.; Lin, D.

    2015-12-01

    The complexity of the Himalayan-Tibetan lithospheric deformation is evident from extensive seismicity and diverse focal mechanism solutions. Here we investigate the focal depths and fault plane solutions of moderate earthquakes in the Himalayan-Tibetan region by teleseismic waveform modeling and a multi-scale double-difference earthquake relocation method. Shallow earthquakes are widespread across the whole study region. In the central Tibet, earthquakes are restricted to the upper crust and originate dominantly by strike-slip faulting, in agreement with low velocity layers observed previously in the lower crust and strong S-wave attenuation zones observed in the uppermost mantle. In the northern and southern Tibet, where the Asian and Indian plate subduct beneath the central Tibet, earthquakes appear to be distributed throughout the thickness of the crust and exhibit dominantly reverse faulting (Bai et al., 2015a). Intermediate-depth earthquakes are mostly located at the eastern and western Himalayan syntaxes, which reflect the ongoing deformation along the plate interface. The continental slab beneath the Indian-Eurasian collision zone deforms in a more complex manner than the oceanic slab subduction, combining tension, shearing and oblique convergence with plate subduction (Bai et al., 2015b). References Bai, L., Li, G., Khan, N.G., Zhao, J., and Ding, L., 2015a. Focal depths and mechanisms of shallow earthquakes in the Himalayan-Tibetan region, Gondwana Research, accepted. Bai, L., and Zhang, T., 2015b. Complex deformation pattern of the Pamir-Hindu Kush region inferred from multi-scale double-difference earthquake relocations, Tectonophysics, 638: 177-184, doi:10.1016/j.tecto.2014.11.006.

  8. The Stress Field of Eastern Africa Deduced From new Focal Mechanisms

    NASA Astrophysics Data System (ADS)

    Barth, A.; Wenzel, F.

    2006-12-01

    The East African Rift intersects the African continent from North to South for over 3000~km. Especially for regions neighbouring the rift only limited information on the stress regime is available. This is primarily due to a lack of earthquake source mechanism information, from which stress orientations can be deduced. Most of strong earthquakes occur within the rift zone, so that for these events focal mechanisms are calculated routinely by the Harvard CMT-group by moment tensor inversion using teleseismic data. However, apart from the rift earthquake magnitudes are often below their threshold of MW ~5.0 and thus CMT-solutions are hardly available. We developed a semi-automatic and frequency sensitive moment tensor inversion that allows us to determine source mechanisms of these light to moderate magnitude events. We present focal mechanism of 40 earthquakes with magnitudes ranging between 4.4~≤ MW ≤~5.4 taken from the years 1995-2002 that were not studied previously. We invert data from permanent recording seismometers with source-receiver distances up to 3000 km within variable frequency bands between 13 mHz and 29 mHz. For the formal stress inversion we use these new results, all 90 CMT-solutions available for Eastern Africa (1977-2005) and 17 focal mechanisms determined by moment tensor inversion from other authors. Finally, we divide Eastern Africa into 11 regions, binning the earthquake source mechanisms to perform the stress inversion. To analyse the dependence of the resulting stress tensors on the binning, we change regional partitioning systematically. We obtain stable stress tensors that show extensional regimes all over Eastern Africa with the maximum horizontal stress SH orientated in North-South direction. Beside this, we observe variations of SH in the vicinity of the Eastern rift branch (Kenya-Rift) towards Lake Victoria, where SH is rotated nearly perpendicular to the rift orientation. Moreover in the high plateau region West of Lake Malawi

  9. Tsunami-generated magnetic fields may constrain focal mechanisms of earthquakes.

    PubMed

    Kawashima, Issei; Toh, Hiroaki

    2016-01-01

    A geomagnetic observatory named SFEMS is being operated on the deep seafloor in the northwest Pacific since August, 2001. SFEMS is capable of measuring both scalar and vector geomagnetic fields as well as the seafloor instrument's precise attitudes, which makes it a powerful tool in detecting the so-called oceanic dynamo effect. It was found that SFEMS captured clear magnetic signals generated by the giant tsunamis of the 2011 Tohoku Earthquake even for an epicentral distance of larger than 1500 km. Here we report estimates of the focal mechanism of a closer tsunamigenic earthquake in January, 2007 on the seaward slope of the Kuril Trench using tsunami-generated variations in the observed downward magnetic component. Three-dimensional solutions of the tsunami-generated magnetic components were calculated by a new numerical code based on non-uniform thin-sheet approximation and particle motions of seawater using the linear Boussinesq approximation. As a result, a southeast dipping fault alone reproduced the dispersive nature of the downward magnetic component, while any northwest dipping faults could not. This implies that the tsunami-generated electromagnetic fields are useful for determination of focal mechanisms of tsunamigenic earthquakes, since fault dips are one of the most difficult source parameters to estimate even in modern seismology. PMID:27353343

  10. Tsunami-generated magnetic fields may constrain focal mechanisms of earthquakes

    PubMed Central

    Kawashima, Issei; Toh, Hiroaki

    2016-01-01

    A geomagnetic observatory named SFEMS is being operated on the deep seafloor in the northwest Pacific since August, 2001. SFEMS is capable of measuring both scalar and vector geomagnetic fields as well as the seafloor instrument’s precise attitudes, which makes it a powerful tool in detecting the so-called oceanic dynamo effect. It was found that SFEMS captured clear magnetic signals generated by the giant tsunamis of the 2011 Tohoku Earthquake even for an epicentral distance of larger than 1500 km. Here we report estimates of the focal mechanism of a closer tsunamigenic earthquake in January, 2007 on the seaward slope of the Kuril Trench using tsunami-generated variations in the observed downward magnetic component. Three-dimensional solutions of the tsunami-generated magnetic components were calculated by a new numerical code based on non-uniform thin-sheet approximation and particle motions of seawater using the linear Boussinesq approximation. As a result, a southeast dipping fault alone reproduced the dispersive nature of the downward magnetic component, while any northwest dipping faults could not. This implies that the tsunami-generated electromagnetic fields are useful for determination of focal mechanisms of tsunamigenic earthquakes, since fault dips are one of the most difficult source parameters to estimate even in modern seismology. PMID:27353343

  11. Tsunami-generated magnetic fields may constrain focal mechanisms of earthquakes

    NASA Astrophysics Data System (ADS)

    Kawashima, Issei; Toh, Hiroaki

    2016-06-01

    A geomagnetic observatory named SFEMS is being operated on the deep seafloor in the northwest Pacific since August, 2001. SFEMS is capable of measuring both scalar and vector geomagnetic fields as well as the seafloor instrument’s precise attitudes, which makes it a powerful tool in detecting the so-called oceanic dynamo effect. It was found that SFEMS captured clear magnetic signals generated by the giant tsunamis of the 2011 Tohoku Earthquake even for an epicentral distance of larger than 1500 km. Here we report estimates of the focal mechanism of a closer tsunamigenic earthquake in January, 2007 on the seaward slope of the Kuril Trench using tsunami-generated variations in the observed downward magnetic component. Three-dimensional solutions of the tsunami-generated magnetic components were calculated by a new numerical code based on non-uniform thin-sheet approximation and particle motions of seawater using the linear Boussinesq approximation. As a result, a southeast dipping fault alone reproduced the dispersive nature of the downward magnetic component, while any northwest dipping faults could not. This implies that the tsunami-generated electromagnetic fields are useful for determination of focal mechanisms of tsunamigenic earthquakes, since fault dips are one of the most difficult source parameters to estimate even in modern seismology.

  12. Geodetic displacements and aftershocks following the 2001 Mw = 8.4 Peru earthquake: Implications for the mechanics of the earthquake cycle along subduction zones

    NASA Astrophysics Data System (ADS)

    Perfettini, H.; Avouac, J.-P.; Ruegg, J.-C.

    2005-09-01

    We analyzed aftershocks and postseismic deformation recorded by the continuous GPS station AREQ following the Mw = 8.4, 23 June 2001 Peru earthquake. This station moved by 50 cm trenchward, in a N235°E direction during the coseismic phase, and continued to move in the same direction for an additional 15 cm over the next 2 years. We compare observations with the prediction of a simple one-dimensional (1-D) system of springs, sliders, and dashpot loaded by a constant force, meant to simulate stress transfer during the seismic cycle. The model incorporates a seismogenic fault zone, obeying rate-weakening friction, a zone of deep afterslip, the brittle creep fault zone (BCFZ) obeying rate-strengthening friction, and a zone of viscous flow at depth, the ductile fault zone (DFZ). This simple model captures the main features of the temporal evolution of seismicity and deformation. Our results imply that crustal strain associated with stress accumulation during the interseismic period is probably not stationary over most of the interseismic period. The BCFZ appears to control the early postseismic response (afterslip and aftershocks), although an immediate increase, by a factor of about 1.77, of ductile shear rate is required, placing constraints on the effective viscosity of the DFZ. Following a large subduction earthquake, displacement of inland sites is trenchward in the early phase of the seismic cycle and reverse to landward after a time ti for which an analytical expression is given. This study adds support to the view that the decay rate of aftershocks may be controlled by reloading due to deep afterslip. Given the ratio of preseismic to postseismic viscous creep, we deduce that frictional stresses along the subduction interface account for probably 70% of the force transmitted along the plate interface.

  13. Direct photofabrication of focal-length-controlled microlens array using photoinduced migration mechanisms of photosensitive sol-gel hybrid materials

    NASA Astrophysics Data System (ADS)

    Kang, Dong Jun; Jeong, Jong-Pil; Bae, Byeong-Soo

    2006-09-01

    Photosensitive sol-gel hybrid (SGH) materials exhibited the peculiar photoinduced migration behavior of unreacted molecules from unexposed areas to exposed areas by selective UV exposure. Using the photoinduced migration mechanism of the photosensitive SGH materials, the microlens array (MLA) with a smooth surface was directly photofabricated, and the focal length was controlled by changing the photoinduced migration parameters. The higher photoactive monomer content and the thicker film creating a higher curvature produced a smaller focal length of the MLA. Thus, a simple fabrication and easy control of the focal length can be applicable to a fabrication of an efficient MLA.

  14. Source Parameters of the Bhuj Mainshock and Larger Aftershocks from Modeling of Broadband Teleseismic and Regional Waveform data

    NASA Astrophysics Data System (ADS)

    Gaur, V.; Maggi, A.; Priestley, K.; Rai, S.; Davuluri, S.

    2001-12-01

    The January 26, 2001 mb 6.9 Bhuj mainshock was well recorded at both teleseismic and regional distances. Many of the larger aftershocks were also well recorded at regional distances by digital broadband seismographs operated by the National Geophysical Research Institute of India, the University of Cambridge and the Indian Meteorological Office. We have modeled the teleseismic P- and SH-waveforms to retrieve the mechanism and focal depth of the mainshock and find a thrust faulting mechanism with a fault strike 281 degrees, dip 42 degrees, rake 107 degrees, a seismic moment of 2.31*E20 Nm and a centroid focal depth of 20 km. The long-period source time function shows a relatively simple source of about 15 seconds duration. We use the source parameters for the mainshock derived from the teleseismic inversion and the records for the mainshock at the regional stations mentioned above to calibrate the 1-D propagation characteristics for these regional paths. Using the calibrated regional propagation paths, we invert the complete regional broadband waveforms (P-wave through the surface wave-train) for the source parameters of the larger aftershocks (M0 1015 to 1017 Nm) which are too small to derive from teleseismic recordings. We model the broadband waveforms using the time-domain, linear moment-tensor inversion code of Randall et al, 1995.

  15. Aftershock process of Chu earthquake

    NASA Astrophysics Data System (ADS)

    Emanov, Alexey; Leskova, Ekaterina; Emanov, Aleksandr; Kolesnikov, Yury; Fateyev, Aleksandr

    2010-05-01

    Chu earthquake of 27.09.2003, Ms =7.3 occurred in joint zone of Chagan-Uzun raised block with North-Chu ridge. Epicentral zone cover a series of contrast geological structures of Mountain Altai (two hollows: Chu and Kurai, devided by Chagan-Uzun block, and mountain range, franking them,: Nort-Chu, Kurai, South-Chu, Aigulak). The seismic process occurred in zone of expressive block structure, and this is embodied in its space-time structure. The high accuracy of hypocental construction in epicenral zone of Chu earthquake is provided by local network of seismological stations (fifteen stations) and experiments with temporary station network in this zone (20-50 stations). The first stage of aftershock process formation is connected with Chagan-Uzun block. The second large aftershock of 01.10.2003 changes cardinally spatial pattern of aftershock process. Instead of round area an elongate aftershock area is formed along boundary of Kurai hollow with North-Chu ridge. In the following process spread out in north-west angle of Chu hollow. Linear elongate aftershock area is subdivided into four elements. The north-west element has form of horse tail, starting as a line in area of outlet of Aktru River in Kurai hollow, and ramifies short of settlement Chibit. Slope of plane of aftershocks for this element is determined from hollow under North-Chu ridge. The seismic process is going not along boundary hollow-mountain ridge, but displaced in hollow side. The central part of element - this are mainly horizontal shift faults, and outlying districts have pronounced vertical components of displacements. The second element stretches from Aktru River to Chagan-Uzun block. Earthquake epicenters in plane make two curved parallel lines. In the angle of Chagan-Uzun block are ceiling amount of uplifts. The third element is the boundary of Chagan-Uzun block with North-Chu ridge. The forth element is formed by aftershocks, leaving in range of Chu hollow. Areal dispersal of earthquakes is

  16. Role of focal adhesions and mechanical stresses in the formation and progression of the lamellipodium-lamellum interface [corrected].

    PubMed

    Shemesh, Tom; Verkhovsky, Alexander B; Svitkina, Tatyana M; Bershadsky, Alexander D; Kozlov, Michael M

    2009-09-01

    Actin network in the front part of a moving cell is organized into a lamellipodium and a lamellum. A distinct lamellipodium-lamellum interface is associated with focal adhesions and consists of a series of arclike segments linking neighboring focal adhesions in the front row. The interface advances by leaping onto new rows of focal adhesions maturating underneath the lamellipodium. We propose a mechanism of the lamellipodium-lamellum boundary generation, shape formation, and progression based on the elastic stresses generated in the lamellipodial actin gel by its friction against the focal adhesions. The crucial assumption of the model is that stretching stresses trigger actin gel disintegration. We compute the stress distribution throughout the actin gel and show that the gel-disintegrating stresses drive formation of a gel boundary passing through the row of focal adhesions. Our computations recover the lamellipodium-lamellum boundary shapes detected in cells and predict the mode of the boundary transition to the row of the newly maturing focal adhesions in agreement with the experimental observations. The model fully accounts for the current phenomenology of the lamellipodium-lamellum interface formation and advancing, and makes experimentally testable predictions on the dependence of these phenomena on the sizes of the focal adhesions, the character of the focal adhesion distribution on the substrate, and the velocity of the actin retrograde flow with respect to the focal adhesions. The phase diagram resulting from the model provides a background for quantitative classification of different cell types with respect to their ability to form a lamellipodium-lamellum interface. In addition, the model suggests a mechanism of nucleation of the dorsal and arclike actin bundles found in the lamellum. PMID:19720013

  17. Forecasting magnitude, time, and location of aftershocks for aftershock hazard

    NASA Astrophysics Data System (ADS)

    Chen, K.; Tsai, Y.; Huang, M.; Chang, W.

    2011-12-01

    In this study we investigate the spatial and temporal seismicity parameters of the aftershock sequence accompanying the 17:47 20 September 1999 (UTC) 7.45 Chi-Chi earthquake Taiwan. Dividing the epicentral zone into north of the epicenter, at the epicenter, and south of the epicenter, it is found that immediately after the earthquake the area close by the epicenter had a lower value than both the northern and southern sections. This pattern suggests that at the time of the Chi-Chi earthquake, the area close by the epicenter remained prone to large magnitude aftershocks and strong shaking. However, with time the value increases. An increasing value indicates a reduced likelihood of large magnitude aftershocks. The study also shows that the value is higher at the southern section of the epicentral zone, indicating a faster rate of decay in this section. The primary purpose of this paper is to design a predictive model for forecasting the magnitude, time, and location of aftershocks to large earthquakes. The developed model is presented and applied to the 17:47 20 September 1999 7.45 Chi-Chi earthquake Taiwan, and the 09:32 5 November 2009 (UTC) Nantou 6.19, and 00:18 4 March 2010 (UTC) Jiashian 6.49 earthquake sequences. In addition, peak ground acceleration trends for the Nantou and Jiashian aftershock sequences are predicted and compared to actual trends. The results of the estimated peak ground acceleration are remarkably similar to calculations from recorded magnitudes in both trend and level. To improve the predictive skill of the model for occurrence time, we use an empirical relation to forecast the time of aftershocks. The empirical relation improves time prediction over that of random processes. The results will be of interest to seismic mitigation specialists and rescue crews. We apply also the parameters and empirical relation from Chi-Chi aftershocks of Taiwan to forecast aftershocks with magnitude M > 6.0 of 05:46 11 March 2011 (UTC) Tohoku 9

  18. Thrust-type focal mechanisms of tectonic tremors in Taiwan: Evidence of subduction

    NASA Astrophysics Data System (ADS)

    Ide, Satoshi; Yabe, Suguru; Tai, Hsin-Ju; Chen, Kate Huihsuan

    2015-05-01

    Unlike tectonic tremors in subduction zones and along transform faults, the hosting structure for tremors in Taiwan remains debated. Tectonic tremors in Taiwan have been discovered at ~30 km depth beneath the southern Central Range, which is a young and active collisional mountain belt. Here we provide the first evidence for the focal mechanism of tremor using moment tensor inversion in the very low frequency band, employing broadband seismograms stacked relative to the hypocentral time of tremor. The best solution corresponds to low-angle thrust faulting, suggesting the subduction of the Eurasian plate. This mechanism is consistent with strong tidal modulation of tremor activity but differs from the normal-type faulting that dominates regional shallow earthquakes. This result suggests vertical variations in the tectonic stress regime. Thrust faulting may be facilitated by a decrease in normal stress due to the buoyant roots of the mountain belt and local high fluid pressure.

  19. Non-shear focal mechanisms of earthquakes at The Geysers, California and Hengill, Iceland, geothermal areas

    USGS Publications Warehouse

    Julian, B.R.; Miller, A.D.; Foulger, G.R.

    1993-01-01

    Several thousand earthquakes were recorded in each area. We report an initial investigation of the focal mechanisms based on P-wave polarities. Distortion by complicated three-dimensional crustal structure was minimized using tomographically derived three-dimensional crustal models. Events with explosive and implosive source mechanisms, suggesting cavity opening and collapse, have been tentatively identified at The Geysers. The new data show that some of these events do not fit the model of tensile cracking accompanied by isotropic pore pressure decreases that was suggested in earlier studies, but that they may instead involve combination of explosive and shear processes. However, the confirmation of earthquakes dominated by explosive components supports the model that the event are caused by crack opening induced by thermal contraction of the heat source.

  20. Some characteristics of the complex El Mayor-Cucapah, MW7.2, April 4, 2010, Baja California, Mexico, earthquake, from well-located aftershock data from local and regional networks.

    NASA Astrophysics Data System (ADS)

    Frez, J.; Nava Pichardo, F. A.; Acosta, J.; Munguia, L.; Carlos, J.; García, R.

    2015-12-01

    Aftershocks from the El Mayor-Cucapah (EMC), MW7.2, April 4, 2010, Baja California, Mexico, earthquake, were recorded over two months by a 31 station local array (Reftek RT130 seismographs loaned from IRIS-PASSCAL), complemented by regional data from SCSN, and CICESE. The resulting data base includes 518 aftershocks with ML ≥ 3.0, plus 181 smaller events. Reliable hypocenters were determined using HYPODD and a velocity structure determined from refraction data for a mesa located to the west of the Mexicali-Imperial Valley. Aftershock hypocenters show that the El Mayor-Cucapah earthquake was a multiple event comprising two or three different ruptures of which the last one constituted the main event. The main event rupture, which extends in a roughly N45°W direction, is complex with well-defined segments having different characteristics. The main event central segment, located close to the first event epicenter is roughly vertical, the northwest segment dips ~68°NE, while the two southeast segments dip ~60°SW and ~52°SW, respectively, which agrees with results of previous studies based on teleseismic long periods and on GPS-INSAR. All main rupture aftershock hypocenters have depths above 10-11km and, except for the central segment, they delineate the edges of zones with largest coseismic displacement. The two southern segments show seismicity concentrated below 5km and 3.5km, respectively; the paucity of shallow seismicity may be caused by the thick layer of non-consolidated sediments in this region. The ruptures delineated by aftershocks in the southern regions correspond to the Indiviso fault, unidentified until the occurrence of the EMC earthquake. The first event was relocated together with the aftershocks; the epicenter lies slightly westwards of published locations, but it definitely does not lie on, or close to, the main rupture. The focal mechanism of the first event, based on first arrival polarities, is predominantly strike-slip; the focal plane

  1. Focal Mechanisms of Three Finnish Earthquakes and Their Connection To Surface Faults

    NASA Astrophysics Data System (ADS)

    Uski, M.; Hyvönen, T.; Korja, A.; Airo, M.-L.

    Focal mechanisms of three recent earthquakes in Finland were determined using P wave polarities as well as SV/P and SH/P phase amplitude ratios. The events occurred on May 11th, 2000 in Toivakka, central Finland (ML=2.4), on September 15th, 2000 in Kuusamo, northeastern Finland (ML=3.5), and on May 2nd, 2001 in Kolari, western Lapland (ML=2.9). In order to obtain reliable estimates of the source parameters, local crust and upper mantle velocity models were derived for the epicenter areas. The events were relocated using P- and S-phase arrival times from the nearest stations and the new velocity models. Synthetic waveforms calculated with the reflectivity method were used to further constrain and verify the source and structural parameters. The well-constrained fault plane solution of the Toivakka earthquake indicates reverse faulting trending 358/42 or 196/50. By comparing the focal planes with magnetic and topographic data of the epicenter area, we suggest the eastward dipping plane to be the actual fault plane. Both the location procedure and synthetic waveform modelling place the focus at the depth of 6 km. The hypocenter parameters of the Kuusamo earthquake are not as well constrained as in the other events, due to lack of seismic stations at distances less than 175 km. The best fitting solution indicates normal-faulting mechanism striking 133/47 or 284/47. Both fault directions are found as pairs of topographic and weak, discontinuous mag- netic lineaments. The focus is located between 12 km and 14 km. The best fitting fault plane solution of the Kolari earthquake suggests pure thrust- faulting mechanism at a shallow depth, 4 km. The strike and dip (030/30) correlates well with the surface observations of postglacial faults in the area.

  2. Focal Mechanisms for Local Earthquakes within a Rapidly Deforming Rhyolitic Magma System, Laguna del Maule, Chile

    NASA Astrophysics Data System (ADS)

    Peterson, D. E.; Keranen, K. M.; Cardona, C.; Thurber, C. H.; Singer, B. S.

    2015-12-01

    Large shallow rhyolitic magma systems like the one underlying the Laguna del Maule Volcanic Field (LdM) atop the Southern Andes, Chile, that comprises the largest concentration of rhyolitic lava and tephra younger than 20 ka at earth's surface, are capable of producing modest to very large explosive eruptions. Moreover, LdM is currently exhibiting magma migration, reservoir growth, and crustal deformation at rates higher than any volcano that is not actively erupting. The long-term build-up of a large silicic magmatic system toward an eruption has yet to be monitored, therefore, precursory phenomena are poorly understood. In January of 2015, 12 broadband, 3-component seismometers were installed at LdM to detect local microearthquakes and tele-seismic events with the goals of determining the migration paths of fluids as well as the boundaries of the magma chamber beneath LdM. These stations complement the 6 permanent stations installed by the Southern Andes Volcano Observatory in 2011. Focal mechanisms were calculated using FOCMEC (Snoke et al., 1984) and P-wave first motions for local events occurring between January and March of 2015 using these 18 broadband stations. Results from six of the largest local events indicate a mixture of normal and reverse faulting at shallow (<10 km) depths surrounding the lake. This may be associated with the opening of fractures to accommodate rising magma in the subsurface and/or stresses induced by the rapid deformation. Two of these events occurred near the center of maximum deformation where seismic swarms have previously been identified. Focal mechanisms from smaller magnitude events will be calculated to better delineate subsurface structure. Source mechanisms will be refined using P-S amplitude ratios and full waveform inversion.

  3. Tectonic implication of local seismic tomography and focal mechanism study in Northeast Taiwan

    NASA Astrophysics Data System (ADS)

    Liao, Y. C.; Li, Y. H.

    2015-12-01

    Evaluation of the stability of host rock and nearby seismic activities are critical for safety issue. Since 2011, a broad-band seismometer array with 15 seismometers has been gradually deployed to date in the study area to collect continuous waveform data for host rock characterization study. In this study, we presented a series of study results, including location/relocation of regional earthquakes, seismic focal mechanisms, and inversion of three dimensional Vp and Vp/Vs models. A double-difference tomography algorithm was adopted in both earthquake relocation and three-dimensional velocity inversion to improve location accuracy and model reliability. Spatial distribution of earthquakes could be separated into two clusters. The eastern group was distributed nearly along the eastern boundary of granite outcrop in the surface; the other group was mainly located beneath the western part of imbricated high-magnetic-susceptibility zones, which were identified by three-dimensional inversion of aeromagnetic data. In-between there exists a clear zone with relatively quiet seismicity. Moreover, our Vp and Vp/Vs inversion results also revealed patterns compatible with previous-mentioned imbricate structures and shown good correlation with the high magnetic susceptibility zones as well. In addition, more than one hundred earthquake events with clear P-wave first motion in waveform were identified for demonstration. Their focal mechanisms were also determined and shown dramatic variation with respect to the depth of hypocenters. Mechanisms of earthquakes in shallow crust with depth less than 10 km are mostly normal faults. In contrast, most of deeper events are reverse faults. It implies that tectonic stress regime in shallow crust is extensional and becomes more compressional in deeper part.

  4. Microseismicity and focal mechanisms of the intermediate-depth Bucaramanga nest, Colombia

    SciTech Connect

    Schneider, J.F.; Pennington, W.D.; Meyer, R.P.

    1987-12-10

    The Bucaramanga nest of intermediate-depth seismicity in northern Colombia was investigated from microearthquakes (m/sub b/less than or equal to4.3) recorded from June 20 to July 6, 1979, by a local array of 12 digital three-component seismographs. Of 161 events studied, 142 are from the nest and 19 define a thin Wadati-Benioff (W-B) zone, mainly from 110 to 190 km depth. The W-B zone, part of the Bucaramanga segment, strikes N10/sup 0/ E with a dip increasing wtih depth from 30/sup 0/ E to near-vertical beneath the nest. The 89 best located events from within the nest define a volume of about 8 km (NW) by 4 km (NE) by 4 km (depth) centered at 161 km depth, with relative location accuracies of +- 0.5 to +- 1.0 km. Double-couple fault plane solutions of 59 events were determined from an objective procedure using P wave polarities and S/P amplitude ratios. There is no dominant trend in focal mechanisms nor any reasonable correlation with regional stress patterns or previously determined mechanisms from teleseismic data. The subduction and assimilation of a linear feature (such as an island arc undergoing a phase transformation) may explain the existence of the Bucaramanga nest. However, the extraordinarily high rate of seismicity suggests that the nest may be moving rate several orders of magnitude faster than the rate of relative plate motion alone. The intense seismicity and variation in focal mechanisms suggest that the nest represents some aspect of stress release associated with the ascent of fluids, perhaps brine or magma, that will ultimately result in the initiation of volcanic activity over this recently emplaced W-B zone. copyright American Geophysical Union 1987

  5. Waveform analysis of aftershocks of the June 29, 1992 Little Skull Mountain, Nevada, earthquake

    SciTech Connect

    Sheehan, A.F.; Zeng, Y.; Smith, K.D. )

    1993-04-01

    Following the 29 June 1992 magnitude 5.6 Little Skull Mountain, Nevada, earthquake, twelve portable three-component digital seismometers were deployed in the region surrounding Little Skull Mountain and Yucca Mountain by researchers at the University of Nevada, Reno, Seismological Laboratory. These stations complemented the 55 permanent analog stations of the Southern Great Basin Seismic Network, and portable deployments of the United States Geological Survey (USGS), Golden, Colorado, and Lawrence Livermore National Laboratory, Livermore, California. The mainshock of the Little Skull Mountain earthquake occurred approximately 20 km southeast of the site at Yucca Mountain, Nevada, that is being characterized as a potential repository for high-level nuclear waste. The pattern of Little Skull Mountain aftershocks defines an L' shape at the southern boundary of the Nevada Test Site. The authors use a full waveform inversion method to study source properties of aftershocks in the epicentral area recorded on the digital stations. They compute the synthetic seismograms in a layered elastic media using the generalized reflection and transmission coefficient technique. The authors future plans include automation of these techniques for use in routine monitoring of seismic activity in the region. Parameters obtained in this study include focal mechanism, stress drop, rupture duration, and seismic moment. These results will allow them to place constraints on the geometry and style of subsurface faulting in the region and aid in the assessment of seismic hazard in the vicinity of Yucca Mountain.

  6. Focal mechanisms of the 2000 swarm in NW-Bohemia/Vogtland anything new in the seismotectonic picture of the area?

    NASA Astrophysics Data System (ADS)

    Horalek, J.; Šílený, J.; Fischer, T.

    2003-04-01

    The Nový Kostel area witnessed the most intensive earthquake swarms of the whole NW-Bohemia/Vogtland swarm region. The Ml = 4.6 swarm of 1985/86, which was the most intensive swarm in the area, showed focal mechanisms compatible with the main fault orientation. By contrast, the recent results of the analysis of the 1997 swarm (Ml = 3) have shown that two types of faulting took place. One of them beards a significant isotropic component in its moment tensors, what may indicate activity of fluids during the rupture process. The events of the most recent 2000 swarm (ML=3.2) lasting for three months were confined to a thin, almost planar, and steeply dipping focal area. The existing, preliminary focal mechanisms of the 2000 swarm show a simple pattern, which is again compatible with the main fault orientation. We made a detailed analysis of swarm seismograms recorded by WEBNET and other local networks in the area to determine precisely the focal mechanisms of all larger events (ML>1.8). We try to find any regularities in the occurrence of different fault mechanisms during the swarm development and across the fault volume. Full moment tensors have been determined for selected events and the rate of shear and non-shear components was critically evaluated. The results are interpreted according to focal mechanisms of the previous swarms occurring in the area and to its seismotectonic regime.

  7. Implications of Secondary Aftershocks for Failure Processes

    NASA Astrophysics Data System (ADS)

    Gross, S. J.

    2001-12-01

    When a seismic sequence with more than one mainshock or an unusually large aftershock occurs, there is a compound aftershock sequence. The secondary aftershocks need not have exactly the same decay as the primary sequence, with the differences having implications for the failure process. When the stress step from the secondary mainshock is positive but not large enough to cause immediate failure of all the remaining primary aftershocks, failure processes which involve accelerating slip will produce secondary aftershocks that decay more rapidly than primary aftershocks. This is because the primary aftershocks are an accelerated version of the background seismicity, and secondary aftershocks are an accelerated version of the primary aftershocks. Real stress perturbations may be negative, and heterogeneities in mainshock stress fields mean that the real world situation is quite complicated. I will first describe and verify my picture of secondary aftershock decay with reference to a simple numerical model of slipping faults which obeys rate and state dependent friction and lacks stress heterogeneity. With such a model, it is possible to generate secondary aftershock sequences with perturbed decay patterns, quantify those patterns, and develop an analysis technique capable of correcting for the effect in real data. The secondary aftershocks are defined in terms of frequency linearized time s(T), which is equal to the number of primary aftershocks expected by a time T, $ s ≡ ∫ t=0T n(t) dt, where the start time t=0 is the time of the primary aftershock, and the primary aftershock decay function n(t) is extrapolated forward to the times of the secondary aftershocks. In the absence of secondary sequences the function s(T)$ re-scales the time so that approximately one event occurs per new time unit; the aftershock sequence is gone. If this rescaling is applied in the presence of a secondary sequence, the secondary sequence is shaped like a primary aftershock sequence

  8. Stress accumulation process in and around the Atotsugawa fault, central Japan, estimated from focal mechanism analysis

    NASA Astrophysics Data System (ADS)

    Takada, Youichiro; Katsumata, Kei; Katao, Hiroshi; Kosuga, Masahiro; Iio, Yoshihisa; Sagiya, Takeshi

    2016-07-01

    We estimated 275 focal mechanisms from P-wave first-motion polarities of small earthquakes obtained in an extensive seismic survey during 2004-2008 in and around the Atotsugawa fault, central Japan, where ongoing dextral shear strain concentration has been observed. Along the fault trace, the azimuth direction of P-axes is oriented WNW-ESE, which agrees well with previous studies. The regional stress disturbance is detected by stress inversion analysis. The azimuth of the maximum principal stress axis systematically rotates counterclockwise as the distance from the fault trace decreases. The regional stress disturbance is explained by a cumulative slip deficit in the shallower portion of the Atotsugawa fault relative to the surrounding fault surface (i.e., the eastern, western, and deeper extensions of the fault plane).

  9. Analysis of crustal deformation in Luzon, Philippines using geodetic observations and earthquake focal mechanisms

    NASA Astrophysics Data System (ADS)

    Galgana, Gerald; Hamburger, Michael; McCaffrey, Robert; Corpuz, Ernesto; Chen, Qizhi

    2007-03-01

    We utilize regional GPS velocities from Luzon, Philippines, with focal mechanism data from the Harvard Centroid Moment Tensor (CMT) Catalog, to constrain tectonic deformation in the complex plate boundary zone between the Philippine Sea Plate and Eurasia (the Sundaland block). Processed satellite imagery and digital elevation models are used with existing gravity anomaly, seismicity, and geologic maps to define a suite of six elastic blocks. Geodetic and focal mechanism data are inverted simultaneously to estimate plate rotations and fault-locking parameters for each of the tectonic blocks and faults comprising Luzon. Major tectonic structures that were found to absorb the plate convergence include the Manila Trench (20-100 mm yr - 1 ) and East Luzon Trough (˜ 9-15 mm yr - 1 )/Philippine Trench (˜ 29-34 mm yr - 1 ), which accommodate eastward and westward subduction beneath Luzon, respectively; the left-lateral strike-slip Philippine Fault (˜ 20-40 mm yr - 1 ), and its northward extensions, the Northern Cordillera Fault (˜ 17-37 mm yr - 1 transtension), and the Digdig Fault (˜ 17-27 mm yr - 1 transpression). The Macolod Corridor, a zone of active volcanism, crustal thinning, extension, and extensive normal and strike-slip faulting in southwestern Luzon, is associated with left-lateral, transtensional slip of ˜ 5-10 mm yr - 1 . The Marikina Fault, which separates the Central Luzon block from the Southwestern Luzon block, reveals ˜ 10-12 mm yr - 1 of left-lateral transpression. Our analysis suggests that much of the Philippine Fault and associated splays are locked to partly coupled, while the Manila and Philippine trenches appear to be poorly coupled. Luzon is best characterized as a tectonically active plate boundary zone, comprising six mobile elastic tectonic blocks between two active subduction zones. The Philippine Fault and associated intra-arc faults accommodate much of the trench-parallel component of relative plate motion.

  10. New techniques for the analysis of earthquake sources from local array data with an application to the 1993 Scotts Mills, Oregon, aftershock sequence

    NASA Astrophysics Data System (ADS)

    Schurr, Bernd; Nábělek, John

    1999-06-01

    We analysed aftershocks recorded by a temporary digital seismic network following the moderate M_w =5.5 1993, Scotts Mills, Oregon, earthquake. A technique to retrieve source moment tensors from local waveforms was developed, tested, and applied to 41 small earthquakes (M_w ranging from 1.6 to 3.2). The derived focal mechanisms, although well resolved, are highly variable and do not share a common nodal plane. In contrast, the majority of the events, relocated with a joint hypocentre determination algorithm, collapse to a well-focused plane. The incompatibility of the nodal planes of most events with the plane defined by their locations suggests that the aftershocks did not occur on the fault plane, but tightly around it, outlining the rupture area rather than defining it. Furthermore, the moment tensors reveal stable P-axes, whereas T-axes plunges are highly dispersed. We detect a rotation of average T-axis plunge with depth, indicating a change from shallower, predominantly dip-slip mechanisms to deeper strike-slip mechanisms. These characteristics are difficult to explain by remnant stress concentrations on the main-shock rupture plane or asperity- and barrier-type models. We suggest that the aftershocks occurred under the ambient regional stress, triggered by a sudden weakening of the region surrounding the main-shock slip, rather than from a shear stress increase due to the main shock.

  11. Mechanically Induced Focal Adhesion Assembly Amplifies Anti-Adipogenic Pathways in Mesenchymal Stem Cells

    PubMed Central

    Sen, Buer; Guilluy, Christophe; Xie, Zhihui; Case, Natasha; Styner, Maya; Thomas, Jacob; Oguz, Ipek; Rubin, Clinton; Burridge, Keith; Rubin, Janet

    2013-01-01

    The fate of pluripotent mesenchymal stem cells (MSC) is determined through integration of chemical, spatial, and physical signals. The suppression of MSC adipogenesis by mechanical stimuli, which requires Akt-induced inhibition of glycogen synthase kinase 3β (GSK3β) with β-catenin activation, can be enhanced by repetitive dosing within a single day. Here, we demonstrate that reapplication of cyclic strain within a 24-hour period leads to amplification of both Akt activation and its subsequent inhibition of GSK3β, such that total cycle number can be reduced while still inhibiting adipogenesis. Amplification of Akt signaling is facilitated by a dynamic restructuring of the cell in response to mechanical signals, as evidenced by a transient increase in focal adhesion (FA) number and increased RhoA activity. Preventing FA assembly or development of tension blocks activation of Akt by mechanical signals, but not by insulin. This indicates that the FA infrastructure is essential to the physical, but not necessarily the chemical, sensitivity, and responsiveness of the cell. Exploiting the transient nature of cytoskeletal remodeling may represent a process to enhance cell responsiveness to mechanical input and ultimately define the fate of MSCs with a minimal input. PMID:21898699

  12. Intraplate Stress Field in Brazil Using Focal Mechanisms: Regional and Local Patterns: Examples of Regional Forces Controlling the Stress Field

    NASA Astrophysics Data System (ADS)

    Dias, F. L.; Assumpcao, M.

    2014-12-01

    The knowledge of stress field is fundamental not only to understand driving forces and plate deformation but also in the study of intraplate seismicity. In Brazil, the stress field has been determined mainly using focal mechanisms and a breakout data and in-situ measurements. However, the stress field still is poorly known in Brazil. We show a recent compilation of focal mechanism determined in Brazil (Fig 1). The focal mechanisms of some recent earthquakes (magnitude lower than 5 mb) were studied using waveform modeling. We stacked the record of several teleseismic stations (> 30°) with a good signal/noise ratio and we grouped then according to distance and azimuth. With the focal mechanisms available in literature and those obtained in this work, we were able to identify some patterns: the central region shows compressional pattern (E-W SHmax), which is predicted by regional theoretical models ( Coblentz & Richardson, 1996 and the TD0 model of Lithgow & Bertelloni, 2004). This compression is mainly due to the interaction of tectonic plate forces. Meanwhile in the Amazon region, we find an indication of SHMax oriented in the SE-NW direction, probably caused by the Caribbean plate interaction (Meijer, 1995) and Amazon Fan, we have flexural stresses caused by sedimentary load with is in agreement with local theoretical models (Watts et al., 2009) . In northern coastal region, the compression rotates following the coastline, which indicates an important local component related to spreading effects at the continental/oceanic transition (Assumpção, 1998). We determine the focal mechanism of several events in Brazil using different techniques according to the available data. The major difficulty is to determine focal mechanism of low magnitudes events (< 5.0 mb) using distant or few seismograph stations. We find examples of stress perturbations induced by local effects (e.g. flexure and continental spreading). The results of this work should be useful for future

  13. Seismic events with implosional focal mechanisms in the Coeur d'Alene mining district, northern Idaho

    NASA Astrophysics Data System (ADS)

    Stickney, Michael C.; Sprenke, Kenneth F.

    1993-04-01

    Rockbursts are a major hazard in the Coeur d'Alene mining district of northern Idaho. To study the source mechanisms of mining-related seismicity, we operated 15 portable seismographs in the Coeur d'Alene mining district for one week in September 1990. We found the velocity model of the district to consist of a halfspace with a P wave velocity of 5.74 km/s and an S wave velocity of 3.47 km/s. In-mine seismic monitoring systems provided excellent control on the velocity model and most hypocenter locations. Twenty-one events, with sufficient focal sphere coverage for fault plane solutions, were recorded. Eleven of the events produced all-dilatational first motions; for all events, 90 percent of first motions observed were dilatational. Ten events produced unsolvable first-motion data in terms of the usual double-couple mechanism, but seven of these unsolvable events were found consistent with an implosional source and two others were consistent with a shear-implosional source. Our results provide firm observational evidence that dilatational first motions are predominant in this deep metal-mining district, probably the result of implosional and shear-implosional source mechanisms.

  14. Integrin binding and mechanical tension induce movement of mRNA and ribosomes to focal adhesions

    NASA Technical Reports Server (NTRS)

    Chicurel, M. E.; Singer, R. H.; Meyer, C. J.; Ingber, D. E.

    1998-01-01

    The extracellular matrix (ECM) activates signalling pathways that control cell behaviour by binding to cell-surface integrin receptors and inducing the formation of focal adhesion complexes (FACs). In addition to clustered integrins, FACs contain proteins that mechanically couple the integrins to the cytoskeleton and to immobilized signal-transducing molecules. Cell adhesion to the ECM also induces a rapid increase in the translation of preexisting messenger RNAs. Gene expression can be controlled locally by targeting mRNAs to specialized cytoskeletal domains. Here we investigate whether cell binding to the ECM promotes formation of a cytoskeletal microcompartment specialized for translational control at the site of integrin binding. High-resolution in situ hybridization revealed that mRNA and ribosomes rapidly and specifically localized to FACs that form when cells bind to ECM-coated microbeads. Relocation of these protein synthesis components to the FAC depended on the ability of integrins to mechanically couple the ECM to the contractile cytoskeleton and on associated tension-moulding of the actin lattice. Our results suggest a new type of gene regulation by integrins and by mechanical stress which may involve translation of mRNAs into proteins near the sites of signal reception.

  15. The 2011 October 23 Mw 7.2 Van-Erciş, Turkey, earthquake and its aftershocks

    NASA Astrophysics Data System (ADS)

    Görgün, Ethem

    2013-11-01

    On 2011 October 23, the Lake Van region in eastern Anatolia was hit by an Mw = 7.2 earthquake. The Van-Erciş earthquake (EQ) occurred 20 km east of Lake Van. Centroid moment tensors (CMT) for 108 events with Mw between 4.0 and 7.2 are computed by applying a waveform inversion method on data from the Kandilli Observatory and Earthquake Research Institute (KOERI) broad-band seismic network. The time span of data covers the period between 2011 October 23 and 2012 February 24. The main shock is a shallow focus thrust event at a depth of 15 km. Focal depths of aftershocks range from 12 to 25 km. The seismic moment (M0) of the main shock is estimated to be 0.75 × 1020 Nm. The focal mechanisms of the aftershocks are mainly thrust faulting with a variable and sometimes significant strike-slip component. This geometry indicates a thrust faulting regime with NE-SW trending direction of T-axis in the entire activated region. A stress tensor inversion of focal mechanism data is performed to obtain a more accurate picture of the Van-Erciş EQ stress field. The stress tensor inversion results show a predominant thrust stress regime with a NW-SE to NNE-SSW oriented maximum horizontal compressive stress (SH). The secondary fault system striking mostly ENE-WSW is activated generally with right-lateral strike-slip in the east of the main shock. This difference in mechanism suggest that towards the east, a different fault system is activated with respect to the NE-SW trending thrust faults beneath Van-Erciş region and more to the west. Thus, to first order, the Lake Van region is characterized by a homogeneous intraplate stress field.

  16. Larger aftershocks happen farther away: Nonseparability of magnitude and spatial distributions of aftershocks

    NASA Astrophysics Data System (ADS)

    Elst, Nicholas J.; Shaw, Bruce E.

    2015-07-01

    Aftershocks may be driven by stress concentrations left by the main shock rupture or by elastic stress transfer to adjacent fault sections or strands. Aftershocks that occur within the initial rupture may be limited in size, because the scale of the stress concentrations should be smaller than the primary rupture itself. On the other hand, aftershocks that occur on adjacent fault segments outside the primary rupture may have no such size limitation. Here we use high-precision double-difference relocated earthquake catalogs to demonstrate that larger aftershocks occur farther away than smaller aftershocks, when measured from the centroid of early aftershock activity—a proxy for the initial rupture. Aftershocks as large as or larger than the initiating event nucleate almost exclusively in the outer regions of the aftershock zone. This observation is interpreted as a signature of elastic rebound in the earthquake catalog and can be used to improve forecasting of large aftershocks.

  17. Focal mechanisms and the state of stress on the San Andreas Fault in southern California

    NASA Astrophysics Data System (ADS)

    Jones, Lucile M.

    1988-08-01

    Focal mechanisms have been determined from P wave first motion polarities for 138 small to moderate (2.6 ≤ M ≤ 4.3) earthquakes that occurred within 10 km of the surface trace of the San Andreas fault in southern California between 1978 and 1985. On the basis of these mechanisms the southern San Andreas fault has been divided into five segments with different stress regimes. Earthquakes in the Fort Tejon segment show oblique reverse sup on east-west and northwest striking faults. The Mojave segment has earthquakes with oblique reverse and right-lateral strikesup motion on northwest strikes. The San Bernardino segment has normal faulting earthquakes on north-south striking planes, while the Banning segment has reverse, strike-sup, and normal faulting events all occurring in the same area. The earthquakes in the Indio segment show strike-slip and oblique normal faulting on northwest to north-south striking planes. These focal mechanism data have been inverted to determine how the stresses acting on the San Andreas fault in southern California vary with position along strike of the fault. One of the principal stresses is vertical in all of the regions. The vertical stress is the minimum principal stress in Fort Tejon and Mojave, the intermediate principal stress in Banning and Indio, and the maximum principal stress in San Bernardino. The orientations of the horizontal principal stresses also vary between the regions. The trend of the maximum horizontal stress rotates over 35°, from N15°W at Fort Tejon to N20° at Indio. Except for the San Bernardino segment, the trend of the maximum horizontal stress is at a constant angle of about 65° to the local strike of the San Andreas fault, implying a weak fault. The largest change in the present stress state occurs at the end of the rupture zone of the 1857 Fort Tejon earthquake. It appears that the 1857 rupture ended when it propagated into an area of low stress amplitude, possibly caused by the 15° angle between the

  18. Shape of the plate interface near the Mejillones Peninsula in Northern Chile inferred from high resolution relocation of Tocopilla aftershocks

    NASA Astrophysics Data System (ADS)

    Fuenzalida, A.; Schurr, B.; Lancieri, M.; Madariaga, R. I.

    2011-12-01

    computed by cross-correlation. The relocated events situated inland, under the TF network collapse into a very thin layer of less than a km width. These events are located mainly in the deep interplate zone in the northern area of the 2007 rupture (30-55km) but become shallower as we approach the Mejillones Peninsula in the South (15-55km). We find clear evidence for a "kink" or plate interface discontinuity at around 30 km depth. Events off-shore are less well-located, but we find clear evidence that some of these aftershocks occurred on active splay faults within the continental plate wedge. We are currently working to confirm this observation using waveform data. Finally we show that the rupture of the main plate interface can produce secondary rupture of the Nazca plate below the plate interface.Focal mechanisms of 452 aftershocks were essentially thrust events due to the subduction process. On other hand,the aftershocks of Michilla earthquake all have the slab- push mechanism of this event and are aligned along a thin vertical zone inside the Nazca plate.

  19. Mechanical design of mounts for IGRINS focal plane arrays and field flattening lenses

    NASA Astrophysics Data System (ADS)

    Oh, Jae Sok; Park, Chan; Cha, Sang-Mok; Yuk, In-Soo; Kim, Kang-Min; Chun, Moo-Young; Ko, Kyeongyeon; Oh, Heeyeong; Jeong, Ueejeong; Nah, Jakyoung; Lee, Hanshin; Pavel, Michael; Jaffe, Daniel T.

    2014-07-01

    IGRINS, the Immersion GRating INfrared Spectrometer, is a near-infrared wide-band high-resolution spectrograph jointly developed by the Korea Astronomy and Space Science Institute and the University of Texas at Austin. IGRINS employs three HAWAII-2RG focal plane array (FPA) detectors. The mechanical mounts for these detectors and for the final (field-flattening) lens in the optical train serve a critical function in the overall instrument design: Optically, they permit the only positional compensation in the otherwise "build to print" design. Thermally, they permit setting and control of the detector operating temperature independently of the cryostat bench. We present the design and fabrication of the mechanical mount as a single module. The detector mount includes the array housing, housing for the SIDECAR ASIC, a field flattener lens holder, and a support base. The detector and ASIC housing will be kept at 65 K and the support base at 130 K. G10 supports thermally isolate the detector and ASIC housing from the support base. The field flattening lens holder attaches directly to the FPA array housing and holds the lens with a six-point kinematic mount. Fine adjustment features permit changes in axial position and in yaw and pitch angles. We optimized the structural stability and thermal characteristics of the mount design using computer-aided 3D modeling and finite element analysis. Based on the computer simulation, the designed detector mount meets the optical and thermal requirements very well.

  20. Present-day Stress Pattern of Turkey from Inversion of Updated Earthquake Focal Mechanism Catalogue

    NASA Astrophysics Data System (ADS)

    Özacar, A.

    2011-12-01

    Active tectonic setting of Turkey is characterized by different stress regimes. In order to analyze present-day tectonic stresses throughout the country, all available earthquake focal mechanisms with updated locations reported by the International Seismological Center (ISC) and national catalogues are compiled between 34° - 43° latitudes and 25° - 46° longitudes. Focal mechanisms of earthquakes with multiple solutions are chosen based on their reliability and consistency with the local tectonic setting. The resultant database which includes 1391 events occurred during the period 1909 - 2010 with magnitudes ranging from 2.0 to 8.0 and depths reaching up to 165 km, constitutes the base information for better active fault characterization in seismic hazard analyses. Using this catalogue, the pressure-tension axes, maximum-minimum horizontal stress axes, and tectonic stress regime of each earthquake are determined following the World Stress Map (WSM) project guidelines and analyzed separately for crustal and intermediate depth earthquakes. During stress inversion, crustal events are grouped in 36 and intermediate depth events in 2 distinct regions on the basis of their geographical proximity, kinematic homogeneity and tectonic setting to minimize the amount of heterogeneity and map the variations in the stress field. In the following stage, results of independent stress inversions including orientations of the three principal compressive stresses (σ1 = maximum, σ2 = intermediate, and σ3 = minimum), ratio of stress magnitudes (σ2 - σ3 / σ1 - σ3), and dominant stress regimes, are analyzed along with seismicity recorded by national seismic networks and previously mapped active faults. Our results reveal widespread strike-slip faulting in the crust throughout Turkey including North Anatolian Fault Zone, North Aegean Trough, Pliny-Strabo Trenches, Paphos Transform Fault, Tuzgölü Fault, East Anatolian Fault Zone, and East Anatolian Plateau. The regions

  1. Focal mechanisms of earthquake multiplets in the western part of the Corinth rift (Greece)

    NASA Astrophysics Data System (ADS)

    Godano, M.; Deschamps, A.; Lambotte, S.; Lyon-Caen, H.; Bernard, P.

    2012-04-01

    The Gulf of Corinth is one of the most seismically active zones in Europe. The seismicity mainly occurs between 5 and 12 km (seismogenic zone, Rigo et al. 1996) and follows a swarm organization with alternation of intensive crisis and more quiescent periods. Fluids seem to play a key role in the occurrence of the seismic activity (Bourouis and Cornet 2009, Pacchiani and Lyon-Caen 2009). In the western part of the Gulf, the Corinth rift laboratory seismological network (CRLNET) is composed of 12 short period 3-component seismometers and records the seismic activity since 2000. The analysis of multiplets (groups of earthquakes with similar waveform) from 2000 to 2007 and a detailed relocation using double-difference techniques have highlighted multiplets located along planar structures (Lambotte et al, in preparation). In this study we determine the composite fault plane solution for 24 of the largest multiplets. The focal mechanisms are computed by jointly inverting P polarity and SV/P, SH/P, SV/SH amplitude ratios of the direct waves. This inversion method is based on the non linear inversion scheme of the direct P, SV and SH amplitudes proposed by Godano et al. (2009). The fault plane solutions are determined using 1D velocity model (Rigo et al. 1996) and 3D velocity model (Gauthier et al. 2006). Solutions computed with the 3D velocity model have a better misfit function than the 1D solutions and are essentially E-NE/W-SW and W-NW/E-SE normal faults which is in accordance with the N-S extensional regime. For 18 multiplets, one of the nodal planes has strike and dip in accordance with the structure delineated by the earthquakes. It is then possible to make the hypothesis that such nodal plane is the fault plane. We can observe a clear decrease of the fault plane dip along the depth and toward the north. This could highlight the rooting of steep dip faults on a low dip structure. We finally discuss the relation between the multiplets (geometry and focal mechanisms

  2. Performance of aftershock forecasts: problem and formulation

    NASA Astrophysics Data System (ADS)

    Jiang, C.; Wu, Z.; Li, L.

    2010-12-01

    WFSD project deals with the problems of earthquake physics, in which one of the important designed aims is the forecast of the on-going aftershock activity of the Wenchuan earthquake, taking the advantage of the fast response to great earthquakes. Correlation between fluid measurements and aftershocks provided heuristic clues to the forecast of aftershocks, invoking the discussion on the performance of such ‘precursory anomalies’, even if in a retrospective perspective. In statistical seismology, one of the critical issues is how to test the statistical significance of an earthquake forecast scheme against real seismic activity. Due to the special characteristics of aftershock series and the feature of aftershock forecasts that it deals with a limited spatial range and specific temporal duration, the test of the performance of aftershock forecasts has to be different from the standard tests for main shock series. In this presentation we address and discuss the possible schemes for testing the performance of aftershock forecasts - a seemingly simple but practically important issue in statistical seismology. As a simple and preliminary approach, we use an alternative form of Receiver Operating Characteristic (ROC) test, as well as other similar tests, considering the properties of aftershock series by using Omori law, ETAS model, and/or CFS calculation. We also discussed the lessons and experiences of the Wenchuan aftershock forecasts, exploring how to make full use of the present knowledge of the regularity of aftershocks to serve the earthquake rescue and relief endeavor as well as the post-earthquake reconstruction.

  3. Self-similar aftershock rates.

    PubMed

    Davidsen, Jörn; Baiesi, Marco

    2016-08-01

    In many important systems exhibiting crackling noise-an intermittent avalanchelike relaxation response with power-law and, thus, self-similar distributed event sizes-the "laws" for the rate of activity after large events are not consistent with the overall self-similar behavior expected on theoretical grounds. This is particularly true for the case of seismicity, and a satisfying solution to this paradox has remained outstanding. Here, we propose a generalized description of the aftershock rates which is both self-similar and consistent with all other known self-similar features. Comparing our theoretical predictions with high-resolution earthquake data from Southern California we find excellent agreement, providing particularly clear evidence for a unified description of aftershocks and foreshocks. This may offer an improved framework for time-dependent seismic hazard assessment and earthquake forecasting. PMID:27627324

  4. Analysis of Focal Mechanism and Microseismicity around the Lusi Mud Eruption Site, East Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Karyono, Karyono; Obermann, Anne; Mazzini, Adriano; Lupi, Matteo; Syafri, Ildrem; Abdurrokhim, Abdurrokhim; Masturyono, Masturyono; Hadi, Soffian

    2016-04-01

    The 29th of May 2006 numerous eruption sites started in northeast Java, Indonesia following to a M6.3 earthquake striking the island.Within a few weeks an area or nearly 2 km2 was covered by boiling mud and rock fragments and a prominent central crater (named Lusi) has been erupting for the last 9.5 years. The M.6.3 seismic event also triggered the activation of the Watukosek strike slip fault system that originates from the Arjuno-Welirang volcanic complex and extends to the northeast of Java hosting Lusi and other mud volcanoes. Since 2006 this fault system has been reactivated in numerous instances mostly following to regional seismic and volcanic activity. However the mechanism controlling this activity have never been investigated and remain poorly understood. In order to investigate the relationship existing between seismicity, volcanism, faulting and Lusi activity, we have deployed a network of 31 seismometers in the framework of the ERC-Lusi Lab project. This network covers a large region that monitors the Lusi activity, the Watukosek fault system and the neighboring Arjuno-Welirang volcanic complex. In particular, to understand the consistent pattern of the source mechanism, relative to the general tectonic stress in the study area, a detailed analysis has been carried out by performing the moment tensor inversion for the near field data collected from the network stations. Furthermore these data have been combined with the near field data from the regional network of the Meteorological, Climatological and Geophysical Agency of Indonesia that covers the whole country on a broader scale. Keywords: Lusi, microseismic event, focal mechanism

  5. The state of stress near the Mendocino Triple Junction from inversion of earthquake focal mechanisms

    NASA Astrophysics Data System (ADS)

    Schwartz, Susan Y.; Hubert, Aurélia

    Focal mechanisms of 70 earthquakes occurring in the region of the Mendocino triple junction between 1977 and 1995 are inverted to obtain the regional stress orientations and relative magnitudes in this technically complex area. A diverse set of earthquake geometries is consistent with a single stress field characterized by north-northwest, horizontal, maximum principal compressive stress. Although this stress direction is almost perpendicular to convergence between the North American and Gorda plates, it is consistent with the stress direction inferred within the Gorda plate northwest of the triple junction. A maximum compressive stress direction nearly parallel to strike of the Cascadia subduction zone implies very low resolved shear stress across this plate boundary. Evidence for failure along the southernmost section of the Cascadia subduction zone comes from the occurrence of the recent 1992 (Ms=7.1) Cape Mendocino underthrusting earthquake as well as from measurements of Holocene surface uplift consistent with the 1992 coseismic uplift pattern. Rupture of the Cascadia subduction zone under this stress regime requires that the southernmost region of the Gorda-North American Plate boundary is weak.

  6. Tectonics earthquake distribution pattern analysis based focal mechanisms (Case study Sulawesi Island, 1993–2012)

    SciTech Connect

    Ismullah M, Muh. Fawzy; Lantu,; Aswad, Sabrianto; Massinai, Muh. Altin

    2015-04-24

    Indonesia is the meeting zone between three world main plates: Eurasian Plate, Pacific Plate, and Indo – Australia Plate. Therefore, Indonesia has a high seismicity degree. Sulawesi is one of whose high seismicity level. The earthquake centre lies in fault zone so the earthquake data gives tectonic visualization in a certain place. This research purpose is to identify Sulawesi tectonic model by using earthquake data from 1993 to 2012. Data used in this research is the earthquake data which consist of: the origin time, the epicenter coordinate, the depth, the magnitude and the fault parameter (strike, dip and slip). The result of research shows that there are a lot of active structures as a reason of the earthquake in Sulawesi. The active structures are Walannae Fault, Lawanopo Fault, Matano Fault, Palu – Koro Fault, Batui Fault and Moluccas Sea Double Subduction. The focal mechanism also shows that Walannae Fault, Batui Fault and Moluccas Sea Double Subduction are kind of reverse fault. While Lawanopo Fault, Matano Fault and Palu – Koro Fault are kind of strike slip fault.

  7. Tectonics earthquake distribution pattern analysis based focal mechanisms (Case study Sulawesi Island, 1993-2012)

    NASA Astrophysics Data System (ADS)

    Ismullah M., Muh. Fawzy; Lantu, Aswad, Sabrianto; Massinai, Muh. Altin

    2015-04-01

    Indonesia is the meeting zone between three world main plates: Eurasian Plate, Pacific Plate, and Indo - Australia Plate. Therefore, Indonesia has a high seismicity degree. Sulawesi is one of whose high seismicity level. The earthquake centre lies in fault zone so the earthquake data gives tectonic visualization in a certain place. This research purpose is to identify Sulawesi tectonic model by using earthquake data from 1993 to 2012. Data used in this research is the earthquake data which consist of: the origin time, the epicenter coordinate, the depth, the magnitude and the fault parameter (strike, dip and slip). The result of research shows that there are a lot of active structures as a reason of the earthquake in Sulawesi. The active structures are Walannae Fault, Lawanopo Fault, Matano Fault, Palu - Koro Fault, Batui Fault and Moluccas Sea Double Subduction. The focal mechanism also shows that Walannae Fault, Batui Fault and Moluccas Sea Double Subduction are kind of reverse fault. While Lawanopo Fault, Matano Fault and Palu - Koro Fault are kind of strike slip fault.

  8. Focal mechanisms and depths of earthquakes in central Pakistan: A tectonic interpretation

    NASA Astrophysics Data System (ADS)

    Quittmeyer, Richard C.; Kafka, Alan L.; Armbruster, John G.

    1984-04-01

    Focal mechanisms and depths for seven earthquakes in central Pakistan were determined from an analysis of Rayleigh waves of 20-to 50-s periods. In east-central Pakistan, the nodal planes for some solutions strike obliquely to the grain of surface structures. This observation supports the contention of other workers that a thin surficial unit, decoupled from the basement along a surface of decollement, characterizes this region. In west-central Pakistan, relative movement between the Indian and Eurasian plates is at least partially accommodated by seismic slip along the Chaman fault. Other faults, which are situated to the east of and lie subparallel to the Chaman fault, may also take up some of the relative plate motion. Observed activity within the zone of convergent-type structure in central Pakistan may be a result of the greater component of convergence across the Indian-Eurasian plate boundary north of Quetta, Pakistan. Appendix is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document B83-010; $2.50. Payment must accompany order.

  9. Molecular mechanism of vinculin activation and nano-scale spatial organization in focal adhesions

    PubMed Central

    Case, Lindsay B.; Baird, Michelle A.; Shtengel, Gleb; Campbell, Sharon L.; Hess, Harald F.; Davidson, Michael W.; Waterman, Clare M.

    2015-01-01

    Focal adhesions (FAs) link the extracellular matrix (ECM) to the actin cytoskeleton to mediate cell adhesion, migration, mechanosensing and signaling. FAs have conserved nanoscale protein organization, suggesting that the position of proteins within FAs regulates their activity and function. Vinculin binds different FA proteins to mediate distinct cellular functions, but how vinculin’s interactions are spatiotemporally organized within FA is unknown. Using interferometric photo-activation localization (iPALM) super-resolution microscopy to assay vinculin nanoscale localization and a FRET biosensor to assay vinculin conformation, we found that upward repositioning within the FA during FA maturation facilitates vinculin activation and mechanical reinforcement of FA. Inactive vinculin localizes to the lower integrin signaling layer in FA by binding to phospho-paxillin. Talin binding activates vinculin and targets active vinculin higher in FA where vinculin can engage retrograde actin flow. Thus, specific protein interactions are spatially segregated within FA at the nano-scale to regulate vinculin activation and function. PMID:26053221

  10. Evolution of pore fluid pressures in a stimulated geothermal reservoir inferred from earthquake focal mechanisms

    NASA Astrophysics Data System (ADS)

    Terakawa, T.; Deichmann, N.

    2014-12-01

    We developed an inversion method to estimate the evolution of pore fluid pressure fields from earthquake focal mechanism solutions based on the Bayesian statistical inference and Akaike's Bayesian information criterion (ABIC). This method's application to induced seismicity in the Basel enhanced geothermal system in Switzerland shows the evolution of pore fluid pressures in response to fluid injection experiments. For a few days following the initiation of the fluid injection, overpressurized fluids are concentrated around the borehole and then anisotropically propagate within the reservoir until the bleed-off time. Then, the pore fluid pressure in the vicinity of the borehole drastically decreases, and overpressurized fluids become isolated in a few major fluid pockets. The pore fluid pressure in these pockets gradually decreases with time. The pore fluid pressure in the reservoir is less than the minimum principal stress at each depth, indicating that the hydraulic fracturing did not occur during stimulation. This suggests that seismic events may play an important role to promote the development of permeable channels, particularly southeast of the borehole where the largest seismic event (ML 3.4) occurred. This is not directly related to a drastic decrease in fault strength at the hypocenter, but rather the positive feedback between permeability enhancement and poro-elastic and stress transfer loading from slipping interfaces. These processes likely contribute to this event's nucleation.

  11. Changes of static stress and aftershocks distribution for the strike-slip earthquakes in the West Pilippine Sea Plate

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Lin, J.

    2013-12-01

    Over the last few decades, several strike-slip type earthquakes have been observed within the West Philippine Sea Plate (WPSP), to the east of the Gagua Ridge area. Nearly all of these earthquakes possessed a similar focal mechanism pattern with one fault plane sub-parallel to approximately N35°E. Based on bathymetric and magnetic anomaly data, several obvious NE-SW ancient fracture zones have been identified in the WPSP and considered to be the main rupture plane of these strike-slip earthquakes. However, the aftershocks distributions of these strike-slip earthquakes show NW-SE trending pattern, which is almost in orthogonal with the fracture zones orientation. Thus, the real rupture plane of these events is still undetermined. Otherwise, many researches have provided evidence that stress increase promotes seismicity: the increase of static Coulomb stress is generally correlated to the high occurrence of aftershocks. In our study, we chose three large earthquakes occurred in the WPSP to analyze the relationship between static Coulomb stress changes and seismicity rate changes, in the aim of determining an appropriate rupture plane for these strike-slip events. In our analysis, two fault planes have been used to estimate the static Coulomb stress change. Then, we compared the aftershocks distribution with the Coulomb stress distribution pattern. Our results shows that when the fault plane is trending NW-SE direction, the aftershocks occurred in the region with positive Coulomb stress changes, while the seismicity was decreased in the region of negative Coulomb stress changes. Otherwise, the other fault plane could not at all explain the observed aftershocks distribution. Consequently, the NW-SE fault plane is the preferred rupture plane for the strike-slip events occurred in the WPSP. The 11 April 2012, Mw 8.6 and Mw 8.2 earthquakes occurred off the west coast of northern Sumatra, Indonesia, are also strike-slip fault events within the Indo-Australia plate. These

  12. Stress Triggering of Conjugate Normal Faulting: Late Aftershocks of the 1983 M 7.3 Borah Peak, Idaho Earthquake

    SciTech Connect

    Suzette J. Payne; James Zollweg; David Rodgers

    2004-06-01

    The 1984 Devil Canyon sequence was a late aftershock sequence of the 28 October 1983 Ms 7.3 Borah Peak, Idaho, earthquake. The sequence began on 22 August 1984 with the ML 5.8 Devil Canyon earthquake, which nucleated at a depth of 12.8 ± 0.7 km between the surface traces of two normal faults, the Challis segment of the Lost River fault and the Lone Pine fault. Two hundred thirty-seven aftershocks were recorded by a temporary array during a 3-week period. Their focal mechanisms and hypocenter distribution define a cross-sectional "V" pattern whose base corresponds to the ML 5.8 event, whose tips correspond to the exposed fault traces, and whose sides define two planar fault zones oriented N25°W, 75°SW (Challis fault segment) and N39°W, 58°NE (Lone Pine fault). This pattern describes a graben bounded by conjugate normal faults. Temporal aspects of the Devil Canyon sequence provide strong evidence that slip on conjugate normal faults occurs sequentially. Aftershocks occurred primarily along the Challis segment until the occurrence of the 8 September 1984 ML 5.0 earthquake along the Lone Pine fault, after which aftershocks primarily occurred along this fault. These observations are consistent with worldwide seismologic and geologic observations and with physical and numerical models of conjugate normal faulting. Aftershocks of the Devil Canyon sequence occurred immediately northwest of the ML 5.8 Devils Canyon earthquake, which itself was immediately northwest of the Thousand Springs segment of the Lost River fault (the fault that slipped in association with the Ms 7.3 Borah Peak earthquake). Coulomb failure stress analysis indicates that stress increases resulting from both the Borah Peak mainshock and Devil Canyon ML 5.8 earthquake were sufficient to induce failure on the Lone Pine fault. These space–time patterns suggest that conjugate normal faults may transfer stress or accommodate stress changes at the terminations of major normal faults in the Basin and

  13. Aftershock and induced seismic activity of the 2011 off the Pacific coast of Tohoku Earthquake in the northern part of Tohoku district, NE Japan

    NASA Astrophysics Data System (ADS)

    Kosuga, M.; Watanabe, K.

    2011-12-01

    We investigated the seismic activity around the northern neighbor of the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0) with special attention to a potential large aftershock in the area. We obtained a combined data set by adding our manually-picked locations to the catalog locations by the Japan Meteorological Agency. The hypocenter distribution delineates active and inactive bands of seismicity. The band of low seismicity corresponds to a zone of a large seismic slip, indicating that aftershocks occurred in peripheral neighbors of the mainshock asperity. The broad band of active seismicity along the coast corresponds to the zone of a large postseismic slip, suggesting the enhancement of the aftershock activity by the slip. Although the northern neighbor of the mainshock fault is a favored region of increased seismicity, as shown from a Coulomb stress calculation, no significant seismic activity is observed within the potential source area except along the Japan Trench and the SW corner. This implies that the zone of interplate moment release by previous large earthquakes and the subsequent slow slip acted as a barrier to the migration of both the mainshock rupture and aftershock activity. However, an aftershock area in the zone may reflect inhomogeneous moment release by past seismic and aseismic sequences. Induced inland seismicity is quite high in the Akita Prefecture on the Japan Sea side apart more than 100 km from the mainshock fault. There are some active clusters including moderate earthquakes with magnitude greater than 5. They are newly formed clusters after the mainshock, while the seismicity of previously active areas decreased significantly. Focal mechanism solutions of earthquakes in the new clusters show the types of strike-slip with consistently NW-SE trending T-axes. The predominant type of focal mechanisms in the Akita area before the mainshock was E-W compressional reverse faulting. Thus the stress field in the area has changed

  14. Studies of the South Napa Earthquake Aftershocks

    NASA Astrophysics Data System (ADS)

    Turcotte, D. L.; Shcherbakov, R.; Yikilmaz, M. B.; Kellogg, L. H.; Rundle, J. B.

    2014-12-01

    In this paper we present studies of the aftershock sequence of the 24 August, 2014, M = 6.0 South Napa earthquake. We give the cumulative frequency-magnitude distributions of the aftershocks for several time intervals following the main shock. We give the magnitude of the largest aftershock (Bath's law) as well as the largest aftershock obtained from a Gutenberg-Richter fit to the frequency-magnitude data (modified form of Bath's law). The latter is a measure of the aftershock productivity. We also give the rates of occurrence of aftershocks as a function of time after the main shock for several magnitude ranges. The fit of this data to Omori's law is discussed. We compare the results of our study of the South Napa earthquake with our previous study of the aftershock statistics of the 28 September, 2004, M = 6.0 Parkfield earthquake. Specifically we will discuss any difference that can be attributed to the large difference in recurrence intervals for the two earthquakes. We also present studies of the three dimensional distribution of aftershock locations as a function of time and their association with the surface rupture. Aftershocks at large distances from the rupture zone will be discussed particularly those in the Geysers geothermal area.

  15. Triggering cascades and statistical properties of aftershocks

    NASA Astrophysics Data System (ADS)

    Gu, C.; Davidsen, J.

    2011-12-01

    Applying a recently introduced general statistical procedure for identifying aftershocks based on complex network theory, we investigate the statistical properties of aftershocks for a high-resolution earthquake catalog covering Southern California. In comparison with earlier studies of aftershock sequences, we show that many features depend sensitively on how one defines aftershocks and whether one includes only first-generation of aftershocks or one also takes all indirectly triggered aftershocks into account. This includes the temporal variation in the rate of aftershocks for mainshocks of small magnitude, for example, as well as the variation in the rate of aftershocks for short to intermediate times after a mainshock. Other features are, however, robust indicating that they truly characterize aftershock sequences. These include the p-values in the Omori-Utsu law for large mainshocks, B{aa}th's law and the productivity law with an exponent smaller than the b-value in the Gutenberg-Richter law. We also find that, for large mainshocks, the dependence of the parameters in the Omori-Utsu law on the lower magnitude cut-off are in excellent agreement with a recent proposition based on B{aa}th's law and the Gutenberg-Richter law, giving rise to a generalized Omori-Utsu law. Our analysis also provides evidence that the exponent p in the Omori-Utsu law does not vary significantly with mainshock magnitude.

  16. Podocin-related mechanisms in posttransplant [corrected] recurrence of focal segmental glomerulosclerosis [corrected].

    PubMed

    Caridi, G; Dagnino, M; Sanna-Cherchi, S; Perfumo, F; Ghiggeri, G M

    2006-12-01

    Posttransplantation recurrence of focal segmental glomerulosclerosis (FSGS) is one of the most disarming events in human pathology with important social and psychological consequences. It usually occurs in 30% to 50% of patients affected by the primary form of the disease with an abrupt onset in the majority of cases occurring within 1 month of the transplantation. Prediction of recurrent cases and early therapy with plasmapheresis are the main goals of the therapy. Although the mechanism of posttransplantation recurrence is still obscure, it has been proposed to be of a multifactorial origin, in which plasma factors determine the shedding of proteins of the slit-diaphragm, such as nephrin and podocin, with structural alterations of the ultra-filtering unit of the glomerulus. Low resynthesis of podocin and/or haplo-insufficiency due to heterozygous mutations should represent significant predisposing factors to proteinuria. In this review, the role of podocin in posttransplantation recurrence will be evaluated focusing on the possibility that resynthesis of the protein could represent a key step also for stable normalization of the renal filter. The recent characterization of the podocin promoter cis- and trans- acting elements and the possibility to characterize low- and high-podocin producer haplotypes offer opportunities to evaluate the capacity for podocin resynthesis in the donor kidney. A review of the literature on posttransplantation recurrence of FSGS in patients originally carrying homozygous and/or heterozygous NPHS2 mutations supports the general idea of a multifactorial origin of the primary disease that can be extended to the pathogenesis of posttransplantation recurrence. PMID:17175312

  17. Inelastic strain in the seismogenic zone, Kyushu, Japan inferred from focal mechanism of earthquakes

    NASA Astrophysics Data System (ADS)

    Matsumoto, Satoshi; Nishimura, Takuya

    2016-04-01

    Strain in the seismogenic zone of the crust is a key parameter to understand crustal dynamics. GNSS data provide us with great information about deformation rate at the surface, which have been investigated by many researches and modeled kinematic behavior as elastic medium. Generally, strain in the earth's medium consists with elastic and inelastic ones. The two kinds of strain result different effects on the stress field. Therefore, detecting inelastic strain is important to know state of stress in the crust as well as elastic one. Inelastic strain is caused by such as fault creep, viscoelastic response, and earthquakes. Here, we showed the inelastic strain in the seismogenic zone of Kyushu, Japan from seismic moments and focal mechanisms data by counting Kostrov's sum in the spatial bins. Seismic moment tensors about 9000 earthquakes with magnitude greater than 2 for 13.5 years were obtained from seismic network data in Kyushu Island and F-net catalog. Total released moment at every spatial bin with 0.15 x 0.15 degree in latitude and longitude was estimated and then strain rate was calculated from the moment, compliance of the medium, and volume of the bin. The estimated maximum strain rate achieves 10^-7 strain/year. This strain rate is comparable with that from GNSS data. However, the strain rate mainly revealed the different principal direction from the one of GNSS. On the other hand, the directions were similar to the behavior of active faults in Kyushu. The result in this study showed that inelastic strain due to earthquakes is enough large, suggesting that the effect should be considered for modeling crustal dynamics.

  18. Triggering of aftershocks in viscoelastic spring-block models

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Shcherbakov, R.

    2013-12-01

    Identifying the mechanisms of the aftershock generation is an important part in the comprehensive theory of earthquake physics. The mechanism of the aftershock generation remains controversial, and models that yield robust aftershock statistics are still in search. The dynamics of earthquake faults can be modelled by a spring-block system, as first proposed by Burridge and Knopoff (1967). However, the quantitative difference between the spring-block model dynamics and the realistic seismicity may be due to the oversimplified setup of the spring-block model, which might not capture effectively the essential physical mechanisms of earthquake dynamics. In particular, the interactions of the spring-block system are purely elastic. The rheology of the fault zone, which plays an important rule in the earthquake dynamics, is thus neglected. In this work, several possible models are studied in order to reproduce the scaling relations of the aftershocks, especially the Omori's law. We adopt the basic picture of the spring-block model, and introduce the crustal relaxation process during the stress redistribution and the global loading. This is implemented by incorporating viscoelastic interactions in the system: the viscoelastic transmission and the viscoelastic driving. The viscoelastic transmission mechanism features an instantaneous response of the stress transmission, which immediately leads to an avalanche followed by the relaxation. The viscoelastic driving mechanism features an instantaneous stress drop, which is later partly restored by the crustal relaxation. We combine the two mechanisms, and find that the dynamics of the system is determined by three parameters, the elastic transmission parameter α, the relaxation time of the viscoelastic driving τ_L , and the relaxation time of the viscoelastic transmission τ. Different with the elastic spring-block model, avalanches can be triggered either by the global loading or by the relaxation in this combined

  19. April 7, 2009, Mw 5.5 aftershock of the L'Aquila earthquake: seismogenic fault geometry and its implication for the central Apennines active extensional tectonics (Italy).

    NASA Astrophysics Data System (ADS)

    Adinolfi, Guido Maria; Lavecchia, Giusy; De Matteis, Raffaella; Nardis Rita, De; Francesco, Brozzetti; Federica, Ferrarini; Zollo, Aldo

    2015-04-01

    On April 6, 2009 (at 01:32 UTC) a Mw 6.3 earthquake hit the town of L'Aquila (central Italy) and surrounding villages causing fatalities and severe damage in the area. After few days, a nearly 40-km-long extensional fault system was activated generating both northward and southward seismicity migration along the NW-SE trending sector of central Apennines. During the intense aftershocks sequence, different sesmogenic sources with a distinct geometry, size and the degree of involvement were reactivated. Among the relevant aftershocks with Mw 5.0 to 5.5, the largest one occurred on April 7 (at 17:47 UTC), 9 km SE-ward of the mainshock involving a source seated at much greater depths (~14 km). Despite the enormous number of studies of the 2009 L'Aquila earthquake, mainly focused on the various geological and seismological aspects of the main Paganica source, the April 7 strongest aftershock (Mw 5.5) has not yet been deeply investigated. Consistent geometric and kinematic correlations between the geological and seismological data about this seismogenic source are missing. There are still open questions concerning its unresolved geometry and the unknown style of the central Apennines structure activated at greater depths during the 2009 L'Aquila seismic sequence. Furthermore, some authors (Lavecchia et al., 2012) have supposed that the April 7, 2009 aftershock (Mw 5.5) occurred onto an high dip segment (~50°) of an east-dipping extensional basal detachment with a potential surface expression outcropping in the area of the eastern Sabina-Simbruini Mts. In this work we propose a seismological analysis of the April 7, 2009 aftershock (Mw 5.5) rupture process. In order to define the unresolved source geometry, we computed the focal mechanism through the time domain, moment tensor full waveform inversion (Dreger and Helmberger, 1993). Also, we estimated the apparent source time functions (ASTFs) by deconvolution of the impulse response of the medium from the recorded data

  20. Spatial distribution of precisely determined hypocenters and focal mechanisms in the Izu-Honshu collision zone, central Japan

    NASA Astrophysics Data System (ADS)

    Yukutake, Y.; Takeda, T.; Honda, R.; Yoshida, A.

    2010-12-01

    In the Tanzawa region, central Japan, where the Izu-Bonin arc collides into the Honshu crust, the Philippine Sea plate (PHS) subducts intricately and the seismicity is particularly high. The configuration of the PHS plate in the region has been estimated based on the hypocenter distribution, seismic velocity tomography, and seismic profile (e.g. Ishida, 1992; Matsubara et al., 2005; Sato et al., 2005). However, the relationship between the structure of the PHP and the seismicity in the collision zone is still not clearly understood. To elucidate the seismotectonics, it is essential to get precisely determined hypocenters and focal mechanisms. We used data from 107 permanent online stations operated by Hot Springs Research Institute of Kanagawa Prefecture, NIED Hi-net and JMA, which are located within 80-km from the epicenters. We relocated hypocenters of 4351 events that occurred in and around the Tanzawa region with the double-difference relocation algorithm (DD method) (Waldhauser and Ellsworth, 2000), using the differential arrival time obtained by both manual picking and waveform cross-correlation analysis. Then, we determined the focal mechanisms of 420 events using the absolute P- and SH-wave amplitudes by adding the P-wave polarities. We found that the earthquakes in the eastern Tanzawa region are distributed along the planar zone slightly dipping toward east. On the other hand, the earthquakes in the western region spread out in the volume of approximately 10 km × 10 km × 10 km. We examined similarity between the focal mechanisms of earthquakes and a reference of focal mechanism that is inferred from the configuration and relative motion of the PHP. We assumed the fault plane direction of the reference focal mechanism based on the fault model of the 1923 Kanto Earthquake (Matsu'ura et al., 1980). The slip direction is assumed so as to be consistent with the relative motion of the PHP with respect to the Eurasian plate in the Kanto region (Seno, 1993). The

  1. Modeling aftershocks as a stretched exponential relaxation

    NASA Astrophysics Data System (ADS)

    Mignan, A.

    2015-11-01

    The decay rate of aftershocks has been modeled as a power law since the pioneering work of Omori in the late nineteenth century. Although other expressions have been proposed in recent decades to describe the temporal behavior of aftershocks, the number of model comparisons remains limited. After reviewing the aftershock models published from the late nineteenth century until today, I solely compare the power law, pure exponential and stretched exponential expressions defined in their simplest forms. By applying statistical methods recommended recently in applied mathematics, I show that all aftershock sequences tested in three regional earthquake catalogs (Southern and Northern California, Taiwan) and with three declustering techniques (nearest-neighbor, second-order moment, window methods) follow a stretched exponential instead of a power law. These results infer that aftershocks are due to a simple relaxation process, in accordance with most other relaxation processes observed in Nature.

  2. Focal Mechanisms at the convergent plate boundary in Southern Aegean, Greece.

    NASA Astrophysics Data System (ADS)

    Moshou, Alexandra; Papadimitriou, Eleftheria; Drakatos, George; Evangelidis, Christos; Karakostas, Vasilios; Vallianatos, Filippos; Makropoulos, Konstantinos

    2014-05-01

    Greece is characterized by high seismicity, mainly due to the collision between the European and the African lithospheric plates and the dextral strike slip motion along the North Anatolia Fault zone and North Aegean Trough. The subduction of the Eastern Mediterranean oceanic plate along the Hellenic Arc under the Aegean microplate along with the accompanied roll back of the descending slab is considered the main tectonic feature of the region (Papazachos and Comninakis 1971; Makropoulos and Burton 1984; Papazachos et al. 2000a, b). The divergent motion between the Aegean block and mainland Europe is indicated by an extension zone in the northern Aegean, with Crete and Aegean diverging from mainland Europe at a rate of about 3.5 cm yr-1 with Africa moving northward relative to Europe at a rate of about 1 cm yr-1 (Dewey et al., 1989; Papazachos et al., 1998; Mc-Clusky et al., 2000; Reilinger et al., 2006). In this tectonically complicated area diverge types of deformation are manifested, in addition to the dominant subduction processes. Aiming to shed more light in the seismotectonic properties and faulting seismological data from the Hellenic Unified Seismological Network (HUSN) were selected and analyzed for determining focal mechanisms using the method of moment tensor inversion, additional to the ones being available from the routine moment tensor solutions and several publications. Thus, 31 new fault plane solutions for events with magnitude M>4.0, are presented in this study, by using the software of Ammon (Randall et al., 1995). For this scope the data from at least 4 stations were used with an adequate azimuthal coverage and with an epicentral distance not more than 350 km. The preparation of the data includes the deconvolution of instruments response, then the velocity was integrated to displacement and finally the horizontal components were rotated to radial and transverse. Following, the signal was inverted using the reflectivity method of Kennett (1983

  3. Focal Mechanisms for Deep Crustal Earthquakes in the Central Foothills and Near Yosemite National Park in the Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    Ryan, J. C.; Frassetto, A.; Hurd, O.; Zandt, G.; Gilbert, H.; Owens, T.; Jones, C.

    2008-12-01

    Past studies have observed seismicity occurring to depths near 40 km beneath the central Sierra Nevada in eastern California, but the cause of this unusual activity remains largely unknown. We use seismograms from a recent deployment of the Sierra Nevada EarthScope Project (SNEP) broadband array and interspersed USArray TA stations to study this deep crustal earthquake activity. From June of 2005 to May of 2006, we recorded 126 earthquakes in the central western flank of the Sierra Nevada that relocated in the depth range from 1.0 to 47.6 km. These earthquakes have small magnitudes (M < 3), occur at a rate of ~10 per month, and occasionally display repeating waveforms. The majority of the earthquakes fall into two distinct clusters. One cluster of earthquakes form a diffuse band under the low foothills north of Fresno and have focal depths mostly between 20 and 35 km. The second cluster underlies the higher western slope of the range in a more compact north-south band extending from the southern edge of Yosemite National Park to the San Joaquin River. These events have focal depths from near surface to 30 km, and are located above occasional deep, long-period (LP) events (Pitt, et al., SRL, 2002). We use P- and S-wave polarity picks and P/SH amplitude ratios to construct focal mechanisms for 23 of the larger, well-recorded earthquakes, 14 in the Foothills Cluster and 9 in the Yosemite Cluster. The focal mechanisms show dominantly near vertical and subhorizontal nodal planes, although several events do show clear normal or reverse mechanisms. Although there is some scatter, a majority of the mechanisms from the Foothills Cluster have S-to-SW steeply dipping T-axes. The majority of earthquakes in the Yosemite Cluster have P-axes moderately dipping to the SW and T-axes moderately dipping to the NE, similar to focal mechanisms of earthquakes associated with the recent magma intrusion event under Lake Tahoe (von Seggern, et al., BSSA, 2008). We suggest that the

  4. Probing mechanical principles of focal contacts in cell–matrix adhesion with a coupled stochastic–elastic modelling framework

    PubMed Central

    Gao, Huajian; Qian, Jin; Chen, Bin

    2011-01-01

    Cell–matrix adhesion depends on the collective behaviours of clusters of receptor–ligand bonds called focal contacts between cell and extracellular matrix. While the behaviour of a single molecular bond is governed by statistical mechanics at the molecular scale, continuum mechanics should be valid at a larger scale. This paper presents an overview of a series of recent theoretical studies aimed at probing the basic mechanical principles of focal contacts in cell–matrix adhesion via stochastic–elastic models in which stochastic descriptions of molecular bonds and elastic descriptions of interfacial traction–separation are unified in a single modelling framework. The intention here is to illustrate these principles using simple analytical and numerical models. The aim of the discussions is to provide possible clues to the following questions: why does the size of focal adhesions (FAs) fall into a narrow range around the micrometre scale? How can cells sense and respond to substrates of varied stiffness via FAs? How do the magnitude and orientation of mechanical forces affect the binding dynamics of FAs? The effects of cluster size, cell–matrix elastic modulus, loading direction and cytoskeletal pretension on the lifetime of FA clusters have been investigated by theoretical arguments as well as Monte Carlo numerical simulations, with results showing that intermediate adhesion size, stiff substrate, cytoskeleton stiffening, low-angle pulling and moderate cytoskeletal pretension are factors that contribute to stable FAs. From a mechanistic point of view, these results provide possible explanations for a wide range of experimental observations and suggest multiple mechanisms by which cells can actively control adhesion and de-adhesion via cytoskeletal contractile machinery in response to mechanical properties of their surroundings. PMID:21632610

  5. Constraints on recent earthquake source parameters, fault geometry and aftershock characteristics in Oklahoma

    NASA Astrophysics Data System (ADS)

    McNamara, D. E.; Benz, H.; Herrmann, R. B.; Bergman, E. A.; McMahon, N. D.; Aster, R. C.

    2014-12-01

    In late 2009, the seismicity of Oklahoma increased dramatically. The largest of these earthquakes was a series of three damaging events (Mw 4.8, 5.6, 4.8) that occurred over a span of four days in November 2011 near the town of Prague in central Oklahoma. Studies suggest that these earthquakes were induced by reactivation of the Wilzetta fault due to the disposal of waste water from hydraulic fracturing ("fracking") and other oil and gas activities. The Wilzetta fault is a northeast trending vertical strike-slip fault that is a well known structural trap for oil and gas. Since the November 2011 Prague sequence, thousands of small to moderate (M2-M4) earthquakes have occurred throughout central Oklahoma. The most active regions are located near the towns of Stillwater and Medford in north-central Oklahoma, and Guthrie, Langston and Jones near Oklahoma City. The USGS, in collaboration with the Oklahoma Geological Survey and the University of Oklahoma, has responded by deploying numerous temporary seismic stations in the region in order to record the vigorous aftershock sequences. In this study we use data from the temporary seismic stations to re-locate all Oklahoma earthquakes in the USGS National Earthquake Information Center catalog using a multiple-event approach known as hypo-centroidal decomposition that locates earthquakes with decreased uncertainty relative to one another. Modeling from this study allows us to constrain the detailed geometry of the reactivated faults, as well as source parameters (focal mechanisms, stress drop, rupture length) for the larger earthquakes. Preliminary results from the November 2011 Prague sequence suggest that subsurface rupture lengths of the largest earthquakes are anomalously long with very low stress drop. We also observe very high Q (~1000 at 1 Hz) that explains the large felt areas and we find relatively low b-value and a rapid decay of aftershocks.

  6. Kinetic Mechanism and Rate-Limiting Steps of Focal Adhesion Kinase-1

    SciTech Connect

    Schneck, Jessica L.; Briand, Jacques; Chen, Stephanie; Lehr, Ruth; McDevitt, Patrick; Zhao, Baoguang; Smallwood, Angela; Concha, Nestor; Oza, Khyati; Kirkpatrick, Robert; Yan, Kang; Villa, James P.; Meek, Thomas D.; Thrall, Sara H.

    2010-12-07

    Steady-state kinetic analysis of focal adhesion kinase-1 (FAK1) was performed using radiometric measurement of phosphorylation of a synthetic peptide substrate (Ac-RRRRRRSETDDYAEIID-NH{sub 2}, FAK-tide) which corresponds to the sequence of an autophosphorylation site in FAK1. Initial velocity studies were consistent with a sequential kinetic mechanism, for which apparent kinetic values k{sub cat} (0.052 {+-} 0.001 s{sup -1}), K{sub MgATP} (1.2 {+-} 0.1 {micro}M), K{sub iMgATP} (1.3 {+-} 0.2 {micro}M), K{sub FAK-tide} (5.6 {+-} 0.4 {micro}M), and K{sub iFAK-tide} (6.1 {+-} 1.1 {micro}M) were obtained. Product and dead-end inhibition data indicated that enzymatic phosphorylation of FAK-tide by FAK1 was best described by a random bi bi kinetic mechanism, for which both E-MgADP-FAK-tide and E-MgATP-P-FAK-tide dead-end complexes form. FAK1 catalyzed the {beta}{gamma}-bridge:{beta}-nonbridge positional oxygen exchange of [{gamma}-{sup 18}O{sub 4}]ATP in the presence of 1 mM [{gamma}-{sup 18}O{sub 4}]ATP and 1.5 mM FAK-tide with a progressive time course which was commensurate with catalysis, resulting in a rate of exchange to catalysis of k{sub x}/k{sub cat} = 0.14 {+-} 0.01. These results indicate that phosphoryl transfer is reversible and that a slow kinetic step follows formation of the E-MgADP-P-FAK-tide complex. Further kinetic studies performed in the presence of the microscopic viscosogen sucrose revealed that solvent viscosity had no effect on k{sub cat}/K{sub FAK-tide}, while k{sub cat} and k{sub cat}/K{sub MgATP} were both decreased linearly at increasing solvent viscosity. Crystallographic characterization of inactive versus AMP-PNP-liganded structures of FAK1 showed that a large conformational motion of the activation loop upon ATP binding may be an essential step during catalysis and would explain the viscosity effect observed on k{sub cat}/K{sub m} for MgATP but not on k{sub cat}/K{sub m} for FAK-tide. From the positional isotope exchange, viscosity, and

  7. Arginine stimulates intestinal cell migration through a focal adhesion kinase dependent mechanism

    PubMed Central

    Rhoads, J M; Chen, W; Gookin, J; Wu, G Y; Fu, Q; Blikslager, A T; Rippe, R A; Argenzio, R A; Cance, W G; Weaver, E M; Romer, L H

    2004-01-01

    Background: l-Arginine is a nutritional supplement that may be useful for promoting intestinal repair. Arginine is metabolised by the oxidative deiminase pathway to form nitric oxide (NO) and by the arginase pathway to yield ornithine and polyamines. Aims: To determine if arginine stimulates restitution via activation of NO synthesis and/or polyamine synthesis. Methods: We determined the effects of arginine on cultured intestinal cell migration, NO production, polyamine levels, and activation of focal adhesion kinase, a key mediator of cell migration. Results: Arginine increased the rate of cell migration in a dose dependent biphasic manner, and was additive with bovine serum concentrate (BSC). Arginine and an NO donor activated focal adhesion kinase (a tyrosine kinase which localises to cell matrix contacts and mediates β1 integrin signalling) after wounding. Arginine stimulated cell migration was dependent on focal adhesion kinase (FAK) signalling, as demonstrated using adenovirus mediated transfection with a kinase negative mutant of FAK. Arginine stimulated migration was dependent on NO production and was blocked by NO synthase inhibitors. Arginine dependent migration required synthesis of polyamines but elevating extracellular arginine concentration above 0.4 mM did not enhance cellular polyamine levels. Conclusions: These results showed that l-arginine stimulates cell migration through NO and FAK dependent pathways and that combination therapy with arginine and BSC may enhance intestinal restitution via separate and convergent pathways. PMID:15016745

  8. Foreshocks and aftershocks of Pisagua 2014 earthquake: time and space evolution of megathrust event.

    NASA Astrophysics Data System (ADS)

    Fuenzalida Velasco, Amaya; Rietbrock, Andreas; Wollam, Jack; Thomas, Reece; de Lima Neto, Oscar; Tavera, Hernando; Garth, Thomas; Ruiz, Sergio

    2016-04-01

    variations in its focal mechanisms. The evolution of the Pisagua sequence point out a rupture by steps, that we suggest to be related to the properties of the upper plate, as well as along in the subduction interface. The spatial distribution of seismicity was compared to the inter-seismic coupling of previous studies, the regional bathymetry and the slip distribution of both the mainshock and the Magnitude 7.6 event. The results show an important relation between the low coupling zones and the areas lacking large magnitude events

  9. A Crustal Structure Study of the Southern Ryukyu Subduction Zone by Using the Aftershock Data

    NASA Astrophysics Data System (ADS)

    Cho, Y.; Lin, J.; Lee, C.

    2011-12-01

    The region along the Ryukyu subduction zone is known as a tsunami disaster zone. The biggest tsunami (85 m) of Japan history was recorded in the Ishigaki Island, Ryukyu, in 1771. The paleo-tsunami events show that it has a frequency of about 150 years. This thread makes the Ryukyu subduction zone as a concerned field for the earthquake studies. However, due to the long distance from the east coast of Taiwan, this is an area out of the effective earthquake detection zone from the Central Weather Bureau network. A main shock of M = 6.9 occurred near the Ishigaki Island in 2009 August 17. After this event, we quickly deployed the OBS and found many aftershocks with the magnitude greater than 5.0. The main shock was 240 km, NE direction from the Hualien city, Taiwan. If a tsunami occurred, it took only less than 15 minutes to arrive the coast. From the recorded data, we picked the P- and S-wave using the 1-D module (iasp91). There were 1500 recorded events during those time range, and most of the earthquakes were located around the Nanao Basin. Based on this, we study the southern Ryukyu subduction zone structure by using the results from focal mechanism solution. From the earthquake relocation it shows that two main groups of aftershocks. They tend in northwest - southeast with a left-lateral strike-slip fault. The left-lateral strike-slip fault is the main structures that link with the splay faults at the southern Ryukyu Trench. The stability and extension of the splay faults are one of the major concerns for the occurrence of mega earthquake. More than 500-km long of the splay fault, such as that in the Indonesia, Chile and Japan subduction zones, has attacked by mega earthquakes in the recent years. The second group of those aftershocks was located in the Gagua Ridge near the Ryukyu Trench. This group may represent the ridge structure relate to the Taitung canyon fault. The front of Ryukyu Trench was being as a locked subduction zone where it is easily to

  10. Neuroprotection of Sanhua Decoction against Focal Cerebral Ischemia/Reperfusion Injury in Rats through a Mechanism Targeting Aquaporin 4

    PubMed Central

    Lu, Lin; Li, Hui-qin; Li, Ji-huang; Liu, Ai-ju

    2015-01-01

    Sanhua decoction (SHD) is a famous classic Chinese herbal prescription for ischemic stroke, and aquaporin 4 (AQP4) is reported to play a key role in ischemic brain edema. This study aimed to investigate neuroprotection of SHD against focal cerebral ischemia/reperfusion (I/R) injury in rats and explore the hypothesis that AQP4 probably is the target of SHD neuroprotection against I/R rats. Lentiviral-mediated AQP4-siRNA was inducted into adult male Sprague-Dawley rats via intracerebroventricular injection. The focal cerebral ischemia/reperfusion model was established by occluding middle cerebral artery. Neurological examinations were performed according to Longa Scale. Brain water content, was determined by wet and dry weight measurement. Western blot was adopted to test the AQP4 expression in ipsilateral hippocampus. After the treatment, SHD alleviated neurological deficits, reduced brain water content and downregulated the expression of AQP4 at different time points following I/R injury. Furthermore, neurobehavioral function and brain edema after I/R were significantly attenuated via downregulation of AQP4 expression when combined with AQP4-siRNA technology. In conclusion, SHD exerted neuroprotection against focal cerebral I/R injury in rats mainly through a mechanism targeting AQP4. PMID:26089944

  11. Fault Simulator with Dilatant Effects Used to Investigate Statistics of Foreshocks/Aftershocks, Including Magnitude Dependent Seismic Quiescence

    NASA Astrophysics Data System (ADS)

    Smith, D. E.; Sacks, S. I.; Rydelek, P. A.

    2011-12-01

    We add dilatant effects to a fault simulator to include physics consistent with observations of seismic quiescence. Using this simulator, we examine precursory and aftershock statistics of major events, changes in b-value, correlations between slip and static stress changes, changes in the in-plane focal mechanisms, and temporal decay of aftershocks. Seismic quiescence has been observed for a number major events including, 1982 Urakawa-Oki earthquake [Taylor et al., 1992], 1994 Hokkaido-Toho-Oki earthquake [Takanami et al., 1996], 1994 Northridge earthquake [Smith and Sacks, 2011], 1995 Kobe earthquake [Enescu et al., 2011], 1988 Spitak earthquake [Wysse and Martirosyan, 1998], and 2011 Tohoku earthquake [Katsumata, in press, 2011]. The physics of dilatancy theory [Nur, 1972; Whitcomb et al., 1973; Scholz et al., 1973], which we include in the simulator, is proposed as an explanation for seismic quiescence [Takanami et al., 1996; Scholz, 2000]. As the fault is loaded toward failure and the stress increases, if the stress is sufficiently high, the rock can begin to dilate. As dilation causes an increase in the rock volume, the pore pressure decreases, the effective normal stress increases, and the fault core strengthens [Rice, 1975]. Because the fault core supports more of the stress, the seismicity of the surrounding region will decrease as is observed. Over time (~2-20 years) the water will percolate back into the fault core from the surrounding region. The pore pressure in the fault core increases again, the normal stress decreases, and failure is encouraged. This dilatant effect on the fault core foreshocks, surrounding quiescence zone, and the aftershocks, can be studied by modifying the fault simulator of Sacks and Rydelek [1995]; Rydelek and Sacks [1996]. Based on simple physics: discrete patches, Coulomb failure, and redistribution of stresses on a specified fault geometry, this simulator (without dilatancy) has already been shown to reproduce Gutenberg

  12. Source Process of the Mw 5.0 Au Sable Forks, New York, Earthquake Sequence from Local Aftershock Monitoring Network Data

    NASA Astrophysics Data System (ADS)

    Kim, W.; Seeber, L.; Armbruster, J. G.

    2002-12-01

    On April 20, 2002, a Mw 5 earthquake occurred near the town of Au Sable Forks, northeastern Adirondacks, New York. The quake caused moderate damage (MMI VII) around the epicentral area and it is well recorded by over 50 broadband stations in the distance ranges of 70 to 2000 km in the Eastern North America. Regional broadband waveform data are used to determine source mechanism and focal depth using moment tensor inversion technique. Source mechanism indicates predominantly thrust faulting along 45° dipping fault plane striking due South. The mainshock is followed by at least three strong aftershocks with local magnitude (ML) greater than 3 and about 70 aftershocks are detected and located in the first three months by a 12-station portable seismographic network. The aftershock distribution clearly delineate the mainshock rupture to the westerly dipping fault plane at a depth of 11 to 12 km. Preliminary analysis of the aftershock waveform data indicates that orientation of the P-axis rotated 90° from that of the mainshock, suggesting a complex source process of the earthquake sequence. We achieved an important milestone in monitoring earthquakes and evaluating their hazards through rapid cross-border (Canada-US) and cross-regional (Central US-Northeastern US) collaborative efforts. Hence, staff at Instrument Software Technology, Inc. near the epicentral area joined Lamont-Doherty staff and deployed the first portable station in the epicentral area; CERI dispatched two of their technical staff to the epicentral area with four accelerometers and a broadband seismograph; the IRIS/PASSCAL facility shipped three digital seismographs and ancillary equipment within one day of the request; the POLARIS Consortium, Canada sent a field crew of three with a near real-time, satellite telemetry based earthquake monitoring system. The Polaris station, KSVO, powered by a solar panel and batteries, was already transmitting data to the central Hub in London, Ontario, Canada within

  13. Preliminary seismicity and focal mechanisms for the southern Great Basin of Nevada and California: January 1992 through September 1992

    SciTech Connect

    Harmsen, S.C.

    1994-06-01

    The telemetered southern Great Basin seismic network (SGBSN) is operated for the Department of Energy`s Yucca Mountain Project (YMP). The US Geological Survey, Branch of Earthquake and Landslide Hazards, maintained this network until September 30, 1992, at which time all operational and analysis responsibilities were transferred to the University of Nevada at Reno Seismological Laboratory (UNRSL). This report contains preliminary earthquake and chemical explosion hypocenter listings and preliminary earthquake focal mechanism solutions for USGS/SGBSN data for the period January 1, 1992 through September 30, 1992, 15:00 UTC.

  14. Preliminary seismicity and focal mechanisms for the Southern Great Basin of Nevada and California, January 1992 - September 1992

    NASA Astrophysics Data System (ADS)

    Harmsen, S. C.

    The telemetered southern Great Basin seismic network (SGBSN) is operated for the Department of Energy's Yucca Mountain Project (YMP). The US Geological Survey, Branch of Earthquake and Landslide Hazards, maintained this network until September 30, 1992, at which time all operational and analysis responsibilities were transferred to the University of Nevada at Reno Seismological Laboratory (UNRSL). This report contains preliminary earthquake and chemical explosion hypocenter listings and preliminary earthquake focal mechanism solutions for USGS/SGBSN data for the period January 1, 1992 through September 30, 1992, 15:00 UTC.

  15. Precise Determination of Hypocenters and Focal Mechanisms of Volcanic Earthquakes by the Volcano Observation Network of NIED

    NASA Astrophysics Data System (ADS)

    Ueda, H.; Kohno, Y.; Nagai, M.; Miyagi, Y.; Fujita, E.; Kozono, T.; Tanada, T.

    2012-12-01

    Volcanic earthquakes are usually observed by a seismometer network on a volcano before and during eruptions, caused by crustal stress changes due to underground magma movements or an accumulation into a magma chamber. Precise hypocentral locations and focal mechanisms of the earthquakes provide information on the magmatic process and allow us to assess and predict the volcanic activity. However, focal mechanisms of volcanic earthquakes are not monitored except for relatively large earthquakes because of small size of volcanic earthquakes (M<3) and heterogeneity of volcanic structures. The obstacles also prevent automatic determination of hypocentral locations which are needed for short term eruption prediction. National Institute for Earth Science and Disaster Prevention (NIED) has been developing the volcano observation networks near the major active volcanos in Japan since 2009. The observation networks are equipped with short period seismometers and pendulum type tiltmeters at the bottom of borehole 200 m deep, and broad band seismometers and GPS antennas on the ground. We developed a monitoring technique for precise determination of hypocenters and focal mechanisms of volcanic earthquakes by using similarity of seismic wave forms and the high quality short period seismometer data of the volcano observation networks. Firstly, we extract earthquake groups which have similar seismic wave forms including P and S waves with correlation coefficient of more than 0.9 on more than three stations. Secondly, we display the wave forms with the similar phases in a row and stack them to reduce noises, and then precisely pick again the phases and first motion polarities of P waves. Thirdly, we relocate the hypocenters by Double-Difference method (Waldhauser and Ellsworth, 2000, BSSA) and estimate focal mechanisms by using P wave first motion polarity and S/P amplitude ratios (Hardebeck and Shearer, 2003, BSSA). We applied the technique to earthquake catalogs of Mt. Fuji and

  16. Aftershocks of the western Argentina (Caucete) earthquake of 23 November 1977: some tectonic implications

    USGS Publications Warehouse

    Langer, C.J.; Bollinger, G.A.

    1988-01-01

    An aftershock survey, using a network of eight portable and two permanent seismographs, was conducted for the western Argentina (Caucete) earthquake (MS 7.3) of November 23, 1977. Monitoring began December 6, almost 2 weeks after the main shock and continued for 11 days. The data set includes 185 aftershock hypocenters that range in the depth from near surface to more than 30 km. The spatial distribution of those events occupied a volume of about 100 km long ??50 km wide ??30 km thick. The volumnar nature of the aftershock distribution is interpreted to be a result of a bimodal distribution of foci that define east- and west-dipping planar zones. Efforts to select which of those zones was associated with the causal faulting include special attention to the determination of the mainshock focal depth and dislocation theory modeling of the coseismic surface deformation in the epicentral region. Our focal depth (25-35 km) and modeling studies lead us to prefer an east-dipping plane as causal. A previous interpretation by other investigators used a shallower focal depth (17 km) and similar modeling calculations in choosing a west-dipping plane. Our selection of the east-dipping plane is physically more appealing because it places fault initiation at the base of the crustal seismogenic layer (rather than in the middle of that layer) which requires fault propagation to be updip (rather than downdip). ?? 1988.

  17. Aftershock patterns and main shock faulting

    USGS Publications Warehouse

    Mendoza, C.; Hartzell, S.H.

    1988-01-01

    We have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms. Our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault. Aftershocks followng earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip. The spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture. -from Authors

  18. Foreshock activity related to enhanced aftershock production

    NASA Astrophysics Data System (ADS)

    Marsan, D.; Helmstetter, A.; Bouchon, M.; Dublanchet, P.

    2014-10-01

    Foreshock activity sometimes precedes the occurrence of large earthquakes, but the nature of this seismicity is still debated, and whether it marks transient deformation and/or slip nucleation is still unclear. We here study at the worldwide scale how foreshock occurrence affects the postseismic phase and find a significant positive correlation between foreshock and aftershock activities: earthquakes preceded by accelerating seismicity rates produce 40% more aftershocks on average, and the length of the aftershock zone after 20 days is 20% larger. These observations cannot be reproduced by standard earthquake clustering models that predict the accelerating pattern of foreshock occurrence but not its impact on aftershock activity. This strongly suggests that slow deformation transients, possibly related to episodic creep, could initiate prior to the main shock and extend past the coseismic phase, resulting in compound ruptures that include a very long period (up to tens of days) component.

  19. Vimentin contributes to epithelial-mesenchymal transition cancer cell mechanics by mediating cytoskeletal organization and focal adhesion maturation

    PubMed Central

    Liu, Ching-Yi; Lin, Hsi-Hui; Tang, Ming-Jer; Wang, Yang-Kao

    2015-01-01

    Modulations of cytoskeletal organization and focal adhesion turnover correlate to tumorigenesis and epithelial-mesenchymal transition (EMT), the latter process accompanied by the loss of epithelial markers and the gain of mesenchymal markers (e.g., vimentin). Clinical microarray results demonstrated that increased levels of vimentin mRNA after chemotherapy correlated to a poor prognosis of breast cancer patients. We hypothesized that vimentin mediated the reorganization of cytoskeletons to maintain the mechanical integrity in EMT cancer cells. By using knockdown strategy, the results showed reduced cell proliferation, impaired wound healing, loss of directional migration, and increased large membrane extension in MDA-MB 231 cells. Vimentin depletion also induced reorganization of cytoskeletons and reduced focal adhesions, which resulted in impaired mechanical strength because of reduced cell stiffness and contractile force. In addition, overexpressing vimentin in MCF7 cells increased cell stiffness, elevated cell motility and directional migration, reoriented microtubule polarity, and increased EMT phenotypes due to the increased β1-integrin and the loss of junction protein E-cadherin. The EMT-related transcription factor slug was also mediated by vimentin. The current study demonstrated that vimentin serves as a regulator to maintain intracellular mechanical homeostasis by mediating cytoskeleton architecture and the balance of cell force generation in EMT cancer cells. PMID:25965826

  20. Focal mechanism determination using high-frequency waveform matching and its application to small magnitude induced earthquakes

    NASA Astrophysics Data System (ADS)

    Li, Junlun; Zhang, Haijiang; Sadi Kuleli, H.; Nafi Toksoz, M.

    2011-03-01

    We present a new method using high-frequency full waveform information to determine the focal mechanisms of small, local earthquakes monitored by a sparse surface network. During the waveform inversion, we maximize both the phase and amplitude matching between the observed and modelled waveforms. In addition, we use the polarities of the first P-wave arrivals and the average S/P amplitude ratios to better constrain the matching. An objective function is constructed to include all four criteria. An optimized grid search method is used to search over all possible ranges of source parameters (strike, dip and rake). To speed up the algorithm, a library of Green's functions is pre-calculated for each of the moment tensor components and possible earthquake locations. Optimizations in filtering and cross correlation are performed to further speed the grid search algorithm. The new method is tested on a five-station surface network used for monitoring induced seismicity at a petroleum field. The synthetic test showed that our method is robust and efficient to determine the focal mechanism when using only the vertical component of seismograms in the frequency range of 3-9 Hz. The application to dozens of induced seismic events showed satisfactory waveform matching between modelled and observed seismograms. The majority of the events have a strike direction parallel with the major NE-SW faults in the region. The normal faulting mechanism is dominant, which suggests the vertical stress is larger than the horizontal stress.

  1. Beamlet focal plane diagnostic

    SciTech Connect

    Caird, J.A.; Nielsen, N.D.; Patton, H.G.; Seppala, L.G.; Thompson, C.E.; Wegner, P.J.

    1996-12-01

    This paper describes the major optical and mechanical design features of the Beamlet Focal Plane Diagnostic system as well as measurements of the system performance, and typical data obtained to date. We also discuss the NIF requirements on the focal spot that we are interested in measuring, and some of our plans for future work using this system.

  2. The Aftershock Risk Index - quantification of aftershock impacts during ongoing strong-seismic sequences

    NASA Astrophysics Data System (ADS)

    Schaefer, Andreas; Daniell, James; Khazai, Bijan; Wenzel, Friedemann

    2016-04-01

    The occurrence and impact of strong earthquakes often triggers the long-lasting impact of a seismic sequence. Strong earthquakes are generally followed by many aftershocks or even strong subsequently triggered ruptures. The Nepal 2015 earthquake sequence is one of the most recent examples where aftershocks significantly contributed to human and economic losses. In addition, rumours about upcoming mega-earthquakes, false predictions and on-going cycles of aftershocks induced a psychological burden on the society, which caused panic, additional casualties and prevented people from returning to normal life. This study shows the current phase of development of an operationalised aftershock intensity index, which will contribute to the mitigation of aftershock hazard. Hereby, various methods of earthquake forecasting and seismic risk assessments are utilised and an integration of the inherent aftershock intensity is performed. A spatio-temporal analysis of past earthquake clustering provides first-hand data about the nature of aftershock occurrence. Epidemic methods can additionally provide time-dependent variation indices of the cascading effects of aftershock generation. The aftershock hazard is often combined with the potential for significant losses through the vulnerability of structural systems and population. A historical database of aftershock socioeconomic effects from CATDAT has been used in order to calibrate the index based on observed impacts of historical events and their aftershocks. In addition, analytical analysis of cyclic behaviour and fragility functions of various building typologies are explored. The integration of many different probabilistic computation methods will provide a combined index parameter which can then be transformed into an easy-to-read spatio-temporal intensity index. The index provides daily updated information about the probability of the inherent seismic risk of aftershocks by providing a scalable scheme fordifferent aftershock

  3. Investigation of the 27 February 2010 Mw 8.8 Chilean earthquake integrating aftershock analysis, back-projection imaging and cGPS results

    NASA Astrophysics Data System (ADS)

    Clévédé, E.; Satriano, C.; Bukchin, B.; Lancieri, M.; Fuenzalida, A.; Vilotte, J.; Lyon-Caen, H.; Vigny, C.; Socquet, A.; Aranda, C.; Campos, J. A.; Scientific Team of the Lia Montessus de Ballore (Cnrs-Insu, U. Chile)

    2010-12-01

    The Mw 8.8 earthquake in central Chile ruptured more than 400 km along the subduction bound between the Nazca and the South American plates. The aftershock distribution clearly shows that this earthquake filled a well-known seismic gap, corresponding to rupture extension of the 1835 earthquake. The triggered post-seismic activity extends farther north of the gap, partially overlapping the 1985 and the 1960 Valparaiso earthquakes. However, the analysis of continuous GPS (cGPS) recordings, and back projection imaging of teleseismic body wave energy, indicate that the rupture stopped south of Valparaiso, around -33.5 degrees of latitude. An important question is how far the rupture actually extended to the north and the potential relation between the northernmost aftershock activity and remaining asperities within the ruptured zone of the previous Valparaiso earthquakes. The extension of the rupture offshore, towards west, also deserves further investigation. The aftershock distribution and the back propagation analysis support the hypothesis that, in the northern part, the rupture may have reached the surface at the trench. In this work, we performed a CMT and depth location study for more than 10 of the immediate largest aftershocks using teleseismic surface wave analysis constrained by P-wave polarity. In parallel, a detailed analysis of aftershocks in the northern part of the rupture, between 2010-03-11 and 2010-05-13, have been performed using the data from the station of the Chilean Servicio Sismológico Nacional (SSN), and of the post-seismic network, deployed by the French CNRS-INSU, GFZ, IRIS, and Caltech. We accurately hand-picked 153 larger events, which have been located using a non-linear probabilistic code, with improved depth location. Focal mechanisms have been computed for the larger events. Those results have been integrated with the analysis of cGPS and teleseismic back projection, and the overall kinematic of the Maule earthquake is discussed as

  4. Molecular mechanisms underlying the force-dependent regulation of actin-to-ECM linkage at the focal adhesions.

    PubMed

    Hirata, Hiroaki; Sokabe, Masahiro; Lim, Chwee Teck

    2014-01-01

    The linkage of the actin cytoskeleton to extracellular matrices (ECMs) at focal adhesions provides a physical path for cells to exert traction forces on substrates during cellular processes such as migration and morphogenesis. Mechanical strength of the actin-to-ECM linkage increases in response to forces loaded at this linkage. This is achieved by local accumulations of actin filaments, as well as linker proteins connecting actins to integrins, at force-bearing adhesion sites, which leads to an increase in the number of molecular bonds between the actin cytoskeleton- and ECM-bound integrins. Zyxin-dependent actin polymerization and filamin-mediated actin bundling are seemingly involved in the force-dependent actin accumulation. Each actin-integrin link is primarily mediated by the linker protein talin, which is strengthened by another linker protein vinculin connecting the actin filaments to talin in a force-dependent manner. This eliminates slippage between the actin cytoskeleton and talin (clutch mechanism), thus playing a crucial role in creating cell membrane protrusions mediated by actin polymerization. Finally, each integrin-ECM bond is also strengthened when a force is loaded on it, which ensures force transmission at focal adhesions, contributing to stable cell-substrate adhesion in cell migration. PMID:25081617

  5. Triggered Swarms and Induced Aftershock Sequences in Geothermal Systems

    NASA Astrophysics Data System (ADS)

    Shcherbakov, R.; Turcotte, D. L.; Yikilmaz, M. B.; Kellogg, L. H.; Rundle, J. B.

    2015-12-01

    Natural geothermal systems, which are used for energy generation, are usually associated with high seismic activity. This can be related to the large-scale injection and extraction of fluids to enhance geothermal recovery. This results in the changes of the pore pressure and pore-elastic stress field and can stimulate the occurrence of earthquakes. These systems are also prone to triggering of seismicity by the passage of seismic waves generated by large distant main shocks. In this study, we analyze clustering and triggering of seismicity at several geothermal fields in California. Particularly, we consider the seismicity at the Geysers, Coso, and Salton Sea geothermal fields. We analyze aftershock sequences generated by local large events with magnitudes greater than 4.0 and earthquake swarms generated by several significant long distant main shocks. We show that the rate of the aftershock sequences generated by the local large events in the two days before and two days after the reference event can be modelled reasonably well by the time dependent Epidemic Type Aftershock Sequence (ETAS) model. On the other hand, the swarms of activity triggered by large distant earthquakes cannot be described by the ETAS model. To model the increase in the rate of seismicity associated with triggering by large distant main shocks we introduce an additional time-dependent triggering mechanism into the ETAS model. In almost all cases the frequency-magnitude statistics of triggered sequences follow Gutenberg-Richter scaling to a good approximation. The analysis indicates that the seismicity triggered by relatively large local events can initiate sequences similar to regular aftershock sequences. In contrast, the distant main shocks trigger swarm like activity with faster decaying rates.

  6. Damped regional-scale stress inversions: Methodology and examples for southern California and the Coalinga aftershock sequence

    USGS Publications Warehouse

    Hardebeck, J.L.; Michael, A.J.

    2006-01-01

    We present a new focal mechanism stress inversion technique to produce regional-scale models of stress orientation containing the minimum complexity necessary to fit the data. Current practice is to divide a region into small subareas and to independently fit a stress tensor to the focal mechanisms of each subarea. This procedure may lead to apparent spatial variability that is actually an artifact of overfitting noisy data or nonuniquely fitting data that does not completely constrain the stress tensor. To remove these artifacts while retaining any stress variations that are strongly required by the data, we devise a damped inversion method to simultaneously invert for stress in all subareas while minimizing the difference in stress between adjacent subareas. This method is conceptually similar to other geophysical inverse techniques that incorporate damping, such as seismic tomography. In checkerboard tests, the damped inversion removes the stress rotation artifacts exhibited by an undamped inversion, while resolving sharper true stress rotations than a simple smoothed model or a moving-window inversion. We show an example of a spatially damped stress field for southern California. The methodology can also be used to study temporal stress changes, and an example for the Coalinga, California, aftershock sequence is shown. We recommend use of the damped inversion technique for any study examining spatial or temporal variations in the stress field.

  7. Periodic variation of stress field in the Koyna-Warna reservoir triggered seismic zone inferred from focal mechanism studies

    NASA Astrophysics Data System (ADS)

    Rao, N. Purnachandra; Shashidhar, D.

    2016-06-01

    The Koyna-Warna region in western India is globally recognized as the premier site of reservoir triggered seismicity (RTS) associated with the Koyna and Warna reservoirs. The region is characterized by continuous seismic activity observed since several decades, including the world's largest triggered earthquake of M6.3 which occurred in Koyna in 1967. While the role of reservoirs in triggering earthquakes has been widely discussed, the actual tectonic mechanism controlling earthquake genesis in this region is hardly understood. The Koyna-Warna region is exclusively governed by earthquakes of strike-slip and normal fault mechanism distinct from the thrust faulting seen in other active zones in the Indian region. In the present study, a comprehensive catalog of 50 focal mechanism solutions of earthquakes that occurred during the last 45 years in the Koyna-Warna region is developed, both from previous literature and from moment tensor inversion studies by the authors using broadband data from a local seismic network operating since 2005. The seismicity and fault plane data have enabled precise delineation of trends of the major causative faults, which are further accentuated using the double-difference technique. Stress inversion of the focal mechanism data has provided the best fitting principal compressive and tensile stress field of the region, which in conjunction with the deciphered fault zones provides a feasible model of seismogenesis in this region. Based on the observed temporal variation of faulting mechanism a model of alternating cycles of predominantly strike-slip and normal faulting is proposed, which is attributed to a periodic peaking and relaxation respectively of the horizontal compressive stress field in this region due to the Indian plate collision with Eurasia.

  8. Seismic source study of the Racha-Dzhava (Georgia) earthquake from aftershocks and broad-band teleseismic body-wave records: An example of active nappe tectonics

    USGS Publications Warehouse

    Fuenzalida, H.; Rivera, L.; Haessler, H.; Legrand, D.; Philip, H.; Dorbath, L.; McCormack, D.; Arefiev, S.; Langer, C.; Cisternas, A.

    1997-01-01

    The Racha-Dzhava earthquake (Ms = 7.0) that occurred on 1991 April 29 at 09:12:48.1 GMT in the southern border of the Great Caucasus is the biggest event ever recorded in the region, stronger than the Spitak earthquake (Ms = 6.9) of 1988. A field expedition to the epicentral area was organised and a temporary seismic network of 37 stations was deployed to record the aftershock activity. A very precise image of the aftershock distribution is obtained, showing an elongated cloud oriented N105??, with one branch trending N310?? in the western part. The southernmost part extends over 80 km, with the depth ranging from 0 to 15 km, and dips north. The northern branch, which is about 30 km long, shows activity that ranges in depth from 5 to 15 km. The complex thrust dips northwards. A stress-tensor inversion from P-wave first-motion polarities shows a state of triaxial compression, with the major principal axis oriented roughly N-S, the minor principal axis being vertical. Body-waveform inversion of teleseismic seismograms was performed for the main shock, which can be divided into four subevents with a total rupture-time duration of 22 s. The most important part of the seismic moment was released by a gentle northerly dipping thrust. The model is consistent with the compressive tectonics of the region and is in agreement with the aftershock distribution and the stress tensor deduced from the aftershocks. The focal mechanisms of the three largest aftershocks were also inverted from body-wave records. The April 29th (Ms = 6.1) and May 5th (Ms = 5.4) aftershocks have thrust mechanisms on roughly E-W-oriented planes, similar to the main shock. Surprisingly, the June 15th (Ms = 6.2) aftershock shows a thrust fault striking N-S. This mechanism is explained by the structural control of the rupture along the east-dipping geometry of the Dzirula Massif close to the Borzhomi-Kazbeg strike-slip fault. In fact, the orientation and shape of the stress tensor produce a thrust on a N

  9. The mysterious nature of bacterial surface (gliding) motility: A focal adhesion-based mechanism in Myxococcus xanthus.

    PubMed

    Islam, Salim T; Mignot, Tâm

    2015-10-01

    Motility of bacterial cells promotes a range of important physiological phenomena such as nutrient detection, harm avoidance, biofilm formation, and pathogenesis. While much research has been devoted to the mechanism of bacterial swimming in liquid via rotation of flagellar filaments, the mechanisms of bacterial translocation across solid surfaces are poorly understood, particularly when cells lack external appendages such as rotary flagella and/or retractile type IV pili. Under such limitations, diverse bacteria at the single-cell level are still able to "glide" across solid surfaces, exhibiting smooth translocation of the cell along its long axis. Though multiple gliding mechanisms have evolved in different bacterial classes, most remain poorly characterized. One exception is the gliding motility mechanism used by the Gram-negative social predatory bacterium Myxococcus xanthus. The available body of research suggests that M. xanthus gliding motility is mediated by trafficked multi-protein (Glt) cell envelope complexes, powered by proton-driven flagellar stator homologues (Agl). Through coupling to the substratum via polysaccharide slime, Agl-Glt assemblies can become fixed relative to the substratum, forming a focal adhesion site. Continued directional transport of slime-associated substratum-fixed Agl-Glt complexes would result in smooth forward movement of the cell. In this review, we have provided a comprehensive synthesis of the latest mechanistic and structural data for focal adhesion-mediated gliding motility in M. xanthus, with emphasis on the role of each Agl and Glt protein. Finally, we have also highlighted the possible connection between the motility complex and a new type of spore coat assembly system, suggesting that gliding and cell envelope synthetic complexes are evolutionarily linked. PMID:26520023

  10. Foreshock and aftershocks in simple earthquake models.

    PubMed

    Kazemian, J; Tiampo, K F; Klein, W; Dominguez, R

    2015-02-27

    Many models of earthquake faults have been introduced that connect Gutenberg-Richter (GR) scaling to triggering processes. However, natural earthquake fault systems are composed of a variety of different geometries and materials and the associated heterogeneity in physical properties can cause a variety of spatial and temporal behaviors. This raises the question of how the triggering process and the structure interact to produce the observed phenomena. Here we present a simple earthquake fault model based on the Olami-Feder-Christensen and Rundle-Jackson-Brown cellular automata models with long-range interactions that incorporates a fixed percentage of stronger sites, or asperity cells, into the lattice. These asperity cells are significantly stronger than the surrounding lattice sites but eventually rupture when the applied stress reaches their higher threshold stress. The introduction of these spatial heterogeneities results in temporal clustering in the model that mimics that seen in natural fault systems along with GR scaling. In addition, we observe sequences of activity that start with a gradually accelerating number of larger events (foreshocks) prior to a main shock that is followed by a tail of decreasing activity (aftershocks). This work provides further evidence that the spatial and temporal patterns observed in natural seismicity are strongly influenced by the underlying physical properties and are not solely the result of a simple cascade mechanism. PMID:25768785

  11. Foreshock and Aftershocks in Simple Earthquake Models

    NASA Astrophysics Data System (ADS)

    Kazemian, J.; Tiampo, K. F.; Klein, W.; Dominguez, R.

    2015-02-01

    Many models of earthquake faults have been introduced that connect Gutenberg-Richter (GR) scaling to triggering processes. However, natural earthquake fault systems are composed of a variety of different geometries and materials and the associated heterogeneity in physical properties can cause a variety of spatial and temporal behaviors. This raises the question of how the triggering process and the structure interact to produce the observed phenomena. Here we present a simple earthquake fault model based on the Olami-Feder-Christensen and Rundle-Jackson-Brown cellular automata models with long-range interactions that incorporates a fixed percentage of stronger sites, or asperity cells, into the lattice. These asperity cells are significantly stronger than the surrounding lattice sites but eventually rupture when the applied stress reaches their higher threshold stress. The introduction of these spatial heterogeneities results in temporal clustering in the model that mimics that seen in natural fault systems along with GR scaling. In addition, we observe sequences of activity that start with a gradually accelerating number of larger events (foreshocks) prior to a main shock that is followed by a tail of decreasing activity (aftershocks). This work provides further evidence that the spatial and temporal patterns observed in natural seismicity are strongly influenced by the underlying physical properties and are not solely the result of a simple cascade mechanism.

  12. MUC16 contributes to the metastasis of pancreatic ductal adenocarcinoma through focal adhesion mediated signaling mechanism

    PubMed Central

    Chugh, Seema; Rachagani, Satyanarayana; Lakshmanan, Imayavaramban; Gupta, Suprit; Seshacharyulu, Parthasarathy; Smith, Lynette M.; Ponnusamy, Moorthy P.; Batra, Surinder K.

    2016-01-01

    MUC16, a heavily glycosylated type-I transmembrane mucin is overexpressed in several cancers including pancreatic ductal adenocarcinoma (PDAC). Previously, we have shown that MUC16 is significantly overexpressed in human PDAC tissues. However, the functional consequences and its role in PDAC is poorly understood. Here, we show that MUC16 knockdown decreases PDAC cell proliferation, colony formation and migration in vitro. Also, MUC16 knockdown decreases the tumor formation and metastasis in orthotopic xenograft mouse model. Mechanistically, immunoprecipitation and immunofluorescence analyses confirms MUC16 interaction with galectin-3 and mesothelin in PDAC cells. Adhesion assay displayed decreased cell attachment of MUC16 knockdown cells with recombinant galectin-1 and galectin-3 protein. Further, CRISPR/Cas9-mediated MUC16 knockout cells show decreased tumor-associated carbohydrate antigens (T and Tn) in PDAC cells. Importantly, carbohydrate antigens were decreased in the region that corresponds to MUC16 and suggests for the decreased MUC16-galectin interactions. Co-immunoprecipitation also revealed a novel interaction between MUC16 and FAK in PDAC cells. Interestingly, we observed decreased expression of mesenchymal and increased expression of epithelial markers in MUC16-silenced cells. Additionally, MUC16 loss showed a decreased FAK-mediated Akt and ERK/MAPK activation. Altogether, these findings suggest that MUC16-focal adhesion signaling may play a critical role in facilitating PDAC growth and metastasis. PMID:27382435

  13. Preliminary results of very fast computation of Moment Magnitude and focal mechanism in the context of tsunami warning

    NASA Astrophysics Data System (ADS)

    Schindelé, François; Roch, Julien; Rivera, Luis

    2015-04-01

    Various methodologies were recently developed to compute the moment magnitude and the focal mechanism, thanks to the real time access to numerous broad-band seismic data. Several methods were implemented at the CENALT, in particular the W-Phase method developed by H. Kanamori and L. Rivera. For earthquakes of magnitudes in the range 6.5-9.0, this method provides accurate results in less than 40 minutes. The context of the tsunami warning in Mediterranean, a small basin impacted in less than one hour, and with small sources but some with high tsunami potential (Boumerdes 2003), a comprehensive tsunami warning system in that region should include very fast computation of the seismic parameters. The results of the values of Mw, the focal depth and the type of fault (reverse, normal, strike-slip) are the most relevant parameters expected for the tsunami warning. Preliminary results will be presented using data in the North-eastern and Mediterranean region for the recent period 2010-2014. This work is funded by project ASTARTE - - Assessment, Strategy And Risk Reduction for Tsunamis in Europe - FP7-ENV2013 6.4-3, Grant 603839

  14. Very Fast Characterization of Focal Mechanism Parameters Through W-Phase Centroid Inversion in the Context of Tsunami Warning

    NASA Astrophysics Data System (ADS)

    Roch, Julien; Duperray, Pierre; Schindelé, François

    2016-03-01

    Most of the tsunami potential seismic sources in the NEAM region are in a magnitude range of 6.5 ≤ Mw ≤ 7.5 (e.g. the tsunami triggered by the Boumerdes earthquake of 2003 with Mw=6.9 ). The CENtre d'ALerte aux Tsunamis (CENALT), in operation since 2012 as the French National Tsunami Warning Centre (NTWC) and Candidate Tsunami Service Provider (CTSP), has to issue warning messages within 15 min of earthquake origin time. These warnings are based on the seismic source parameters (Mw magnitude, focal depth and type of fault), which are computed by focal mechanisms and centroid inversion methods. The W-phase method, developed by Kanamori and Rivera, allows quick computation of seismic source parameters due to the early arrival time between P-waves and surface waves, and is therefore particularly useful for monitoring. We assess the W-phase method with 29 events of magnitude M_w ≥ 5.8 for the period 2010-2015 in the NEAM region. Results with 10 min of signal length are in good agreement compared to the Global Centroid Moment Tensor (GCMT) catalog.

  15. The Constantine (northeast Algeria) earthquake of October 27, 1985: surface ruptures and aftershock study

    NASA Astrophysics Data System (ADS)

    Bounif, A.; Haessler, H.; Meghraoui, M.

    1987-10-01

    An earthquake of magnitude Ms = 6.0 (CSEM, Strasbourg) occurred at Constantine (Algeria) on 27 October 1985. This seismic event is the strongest felt in the Tellian Atlas since the El Asnam seismic crisis of October 10, 1980. A team from the Centre de Recherche d'Astronomie, d'Astrophysique et de Géophysique (CRAAG, Algeria), utilising 8 portable stations, registered the activity a few days after the main shock. The aftershocks follow a N045° direction, and show the existence of three ruptured segments. Cross sections display a remarkable vertical fault plane and suggest asperities in the rupture process. Surface breaks were found affecting Quaternary deposits. The principal segment is about 3.8 km long showing “enéchelon” cracks with left-lateral displacement while the main direction of the rupture is N055°. Although the vertical motion is small, the northwestern block shows a normal component of the main surface faulting, while the left-lateral displacement is about 10 cm. The strike-slip focal mechanism solution determined from the global seismic network and field observations are in good agreement.

  16. Overpressured fluid imaging from focal mechanisms during the 2003-2004 Ubaye seismic swarm (Southern-Alps, France)

    NASA Astrophysics Data System (ADS)

    Leclère, H.; Daniel, G.; Fabbri, O.; Cappa, F.

    2012-04-01

    The development of fluid pressure is thought to play a major role in earthquake triggering and in fault reactivation (Nur & Booker, 1972; Sibson, 1985; Miller et al., 2004; Hainzl et al., 2006; Cappa et al., 2009; Terakawa et al., 2010) In this study, we present an analysis of the potential key role of fluid pressure on the triggering of the 2003-2004 Ubaye (France) seismic swarm. Our aim is to provide a better understanding of fluid pressure build-up along fault zones and its influence on earthquake triggering. More than 16,000 microseismic events were detected during the Ubaye swarm. This swarm occurred over an area located between the Argentera-Mercantour and the Pelvoux crystalline massifs, below the Embrunais-Ubaye nappes (Jenatton et al., 2007). Hypocentral depths were comprised between 3 and 8 km and the spatial distribution of hypocenters was parallel to the azimuth of major regional NW-SE faults. This suggests that seismic ruptures reactivated a preexisting fault zone in the crystalline basement (Leclère et al., in press). Based on Mohr-Coulomb theory and a fault zone orientation of the seismic swarm computed by Daniel et al. (2011), we estimate the overpressured fluid required to reactivate this fault to be between 7 and 26 MPa (Leclère et al., in press). This result is in good agreement with a previous study by Daniel et al. (2011). We propose a mechanism for the development of overpressured fluid conditions that accounts for the presence of thermal springs, fault zone compaction processes and hydraulic barriers (Leclère et al., in press). In a further step, we analyze an extended focal mechanism dataset and we focus on overpressured fluid conditions required to reactivate individual fault planes related to each focal mechanism. We then investigate the correlation between changes in overpressured fluid conditions and changes in the seismicity rate. We also discuss the spatial heterogeneity of overpressured fluid conditions.

  17. Stress Patterns in Northern Iraq and Surrounding Regions from Formal Stress Inversion of Earthquake Focal Mechanism Solutions

    NASA Astrophysics Data System (ADS)

    Abdulnaby, Wathiq; Mahdi, Hanan; Al-Shukri, Haydar; Numan, Nazar M. S.

    2014-09-01

    The collision zone between the Arabian and Eurasian plates is one of the most seismically active regions. Northern Iraq represents the northeastern part of the Arabian plate that has a suture zone with the Turkish and Iranian plates called the Bitlis-Zagros suture zone. The orientations of the principal stress axes can be estimated by the formal stress inversion of focal mechanism solutions. The waveform moment tensor inversion method was used to derive a focal mechanism solution of 65 earthquakes with magnitudes range from 3.5 to 5.66 in the study area. From focal mechanism solutions, the direction of slip and the orientations of the moment stress axes ( P, N, and T) on the causative fault surface during an earthquake were determined. The dataset of the moment stress axes have been used to infer the regional principal stress axes ( σ 1, σ 2, and σ 3) by the formal stress inversion method. Two inversion methods, which are the new right dihedron and the rotational optimization methods, were used. The results show that six stress regime categories exist in the study area. However, the most common tectonic regimes are the strike-slip faulting (43.94 %), unspecified oblique faulting (27.27 %), and thrust faulting (13.64 %) regimes. In most cases, the strike-slip movement on the fault surfaces consists of left-lateral (sinistral) movement. The normal faulting is located in one small area and is due to a local tensional stress regime that develops in areas of strike-slip displacements as pull-apart basins. The directions of the horizontal stress axes show that the compressional stress regime at the Bitlis-Zagros suture zone has two directions. One is perpendicular to the suture zone near the Iraq-Iran border and the second is parallel in places as well as perpendicular in others to the suture zone near the Iraq-Turkey border. In addition, the principal stress axes in the Sinjar area near the Iraq-Syria border have a E-W direction. These results are compatible with the

  18. Local tomography and focal mechanisms in the south-western Alps: Comparison of methods and tectonic implications

    NASA Astrophysics Data System (ADS)

    Nicole, Béthoux; Christian, Sue; Anne, Paul; Jean, Virieux; Julien, Fréchet; François, Thouvenot; Marco, Cattaneo

    2007-03-01

    We investigate how focal solutions and hypocenter locations may depend on the ray tracing algorithm and the strategy of velocity inversion. Using arrival times from a temporary seismological network in the south-western Alps, a local earthquake tomography has been performed by Paul et al. [Paul, A., Cattaneo, M., Thouvenot, F., Spallarossa, D., Béthoux, N., and Fréchet, J., 2001. A three-dimensional crustal velocity model of the south-western Alps from local earthquake tomography. J. Geophys. Res. 106, 19367-19390.] with the method developed by Thurber [Thurber, C.H., 1993. Local earthquake tomography: velocity and Vp/Vs-Theory, in Seismic Tomography: Theory and practice, Iyer, H.M., and Irahara eds., Chapman and Hall, New York, 563-583.]. Another inversion of the same data set is performed here using a different tomography code relying on a shooting paraxial method and cubic interpolation of velocities. The resulting images display the same main features, although Thurber's code appears to be more robust in regions with scarce ray coverage and strong velocity contrasts. Concerning hypocenter location in Piemont units, one major result is the concentration of hypocenters at the boundary between the mantle wedge of the Ivrea body and the European crust. Forty-six focal mechanisms are shown that were computed using both the take-off angles in the minimum 1-D model and in the 3-D velocity structures resulting from the two inversions. The sets of focal solutions are very similar, proving the reliability and the coherency of the focal solutions. The widespread extension in the core of the western Alps is confirmed whereas a few compressive solutions are found east of the Piemont units. These results constrain the sharp change of stress tensor and evidence a decoupling of strain beneath the east of Dora Maira massif up to beneath the north of Argentera massif. On a geodynamical point of view seismicity and focal mechanism distribution are compatible with the present

  19. Aftershock production rate of driven viscoelastic interfaces

    NASA Astrophysics Data System (ADS)

    Jagla, E. A.

    2014-10-01

    We study analytically and by numerical simulations the statistics of the aftershocks generated after large avalanches in models of interface depinning that include viscoelastic relaxation effects. We find in all the analyzed cases that the decay law of aftershocks with time can be understood by considering the typical roughness of the interface and its evolution due to relaxation. In models where there is a single viscoelastic relaxation time there is an exponential decay of the number of aftershocks with time. In models in which viscoelastic relaxation is wave-vector dependent we typically find a power-law dependence of the decay rate that is compatible with the Omori law. The factors that determine the value of the decay exponent are analyzed.

  20. Aftershock production rate of driven viscoelastic interfaces.

    PubMed

    Jagla, E A

    2014-10-01

    We study analytically and by numerical simulations the statistics of the aftershocks generated after large avalanches in models of interface depinning that include viscoelastic relaxation effects. We find in all the analyzed cases that the decay law of aftershocks with time can be understood by considering the typical roughness of the interface and its evolution due to relaxation. In models where there is a single viscoelastic relaxation time there is an exponential decay of the number of aftershocks with time. In models in which viscoelastic relaxation is wave-vector dependent we typically find a power-law dependence of the decay rate that is compatible with the Omori law. The factors that determine the value of the decay exponent are analyzed. PMID:25375460

  1. Quantifying capability of a local seismic network in terms of locations and focal mechanism solutions of weak earthquakes

    NASA Astrophysics Data System (ADS)

    Fojtíková, Lucia; Kristeková, Miriam; Málek, Jiří; Sokos, Efthimios; Csicsay, Kristián; Zahradník, Jiří

    2016-01-01

    Extension of permanent seismic networks is usually governed by a number of technical, economic, logistic, and other factors. Planned upgrade of the network can be justified by theoretical assessment of the network capability in terms of reliable estimation of the key earthquake parameters (e.g., location and focal mechanisms). It could be useful not only for scientific purposes but also as a concrete proof during the process of acquisition of the funding needed for upgrade and operation of the network. Moreover, the theoretical assessment can also identify the configuration where no improvement can be achieved with additional stations, establishing a tradeoff between the improvement and additional expenses. This paper presents suggestion of a combination of suitable methods and their application to the Little Carpathians local seismic network (Slovakia, Central Europe) monitoring epicentral zone important from the point of seismic hazard. Three configurations of the network are considered: 13 stations existing before 2011, 3 stations already added in 2011, and 7 new planned stations. Theoretical errors of the relative location are estimated by a new method, specifically developed in this paper. The resolvability of focal mechanisms determined by waveform inversion is analyzed by a recent approach based on 6D moment-tensor error ellipsoids. We consider potential seismic events situated anywhere in the studied region, thus enabling "mapping" of the expected errors. Results clearly demonstrate that the network extension remarkably decreases the errors, mainly in the planned 23-station configuration. The already made three-station extension of the network in 2011 allowed for a few real data examples. Free software made available by the authors enables similar application in any other existing or planned networks.

  2. Aftershocks in a time-to-failure slider-block model

    NASA Astrophysics Data System (ADS)

    Gran, J. D.; Rundle, J. B.; Turcotte, D. L.

    2011-12-01

    Several earthquake models have been used to study the mechanisms that lead to a Gutenberg-Richter distribution of earthquake magnitudes. One such model is the cellular automaton (CA) slider-block model. Events (earthquakes) in this model are initiated by a loader plate increasing stress uniformly on all blocks until a single block reaches a static friction failure threshold which can trigger a cascade of failures of blocks. This model, although useful, misses a key part of the earthquake process, i.e. aftershocks. Aftershocks occur within a short time period following the main-shock and are due to stress redistributions within the earth's crust rather than movement of the interacting tectonic plates. We describe here a modified version of CA slider-block model, which includes a time-to-failure mode, that allows blocks to fail below the static threshold value if enough time passes. This new feature allows multiple independent events to occur during a single plate update. We measure time in Monte Carlo steps and have tested various functions for the time-to-failure to understand the connection between the time-to-failure and Omori's law for the frequency of aftershocks following the main-shock. After each loader plate update, we see a main-shock followed in time by multiple aftershocks that decay in magnitude. We believe this to be another mechanism for the occurrence of aftershocks in addition to that found by Dietrich, JGR(1994).

  3. Triggering of Aftershocks by Free Oscillations

    NASA Astrophysics Data System (ADS)

    Bufe, C. G.; Varnes, D. J.

    2001-12-01

    Periodicities observed in aftershock sequences may result from earthquake triggering by free oscillations of the Earth produced by the main shock. Using an algorithm we developed to compute spectra of inter-event times, we examine inter-event intervals of teleseismically recorded aftershock sequences from large (M>7.5) main shocks that occurred during 1980-2001. Observed periodicities may result from triggering at intervals that are multiples of normal mode periods. We have focussed our analysis of inter-event times on identification of triggering by free oscillations at periods in the range 6-60 minutes. In this paper we describe our most commonly observed aftershock inter-event times and the free oscillation modes most likely to be the triggers. Because of their separation, the longer period modes are easiest to identify in the aftershock data (0S2 at 53.9 minutes, 0S3 at 35.6 minutes, 0S4 at 25.8 minutes, and 0T2 at 43.9 minutes). Evidence of triggering by 0S2 and 0T2 was also found in the aftershocks of the 1989 Loma Prieta, CA (M 7) earthquake (Kamal and Mansinha, 1996). Because of the plethora of higher modes, shorter inter-event periods are more difficult to identify with a particular mode. Preliminary analysis of the 2001 Bhuj, India (M 7.7) earthquake sequence tentatively identifies a contribution to triggering of the first four large aftershocks by multiples of 0S12 (8.37 minutes).

  4. How Long is an Aftershock Sequence?

    NASA Astrophysics Data System (ADS)

    Godano, Cataldo; Tramelli, Anna

    2016-06-01

    The occurrence of a mainschok is always followed by aftershocks spatially distributed within the fault area. The aftershocks rate decay with time is described by the empirical Omori law which was inferred by catalogues analysis. The sequences discrimination within catalogues is not a straightforward operation, especially for low-magnitude mainshocks. Here, we describe the rate decay of the Omori law obtained using different sequence discrimination tools and we discover that, when the background seismicity is excluded, the sequences tend to last for the temporal extension of the catalogue.

  5. Processing Aftershock Sequences Using Waveform Correlation

    NASA Astrophysics Data System (ADS)

    Resor, M. E.; Procopio, M. J.; Young, C. J.; Carr, D. B.

    2008-12-01

    For most event monitoring systems, the objective is to keep up with the flow of incoming data, producing a bulletin with some modest, relatively constant, time delay after present time, often a period of a few hours or less. Because the association problem scales exponentially and not linearly with the number of detections, a dramatic increase in seismicity due to an aftershock sequence can easily cause the bulletin delay time to increase dramatically. In some cases, the production of a bulletin may cease altogether, until the automatic system can catch up. For a nuclear monitoring system, the implications of such a delay could be dire. Given the expected similarity between a mainshock and aftershocks, it has been proposed that waveform correlation may provide a powerful means to simultaneously increase the efficiency of processing aftershock sequences, while also lowering the detection threshold and improving the quality of the event solutions. However, many questions remain unanswered. What are the key parameters for achieving the best correlations between waveforms (window length, filtering, etc.), and are they sequence-dependent? What is the overall percentage of similar events in an aftershock sequence, i.e. what is the maximum level of efficiency that a waveform correlation could be expected to achieve? Finally, how does this percentage of events vary among sequences? Using data from the aftershock sequence for the December 26, 2004 Mw 9.1 Sumatra event, we investigate these issues by building and testing a prototype waveform correlation event detection system that automatically expands its library of known events as new signatures are indentified in the aftershock sequence (by traditional signal detection and event processing). Our system tests all incoming data against this dynamic library, thereby identify any similar events before traditional processing takes place. In the region surrounding the Sumatra event, the NEIC EDR contains 4997 events in the 9

  6. How Long is an Aftershock Sequence?

    NASA Astrophysics Data System (ADS)

    Godano, Cataldo; Tramelli, Anna

    2016-07-01

    The occurrence of a mainschok is always followed by aftershocks spatially distributed within the fault area. The aftershocks rate decay with time is described by the empirical Omori law which was inferred by catalogues analysis. The sequences discrimination within catalogues is not a straightforward operation, especially for low-magnitude mainshocks. Here, we describe the rate decay of the Omori law obtained using different sequence discrimination tools and we discover that, when the background seismicity is excluded, the sequences tend to last for the temporal extension of the catalogue.

  7. Improvements of Real Time First Motion Focal Mechanism and Noise Characteristics of New Sites at the Puerto Rico Seismic Network

    NASA Astrophysics Data System (ADS)

    Williams, D. M.; Lopez, A. M.; Huerfano, V.; Lugo, J.; Cancel, J.

    2011-12-01

    Seismic networks need quick and efficient ways to obtain information related to seismic events for the purposes of seismic activity monitoring, risk assessment, and scientific knowledge among others. As part of an IRIS summer internship program, two projects were performed to provide a tool for quick faulting mechanism and improve seismic data at the Puerto Rico Seismic Network (PRSN). First, a simple routine to obtain a focal mechanisms, the geometry of the fault, based on first motions was developed and implemented for data analysts routine operations at PRSN. The new tool provides the analyst a quick way to assess the probable faulting mechanism that occurred while performing the interactive earthquake location procedure. The focal mechanism is generated on-the-fly when data analysts pick P wave arrivals onsets and motions. Once first motions have been identified, an in-house PRSN utility is employed to obtain the double couple representation and later plotted using GMT's psmeca utility. Second, we addressed the issue of seismic noise related to thermal fluctuations inside seismic vaults. Seismic sites can be extremely noisy due to proximity to cultural activities and unattended thermal fluctuations inside sensor housings, thus resulting in skewed readings. In the past, seismologists have used different insulation techniques to reduce the amount of unwanted noise that a seismometers experience due to these thermal changes with items such as Styrofoam, and fiber glass among others. PRSN traditionally uses Styrofoam boxes to cover their seismic sensors, however, a proper procedure to test how these method compare to other new techniques has never been approached. The deficiency of properly testing these techniques in the Caribbean and especially Puerto Rico is that these thermal fluctuations still happen because of the intense sun and humidity. We conducted a test based on the methods employed by the IRIS Transportable Array, based on insulation by sand burial of

  8. Fine fracture structures in the geothermal region of Hakone volcano, revealed by well-resolved earthquake hypocenters and focal mechanisms

    NASA Astrophysics Data System (ADS)

    Yukutake, Y.; Tanada, T.; Honda, R.; Harada, M.; Ito, H.; Yoshida, A.

    2009-12-01

    Occurrence of swarm earthquake in volcanically or geothermally active regions has been thought to be caused by the migration of the magmatic and/or hydrothermal fluid (e.g. Hill, 1977; Sibson, 1996; Spicak and Horalek, 2001; Hensch et al., 2008). It has been suggested that the fault-related fracture systems are responsible for the migration of fluid flow (e.g. Hill, 1977; Sibson, 1987; Sibson, 1996). For example, Sibson (1987) and Curewitz and Karson (1997) supposed that high permeable fracture system is mainly developed by the interaction between active faults at a pull- apart region (dilational fault jogs). However, it has not been shown that the fracture system is actually related to clustering of earthquakes in swarm activities. We investigated precise hypocentral distribution and mechanisms of small earthquakes in the geothermal region of Hakone volcano, near Tokyo Metropolitan Area central Japan, where swarm activities have been frequently observed. Hakone volcano is located in the northern boundary zone of the Izu-Mariana volcanic arc. The surface traces of the Hirayama and Tanna Fault are also located at the northern and southern part of Hakone volcano, respectively. The precise hypocenter determination is decisively important to elucidate occurrence mechanism of swarm earthquakes as well as to mitigate volcanic hazard at a world-famous sight-seeing spot near Tokyo Metropolitan Area, Japan. We first determined initial hypocenters, using the station corrections and one-dimensional velocity structures estimated by the joint hypocenter determination method (Kissling et al., 1994). Then, we applied the double-difference method (Waldhauser and Ellsworth, 2000) to relocate the initial hypocenters using the differential arrival time obtained by both manual picking and waveform cross-correlation analysis. Subsequently, we determined the focal mechanisms from the absolute P- and SH-wave amplitudes by adding the P-wave polarities. We found that most swarm earthquakes

  9. The Mw 5.8 Virginia Earthquake of August 23, 2011 and its Aftershocks: A Shallow High Stress Drop Event

    NASA Astrophysics Data System (ADS)

    Ellsworth, W. L.; Imanishi, K.; Luetgert, J. H.; Kruger, J.; Hamilton, J.

    2011-12-01

    We analyze the hypocentral distribution and source parameters of the aftershocks of the Virginia Earthquake of August 23, 2011 using a temporary array of telemetered instruments deployed within 20 km of the main shock. Our data come from four USGS NetQuakes accelerometers and seven IRIS/PASSCAL seismometers that were established within a few days of the earthquake. Aftershock seismograms at these near-source stations are characterized by impulsive, high-frequency P and S phases at most sites. In addition, we use the five closest permanent stations (60 - 310 km distance) to analyze the main shock. Hypocenters, crustal velocity model and station corrections were determined using the program VELEST (Kissling, et al, 1994). The aftershocks define a 10-km-long, N 30 degree E striking, 45 degree ESE dipping fault. This fault plane agrees well with the USGS moment tensor solutions for the main shock. Aftershock depths range from 2.5 to 8 km, placing the sequence in the Cambrian metamorphic rocks of the Eastern Piedmont thrust sheet. We relocated the main shock relative to a well-located Mw 3.5 aftershock using the P-wave arrival times at the five permanent stations. The main shock epicenter lies in the middle of the aftershock zone. Its focal depth, although not well constrained, is similar to the aftershocks. A crustal-scale seismic reflection profile was acquired by the USGS in 1981 along I-64 just 4 km southwest of the nearest aftershocks. This profile runs nearly parallel to the dip direction of the aftershock zone and has been interpreted to contain many ESE-dipping reverse faults in the allochthonous upper crust (Harris et al., 1986; Pratt, et al., 1988). When projected onto the reflection profile the aftershocks locate within a relatively non-reflective zone bounded above and below by prominent bands of more shallowly dipping reflectors reported by Pratt et al. (1988) raising the question whether or not the earthquake reactivated a pre-existing fault. Seismic

  10. Seismological aspects of the 27 June 2015 Gulf of Aqaba earthquake and its sequence of aftershocks

    NASA Astrophysics Data System (ADS)

    Abd el-aal, Abd el-aziz Khairy; Badreldin, Hazem

    2016-04-01

    On 27 June 2015, a moderate earthquake with magnitude Mb 5.2 struck the Gulf of Aqaba near Nuweiba City. This event was instrumentally recorded by the Egyptian National Seismic Network (ENSN) and many other international seismological centres. The event was felt in all the cities on the Gulf of Aqaba, as well as Suez City, Hurghada City, the greater Cairo Metropolitan Area, Israel, Jordan and the north-western part of Saudi Arabia. No casualties were reported, however. Approximately 95 aftershocks with magnitudes ranging from 0.7 to 4.2 were recorded by the ENSN following the mainshock. In the present study, the source characteristics of both the mainshock and the aftershocks were estimated using the near-source waveform data recorded by the very broadband stations of the ENSN, and these were validated by the P-wave polarity data from short period stations. Our analysis reveals that an estimated seismic moment of 0.762 × 1017 Nm was released, corresponding to a magnitude of Mw 5.2, a focal depth of 14 km, a fault radius of 0.72 km and a rupture area of approximately 1.65 km2. Monitoring the sequence of aftershocks reveals that they form a cluster around the mainshock and migrated downwards in focal depth towards the west. We compared the results we obtained with the published results from the international seismological centres. Our results are more realistic and accurate, in particular with respect to the epicenteral location, magnitude and fault plane solution which are in accordance with the hypocentre distribution of the aftershocks.

  11. Seismological aspects of the 27 June 2015 Gulf of Aqaba earthquake and its sequence of aftershocks

    NASA Astrophysics Data System (ADS)

    Abd el-aal, Abd el-aziz Khairy; Badreldin, Hazem

    2016-07-01

    On 27 June 2015, a moderate earthquake with magnitude Mb 5.2 struck the Gulf of Aqaba near Nuweiba City. This event was instrumentally recorded by the Egyptian National Seismic Network (ENSN) and many other international seismological centres. The event was felt in all the cities on the Gulf of Aqaba, as well as Suez City, Hurghada City, the greater Cairo Metropolitan Area, Israel, Jordan and the north-western part of Saudi Arabia. No casualties were reported, however. Approximately 95 aftershocks with magnitudes ranging from 0.7 to 4.2 were recorded by the ENSN following the mainshock. In the present study, the source characteristics of both the mainshock and the aftershocks were estimated using the near-source waveform data recorded by the very broadband stations of the ENSN, and these were validated by the P-wave polarity data from short period stations. Our analysis reveals that an estimated seismic moment of 0.762 × 1017 Nm was released, corresponding to a magnitude of Mw 5.2, a focal depth of 14 km, a fault radius of 0.72 km and a rupture area of approximately 1.65 km2. Monitoring the sequence of aftershocks reveals that they form a cluster around the mainshock and migrated downwards in focal depth towards the west. We compared the results we obtained with the published results from the international seismological centres. Our results are more realistic and accurate, in particular with respect to the epicenteral location, magnitude and fault plane solution which are in accordance with the hypocentre distribution of the aftershocks.

  12. Aftershock triggering by postseismic stresses: A study based on Coulomb rate-and-state models

    NASA Astrophysics Data System (ADS)

    Cattania, Camilla; Hainzl, Sebastian; Wang, Lifeng; Enescu, Bogdan; Roth, Frank

    2015-04-01

    The spatiotemporal clustering of earthquakes is a feature of medium- and short-term seismicity, indicating that earthquakes interact. However, controversy exists about the physical mechanism behind aftershock triggering: static stress transfer and reloading by postseismic processes have been proposed as explanations. In this work, we use a Coulomb rate-and-state model to study the role of coseismic and postseismic stress changes on aftershocks and focus on two processes: creep on the main shock fault plane (afterslip) and secondary aftershock triggering by previous aftershocks. We model the seismic response to Coulomb stress changes using the Dieterich constitutive law and focus on two events: the Parkfield, Mw = 6.0, and the Tohoku, Mw = 9.0, earthquakes. We find that modeling secondary triggering systematically improves the maximum log likelihood fit of the sequences. The effect of afterslip is more subtle and difficult to assess for near-fault events, where model errors are largest. More robust conclusions can be drawn for off-fault aftershocks: following the Tohoku earthquake, afterslip promotes shallow crustal seismicity in the Fukushima region. Simple geometrical considerations indicate that afterslip-induced stress changes may have been significant on trench parallel crustal fault systems following several of the largest recorded subduction earthquakes. Moreover, the time dependence of afterslip strongly enhances its triggering potential: seismicity triggered by an instantaneous stress change decays more quickly than seismicity triggered by gradual loading, and as a result we find afterslip to be particularly important between few weeks and few months after the main shock.

  13. Evolution of aftershock statistics with depth

    NASA Astrophysics Data System (ADS)

    Narteau, C.; Shebalin, P.; Holschneider, M.

    2013-12-01

    The deviatoric stress varies with depth and may strongly affect earthquake statistics. Nevertheless, if the Anderson faulting theory may be used to define the relative stress magnitudes, it remains extremely difficult to observe significant variations of earthquake properties from the top to the bottom of the seismogenic layer. Here, we concentrate on aftershock sequences in normal, strike-slip and reverse faulting regimes to isolate specific temporal properties of this major relaxation process with respect to depth. More exactly, we use Bayesian statistics of the Modified Omori Law to characterize the exponent p of the power-law aftershock decay rate and the duration c of the early stage of aftershock activity that does not fit with this power-law regime. Preliminary results show that the c-value decreases with depth without any significant variation of the p-value. Then, we infer the duration of a non power-law aftershock decay rate over short times can be related to the level of stress in the seismogenic crust.

  14. Cellular mechanisms of deep brain stimulation: activity-dependent focal circuit reprogramming?

    PubMed Central

    Veerakumar, Avin; Berton, Olivier

    2015-01-01

    Deep brain stimulation (DBS) is a well-established treatment modality for movement disorders. As more behavioral disorders are becoming understood as specific disruptions in neural circuitry, the therapeutic realm of DBS is broadening to encompass a wider range of domains, including disorders of compulsion, affect, and memory, but current understanding of the cellular mechanisms of DBS remains limited. We review progress made during the last decade focusing in particular on how recent methods for targeted circuit manipulations, imaging and reconstruction are fostering preclinical and translational advances that improve our neurobiological understanding of DBS’s action in psychiatric disorders. PMID:26719852

  15. Mechanisms of Stretch Induced Atrial Fibrillation in the Presence and the Absence of Adreno-Cholinergic Stimulation: Interplay between Rotors and Focal Discharges

    PubMed Central

    Yamazaki, Masatoshi; Vaquero, Luis M.; Hou, Luqia; Campbell, Katherine; Zlochiver, Sharon; Klos, Matthew; Mironov, Sergey; Berenfeld, Omer; Honjo, Haruo; Kodama, Itsuo; Jalife, José; Kalifa, Jérôme

    2009-01-01

    BACKGROUND Both atrial stretch and combined adreno-cholinergic stimulation (ACS) have been shown to favor initiation and maintenance of atrial fibrillation (AF). Their respective contribution to the electrophysiological mechanism remains, however, incompletely understood. OBJECTIVE We endeavored to determine the mechanism of maintenance of stretch-related AF (SRAF) in the presence and absence of ACS, and to assess how focal discharges interact with rotors to modify the level of complexity in the activation patterns to perpetuate AF. METHODS Video imaging of AF dynamics was carried out using a SRAF model in isolated sheep hearts (n=24). Pharmacological approaches were used to (i) mimic ACS with acetylcholine (1 μM) plus isoproterenol (0.03 μM); and (ii) abolish triggered activity, in response to sarcoplasmic reticulum calcium release, with caffeine (5 mM, CA) or ryanodine (10-40 μM, RYA). RESULTS In the absence of ACS, upon perfusion of CA or RYA, focal discharges were abolished and SRAF terminated in most of the cases (10/13 experiments). In the presence of ACS, multiple drifting rotors as well as a large number of focal discharges were identified and only 1/11 AF episodes terminated. CONCLUSIONS In the absence of ACS, SRAF is maintained by high-frequency focal discharges that generate fibrillatory conduction and wavebreaks. In the presence of ACS, SRAF dynamics is characterized by multiple high frequency rotors that are rendered unstable by spatially distributed focal discharges. PMID:19560089

  16. Tests of remote aftershock triggering by small mainshocks using Taiwan's earthquake catalog

    NASA Astrophysics Data System (ADS)

    Peng, W.; Toda, S.

    2014-12-01

    To understand earthquake interaction and forecast time-dependent seismic hazard, it is essential to evaluate which stress transfer, static or dynamic, plays a major role to trigger aftershocks and subsequent mainshocks. Felzer and Brodsky focused on small mainshocks (2≤M<3) and their aftershocks, and then argued that only dynamic stress change brings earthquake-to-earthquake triggering, whereas Richards-Dingers et al. (2010) claimed that those selected small mainshock-aftershock pairs were not earthquake-to-earthquake triggering but simultaneous occurrence of independent aftershocks following a larger earthquake or during a significant swarm sequence. We test those hypotheses using Taiwan's earthquake catalog by taking the advantage of lacking any larger event and the absence of significant seismic swarm typically seen with active volcano. Using Felzer and Brodsky's method and their standard parameters, we only found 14 mainshock-aftershock pairs occurred within 20 km distance in Taiwan's catalog from 1994 to 2010. Although Taiwan's catalog has similar number of earthquakes as California's, the number of pairs is about 10% of the California catalog. It may indicate the effect of no large earthquakes and no significant seismic swarm in the catalog. To fully understand the properties in the Taiwan's catalog, we loosened the screening parameters to earn more pairs and then found a linear aftershock density with a power law decay of -1.12±0.38 that is very similar to the one in Felzer and Brodsky. However, none of those mainshock-aftershock pairs were associated with a M7 rupture event or M6 events. To find what mechanism controlled the aftershock density triggered by small mainshocks in Taiwan, we randomized earthquake magnitude and location. We then found that those density decay in a short time period is more like a randomized behavior than mainshock-aftershock triggering. Moreover, 5 out of 6 pairs were found in a swarm-like temporal seismicity rate increase

  17. Discrete characteristics of the aftershock sequence of the 2011 Van earthquake

    NASA Astrophysics Data System (ADS)

    Toker, Mustafa

    2014-10-01

    An intraplate earthquake of magnitude Mw 7.2 occurred on a NE-SW trending blind oblique thrust fault in accretionary orogen, the Van region of Eastern Anatolia on October 23, 2011. The aftershock seismicity in the Van earthquake was not continuous but, rather, highly discrete. This shed light on the chaotic nonuniformity of the event distribution and played key roles in determining the seismic coupling between the rupturing process and seismogeneity. I analyzed the discrete statistical mechanics of the 2011 Van mainshock-aftershock sequence with an estimation of the non-dimensional tuning parameters consisting of; temporal clusters (C) and the random (RN) distribution of aftershocks, range of size scales (ROSS), strength change (εD), temperature (T), P-value of temporal decay, material parameter R-value, seismic coupling χ, and Q-value of aftershock distribution. I also investigated the frequency-size (FS), temporal (T) statistics and the sequential characteristics of aftershock dynamics using discrete approach and examined the discrete evolutionary periods of the Van earthquake Gutenberg-Richter (GR) distribution. My study revealed that the FS and T statistical properties of aftershock sequence represent the Gutenberg-Richter (GR) distribution, clustered (C) in time and random (RN) Poisson distribution, respectively. The overall statistical behavior of the aftershock sequence shows that the Van earthquake originated in a discrete structural framework with high seismic coupling under highly variable faulting conditions. My analyses relate this larger dip-slip event to a discrete seismogenesis with two main components of complex fracturing and branching framework of the ruptured fault and dynamic strengthening and hardening behavior of the earthquake. The results indicate two dynamic cases. The first is associated with aperiodic nature of aftershock distribution, indicating a time-independent Poissonian event. The second is associated with variable slip model

  18. Effects of cue focality on the neural mechanisms of prospective memory: A meta-analysis of neuroimaging studies

    PubMed Central

    Cona, Giorgia; Bisiacchi, Patrizia Silvia; Sartori, Giuseppe; Scarpazza, Cristina

    2016-01-01

    Remembering to execute pre-defined intentions at the appropriate time in the future is typically referred to as Prospective Memory (PM). Studies of PM showed that distinct cognitive processes underlie the execution of delayed intentions depending on whether the cue associated with such intentions is focal to ongoing activity processing or not (i.e., cue focality). The present activation likelihood estimation (ALE) meta-analysis revealed several differences in brain activity as a function of focality of the PM cue. The retrieval of intention is supported mainly by left anterior prefrontal cortex (Brodmann Area, BA 10) in nonfocal tasks, and by cerebellum and ventral parietal regions in focal tasks. Furthermore, the precuneus showed increased activation during the maintenance phase of intentions compared to the retrieval phase in nonfocal tasks, whereas the inferior parietal lobule showed increased activation during the retrieval of intention compared to maintenance phase in the focal tasks. Finally, the retrieval of intention relies more on the activity in anterior cingulate cortex for nonfocal tasks, and on posterior cingulate cortex for focal tasks. Such focality-related pattern of activations suggests that prospective remembering is mediated mainly by top-down and stimulus-independent processes in nonfocal tasks, whereas by more automatic, bottom-up, processes in focal tasks. PMID:27185531

  19. Effects of cue focality on the neural mechanisms of prospective memory: A meta-analysis of neuroimaging studies.

    PubMed

    Cona, Giorgia; Bisiacchi, Patrizia Silvia; Sartori, Giuseppe; Scarpazza, Cristina

    2016-01-01

    Remembering to execute pre-defined intentions at the appropriate time in the future is typically referred to as Prospective Memory (PM). Studies of PM showed that distinct cognitive processes underlie the execution of delayed intentions depending on whether the cue associated with such intentions is focal to ongoing activity processing or not (i.e., cue focality). The present activation likelihood estimation (ALE) meta-analysis revealed several differences in brain activity as a function of focality of the PM cue. The retrieval of intention is supported mainly by left anterior prefrontal cortex (Brodmann Area, BA 10) in nonfocal tasks, and by cerebellum and ventral parietal regions in focal tasks. Furthermore, the precuneus showed increased activation during the maintenance phase of intentions compared to the retrieval phase in nonfocal tasks, whereas the inferior parietal lobule showed increased activation during the retrieval of intention compared to maintenance phase in the focal tasks. Finally, the retrieval of intention relies more on the activity in anterior cingulate cortex for nonfocal tasks, and on posterior cingulate cortex for focal tasks. Such focality-related pattern of activations suggests that prospective remembering is mediated mainly by top-down and stimulus-independent processes in nonfocal tasks, whereas by more automatic, bottom-up, processes in focal tasks. PMID:27185531

  20. Aftershock Decay Rates in the Iranian Plateau

    NASA Astrophysics Data System (ADS)

    Ommi, S.; Zafarani, H.; Zare, M.

    2016-07-01

    Motivated by the desire to have more information following the occurrence of damaging events, the main purpose of this article is to study aftershock sequence parameters in the Iranian plateau. To this end, the catalogue of the Iranian earthquakes between 2002 to the end of 2013 has been collected and homogenized among which 15 earthquakes have been selected to study their aftershock decay rates. For different tectonic provinces, the completeness magnitudes ( M c) of the earthquake catalogue have been calculated in different time intervals. Also, the M c variability in spatial and temporal windows has been determined for each selected event. For major Iranian earthquakes, catalogue of aftershocks has been collected thanks to three declustering methods: first, the classical windowing method of Gardner and Knopoff (Bull Seismol Soc Am 64:1363-1367, 1974); second, a modified version of this using spatial windowing based on the Wells and Coppersmith (Bull Seismol Soc Am 84:974-1002, 1994) relations; and third, the Burkhard and Grünthal (Swiss J Geosci 102:149-188, 2009) scheme. Effects of the temporal windows also have been investigated using the time periods of 1 month, 100 days, and 1 year in the declustering method of Gardner and Knopoff (Bull Seismol Soc Am 64:1363-1367, 1974). In the next step, the modified Omori law coefficients have been calculated for the 15 selected earthquakes. The calibrated regional generic model describing the temporal and magnitude distribution of aftershocks is of interest for time-dependent seismic hazard forecasts. The regional characteristics of the aftershock decay rates have been studied for the selected Iranian earthquakes in the Alborz, Zagros and Central Iran regions considering their different seismotectonics regimes. However, due to the lack of sufficient data, no results have been reported for the Kopeh-Dagh and Makran seismotectonic regions.

  1. Aftershock Decay Rates in the Iranian Plateau

    NASA Astrophysics Data System (ADS)

    Ommi, S.; Zafarani, H.; Zare, M.

    2016-04-01

    Motivated by the desire to have more information following the occurrence of damaging events, the main purpose of this article is to study aftershock sequence parameters in the Iranian plateau. To this end, the catalogue of the Iranian earthquakes between 2002 to the end of 2013 has been collected and homogenized among which 15 earthquakes have been selected to study their aftershock decay rates. For different tectonic provinces, the completeness magnitudes (M c) of the earthquake catalogue have been calculated in different time intervals. Also, the M c variability in spatial and temporal windows has been determined for each selected event. For major Iranian earthquakes, catalogue of aftershocks has been collected thanks to three declustering methods: first, the classical windowing method of uc(Gardner) and uc(Knopoff) (Bull Seismol Soc Am 64:1363-1367, 1974); second, a modified version of this using spatial windowing based on the uc(Wells) and uc(Coppersmith) (Bull Seismol Soc Am 84:974-1002, 1994) relations; and third, the uc(Burkhard) and uc(Grünthal) (Swiss J Geosci 102:149-188, 2009) scheme. Effects of the temporal windows also have been investigated using the time periods of 1 month, 100 days, and 1 year in the declustering method of uc(Gardner) and uc(Knopoff) (Bull Seismol Soc Am 64:1363-1367, 1974). In the next step, the modified Omori law coefficients have been calculated for the 15 selected earthquakes. The calibrated regional generic model describing the temporal and magnitude distribution of aftershocks is of interest for time-dependent seismic hazard forecasts. The regional characteristics of the aftershock decay rates have been studied for the selected Iranian earthquakes in the Alborz, Zagros and Central Iran regions considering their different seismotectonics regimes. However, due to the lack of sufficient data, no results have been reported for the Kopeh-Dagh and Makran seismotectonic regions.

  2. Detailed source process of the 2007 Tocopilla earthquake and its main aftershocks

    NASA Astrophysics Data System (ADS)

    Peyrat, S.; Madariaga, R.; Buforn, E.; Meneses, G.; Campos, J.; Favreau, P.; Bernard, P.; Vilotte, J.

    2008-12-01

    We investigated the detail rupture process of the Tocopilla earthquake (Mw 7.7) of the 14 November 2007 and of the main aftershocks that occurred in the southern part of the North Chile seismic gap using teleseismic broadband and strong motion data. The earthquake happen in the middle of the permanent broad band and strong motion network IPOC newly installed by GFZ and IPGP-CNRS, and of a digital strong- motion network operated by the University of Chile. The Tocopilla earthquake is the last large thrust subduction earthquake since the major Iquique 1877 earthquake which produced a destructive tsunami. The Arequipa (2001) and Antofagasta (1995) earthquakes already ruptured the northern and southern parts of the gap, and the intraplate intermediate depth Tarapaca earthquake (2005) may have changed the tectonic loading of this part of the Peru-Chile subduction zone. The Tocopilla earthquake raises some disturbing questions: why this earthquake didn't extent further north ; what has been the role of the Mejillones peninsula in the south which seems to act as a barrier? We studied the detailed source process using the strong motion data available. The strong-motion data show clearly two S-waves arrivals, allowing the localization of two sources. The main shock started north of the segment close to Tocopilla. The rupture propagated southward. The second source was identified to start about 20 seconds later and located 50 km south from the hypocenter. The earthquake ruptured the interplate seismic zone over more than 150 km and generated several large aftershocks, mainly located south of the rupture area with the same focal mechanism, except for the largest one that took place on the 16 December. This event is a down-dip compressional event (slab push) placed down dip of the main interplate coupling zone at the southern end of the main event rupture zone. Finally in order to understand whether the northern gap has actually been reduced or not by the occurrence of the

  3. A Statistical Study on VLF Subionospheric Perturbations Associated with Major Earthquakes: A View from Focal Mechanism

    NASA Astrophysics Data System (ADS)

    Kawano, T.; Tatsuta, K.; Hobara, Y.

    2015-12-01

    Continuous monitoring of signal amplitudes of worldwide VLF transmitters is a powerful tool to study the lower ionospheric condition. Although, lower ionospheric perturbations prior to some of the major earthquakes have been reported for years, their occurrence and coupling mechanism between the ground and overlaying ionosphere prior to the earthquakes are not clear yet. In this paper, we carried out a statistical analysis based on the nighttime averaged signal amplitude data from the UEC's VLF/LF transmitter observation network. Two hundred forty three earthquakes were occurred within the 5th Fresnel zone of transmitter-receiver paths around Japan during the time period of 2007 to 2012. These earthquakes were characterized into three different groups based on the Centroid-Moment-Tensor (CMT) solution such as reverse fault type, normal fault type and stress slip type. The ionospheric anomaly was identified by a large change in the VLF/LF amplitude during nighttime. As a result, we found the ionospheric perturbations associated with both ground and sea earthquakes. Remarkably, the reverse fault type earthquakes have the highest occurrence rate of ionospheric perturbation among the three types both for sea (41%) and ground events (61%). The occurrence rates for normal type fault are 35% and 56% for sea and ground earthquakes respectively and the same for stress slip type are 39% and 20% for sea and ground earthquakes respectively. In both cases the occurrence rates are smaller than the reverse fault type. The clear difference of occurrence rate of the ionospheric perturbations may indicate that the coupling efficiency of seismic activity into the overlaying ionosphere is controlled by the pressure in the earth's crust. This gives us further physical insight of Lithosphere-Atmosphere-Ionosphere (LAI) coupling processes.

  4. Aftershock Characteristics as a Means of Discriminating Explosions from Earthquakes

    SciTech Connect

    Ford, S R; Walter, W R

    2009-05-20

    The behavior of aftershock sequences around the Nevada Test Site in the southern Great Basin is characterized as a potential discriminant between explosions and earthquakes. The aftershock model designed by Reasenberg and Jones (1989, 1994) allows for a probabilistic statement of earthquake-like aftershock behavior at any time after the mainshock. We use this model to define two types of aftershock discriminants. The first defines M{sub X}, or the minimum magnitude of an aftershock expected within a given duration after the mainshock with probability X. Of the 67 earthquakes with M > 4 in the study region, 63 of them produce an aftershock greater than M{sub 99} within the first seven days after a mainshock. This is contrasted with only six of 93 explosions with M > 4 that produce an aftershock greater than M{sub 99} for the same period. If the aftershock magnitude threshold is lowered and the M{sub 90} criteria is used, then no explosions produce an aftershock greater than M{sub 90} for durations that end more than 17 days after the mainshock. The other discriminant defines N{sub X}, or the minimum cumulative number of aftershocks expected for given time after the mainshock with probability X. Similar to the aftershock magnitude discriminant, five earthquakes do not produce more aftershocks than N{sub 99} within 7 days after the mainshock. However, within the same period all but one explosion produce less aftershocks then N{sub 99}. One explosion is added if the duration is shortened to two days after than mainshock. The cumulative number aftershock discriminant is more reliable, especially at short durations, but requires a low magnitude of completeness for the given earthquake catalog. These results at NTS are quite promising and should be evaluated at other nuclear test sites to understand the effects of differences in the geologic setting and nuclear testing practices on its performance.

  5. Offshore observations of aftershocks following the January 5th 2013 Mw 7.5 Queen Charlotte-Fairweather fault earthquake, southeast Alaska

    NASA Astrophysics Data System (ADS)

    Roland, E. C.; Gulick, S. P.; Levoir, M. A.; Haeussler, P. J.

    2013-12-01

    We present initial results from a rapid-response ocean bottom seismometer (OBS) deployment that recorded aftershock activity on the Queen Charlotte-Fairweather (QC-F) fault following the Mw 7.5 earthquake on January 5th 2013 near Craig, Alaska. This earthquake was the second of two Mw > 7 events on this fault system in a 3 month time period; the Craig earthquake followed a Mw 7.8 thrust event that occurred in October 2012, west of Haida Gwaii, British Columbia. Although the QC-F is a major plate boundary fault, little is known about the regional fault structure, interseismic coupling, and rheological controls on the depth distribution of seismic slip along the continent-ocean transform. The majority of the QC-F fault system extends offshore western British Columbia and southeast Alaska, making it difficult to characterize earthquakes and fault deformation with land-based seismic and geodetic instruments. This experiment is the first ever offshore seismometer deployment to record earthquake activity along this northern segment of the QC-F system, and was set in motion with help from the US Coast Guard, who provided a vessel and crew to deploy and recover the OBS array on short notice. The seismic array utilized 6 GeoPro short period OBS from the University of Texas Institute for Geophysics, which recorded approximately 3 weeks of aftershock activity in April-May of 2013. Combining high-quality local OBS recordings with land-based seismic observations from Alaska Earthquake Information Center (AEIC) stations to the east, we present more precise aftershock locations and depths that help to better characterize fault zone architecture along the northern section of the QC-F. Although moment tensor solutions indicate that the January 5th mainshock sustained slip consistent with Pacific-North America plate motions, aftershock focal mechanisms indicate some interaction with neighboring faults, such as the Chatham Straight fault. This new OBS dataset will also help to

  6. Focal vibration in neurorehabilitation.

    PubMed

    Murillo, N; Valls-Sole, J; Vidal, J; Opisso, E; Medina, J; Kumru, H

    2014-04-01

    During the last decade, many studies have been carried out to understand the effects of focal vibratory stimuli at various levels of the central nervous system and to study pathophysiological mechanisms of neurological disorders as well as the therapeutic effects of focal vibration in neurorehabilitation. This review aimed to describe the effects of focal vibratory stimuli in neurorehabilitation including the neurological diseases or disorders like stroke, spinal cord injury, multiple sclerosis, Parkinson's' disease and dystonia. In conclusion, focal vibration stimulation is well tolerated, effective and easy to use, and it could be used to reduce spasticity, to promote motor activity and motor learning within a functional activity, even in gait training, independent from etiology of neurological pathology. Further studies are needed in the future well-designed trials with bigger sample size to determine the most effective frequency, amplitude and duration of vibration application in the neurorehabilitation. PMID:24842220

  7. Subduction Zone Characterization of the Northeast Caribbean Using Increased Constraints on Focal Mechanism Solutions from Data Collected with AN Ocean Bottom Seismograph Deployment

    NASA Astrophysics Data System (ADS)

    Mintz, H. E.; Pulliam, J.; López Venegas, A. M.; ten Brink, U. S.; Huerfano, V. A.; von Hillebrandt-Andrade, C.

    2010-12-01

    Over the last thirty years seismic swarm activity has frequently occurred offshore northeast of Puerto Rico. Seismic swarms have been recorded lasting from one day up to several weeks with magnitudes commonly no more than mb 4. Causes of these swarms have yet to be determined; however, some have proposed a tear, or crumpling, of the subducting North American Plate could produce such swarms. Tearing is suggested because it would accommodate the reactivation of faults and relieve strain built up within the sharp curvature of the subducting slab and subducting ridges. Swarm hypocenters were commonly determined using data collected only from land-based stations of the Puerto Rico Seismic Network (PRSN), which alone lacks the necessary distribution of seismic azimuths to constrain focal depths. Five ocean bottom seismographs were temporarily deployed in 2007 in and around the active region. These seismographs provided full azimuthal coverage and recorded two seismic swarms during their six-month deployment. This new dataset combined with data from the PRSN provides strong constraints on the earthquake swarm hypocenters, particularly focal depths. Fault plane solutions were calculated using two different focal mechanism programs and their results were compared. FPFIT (Reasenberg and Oppenheimer, 1985) calculates double-couple fault plane solutions from P wave first motion polarity data. When applied to the combined observations from ocean bottom seismographs and PRSN stations, the FPFIT method produced multiple focal mechanisms, indicating that the constraints imposed by the station distribution were often insufficient to identify unique solutions. HASH (Hardebeck and Shearer, 2002) is a program that computes best-fit focal mechanisms using P wave first motion polarities and S/P amplitude ratios, for additional constraints and, therefore, reduced ambiguity. We will compare the patterns of mechanisms produced using FPFIT and HASH and interpret the mechanisms in terms of

  8. The regional moment tensor of the 5 May 2014 Chiang Rai earthquake (Mw = 6.5), Northern Thailand, with its aftershocks and its implication to the stress and the instability of the Phayao Fault Zone

    NASA Astrophysics Data System (ADS)

    Noisagool, Sutthipong; Boonchaisuk, Songkhun; Pornsopin, Patinya; Siripunvaraporn, Weerachai

    2016-09-01

    On 5 May 2014, the largest earthquake in Thailand modern history occurred in Northern Thailand with over a thousand aftershocks. Most of the epicenters are located within the transition area of the Mae Lao segment (north) and Pan segment (central) of the Phayao Fault Zone (PFZ). Good quality data from all events (ML > 4) are only available for the seismic stations closer to the epicenters (<500 km). The regional moment tensor (RMT) inversion was applied to derive a sequence of thirty focal mechanisms, moment magnitudes and source depths generated along the PFZ. Our studies reveal that 24 events are strike - slip with normal (transtensional), four are strike - slip with thrust (transpressional), and two are reverse. The main shock has an Mw of 6.5, slightly larger than previously estimated (ML 6.3) while Mw of the aftershocks is mostly lower than ML. This suggests that a regional magnitude calibration is necessary. The hypocenter depths of most events are around 11 km, not as shallow as estimated earlier. In addition, a stress inversion was applied to these 30 focal mechanisms to determine the stresses of the region, the Mohr's diagram, and the principal fault planes. The retrieved maximum stress direction (N18E) is in agreement with other studies. One of the derived principal fault plane with a strike of N48E is in good agreement with that of the Mae Lao segment. Both estimated shape ratio and plunges led us to conclude that this area has a uniaxial horizontal compression in NNE-SSW with small WNW-ESE extension, similar to the interpretation of Tingay et al. (2010). Based on the Mohr's diagram of fault plane solutions, we provide geophysical evidence which reveals that the high shear stress Mae Lao segment is likely to slip first producing the main shock on 5 May 2014. The energy transfer between the segments has then led to many aftershocks with mixed mechanisms. At the end, we re-visited the analysis of the former largest earthquake in Northern Thailand in the

  9. Therapeutic effects of tyroservatide on metastasis of lung cancer and its mechanism affecting integrin–focal adhesion kinase signal transduction

    PubMed Central

    Huang, Yu-ting; Zhao, Lan; Fu, Zheng; Zhao, Meng; Song, Xiao-meng; Jia, Jing; Wang, Song; Li, Jin-ping; Zhu, Zhi-feng; Lin, Gang; Lu, Rong; Yao, Zhi

    2016-01-01

    Tyroservatide (YSV) can inhibit the growth and metastasis of mouse lung cancer significantly. This study investigated the therapeutic effects of tripeptide YSV on metastasis of human lung cancer cells and explored its possible mechanism that affects integrin–focal adhesion kinase (FAK) signal transduction in tumor cells. YSV significantly inhibited the adhesion and the invasion of highly metastatic human lung cancer cell lines 95D, A549, and NCI-H1299. In addition, YSV significantly inhibited phosphorylation of FAK Tyr397 and FAK Tyr576/577 in the 95D, A549, and NCI-H1299 human lung cancer cells in vitro. And the mRNA level and protein expression of FAK in these human lung cancer cells decreased at the same time. YSV also significantly inhibited mRNA and protein levels of integrin β1 and integrin β3 in the 95D, A549, and NCI-H1299 human lung cancer cells. Our research showed that YSV inhibited adhesion and invasion of human lung cancer cells and exhibited therapeutic effects on metastasis of lung cancer. PMID:27041993

  10. Seismic Study of the Velocity Structure and Earthquake FocalMechanisms beneath the Krafla Central Volcano, NE Iceland

    NASA Astrophysics Data System (ADS)

    Martens, H. R.; Schuler, J.; Greenfield, T. S.; White, R. S.; Roecker, S. W.; Brandsdottir, B.; Stock, J. M.; Tarasewicz, J.; Pugh, D. J.

    2015-12-01

    We investigated the seismic velocity structure of the Krafla central volcano, NE Iceland, and its shallow geothermal fields. In our 3D tomographic inversions, we used passive seismic data recorded between 2009-2012 from a temporary local network as well as active seismic legacy data to constrain the velocity models. We find high P-wave velocities (Vp) underneath regions of elevated topographic relief as well as two low-Vp anomalies that coincide spatially with two attenuating bodies outlined from S-wave shadows during the Krafla rifting episode of 1974-1985. Within the Krafla geothermal reservoir, which is developed for energy production, we imaged a shallow low-Vp/Vs zone overlying a deeper high-Vp/Vs zone and interpreted them as steam- and brine-bearing formations, respectively. Previously undertaken borehole measurements support our findings. A prominent low-Vp/Vs anomaly underlies these zones at rock depths greater than 1.5 km, where a super-heated zone within felsic overlies rhyolitic within the geothermal melt. Calculations systems show that of the most earthquake focal events are mechanisms consistent double-couple source models with only a few clear non-shear source models.

  11. High frequencies are a critical component of aftershock triggering at <100-150 km (Invited)

    NASA Astrophysics Data System (ADS)

    Felzer, K. R.

    2010-12-01

    Triggered earthquakes at large distances from the mainshock have been observed to closely follow the arrival of ~0.03-0.6 Hz surface waves (Hill, 2008). Triggering by body waves at these distances is generally not observed. At distances closer than 50-100 km, however, surface waves are not well developed and have minimal amplitude. Thus triggering at these distances is presumably accomplished by static stress change and/or by body waves via a mechanism that does not work at further distances. Pollitz (2006) demonstrated that slow slip events on the San Andreas fault do not trigger many aftershocks, suggesting that static stresses alone are not effective triggers, while Felzer and Brodsky (2006) demonstrated that dynamic stresses alone do appear to trigger aftershocks at least in the 10--50 km range. Yet Parsons and Velasco (2009) found that underground nuclear tests, which are essentially dynamic-only sources, do not produce aftershocks at regional distances. Here we demonstrate that Southern California quarry blasts also fail to produce aftershocks. Both nuclear tests and quarry blasts are depleted in high frequency energy in comparison to tectonic earthquakes (Su et al. 1991; Allman et al. 2008). Therefore the observation that both slow slip events and blasts fail to trigger many aftershocks suggests that the missing ingredient of high frequency body wave energy plays a critical role in the triggering process. Quarry blast spectra data and scaling considerations allow the critical triggering frequency to be constrained to > 20-60 Hz. Energy in this frequency band may be expected to persist at depth at least out to 100 km (Leary, 1995). Huc and Main (2003) found that aftershock triggering by global earthquakes follows a continuous decay curve out to ~150 km, suggesting that triggering by high frequency body waves might extend this far. At much further distances the high frequencies are likely attenuated, explaining why only low frequency surface wave triggering

  12. Efficacy of focal mechanic vibration treatment on balance in Charcot-Marie-Tooth 1A disease: a pilot study.

    PubMed

    Pazzaglia, Costanza; Camerota, F; Germanotta, M; Di Sipio, E; Celletti, C; Padua, L

    2016-07-01

    Patients affected by Charcot-Marie-Tooth (CMT) disease experience an impaired balance. Although the causes of the postural instability are not fully understood, somatosensory system seems to play a key role. Mechanical vibration seems to act on the somatosensory system and to improve its function. The aim of our study was to evaluate the effects of focal mechanical vibration (fMV) on the balance of CMT 1A patients. We enrolled 14 genetically confirmed CMT 1A patients (8 female and 6 male, mean age 492 years, range 32-74, mean duration of disease: 13 years, range 1-30). Patients underwent a 3-day fMV treatment on quadriceps and triceps surae and were evaluated before the treatment as well as 1 week and 1 month after the end of the treatment. The primary outcome measure was the Berg Balance Scale (BBS) and the secondary were the Dynamic Gait Index (DGI), the 6 Min Walking Test (6MWT), the muscular strength of lower limbs, the Quality of Life (QoL) questionnaire and the stabilometric variables. The statistical analysis showed a significant modification of the BBS due to the effect of treatment (p < 0.05). A significant modification was also found in the DGI (p < 0.05). Concerning the stabilometric variables we found significant changes only for the eyes closed condition; in particular, a significant decrease was found in VelocityML (p < 0.05) and Sway path length (p < 0.05). The fMV treatment applied on lower limbs of CMT 1A patients determined an improvement of balance as detected by the BBS. The concurrent improvement of stabilometric variables in the eyes closed condition only suggests that fMV acts mostly on somatosensory afferences. Further studies are needed to confirm these data on a larger sample of CMT patients. PMID:27177999

  13. The aftershock signature of supershear earthquakes.

    PubMed

    Bouchon, Michel; Karabulut, Hayrullah

    2008-06-01

    Recent studies show that earthquake faults may rupture at speeds exceeding the shear wave velocity of rocks. This supershear rupture produces in the ground a seismic shock wave similar to the sonic boom produced by a supersonic airplane. This shock wave may increase the destruction caused by the earthquake. We report that supershear earthquakes are characterized by a specific pattern of aftershocks: The fault plane itself is remarkably quiet whereas aftershocks cluster off the fault, on secondary structures that are activated by the supershear rupture. The post-earthquake quiescence of the fault shows that friction is relatively uniform over supershear segments, whereas the activation of off-fault structures is explained by the shock wave radiation, which produces high stresses over a wide zone surrounding the fault. PMID:18535239

  14. Aftershocks in a frictional earthquake model.

    PubMed

    Braun, O M; Tosatti, Erio

    2014-09-01

    Inspired by spring-block models, we elaborate a "minimal" physical model of earthquakes which reproduces two main empirical seismological laws, the Gutenberg-Richter law and the Omori aftershock law. Our point is to demonstrate that the simultaneous incorporation of aging of contacts in the sliding interface and of elasticity of the sliding plates constitutes the minimal ingredients to account for both laws within the same frictional model. PMID:25314453

  15. The 2012 August 11 MW 6.5, 6.4 Ahar-Varzghan earthquakes, NW Iran: aftershock sequence analysis and evidence for activity migration

    NASA Astrophysics Data System (ADS)

    Rezapour, Mehdi

    2016-02-01

    The Ahar-Varzghan doublet earthquakes with magnitudes MW 6.5 and 6.4 occurred on 2012 August 11 in northwest Iran and were followed by many aftershocks. In this paper, we analyse ˜5 months of aftershocks of these events. The Ahar-Varzghan earthquakes occurred along complex faults and provide a new constraint on the earthquake hazard in northwest Iran. The general pattern of relocated aftershocks defines a complex seismic zone covering an area of approximately 25 × 10 km2. The Ahar-Varzghan aftershock sequence shows a secondary activity which started on November 7, approximately 3 months after the main shocks, with a significant increase in activity, regarding both number of events and their magnitude. This stage was characterized by a seismic zone that propagated to the west of the main shocks. The catalogue of aftershocks for the doublet earthquake has a magnitude completeness of Mc 2.0. A below-average b-value for the Ahar-Varzghan sequence indicates a structural heterogeneity in the fault plane and the compressive stress state of the region. Relocated aftershocks occupy a broad zone clustering east-west with near-vertical dip which we interpret as the fault plane of the first of the doublet main shocks (MW 6.5). The dominant depth range of the aftershocks is from 3 to about 20 km, and the focal depths decrease toward the western part of the fault. The aftershock activity has its highest concentration in the eastern and middle parts of the active fault, and tapers off toward the western part of the active fault segment, indicating mainly a unilateral rupture toward west.

  16. Do aftershock probabilities decay with time?

    USGS Publications Warehouse

    Michael, Andrew J.

    2012-01-01

    So, do aftershock probabilities decay with time? Consider a thought experiment in which we are at the time of the mainshock and ask how many aftershocks will occur a day, week, month, year, or even a century from now. First we must decide how large a window to use around each point in time. Let's assume that, as we go further into the future, we are asking a less precise question. Perhaps a day from now means 1 day 10% of a day, a week from now means 1 week 10% of a week, and so on. If we ignore c because it is a small fraction of a day (e.g., Reasenberg and Jones, 1989, hereafter RJ89), and set p = 1 because it is usually close to 1 (its value in the original Omori law), then the rate of earthquakes (K=t) decays at 1=t. If the length of the windows being considered increases proportionally to t, then the number of earthquakes at any time from now is the same because the rate decrease is canceled by the increase in the window duration. Under these conditions we should never think "It's a bit late for this to be an aftershock."

  17. Aftershock Imaging with Dense Arrays (AIDA): Results and lessons learned from the dense deployment of EarthScope portable instruments following the August 23, 2011, Mw 5.8, Virginia Earthquake

    NASA Astrophysics Data System (ADS)

    Brown, L. D.; Davenport, K.; Quiros, D. A.; Hole, J. A.; Han, L.; Horowitz, F. G.; Chen, C.; Mooney, W. D.; Barnhart, W. D.; Lohman, R.; Bastien, P.; Fennig, N.; Ferguson, A.

    2012-12-01

    The Mw 5.8 Virginia earthquake of August 23, 2011, provided an opportunity to explore the feasibility of deploying large numbers of portable seismographs at close spacing to record aftershocks and the value of their recordings for improved characterization of the rupture process and structure in the hypocentral region. The main event, which occurred in the previously recognized "Central Virginia Seismic Zone", had a NE-striking reverse focal mechanism, hypocentral depth of 6 km (USGS). As this event passes with ca. 15 km of a NW-SE oriented deep seismic reflection profile contracted in 1981 by the USGS, there exists a rare opportunity for the eastern U.S. to link seismicity. The preliminary hypocentral estimate suggests that the earthquake occurred within a complex zone of east-dipping reflections that define an imbricated Paleozoic thrust sheet of the central Appalachian Piedmont that is underlain by Grenville basement at a depth of ca. 9 km. On August 27, 2011, four days after the main shock, we deployed 103 portable "Texan" one component, short-period recorders along two linear profiles over the hypocentral zone. An additional 105 "Texan" instruments were added six days later to extend the array more directly over the aftershock zone and along a regional NE-SW profile. The latter employed three component sensors to quantify regional attenuation characteristics of both P and S waves. Our initial analyses has focused on the contribution of the dense arrays to a) lowering the threshold for detecting/locating aftershocks b) improving hypocentral locations , c) computing more detailed velocity models (e.g. via tomography), and d) imaging crustal structure within and below the hypocenters using reflection P and S phases. Of particular interest was evaluating the usefulness of interferometric techniques by treating the aftershocks as a distributed "ambient noise" source. In addition to confirming our original expectations regarding improved event detection

  18. A Comparison between Deep and Shallow Stress Fields in Korea Using Earthquake Focal Mechanism Inversions and Hydraulic Fracturing Stress Measurements

    NASA Astrophysics Data System (ADS)

    Lee, Rayeon; Chang, Chandong; Hong, Tae-kyung; Lee, Junhyung; Bae, Seong-Ho; Park, Eui-Seob; Park, Chan

    2016-04-01

    We are characterizing stress fields in Korea using two types of stress data: earthquake focal mechanism inversions (FMF) and hydraulic fracturing stress measurements (HF). The earthquake focal mechanism inversion data represent stress conditions at 2-20 km depths, whereas the hydraulic fracturing stress measurements, mostly conducted for geotechnical purposes, have been carried out at depths shallower than 1 km. We classified individual stress data based on the World Stress Map quality ranking scheme. A total of 20 FMF data were classified into A-B quality, possibly representing tectonic stress fields. A total of 83 HF data out of compiled 226 data were classified into B-C quality, which we use for shallow stress field characterization. The tectonic stress, revealed from the FMF data, is characterized by a remarkable consistency in its maximum stress (σ1) directions in and around Korea (N79±2° E), indicating a quite uniform deep stress field throughout. On the other hand, the shallow stress field, represented by HF data, exhibits local variations in σ1 directions, possibly due to effects of topography and geologic structures such as faults. Nonetheless, there is a general similarity in σ1 directions between deep and shallow stress fields. To investigate the shallow stress field statistically, we follow 'the mean orientation and wavelength analysis' suggested by Reiter et al. (2014). After the stress pattern analysis, the resulting stress points distribute sporadically over the country, not covering the entire region evenly. In the western part of Korea, the shallow σ1directions are generally uniform with their search radius reaching 100 km, where the average stress direction agrees well with those of the deep tectonic stress. We note two noticeable differences between shallow and deep stresses in the eastern part of Korea. First, the shallow σ1 orientations are markedly non-uniform in the southeastern part of Korea with their search radius less than 25 km

  19. Forecasting large aftershocks within one day after the main shock

    PubMed Central

    Omi, Takahiro; Ogata, Yosihiko; Hirata, Yoshito; Aihara, Kazuyuki

    2013-01-01

    Forecasting the aftershock probability has been performed by the authorities to mitigate hazards in the disaster area after a main shock. However, despite the fact that most of large aftershocks occur within a day from the main shock, the operational forecasting has been very difficult during this time-period due to incomplete recording of early aftershocks. Here we propose a real-time method for efficiently forecasting the occurrence rates of potential aftershocks using systematically incomplete observations that are available in a few hours after the main shocks. We demonstrate the method's utility by retrospective early forecasting of the aftershock activity of the 2011 Tohoku-Oki Earthquake of M9.0 in Japan. Furthermore, we compare the results by the real-time data with the compiled preliminary data to examine robustness of the present method for the aftershocks of a recent inland earthquake in Japan. PMID:23860594

  20. Present-day deformation of the Pyrenees revealed by GPS surveying and earthquake focal mechanisms until 2011

    NASA Astrophysics Data System (ADS)

    Rigo, A.; Vernant, P.; Feigl, K. L.; Goula, X.; Khazaradze, G.; Talaya, J.; Morel, L.; Nicolas, J.; Baize, S.; Chéry, J.; Sylvander, M.

    2015-05-01

    The Pyrenean mountain range is a slowly deforming belt with continuous and moderate seismic activity. To quantify its deformation field, we present the velocity field estimated from a GPS survey of the Pyrenees spanning 18 yr. The PotSis and ResPyr networks, including a total of 85 GPS sites, were installed and first measured in 1992 and 1995-1997, respectively, and remeasured in 2008 and 2010. We obtain a deformation field with velocities less than 1 mm yr-1 across the range. The estimated velocities for individual stations do not differ significantly from zero with 95 per cent confidence. Even so, we estimate a maximum extensional horizontal strain rate of 2.0 ± 1.7 nanostrain per year in a N-S direction in the western part of the range. We do not interpret the vertical displacements due to their large uncertainties. In order to compare the horizontal strain rates with the seismic activity, we analyse a set of 194 focal mechanisms using three methods: (i) the `r' factor relating their P and T axes, (ii) the stress tensors obtained by fault slip inversion and (iii) the strain-rate tensors. Stress and strain-rate tensors are estimated for: (i) the whole data set, (ii) the eastern and western parts of the range separately, and (iii) eight zones, which are defined based on the seismicity and the tectonic patterns of the Pyrenees. Each of these analyses reveals a lateral variation of the deformation style from compression and extension in the east to extension and strike-slip in the west of the range. Although the horizontal components of the strain-rate tensors estimated from the seismic data are slightly smaller in magnitude than those computed from the GPS velocity field, they are consistent within the 2σ uncertainties. Furthermore, the orientations of their principal axes agree with the mapped active faults.

  1. Locations and focal mechanisms of deep long period events beneath Aleutian Arc volcanoes using back projection methods

    NASA Astrophysics Data System (ADS)

    Lough, A. C.; Roman, D. C.; Haney, M. M.

    2015-12-01

    Deep long period (DLP) earthquakes are commonly observed in volcanic settings such as the Aleutian Arc in Alaska. DLPs are poorly understood but are thought to be associated with movements of fluids, such as magma or hydrothermal fluids, deep in the volcanic plumbing system. These events have been recognized for several decades but few studies have gone beyond their identification and location. All long period events are more difficult to identify and locate than volcano-tectonic (VT) earthquakes because traditional detection schemes focus on high frequency (short period) energy. In addition, DLPs present analytical challenges because they tend to be emergent and so it is difficult to accurately pick the onset of arriving body waves. We now expect to find DLPs at most volcanic centers, the challenge lies in identification and location. We aim to reduce the element of human error in location by applying back projection to better constrain the depth and horizontal position of these events. Power et al. (2004) provided the first compilation of DLP activity in the Aleutian Arc. This study focuses on the reanalysis of 162 cataloged DLPs beneath 11 volcanoes in the Aleutian arc (we expect to ultimately identify and reanalyze more DLPs). We are currently adapting the approach of Haney (2014) for volcanic tremor to use back projection over a 4D grid to determine position and origin time of DLPs. This method holds great potential in that it will allow automated, high-accuracy picking of arrival times and could reduce the number of arrival time picks necessary for traditional location schemes to well constrain event origins. Back projection can also calculate a relative focal mechanism (difficult with traditional methods due to the emergent nature of DLPs) allowing the first in depth analysis of source properties. Our event catalog (spanning over 25 years and volcanoes) is one of the longest and largest and enables us to investigate spatial and temporal variation in DLPs.

  2. Role of ornithine decarboxylase/polyamine pathway in focal cerebral ischemia-reperfusion injury and its mechanism in rats

    PubMed Central

    Ding, Li; Ba, Xiao-Hong

    2015-01-01

    Objective: To observe the role of ornithine decarboxylase (ODC)/polyamine pathway in focal cerebral ischemia-reperfusion injury and to explore its mechanism in rats. Methods: This study was randomly divided into 3 groups including sham-operation (sham) group, ischemia-reperfusion (I/R) group and α-difluoromethylornithine (DFMO) group (each group with 80 rats). In DFMO group, 300 mg/kg of DFMO was injected by tail vein 24 h before reperfusion. According to different time points (3 h, 12 h, 24 h, 48 h and 72 h) after reperfusion, each group was divided into 5 subgroups (each subgroup with 16 rats). Results: In I/R group, apoptosis began increasing 3 h after reperfusion, reached a peak 24 h after perfusion and began decreasing 48 h after perfusion. Compared with sham group, apoptosis significantly increased in I/R and DFMO groups (P<0.05). However, apoptosis was significantly lower in DFMO group than in I/R group at each time point (P<0.05). In I/R group, CHOP expression began increasing 3 h after reperfusion, reached a peak 24 h after perfusion and began decreasing 48 h after perfusion. CHOP expression was significantly lower in DFMO group than in I/R group at each time point (P<0.05). The level of polyamines was significantly higher in I/R and DFMO groups than in sham group, and in I/R group than in DFMO group 12 h, 24 h and 48 h, respectively (P<0.05). Conclusion: Down-regulation of ODC/polyamine pathway may inhibit CHOP-mediated apoptosis caused by endoplasmic reticulum stress and plays a protective role in cerebral I/R injury. PMID:26884982

  3. How ubiquitous are aftershock sequences driven by high pressure fluids at depth?

    NASA Astrophysics Data System (ADS)

    Miller, S. A.

    2008-12-01

    Strong evidence suggests that two earthquake-aftershock episodes, the 2004 Niigata (Japan) sequence and the 1997 Umbria-Marche (Italy) sequence, were driven by high pressure fluids at depth. Since Niigata was in a compressional environment and Umbria-Marche in extension, a question arises about whether such a mechanism is more general than just these two cases. Although it is not clear by what mechanism fluids of sufficient volume can be trapped in the lower crust, if such pockets of high pressure fluids exist, then they must necessarily be expelled when a large earthquake provides the hydraulic connection to the hydrostatically pressured free surface. In this talk, aftershock data is analyzed for a number of different earthquakes in a variety of tectonic settings, including 1992 Landers, 1994 Northridge, and the 2001 Bhuj earthquakes. Comparisons are made between model results of the evolved fluid pressure state from a high pressure source at depth, and the spatio-temporal distributions of aftershocks. The data is further analyzed and compared with model results for differences in the rate of aftershocks (p-value in Omori's Law) and their dependence on the orientation of the mainshock relative to the prevailing regional stress field.

  4. Escherichia coli alpha-haemolysin induces focal leaks in colonic epithelium: a novel mechanism of bacterial translocation.

    PubMed

    Troeger, Hanno; Richter, Jan F; Beutin, Lothar; Günzel, Dorothee; Dobrindt, Ulrich; Epple, Hans-Jörg; Gitter, Alfred H; Zeitz, Martin; Fromm, Michael; Schulzke, Jörg-Dieter

    2007-10-01

    Extraintestinal pathogenic Escherichia coli (ExPEC) are usually harmless colonizer of the intestinal microflora. However, they are capable to translocate and cause life-threatening disease. Translocation of ExPEC isolates was quantified in colonic monolayers. Transepithelial resistance (R(t)) was monitored and local changes in conductivity analysed with conductance scanning. Confocal microscopy visualized the translocation route. Corroboratory experiments were performed on native rat colon. One translocating strain E. coli O4 was identified. This translocation process was associated with an R(t) decrease (36 +/- 1% of initial resistance) beginning only 2 h after inoculation. The sites of translocation were small defects in epithelial integrity (focal leaks) exhibiting highly increased local ion permeability. Translocation was enhanced by preincubation of monolayers with tumour necrosis factor-alpha or interleukin-13. Mutant strains lacking alpha-haemolysin lost the ability to induce focal leaks, while this effect could be restored by re-introducing the haemolysin determinant. Filtrate of a laboratory strain carrying the alpha-haemolysin operon was sufficient for focal leak induction. In native rat colon, E. coli O4 decreased R(t) and immunohistology demonstrated focal leaks resembling those in cell monolayers. E. coli alpha-haemolysin is able to induce focal leaks in colonic cell cultures as well as in native colon. This process represents a novel route of bacterial translocation facilitated by pro-inflammatory cytokines. PMID:17587334

  5. Model for the Distribution of Aftershock Interoccurrence Times

    SciTech Connect

    Shcherbakov, Robert; Yakovlev, Gleb; Rundle, John B.; Turcotte, Donald L.

    2005-11-18

    In this work the distribution of interoccurrence times between earthquakes in aftershock sequences is analyzed and a model based on a nonhomogeneous Poisson (NHP) process is proposed to quantify the observed scaling. In this model the generalized Omori's law for the decay of aftershocks is used as a time-dependent rate in the NHP process. The analytically derived distribution of interoccurrence times is applied to several major aftershock sequences in California to confirm the validity of the proposed hypothesis.

  6. Empirical Green's functions from small earthquakes: A waveform study of locally recorded aftershocks of the 1971 San Fernando earthquake

    SciTech Connect

    Hutchings, L.; Wu, F. )

    1990-02-10

    Seismograms from 52 aftershocks of the 1971 San Fernando earthquake recorded at 25 stations distributed across the San Fernando Valley are examined to identify empirical Green's functions, and characterize the dependence of their waveforms on moment, focal mechanism, source and recording site spatial variations, recording site geology, and recorded frequency band. Recording distances ranged from 3.0 to 33.0 km, hypocentral separations ranged from 0.22 to 28.4 km, and recording site separations ranged from 0.185 to 24.2 km. The recording site geologies are diorite gneiss, marine and nonmarine sediments, and alluvium of varying thicknesses. Waveforms of events with moment below about 1.5 {times} 10{sup 21} dyn cm are independent of the source-time function and are termed empirical Green's functions. Waveforms recorded at a particular station from events located within 1.0 to 3.0 km of each other, depending upon site geology, with very similar focal mechanism solutions are nearly identical for frequencies up to 10 Hz. There is no correlation to waveforms between recording sites at least 1.2 km apart, and waveforms are clearly distinctive for two sites 0.185 km apart. The geologic conditions of the recording site dominate the character of empirical Green's functions. Even for source separations of up to 20.0 km, the empirical Green's functions at a particular site are consistent in frequency content, amplification, and energy distribution. Therefore, it is shown that empirical Green's functions can be used to obtain site response functions. The observations of empirical Green's functions are used as a basis for developing the theory for using empirical Green's functions in deconvolution for source pulses and synthesis of seismograms of larger earthquakes.

  7. Properties of the Aftershock Sequences of the 2003 Bingöl, M D = 6.4, (Turkey) Earthquake

    NASA Astrophysics Data System (ADS)

    Öztürk, S.; Çinar, H.; Bayrak, Y.; Karsli, H.; Daniel, G.

    2008-02-01

    after the main shock and it is interpreted that this situation may be caused by the alluvium structure of the region. These results indicate that the spatial distribution in b and p values are generally related to the rupture mechanism and material properties of an aftershock area.

  8. Bayesian Predictive Distribution for the Magnitude of the Largest Aftershock

    NASA Astrophysics Data System (ADS)

    Shcherbakov, R.

    2014-12-01

    Aftershock sequences, which follow large earthquakes, last hundreds of days and are characterized by well defined frequency-magnitude and spatio-temporal distributions. The largest aftershocks in a sequence constitute significant hazard and can inflict additional damage to infrastructure. Therefore, the estimation of the magnitude of possible largest aftershocks in a sequence is of high importance. In this work, we propose a statistical model based on Bayesian analysis and extreme value statistics to describe the distribution of magnitudes of the largest aftershocks in a sequence. We derive an analytical expression for a Bayesian predictive distribution function for the magnitude of the largest expected aftershock and compute the corresponding confidence intervals. We assume that the occurrence of aftershocks can be modeled, to a good approximation, by a non-homogeneous Poisson process with a temporal event rate given by the modified Omori law. We also assume that the frequency-magnitude statistics of aftershocks can be approximated by Gutenberg-Richter scaling. We apply our analysis to 19 prominent aftershock sequences, which occurred in the last 30 years, in order to compute the Bayesian predictive distributions and the corresponding confidence intervals. In the analysis, we use the information of the early aftershocks in the sequences (in the first 1, 10, and 30 days after the main shock) to estimate retrospectively the confidence intervals for the magnitude of the expected largest aftershocks. We demonstrate by analysing 19 past sequences that in many cases we are able to constrain the magnitudes of the largest aftershocks. For example, this includes the analysis of the Darfield (Christchurch) aftershock sequence. The proposed analysis can be used for the earthquake hazard assessment and forecasting associated with the occurrence of large aftershocks. The improvement in instrumental data associated with early aftershocks can greatly enhance the analysis and

  9. Influence of depth, focal mechanism, and tectonic setting on the shape and duration of earthquake source time functions

    NASA Astrophysics Data System (ADS)

    Houston, Heidi

    2001-06-01

    Source time functions of 255 moderate to great earthquakes obtained from inversions of teleseismic body waves by Tanioka and Ruff [1997] and coworkers were compared in a systematic way. They were scaled to remove the effect of moment and to allow the direct comparison and averaging of time function shape as well as duration. Time function durations picked by Tanioka and Ruff [1997] are proportional to the cube root of seismic moment if moments from the Harvard centroid moment tensor catalog are used. The average duration of scaled time functions is shorter and the average shape has a more abrupt termination for deeper events than shallower ones, with a distinct change occurring at ˜40 km depth. The complexity of the time functions, as quantified by the number of subevents, appears to decrease below ˜40 km depth. Furthermore, among events shallower than 40 km, the average duration of scaled time functions is shorter, and their average shape has a more abrupt termination (1) for events with strike-slip focal mechanisms compared to thrust events and (2) for the few thrust events associated with an intraplate setting compared to the majority associated with an interplate (subduction) boundary. In each of these cases, events in more technically and seismically active settings have a longer duration and a more gradual termination. This can be interpreted in terms of lower stress drops and/or slower rupture velocities at active plate boundaries, suggesting that fault rheology depends on slip rate and may evolve as total fault slip accumulates. Furthermore, differences in average time function shape and duration associated with different subduction zones suggest that differences exist in the rheology on the plate boundaries at the various subduction zones. Supporting data table is available via Web browser or via Anonymous FTP from ftp://kosmos.agu.org, directory "append" (Username = "anonymous", Password = "guest"); subdirectories in the ftp site are arranged by paper

  10. Transpressional Strain Partitioning and the Compatibility of GPS Velocities and Earthquakes Focal Mechanisms in the Aleutian Arc

    NASA Astrophysics Data System (ADS)

    Apel, E. V.; Oldow, J. S.; Lewis, D. S.; Hans, A.

    2002-12-01

    Oblique plate convergence is commonly partitioned into boundary normal and parallel components resulting in displacement of the frontal portion of the overriding plate with respect to the backarc region along arc-parallel strike-slip faults. In the Aleutian Islands, the east to west increase in relative plate motion between the North American and Pacific plates from 65 mm/yr to 75 mm/yr is accompanied by a change from normal convergence to boundary parallel displacement. The convergence obliquity increases from near zero to ~80 degrees along strike together with an observed increase in velocities based on GPS measurements from 1996, 1998, 1999, and 2000. GPS velocities have a strong arc-parallel orientation and systematically increase around the curved arc from 4 mm/yr in the east (Unalaska), to 7-10 mm/yr in the center (Atka and Adak), and 25-31 mm/yr in the west (Shemya and Attu). In all cases, GPS velocities record a small arc-normal component of displacement. The orientation of the incremental shortening axis derived from earthquake focal mechanisms on the Aleutian megathrust has an obliquity that varies systematically from zero (normal to the plate boundary) in the east to ~35 degrees in the west. The variation in incremental shortening axes, however, does not document displacement field partitioning but rather is a consequence of transpressional nonplane strain. Existence of displacement partitioning can only be assessed by direct measurement. Unfortunately, GPS velocities record permanent and recoverable strain, necessitating determination of the elastic strain component in the velocity field. The incremental shortening axis related to megathrust deformation constrains the azimuth of the elastic component of the GPS velocity field and yields minimum arc-parallel displacement components of 4 mm/yr in the east, 5-6 mm/yr in the central Aleutian chain, and 22-27 mm/yr in the west. GPS velocities along the Aleutian chain record a lateral variation in

  11. Spatial distribution of the contemporary stress field in the Kurile Wadati-Benioff zone by inversion of earthquake focal mechanisms

    NASA Astrophysics Data System (ADS)

    Christova, C. V.

    2015-01-01

    The study addresses the spatial distribution of the contemporary stress field and stress regime in the Kurile Wadati-Benioff zone (WBZ) based on homogeneous data of earthquake focal mechanism solutions (FMS) and the inverse technique by Gephart and Forsyth (1984). The data set used consists of 829 Centroid Moment Tensor solutions (time period 1977-2010) and 38 FMS listed in previous studies for intermediate-depth and deep events that occurred prior to 1977. The detailed analysis of the spatial distribution of orientation of P (compression) and T (tension) axes of the individual FMS relative to the local geometry of the subducting slab allowed the outlining of 19 WBZ subvolumes along and across the arc for which the stress field parameters and stress regime (based on the orientations of the principal stresses in a slab's reference frame and the value of R) were evaluated. The stress inversion results show that the shallow portion of the slab (5 WBZ subvolumes), is characterized by sub-horizontal and close to strike-normal maximum compression σ1 and down-dipping minimum compression σ3, the stress regime is of general tension. A two-planar stress pattern with slab-parallel or in-slab σ1 and σ3 in the upper and lower planes, respectively, is observed at intermediate depth all along the arc. An exception of this pattern is found for the slab segment beneath Iturup island where the upper plane is 'missing' and the orientations of principal stresses in the depth range 61-140 km are similar to these for the lower plane in the slab segment located to the south. Five sub-volumes have been outlined within the Kurile slab at depth greater than 220 km, each with their own characteristic focal mechanisms and stress distribution. The subvolume V1 (depth range 225-380 km), stretching along the entire arc, is characterized by σ1 and σ3 of SW and ENE orientation, respectively, the stress regime being compressional. The results obtained for the deep portion of the slab indicate

  12. The Mechanical Design of a Kinematic Mount for the Mid Infrared Instrument Focal Plane Module on the James Webb Space Telescope

    NASA Technical Reports Server (NTRS)

    Thelen, Michael P.; Moore, Donald M.

    2009-01-01

    The detector assembly for the Mid Infrared Instrument (MIRI) of the James Webb Space Telescope (JWST) is mechanically supported in the Focal Plane Module (FPM) Assembly with an efficient hexapod design. The kinematic mount design allows for precision adjustment of the detector boresight to assembly alignment fiducials and maintains optical alignment requirements during flight conditions of launch and cryogenic operations below 7 Kelvin. This kinematic mounting technique is able to be implemented in a variety of optical-mechanical designs and is capable of micron level adjustment control and stability over wide dynamic and temperature ranges.

  13. Linking the dynamics of the 2000 dike intrusion at Miyakejima to the focal mechanisms and the statistics of the induced seismicity

    NASA Astrophysics Data System (ADS)

    Rivalta, E.; Passarelli, L.; Cesca, S.; Aoki, Y.

    2014-12-01

    Faulting in volcanic environment is the result of the interaction of pressurized fluid-filled conduits and cracks with the host rocks. Faulting styles are also influenced by the local and regional tectonic setting. Seismicity in volcanic areas usually shows complex patterns difficult to decipher and there is a need of physics-based models linking observations to the mechanics of fluid-filled sources. Magma-filled dikes often induce abundant seismicity in form of swarms thought to occur close to the propagating tip (or edges, in 3D) of the dike, where stresses are concentrated, and in areas where pre-diking seismicity was high. The spatial distribution and focal mechanisms of the earthquakes bear information on the interaction of the dike stress field and the tectonic setting of the area. Here we use data of the 2000 dike intrusion at Miyakejima volcano (Izu Archipelago, Japan) to study the relation between the shape of the dike and the faulting style of the induced seismicity. We find that the strike and rake angles of the focal mechanisms are correlated with each other and are consistent with the dike shape and optimally- oriented faults according to the expected Coulomb stress changes from the 3D dike-induced stress field. We perform a clustering analysis on the FM solutions and relate them to the dike stress field and to the scaling relationships of the earthquakes. We calculate the frequency-size distribution of the clustered sets finding that focal mechanisms with a large strike- slip component are consistent with the Gutenberg-Richter relation with b-value about 1. Conversely, events with large normal faulting components deviate from the Gutenberg-Richter distribution with a marked roll-off on its right-hand tail suggesting a lack of large magnitude events (M>5.5). This can be interpreted as resulting from a limited thickness or localized weakness of the layer of rock above the dike, where normal faulting is expected.

  14. Problematic Location and Focal Mechanism of Weak Earthquakes: Example From The February-july 2001 Sequence In Aegion, Greece

    NASA Astrophysics Data System (ADS)

    Sokos, E.; Zahradnik, J.; Jansky, J.; Serpetsidaki, A.

    An earthquake sequence comprising of almost 200 events, with ML 2.0 to 4.7 oc- curred at about 10 km south of Aegion, the town heavily damaged by the ML = 6.2 earthquake of 1995. This region is of interest to the EC project cluster, the "Corinth Rift Laboratory". The sequence started in February 2001 and ended in July 2001. It was located by the regional short-period network of the University of Patras, PATNET, covering the Western Greece. The HYPO71PC method of Lee and Valdes (using var- ious constant-velocity layered crustal models and various starting depths) indicated that the earthquakes occupied a relatively large volume, whose horizontal and verti- cal extent is 10 x 10 km, and 20 km, respectively. The grid-search method applied in the same models, and also in a crustal model composed of gradient layers, confirmed this result but it also revealed existence of a dense cluster in the depth range 14 to 20 km, close to the mainshock depth. To retrieve the focal mechanism of the main- shock (April 8, ML=4.7), the amplitude spectra of complete waveforms at 0.1 to 0.2 Hz, below the corner frequency, were grid-searched for the strike, dip, and rake, using several trial depths. Three stations were employed: KER (Kernitsa, distance 17 km) and SER (Sergoula, 26 km) with digital accelerographs CMG5-T (Guralp), and DES (Desfina, 56 km), equipped by LE-3D/5s (Lennartz) instrument; DES is operated by the Seismological Laboratory of the University of Athens. The synthetic spectra were calculated by the discrete wavenumber method of Bouchon. The best solution (depth 8 km) is given by the strike = 220, dip = 40 , rake = -160, and its conjugate 114, 77, -52. The scalar seismic moment is 2.5e15 Nm, which gives the moment magnitude Mw=4.3. To assess the fault size, the waveforms (0.1 to 5.0 Hz) were fitted with a triangular moment-rate function. The best fit was obtained for the source duration of 0.3-0.4 sec, corresponding to the fault size of about 1 km. This implies average

  15. The May 29 2008 earthquake aftershock sequence within the South Iceland Seismic Zone: Fault locations and source parameters of aftershocks

    NASA Astrophysics Data System (ADS)

    Brandsdottir, B.; Parsons, M.; White, R. S.; Gudmundsson, O.; Drew, J.

    2010-12-01

    The mid-Atlantic plate boundary breaks up into a series of segments across Iceland. The South Iceland Seismic Zone (SISZ) is a complex transform zone where left-lateral E-W shear between the Reykjanes Peninsula Rift Zone and the Eastern Volcanic Zone is accommodated by bookshelf faulting along N-S lateral strike-slip faults. The SISZ is also a transient feature, migrating sideways in response to the southward propagation of the Eastern Volcanic Zone. Sequences of large earthquakes (M > 6) lasting from days to years and affecting most of the seismic zone have occurred repeatedly in historical time (last 1100 years), separated by intervals of relative quiescence lasting decades to more than a century. On May 29 2008, a Mw 6.1 earthquake struck the western part of the South Iceland Seismic Zone, followed within seconds by a slightly smaller event on a second fault ~5 km further west. Aftershocks, detected by a temporal array of 11 seismometers and three permanent Icelandic Meteorological Office stations were located using an automated Coalescence Microseismic Mapping technique. The epicenters delineate two major and several smaller N-S faults as well as an E-W zone of activity stretching further west into the Reykjanes Peninsula Rift Zone. Fault plane solutions show both right lateral and oblique strike slip mechanisms along the two major N-S faults. The aftershocks deepen from 3-5 km in the north to 8-9 km in the south, suggesting that the main faults dip southwards. The faulting is interpreted to be driven by the local stress due to transform motion between two parallel segments of the divergent plate boundary crossing Iceland.

  16. Identification of Focal Mechanisms of Seisms Occurring in the San Salvador Volcano-Ilopango Lake Area Between 1994 and March 2005

    SciTech Connect

    Maria Mendez Martinez, Luz de; Portillo, Mercy

    2009-04-19

    We studied the geographic area located in the central part of El Salvador, between the San Salvador Volcano (Quezaltepec) and Ilopango Lake. Its latitude is between 13 deg. 36' and 13 deg. 54', and longitude is between -89 deg. 18' and -88 deg. 57'. This area is directly affected by the WNW axis, the most prominent weak tectonic system in the region. Our research aimed to determine the focal mechanisms of seisms occurring in the studied area between 1994 and March 2005. Our analysis provided information about displacement types of the geological faults, using the wave impulse P method and computer applications ARCGIS and SEISAN, with the subroutine FOCMEC. Information of the studied seisms was obtained from the National Service of Territorial Studies (SNET) database. Geographic models used in the preparation of maps are from the geographic information system of the School of Physics at the University of El Salvador. The 37 focal mechanisms on the map of faults were identified in digital seismographs to determinate the arrival polarity of the wave P for each seism station. Data from the focal mechanisms were analyzed and correlated with their replications. The analysis allowed us to identify evidences to consider the fault continuity not reported by the last geological mission in El Salvador conducted in the 1970s. The fault continuity is located northwest of the studied geographical area, between San Salvador City and the San Salvador Volcano. The compression and strain axes for this area are two main horizontal force axes. The average orientation for the strain axis is NNE-SSW, and WNW-SEE for the compression axis. There is also important seismic activity in the Ilopango Lake and surrounding area. However, data did not allow us to make any inference. The tensors distribution resulted in a high dispersion corresponding to typical fauces models.

  17. Reduced Aftershock Productivity in Regions with Known Slow Slip Events

    NASA Astrophysics Data System (ADS)

    Collins, G.; Mina, A.; Richardson, E.; McGuire, J. J.

    2013-12-01

    Reduced aftershock activity has been observed in areas with high rates of aseismic slip, such as transform fault zones and some subduction zones. Fault conditions that could explain both of these observations include a low effective normal stress regime and/or a high temperature, semi-brittle/plastic rheology. To further investigate the possible connection between areas of aseismic slip and reduced aftershock productivity, we compared the mainshock-aftershock sequences in subduction zones where aseismic slip transients have been observed to those of adjacent (along-strike) regions where no slow slip events have been detected. Using the Advanced National Seismic System (ANSS) catalog, we counted aftershocks that occurred within 100 km and 14 days of 112 M>=5.0 slab earthquake mainshocks from January 1980 - July 2013, including 90 since January 2000, inside observed regions of detected slow slip: south central Alaska, Cascadia, the Nicoya Peninsula (Costa Rica), Guerrero (Mexico), and the North Island of New Zealand. We also compiled aftershock counts from 97 mainshocks from areas adjacent to each of these regions using the same criteria and over the same time interval. Preliminary analysis of these two datasets shows an aftershock triggering exponent (alpha in the ETAS model) of approximately 0.8, consistent with previous studies of aftershocks in a variety of tectonic settings. Aftershock productivity for both datasets is less than that of continental earthquakes. Contrasting the two datasets, aftershock productivity inside slow slip regions is lower than in adjacent areas along the same subduction zone and is comparable to that of mid-ocean ridge transform faults.

  18. Thermoelectric infrared detectors with improved mechanical stability for the composite infrared spectrometer (CIRS) far-infrared focal plane

    NASA Astrophysics Data System (ADS)

    Fettig, Rainer; Lakew, Brook; Brasunas, John C.; Crooke, Julie A.; Hakun, Claef F.; Orloff, Jon

    1998-09-01

    The Composite InfraRed Spectrometer (CIRS) instrument aboard the Cassini spacecraft en route to Saturn is a cryogenic spectrometer with far-infrared (FIR) and mid-infrared channels. The CIRS FIR focal plane, which covers the spectral range of 10 - 600 cm-1, consists of focusing optics and an output polarizer/analyzer that splits the output radiation according to polarization. The reflected and transmitted components are focused by concentrating cones onto thermoelectric detectors. These thermoelectric detectors consist of a gold black absorber on top of a gold foil that is welded to a thermoelement consisting of two semiconductor pyramids. After the detectors were integrated into the focal plane assembly and the CIRS instrument, the detectors proved to be extremely susceptible to two environmental survivability conditions: acoustics and airflow. Several changes were investigated to improve the integrity of the detectors including detector airflow geometry, structural changes to the detectors, and more intensive screening methods. The geometry of the air paths near the sensing elements was modified. Two structural modifications were implemented to improve the stability of the sensing elements. These were changes in the geometry of the thermoelectric pyramids by ion milling, and a change in the gold foil thickness. New screening methods, centrifuge and modulated force testing, were developed to select the most rugged detectors. Although several methods gave significant improvements to the detector's stability, the modification that allowed the detectors to meet the environmental survivability requirements was the change in the geometry of the air paths near the sensing elements.

  19. Aftershocks in coherent-noise models

    NASA Astrophysics Data System (ADS)

    Wilke, C.; Altmeyer, S.; Martinetz, T.

    1998-09-01

    The decay pattern of aftershocks in the so-called ‘coherent-noise’ models [M.E.J. Newman, K. Sneppen, Phys. Rev. E 54 (1996) 6226] is studied in detail. Analytical and numerical results show that the probability to find a large event at time t after an initial major event decreases as t- τ for small t, with the exponent τ ranging from 0 to values well above 1. This is in contrast to Sneppen and Newman, who stated that the exponent is about 1, independent of the microscopic details of the simulation. Numerical simulations of an extended model [C. Wilke, T. Martinetz, Phys. Rev. E 56 (1997) 7128] show that the power-law is only a generic feature of the original dynamics and does not necessarily appear in a more general context. Finally, the implications of the results to the modelling of earthquakes are discussed.

  20. Aftershock triggering by complete Coulomb stress changes

    USGS Publications Warehouse

    Kilb, Debi; Gomberg, J.; Bodin, P.

    2002-01-01

    We examine the correlation between seismicity rate change following the 1992, M7.3, Landers, California, earthquake and characteristics of the complete Coulomb failure stress (CFS) changes (??CFS(t)) that this earthquake generated. At close distances the time-varying "dynamic" portion of the stress change depends on how the rupture develops temporally and spatially and arises from radiated seismic waves and from permanent coseismic fault displacement. The permanent "static" portion (??CFS) depends only on the final coseismic displacement. ??CFS diminishes much more rapidly with distance than the transient, dynamic stress changes. A common interpretation of the strong correlation between ??CFS and aftershocks is that load changes can advance or delay failure. Stress changes may also promote failure by physically altering properties of the fault or its environs. Because it is transient, ??CFS(t) can alter the failure rate only by the latter means. We calculate both ??CFS and the maximum positive value of ??CFS(t) (peak ??CFS(t)) using a reflectivity program. Input parameters are constrained by modeling Landers displacement seismograms. We quantify the correlation between maps of seismicity rate changes and maps of modeled ??CFS and peak ??CFS(t) and find agreement for both models. However, rupture directivity, which does not affect ??CFS, creates larger peak ??CFS(t) values northwest of the main shock. This asymmetry is also observed in seismicity rate changes but not in ??CFS. This result implies that dynamic stress changes are as effective as static stress changes in triggering aftershocks and may trigger earthquakes long after the waves have passed.

  1. The quality of focal mechanism solutions and its impact on the statistical correlation between tidally-induced stresses and earthquake timing.

    NASA Astrophysics Data System (ADS)

    Bucholc, Magda; Steacy, Sandy; Simão, Nuno

    2015-04-01

    The effect of Earth tides on earthquake timings has been widely investigated for many years. However, the evidence of tidally triggered seismicity is often variable and inconclusive. Tidal modulation of earthquake timings is based on the assumption that a critically-stressed seismic fault can be tidally activated only if tidal stresses are oriented along the faults natural slipping direction and therefore, enhance an existing tectonic stress. In this situation, the accuracy of tidal calculations is essential and depends greatly on the quality of earthquake focal mechanism solutions. The focal parameters provide necessary information about the geometry and kinematics of the fault. At the same time, they can be sensitive to numerous factors (e.g. the accuracy of the earthquake location, distribution of seismic stations, assumed velocity model) and thus, the fault-plane orientation and slip direction will always carry some degree of uncertainty. In this project, we conduct a sensitivity test to see how the orientation variability of the fault planes can affect the statistical significance of results on tidally-induced seismicity. We use a Monte Carlo simulation to generate a number of synthetic catalogues with the same properties as the original catalog. However, fault plane parameters of the synthetic catalogs are randomly drawn from the bounded range of uncertainties associated with an earthquake focal mechanism solution. The significance of correlation between Earth tides and earthquake occurrence is then evaluated separately for each catalog using the Shuster test. Firstly, we assign the tidal phase angle at the earthquake occurrence time. The phase angle is measured from the time series of the tidal stress calculated at the location of each event. The value is assigned by linearly dividing the time interval from 0° to 180° or from 180° to 0°, where 0° and ±180° corresponds to the maximum and the minimum of the tidal stress immediately before or after each

  2. The Pegasus Bay aftershock sequence of the Mw 7.1 Darfield (Canterbury), New Zealand earthquake

    NASA Astrophysics Data System (ADS)

    Ristau, John; Holden, Caroline; Kaiser, Anna; Williams, Charles; Bannister, Stephen; Fry, Bill

    2013-10-01

    The Pegasus Bay aftershock sequence is the most recent aftershock sequence of the 2010 September 3 UTC moment magnitude (Mw) 7.1 Darfield earthquake in the Canterbury region of New Zealand. The Pegasus Bay aftershock sequence began on 2011 December 23 UTC with three events of Mw 5.4-5.9 located in the offshore region of Pegasus Bay, east of Christchurch city. We present a summary of key aspects of the sequence derived using various geophysical methods. Relocations carried out using double-difference tomography show a well-defined NNE-SSW to NE-SW series of aftershocks with most of the activity occurring at depths >5 km and an average depth of ˜10 km. Regional moment tensor solutions calculated for the Pegasus Bay sequence indicate that the vast majority (45 of 53 events) are reverse-faulting events with an average P-axis azimuth of 125°. Strong-motion data inversion favours a SE-dipping fault plane for the largest event (Mw 5.9) with a slip patch of 18 km × 15 km and a maximum slip of 0.8 m at 3.5 km depth. Peak ground accelerations ranging up to 0.98 g on the vertical component were recorded during the sequence, and the largest event produced horizontal accelerations of 0.2-0.4 g in the Christchurch central business district. Apparent stress estimates for the two largest events are 1.1 MPa (Mw 5.9) and 0.2 MPa (Mw 5.8), which are compatible with global averages, although lower than other large events in the Canterbury aftershock sequence. Coulomb stress analysis indicates that previous large earthquakes in the Canterbury sequence generate Coulomb stress increases for the two events only at relatively shallow depths (3-5 km). At greater depths, Coulomb stress decreases are predicted at the locations of the two events. The trend of the aftershocks is similar to mapped reverse faults north of Christchurch, and the high number of reverse-faulting mechanisms suggests that similar reverse-faulting structures are present in the offshore region east of Christchurch.

  3. Relocation and focal mechanisms of earthquakes in the south-central sector of the Aeolian Archipelago: New structural and volcanological insights

    NASA Astrophysics Data System (ADS)

    Gambino, Salvatore; Milluzzo, Vincenzo; Scaltrito, Antonio; Scarfì, Luciano

    2012-02-01

    To recognize possible spatial clusters and identify active seismogenic zones and structures in the Aeolian Archipelago, in the south of Italy, we analyzed the spatial pattern of seismicity between 1993 and 2010 in a selected area comprising Vulcano, Lipari, Salina and Filicudi and calculated 22 fault plane solutions (FPSs) for shocks with magnitude greater than 2.7. First, we computed a 1-D velocity model for this area including information from recorded earthquakes by a joint hypocenter-velocity inversion (Kissling et al., 1994). Successively, we applied the double-difference approach of Waldhauser and Ellsworth (2000), finding that a certain part of the scattered epicenter locations collapse in roughly linear features. Relocated seismicity evidenced three main alignments, oriented NNW-SSE and NE-SW at different depths that concur well with the known tectonic lineaments and focal mechanisms. A detailed discussion is focused on a seismogenetic structure, NE-SW oriented, 3-8 km deep, located in the northern area of Vulcano island. This recognized element could represent a link between magma accumulation zones, thus representing a possible preferential pathway along which magma may intrude. Two earthquake clusters, located south-west and east of Vulcano, with their focal mechanisms, highlight the Aeolian-Tindari-Letojanni Fault System seismic activity and the existence of a transitional zone going from the N-S compressive domain that dominates the Aeolian Islands to the NW-SE extensional domain characterizing the south-eastern Tyrrhenian.

  4. The application of striation analysis and focal mechanism stress inversion in deducing the kinematic history of faults: Examples from the Bristol Channel UK and the Ionian Zone Greece

    NASA Astrophysics Data System (ADS)

    Melis, Nikolaos S.; Miliorizos, Marios N.; Oshoano Aipoh, Hilary

    2013-04-01

    The present work compliments the application of a methodology, in reviewing and investigating further the kinematic history of faults, based on striation analysis and stress inversion of earthquake focal mechanisms and combines them to refine tectonic modelling and hence improve further hazard assessment. Two areas are chosen for this application: the Bristol Channel, UK and the Ionian Zone, Greece. Striation analysis is carried out in two complementary fault terranes. The first along the northern margin of the Inner Bristol Channel, UK, offers a natural laboratory to study in detail the reactivation history of the inverted Bristol Channel basin; and, the second along the north western coastline of the Ionian Zone, Greece, presents an opportunity to illustrate the relationship between movement of a framework of faults within the external orogenic zone of the Hellenides and the stress deduced from focal mechanisms of earthquakes in the region. The UK example reveals phases of Mesozoic negative inversion of Late Palaeozoic basement frontal and oblique ramp thrust faults, followed by Caenozoic positive inversions of Mesozoic normal and strike slip faults. The Greek example shows an equally composite history of faulting; Tethyan basement strata contain normal faults that pass up sequence and across unconformities into Mesozoic and Caenozoic strata, with thrusts and positively inverted faults recording typical dextral transpression. The fault framework in older strata and the veneers of Recent strata above them display Neotectonic fault histories of sinistral transtension, in addition to the transpression. Since the Ionian Zone lies suitably in the external zone, deformation favours the reactivation of fault lineaments, rather than the genesis of pristine faults. Both examples are used to demonstrate this structural principle. Focal mechanisms of Greek earthquake data are used in stress inversion and the results are applied upon the inherited fault framework and are

  5. Distribution of similar earthquakes in aftershocks of inland earthquakes

    NASA Astrophysics Data System (ADS)

    Hayashi, M.; Hiramatsu, Y.; Aftershock Observations Of 2007 Noto Hanto, G.

    2010-12-01

    Frictional properties control the slip behavior on a fault surface such as seismic slip and aseismic slip. Asperity, as a seismic slip area, is characterized by a strong coupling in the interseismic period and large coseismic slip. On the other hand, steady slip or afterslip occurs in an aseismic slip area around the asperity. If an afterslip area includes small asperities, a repeating rupture of single asperity can generate similar earthquakes due to the stress accumulation caused by the afterslip. We here investigate a detail distribution of similar earthquakes in the aftershocks of the 2007 Noto Hanto earthquake (Mjma 6.9) and the 2000 Western Tottori earthquake (Mjma 7.3), inland large earthquakes in Japan. We use the data obtained by the group for the aftershock observations of the 2007 Noto Hanto Earthquake and by the group for the aftershock observations of the 2000 Western Tottori earthquake. First, we select pairs of aftershocks whose cross correlation coefficients in 10 s time window of band-pass filtered waveforms of 1~4 Hz are greater than 0.95 at more than 5 stations and divide those into groups by a link of the cross correlation coefficients. Second, we reexamine the arrival times of P and S waves and the maximum amplitude for earthquakes of each group and apply the double-difference method (Waldhouser and Ellsworth, 2000) to relocate them. As a result of the analysis, we find 24 groups of similar earthquakes in the aftershocks on the source fault of the 2007 Noto Hanto Earthquake and 86 groups of similar earthquakes in the aftershocks on the source fault of the 2000 Western Tottori Earthquake. Most of them are distributed around or outside the asperity of the main shock. Geodetic studies reported that postseismic deformation was detected for the both earthquakes (Sagiya et al., 2002; Hashimoto et al., 2008). The source area of similar earthquakes seems to correspond to the afterslip area. These features suggest that the similar earthquakes observed

  6. A case study of two M~5 mainshocks in Anza, California: Is the footprint of an aftershock sequence larger than we think?

    USGS Publications Warehouse

    Fritts, Karen R.; Kilb, Debi

    2009-01-01

    It has been traditionally held that aftershocks occur within one to two fault lengths of the mainshock. Here we demonstrate that this perception has been shaped by the sensitivity of seismic networks. The 31 October 2001 Mw 5.0 and 12 June 2005 Mw 5.2 Anza mainshocks in southern California occurred in the middle of the densely instrumented ANZA seismic network and thus were unusually well recorded. For the June 2005 event, aftershocks as small as M 0.0 could be observed stretching for at least 50 km along the San Jacinto fault even though the mainshock fault was only ∼4.5 km long. It was hypothesized that an observed aseismic slipping patch produced a spatially extended aftershock-triggering source, presumably slowing the decay of aftershock density with distance and leading to a broader aftershock zone. We find, however, the decay of aftershock density with distance for both Anza sequences to be similar to that observed elsewhere in California. This indicates there is no need for an additional triggering mechanism and suggests that given widespread dense instrumentation, aftershock sequences would routinely have footprints much larger than currently expected. Despite the large 2005 aftershock zone, we find that the probability that the 2005 Anza mainshock triggered the M 4.9 Yucaipa mainshock, which occurred 4.2 days later and 72 km away, to be only 14%±1%. This probability is a strong function of the time delay; had the earthquakes been separated by only an hour, the probability of triggering would have been 89%.

  7. Pulsed ultrasound promotes melanoblast migration through upregulation of macrophage colony-stimulating factor/focal adhesion kinase autocrine signaling and paracrine mechanisms.

    PubMed

    Liao, Yi-Hua; Huang, Yu-Ting; Deng, Jhu-Yun; Chen, Wen-Shiang; Jee, Shiou-Hwa

    2013-09-01

    Repigmentation of vitiliginous lesions relies on the proliferation and migration of melanoblasts from hair follicles to the epidermis. Pulsed ultrasound has been demonstrated to have stimulatory effects on cell proliferation and migration and has been applied clinically to enhance tissue repair. To clarify the biologic effects and signaling mechanisms of pulsed ultrasound on melanoblast proliferation and migration, two melanoblast cell lines, the undifferentiated NCCmelb4 cells and the differentiated NCCmelan5 cells, were examined. We demonstrated that pulsed ultrasound increased cell migration in a dose-dependent manner without altering cell proliferation. Pulsed ultrasound enhanced autocrine secretion of macrophage colony-stimulating factor (M-CSF), which subsequently activated the focal adhesion kinase (FAK) pathway to promote melanoblast migration. Furthermore, conditioned medium from mouse embryonic fibroblasts NIH 3T3 and primary human keratinocytes treated with pulsed ultrasound could stimulate melanoblast migration through a paracrine effect. Our results provide a novel mechanism to promote migration of melanoblasts by pulsed ultrasound stimulation. PMID:23725022

  8. Mapping the Tohoku forearc: Implications for the mechanism of the 2011 East Japan earthquake (Mw 9.0)

    NASA Astrophysics Data System (ADS)

    Wang, Zhi; Huang, Wenli; Zhao, Dapeng; Pei, Shunping

    2012-02-01

    To investigate the generation mechanism of the 2011 great East Japan (GEJ) earthquake (M 9.0), we determined a three-dimensional (3-D) seismic model under the NE Japan forearc region using a large number of P and S wave arrival times from local earthquakes. Our results show that the GEJ main-shock occurred in a high-velocity (Vp, Vs) zone with higher Poisson's ratio (σ). The aftershocks relocated with a master-event location (MEL) procedure indicate that most of them are located at the corner of the mantle wedge along the upper boundary of the subducting Pacific slab, and their focal depths are slightly shallower than the background seismicity. The tomographic images and spatial distribution of the aftershocks imply strong interplate coupling (asperity) in the main-shock area and weak coupling in the surrounding areas of the megathrust zone. We think that fluids in the crust and uppermost mantle in the subduction zone could have affected the earthquake generation through the physical role of fluid pressure and a variety of chemical effects. We conclude that the 2011 GEJ earthquake initiation and the rupture processes of the aftershock sequence were influenced by fluid extrusion into the rupture zone due to the dehydration of the subducting Pacific slab. Fluid-bearing structural heterogeneities with thermal-petrologic variations in the megathrust zone played a key role in the initiation of the 2011 GEJ earthquake and its aftershocks.

  9. Determination of focal mechanisms of intermediate-magnitude earthquakes in Mexico, based on Greens functions calculated for a 3D Earth model

    NASA Astrophysics Data System (ADS)

    Rodrigo Rodríguez Cardozo, Félix; Hjörleifsdóttir, Vala

    2015-04-01

    One important ingredient in the study of the complex active tectonics in Mexico is the analysis of earthquake focal mechanisms, or the seismic moment tensor. They can be determined trough the calculation of Green functions and subsequent inversion for moment-tensor parameters. However, this calculation is gets progressively more difficult as the magnitude of the earthquakes decreases. Large earthquakes excite waves of longer periods that interact weakly with laterally heterogeneities in the crust. For these earthquakes, using 1D velocity models to compute the Greens fucntions works well. The opposite occurs for smaller and intermediate sized events, where the relatively shorter periods excited interact strongly with lateral heterogeneities in the crust and upper mantle and requires more specific or regional 3D models. In this study, we calculate Greens functions for earthquakes in Mexico using a laterally heterogeneous seismic wave speed model, comprised of mantle model S362ANI (Kustowski et al 2008) and crustal model CRUST 2.0 (Bassin et al 1990). Subsequently, we invert the observed seismograms for the seismic moment tensor using a method developed by Liu et al (2004) an implemented by Óscar de La Vega (2014) for earthquakes in Mexico. By following a brute force approach, in which we include all observed Rayleigh and Love waves of the Mexican National Seismic Network (Servicio Sismológico Naciona, SSN), we obtain reliable focal mechanisms for events that excite a considerable amount of low frequency waves (Mw > 4.8). However, we are not able to consistently estimate focal mechanisms for smaller events using this method, due to high noise levels in many of the records. Excluding the noisy records, or noisy parts of the records manually, requires interactive edition of the data, using an efficient tool for the editing. Therefore, we developed a graphical user interface (GUI), based on python and the python library ObsPy, that allows the edition of observed and

  10. Mechanically assisted 3D ultrasound for pre-operative assessment and guiding percutaneous treatment of focal liver tumors

    NASA Astrophysics Data System (ADS)

    Sadeghi Neshat, Hamid; Bax, Jeffery; Barker, Kevin; Gardi, Lori; Chedalavada, Jason; Kakani, Nirmal; Fenster, Aaron

    2014-03-01

    Image-guided percutaneous ablation is the standard treatment for focal liver tumors deemed inoperable and is commonly used to maintain eligibility for patients on transplant waitlists. Radiofrequency (RFA), microwave (MWA) and cryoablation technologies are all delivered via one or a number of needle-shaped probes inserted directly into the tumor. Planning is mostly based on contrast CT/MRI. While intra-procedural CT is commonly used to confirm the intended probe placement, 2D ultrasound (US) remains the main, and in some centers the only imaging modality used for needle guidance. Corresponding intraoperative 2D US with planning and other intra-procedural imaging modalities is essential for accurate needle placement. However, identification of matching features of interest among these images is often challenging given the limited field-of-view (FOV) and low quality of 2D US images. We have developed a passive tracking arm with a motorized scan-head and software tools to improve guiding capabilities of conventional US by large FOV 3D US scans that provides more anatomical landmarks that can facilitate registration of US with both planning and intra-procedural images. The tracker arm is used to scan the whole liver with a high geometrical accuracy that facilitates multi-modality landmark based image registration. Software tools are provided to assist with the segmentation of the ablation probes and tumors, find the 2D view that best shows the probe(s) from a 3D US image, and to identify the corresponding image from planning CT scans. In this paper, evaluation results from laboratory testing and a phase 1 clinical trial for planning and guiding RFA and MWA procedures using the developed system will be presented. Early clinical results show a comparable performance to intra-procedural CT that suggests 3D US as a cost-effective alternative with no side-effects in centers where CT is not available.

  11. Relocation of aftershocks of the 2001 Bhuj earthquake: A new insight into seismotectonics of the Kachchh seismic zone, Gujarat, India

    NASA Astrophysics Data System (ADS)

    Mandal, Prantik; Pandey, O. P.

    2010-05-01

    In view of an anomalous crust-mantle structure beneath the 2001 Bhuj earthquake region, double-difference relocations of 1402 aftershocks of the 2001 Bhuj earthquake were determined, using an improved 1D velocity model constructed from 3D velocity tomograms based on data from 10 to 58 three-component seismograph stations. This clearly delineated four major tectonic features: (i) south-dipping north Wagad fault (NWF), (ii and iii) south-dipping south Wagad faults 1 and 2 (SWF 1, SWF 2), and (iv) a northeast dipping transverse fault (ITF), which is a new find. The relocated aftershocks correlate satisfactorily with the geologically mapped and inferred faults in the epicentral region. The relocated focal depths delineate a marked variation to the tune of 12 km in the brittle-ductile transition depths beneath the central aftershock zone that could be attributed to a lateral variation in crustal composition (more or less mafic) or in the level of fracturing across the fault zone. A fault intersection between the NWF and ITF has been clearly mapped in the 10-20 km depth range beneath the central aftershock zone. It is inferred that large intraplate stresses associated with the fault intersection, deepening of the brittle-ductile transition to a depth of 34 km due to the presence of mafic/ultramafic material in the crust-mantle transition zone, and the presence of aqueous fluids (released during the metamorphic process of eclogitisation of lower crustal olivine-rich rocks) and volatile CO 2 at the hypocentral depths, might have resulted in generating the 2001 Bhuj earthquake sequence covering the entire lower crust.

  12. On the adaptive daily forecasting of seismic aftershock hazard

    NASA Astrophysics Data System (ADS)

    Ebrahimian, Hossein; Jalayer, Fatemeh; Asprone, Domenico; Lombardi, Anna Maria; Marzocchi, Warner; Prota, Andrea; Manfredi, Gaetano

    2013-04-01

    Post-earthquake ground motion hazard assessment is a fundamental initial step towards time-dependent seismic risk assessment for buildings in a post main-shock environment. Therefore, operative forecasting of seismic aftershock hazard forms a viable support basis for decision-making regarding search and rescue, inspection, repair, and re-occupation in a post main-shock environment. Arguably, an adaptive procedure for integrating the aftershock occurrence rate together with suitable ground motion prediction relations is key to Probabilistic Seismic Aftershock Hazard Assessment (PSAHA). In the short-term, the seismic hazard may vary significantly (Jordan et al., 2011), particularly after the occurrence of a high magnitude earthquake. Hence, PSAHA requires a reliable model that is able to track the time evolution of the earthquake occurrence rates together with suitable ground motion prediction relations. This work focuses on providing adaptive daily forecasts of the mean daily rate of exceeding various spectral acceleration values (the aftershock hazard). Two well-established earthquake occurrence models suitable for daily seismicity forecasts associated with the evolution of an aftershock sequence, namely, the modified Omori's aftershock model and the Epidemic Type Aftershock Sequence (ETAS) are adopted. The parameters of the modified Omori model are updated on a daily basis using Bayesian updating and based on the data provided by the ongoing aftershock sequence based on the methodology originally proposed by Jalayer et al. (2011). The Bayesian updating is used also to provide sequence-based parameter estimates for a given ground motion prediction model, i.e. the aftershock events in an ongoing sequence are exploited in order to update in an adaptive manner the parameters of an existing ground motion prediction model. As a numerical example, the mean daily rates of exceeding specific spectral acceleration values are estimated adaptively for the L'Aquila 2009

  13. Earthquake rupture at focal depth, part II: mechanics of the 2004 M2.2 earthquake along the Pretorius Fault, TauTona Mine, South Africa

    USGS Publications Warehouse

    Heesakkers, V.; Murphy, S.; Lockner, D.A.; Reches, Z.

    2011-01-01

    We analyze here the rupture mechanics of the 2004, M2.2 earthquake based on our observations and measurements at focal depth (Part I). This event ruptured the Archean Pretorius fault that has been inactive for at least 2 Ga, and was reactivated due to mining operations down to a depth of 3.6 km depth. Thus, it was expected that the Pretorius fault zone will fail similarly to an intact rock body independently of its ancient healed structure. Our analysis reveals a few puzzling features of the M2.2 rupture-zone: (1) the earthquake ruptured four, non-parallel, cataclasite bearing segments of the ancient Pretorius fault-zone; (2) slip occurred almost exclusively along the cataclasite-host rock contacts of the slipping segments; (3) the local in-situ stress field is not favorable to slip along any of these four segments; and (4) the Archean cataclasite is pervasively sintered and cemented to become brittle and strong. To resolve these observations, we conducted rock mechanics experiments on the fault-rocks and host-rocks and found a strong mechanical contrast between the quartzitic cataclasite zones, with elastic-brittle rheology, and the host quartzites, with damage, elastic–plastic rheology. The finite-element modeling of a heterogeneous fault-zone with the measured mechanical contrast indicates that the slip is likely to reactivate the ancient cataclasite-bearing segments, as observed, due to the strong mechanical contrast between the cataclasite and the host quartzitic rock.

  14. Earthquake Rupture at Focal Depth, Part II: Mechanics of the 2004 M2.2 Earthquake Along the Pretorius Fault, TauTona Mine, South Africa

    NASA Astrophysics Data System (ADS)

    Heesakkers, V.; Murphy, S.; Lockner, D. A.; Reches, Z.

    2011-12-01

    We analyze here the rupture mechanics of the 2004, M2.2 earthquake based on our observations and measurements at focal depth (Part I). This event ruptured the Archean Pretorius fault that has been inactive for at least 2 Ga, and was reactivated due to mining operations down to a depth of 3.6 km depth. Thus, it was expected that the Pretorius fault zone will fail similarly to an intact rock body independently of its ancient healed structure. Our analysis reveals a few puzzling features of the M2.2 rupture-zone: (1) the earthquake ruptured four, non-parallel, cataclasite bearing segments of the ancient Pretorius fault-zone; (2) slip occurred almost exclusively along the cataclasite-host rock contacts of the slipping segments; (3) the local in-situ stress field is not favorable to slip along any of these four segments; and (4) the Archean cataclasite is pervasively sintered and cemented to become brittle and strong. To resolve these observations, we conducted rock mechanics experiments on the fault-rocks and host-rocks and found a strong mechanical contrast between the quartzitic cataclasite zones, with elastic-brittle rheology, and the host quartzites, with damage, elastic-plastic rheology. The finite-element modeling of a heterogeneous fault-zone with the measured mechanical contrast indicates that the slip is likely to reactivate the ancient cataclasite-bearing segments, as observed, due to the strong mechanical contrast between the cataclasite and the host quartzitic rock.

  15. Prediction model of earthquake with the identification of earthquake source polarity mechanism through the focal classification using ANFIS and PCA technique

    NASA Astrophysics Data System (ADS)

    Setyonegoro, W.

    2016-05-01

    Incidence of earthquake disaster has caused casualties and material in considerable amounts. This research has purposes to predictability the return period of earthquake with the identification of the mechanism of earthquake which in case study area in Sumatra. To predict earthquakes which training data of the historical earthquake is using ANFIS technique. In this technique the historical data set compiled into intervals of earthquake occurrence daily average in a year. Output to be obtained is a model return period earthquake events daily average in a year. Return period earthquake occurrence models that have been learning by ANFIS, then performed the polarity recognition through image recognition techniques on the focal sphere using principal component analysis PCA method. The results, model predicted a return period earthquake events for the average monthly return period showed a correlation coefficient 0.014562.

  16. Focal adhesions in osteoneogenesis

    PubMed Central

    Biggs, M.J.P; Dalby, M.J

    2010-01-01

    As materials technology and the field of tissue engineering advances, the role of cellular adhesive mechanisms, in particular the interactions with implantable devices, becomes more relevant in both research and clinical practice. A key tenet of medical device technology is to use the exquisite ability of biological systems to respond to the material surface or chemical stimuli in order to help develop next-generation biomaterials. The focus of this review is on recent studies and developments concerning focal adhesion formation in osteoneogenesis, with an emphasis on the influence of synthetic constructs on integrin mediated cellular adhesion and function. PMID:21287830

  17. Delayed functional expression of neuronal chemokine receptors following focal nerve demyelination in the rat: a mechanism for the development of chronic sensitization of peripheral nociceptors

    PubMed Central

    Bhangoo, Sonia; Ren, Dongjun; Miller, Richard J; Henry, Kenneth J; Lineswala, Jayana; Hamdouchi, Chafiq; Li, Baolin; Monahan, Patrick E; Chan, David M; Ripsch, Matthew S; White, Fletcher A

    2007-01-01

    Background Animal and clinical studies have revealed that focal peripheral nerve axon demyelination is accompanied by nociceptive pain behavior. C-C and C-X-C chemokines and their receptors have been strongly implicated in demyelinating polyneuropathies and persistent pain syndromes. Herein, we studied the degree to which chronic nociceptive pain behavior is correlated with the neuronal expression of chemokines and their receptors following unilateral lysophosphatidylcholine (LPC)-induced focal demyelination of the sciatic nerve in rats. Results Focal nerve demyelination increased behavioral reflex responsiveness to mechanical stimuli between postoperative day (POD) 3 and POD28 in both the hindpaw ipsilateral and contralateral to the nerve injury. This behavior was accompanied by a bilateral increase in the numbers of primary sensory neurons expressing the chemokine receptors CCR2, CCR5, and CXCR4 by POD14, with no change in the pattern of CXCR3 expression. Significant increases in the numbers of neurons expressing the chemokines monocyte chemoattractant protein-1 (MCP-1/CCL2), Regulated on Activation, Normal T Expressed and Secreted (RANTES/CCL5) and interferon γ-inducing protein-10 (IP-10/CXCL10) were also evident following nerve injury, although neuronal expression pattern of stromal cell derived factor-1α (SDF1/CXCL12) did not change. Functional studies demonstrated that acutely dissociated sensory neurons derived from LPC-injured animals responded with increased [Ca2+]i following exposure to MCP-1, IP-10, SDF1 and RANTES on POD 14 and 28, but these responses were largely absent by POD35. On days 14 and 28, rats received either saline or a CCR2 receptor antagonist isomer (CCR2 RA-[R]) or its inactive enantiomer (CCR2 RA-[S]) by intraperitoneal (i.p.) injection. CCR2 RA-[R] treatment of nerve-injured rats produced stereospecific bilateral reversal of tactile hyperalgesia. Conclusion These results suggest that the presence of chemokine signaling by both injured

  18. Comparison of the non-proliferation event aftershocks with other Nevada Test Site events

    SciTech Connect

    Jarpe, S.; Goldstein, P.; Zucca, J.J.

    1994-04-01

    As part of a larger effort to develop technology for on-site inspection of ambiguous underground seismic events, we have been working to identify phenomenology of aftershock seismicity which would be useful for discriminating between nuclear explosions, chemical explosions, earthquakes or other seismic events. Phenomenology we have investigated includes; the spatial distribution of aftershocks, the number of aftershocks as a function of time after the main event, the size of the aftershocks, and waveform frequency content. Our major conclusions are: (1) Depending on local geologic conditions, aftershock production rate two weeks after zero time ranges from 1 to 100 per day. (2) Aftershocks of concentrated chemical explosions such as the NPE are indistinguishable from aftershocks of nuclear explosions. (3) Earthquake and explosion aftershock sequences may be differentiated on the basis of depth, magnitude, and in some cases, frequency content of seismic signals.

  19. Aftershocks and triggered events of the Great 1906 California earthquake

    USGS Publications Warehouse

    Meltzner, A.J.; Wald, D.J.

    2003-01-01

    The San Andreas fault is the longest fault in California and one of the longest strike-slip faults in the world, yet little is known about the aftershocks following the most recent great event on the San Andreas, the Mw 7.8 San Francisco earthquake on 18 April 1906. We conducted a study to locate and to estimate magnitudes for the largest aftershocks and triggered events of this earthquake. We examined existing catalogs and historical documents for the period April 1906 to December 1907, compiling data on the first 20 months of the aftershock sequence. We grouped felt reports temporally and assigned modified Mercalli intensities for the larger events based on the descriptions judged to be the most reliable. For onshore and near-shore events, a grid-search algorithm (derived from empirical analysis of modern earthquakes) was used to find the epicentral location and magnitude most consistent with the assigned intensities. For one event identified as far offshore, the event's intensity distribution was compared with those of modern events, in order to contrain the event's location and magnitude. The largest aftershock within the study period, an M ???6.7 event, occurred ???100 km west of Eureka on 23 April 1906. Although not within our study period, another M ???6.7 aftershock occurred near Cape Mendocino on 28 October 1909. Other significant aftershocks included an M ???5.6 event near San Juan Bautista on 17 May 1906 and an M ???6.3 event near Shelter Cove on 11 August 1907. An M ???4.9 aftershock occurred on the creeping segment of the San Andreas fault (southeast of the mainshock rupture) on 6 July 1906. The 1906 San Francisco earthquake also triggered events in southern California (including separate events in or near the Imperial Valley, the Pomona Valley, and Santa Monica Bay), in western Nevada, in southern central Oregon, and in western Arizona, all within 2 days of the mainshock. Of these trigerred events, the largest were an M ???6.1 earthquake near Brawley

  20. International Aftershock Forecasting: Lessons from the Gorkha Earthquake

    NASA Astrophysics Data System (ADS)

    Michael, A. J.; Blanpied, M. L.; Brady, S. R.; van der Elst, N.; Hardebeck, J.; Mayberry, G. C.; Page, M. T.; Smoczyk, G. M.; Wein, A. M.

    2015-12-01

    Following the M7.8 Gorhka, Nepal, earthquake of April 25, 2015 the USGS issued a series of aftershock forecasts. The initial impetus for these forecasts was a request from the USAID Office of US Foreign Disaster Assistance to support their Disaster Assistance Response Team (DART) which coordinated US Government disaster response, including search and rescue, with the Government of Nepal. Because of the possible utility of the forecasts to people in the region and other response teams, the USGS released these forecasts publicly through the USGS Earthquake Program web site. The initial forecast used the Reasenberg and Jones (Science, 1989) model with generic parameters developed for active deep continental regions based on the Garcia et al. (BSSA, 2012) tectonic regionalization. These were then updated to reflect a lower productivity and higher decay rate based on the observed aftershocks, although relying on teleseismic observations, with a high magnitude-of-completeness, limited the amount of data. After the 12 May M7.3 aftershock, the forecasts used an Epidemic Type Aftershock Sequence model to better characterize the multiple sources of earthquake clustering. This model provided better estimates of aftershock uncertainty. These forecast messages were crafted based on lessons learned from the Christchurch earthquake along with input from the U.S. Embassy staff in Kathmandu. Challenges included how to balance simple messaging with forecasts over a variety of time periods (week, month, and year), whether to characterize probabilities with words such as those suggested by the IPCC (IPCC, 2010), how to word the messages in a way that would translate accurately into Nepali and not alarm the public, and how to present the probabilities of unlikely but possible large and potentially damaging aftershocks, such as the M7.3 event, which had an estimated probability of only 1-in-200 for the week in which it occurred.

  1. Statistical signatures of aftershock sequences generated by supershear mainshocks

    NASA Astrophysics Data System (ADS)

    Bhattacharya, P.; Shcherbakov, R.; Tiampo, K. F.; Mansinha, L.

    2010-12-01

    The rupture process during supershear earthquakes generates a seismic shock wave redistributing stress away from the fault resembling a sonic boom produced by a supersonic aircraft. This leads to a relative quiescence in aftershock activity along the supershear segment of the rupture. The occurrence of supershear ruptures is also generally associated with a region of local high pre-stress and an unusually smooth friction profile over the supershear segment, leading to a conspicuous absence of high frequency ground motions. We have considered the aftershock sequences of five well-known supershear earthquakes from around the world (1979 Imperial Valley, 1992 Landers, 1999 Izmit and Duzce and 2002 Denali earthquakes) to test whether the aftershock statistics around the supershear rupture are different from the statistics in the rest of the region due to the aforementioned stress conditions and redistributions. Specifically, we have looked at the frequency-magnitude distribution in order to study the variation of the b value for each of the sequences and observe statistically significant variations. In particular, we have determined that the b value is always higher in the zone surrounding a supershear segment than in the rest of the aftershock region. The Omori Law, however, does not show such clear trends. We also looked at the average difference in magnitude between the mainshock and the largest aftershock and found it is larger than that predicted by Bath's law. The results certainly point towards a relationship between aftershock statistics and the mainshock rupture process and might facilitate a physical process based understanding of the empirical laws of earthquake statistics.

  2. A numerical method for determining the state of stress using focal mechanisms of earthquake populations: application to Tibetan teleseisms and microseismicity of Southern Peru

    NASA Astrophysics Data System (ADS)

    Carey-Gailhardis, Evelyne; Louis Mercier, Jacques

    1987-03-01

    The numerical method described in this paper enables the study in terms of stress of the kinematics of seismic faults provided by focal mechanisms. This method assumes a mean state of stress in the source region and is based on the simple mechanical model used for fault population analysis which supposes slip in the direction of the resolved shear stress acting on the fault plane. The proposed algorithm first defines compressional and tensional zones resulting from superimposition of the compressional and tensional quadrants limited by the nodal planes. This enables one to test the data homogeneity. Furthermore, this restricts the space where the principal stress axes have to be searched. Then, for each principal stress reference whose location is constrained by above confined zones, the R value (chosen equal to (σ 2' - σ 1')/(σ 3' - σ 1') ) is computed which fits the slip vector on each nodal plane. This permits one to select a set of preferred seismic fault planes from a set of auxiliary planes. Finally, a state of stress is computed from the preferred seismic fault plane set using the non-linear simplex method already applied to fault populations. This algorithm is constructed so as to avoid two major difficulties: misleading estimation of the deviatoric stress tensor which may result from excessive emphasis by minimizing the residuals by a least squares method if some of the data are wrong and a lengthy prospection of the stress references over all the space of directions. This calculation does not take into account possible changes of the strike and dip of the nodal planes. However, we use rotations of nodal planes in agreement with the first arrival data to test the compatibility of these data with the computed state of stress. Tibetan teleseisms and southern Peruvian microseisms are analyzed and results are compared with kinematics of superficial recent and active faults measured in field in the same regions. This suggests that major seismic events may

  3. Simulating Aftershocks for an On Site Inspection (OSI) Exercise

    SciTech Connect

    Sweeney, J. J.; Ford, S. R.

    2015-10-05

    The experience of IFE14 emphasizes the need for a better way to simulate aftershocks during an OSI exercise. The obvious approach is to develop a digital model of aftershocks that can be used either for a real field exercise or for a computer simulation that can be done in an office, for training for example. However, this approach involves consideration of several aspects, such as how and when to introduce waveforms in a way that maximizes the realism of the data and that will be convincing to a savvy, experienced seismic analyst. The purpose of this report is to outline a plan for how this approach can be implemented.

  4. MicroRNA-124 protects against focal cerebral ischemia via mechanisms involving Usp14-dependent REST degradation.

    PubMed

    Doeppner, Thorsten R; Doehring, Maria; Bretschneider, Eva; Zechariah, Anil; Kaltwasser, Britta; Müller, Barbara; Koch, Jan C; Bähr, Mathias; Hermann, Dirk M; Michel, Uwe

    2013-08-01

    MicroRNAs (miRNAs) are highly conserved non-coding RNAs modulating gene expression via mRNA binding. Recent work suggests an involvement of miRNAs in cardiovascular diseases including stroke. As such, the brain-abundant miR-124 and its transcriptional repressor RE1-silencing transcription factor (REST) do not only have elementary roles in the developing and the adult brain, but also alter expression upon cerebral ischemia. However, the therapeutic potential of miR-124 against stroke and the mechanisms involved remain elusive. Here, we analyzed the therapeutic potential of ectopic miR-124 against stroke and its underlying mechanisms with regard to the interaction between miR-124 and REST. Our results show that viral vector-mediated miR-124 delivery increased the resistance of cultured oxygen-glucose-deprived cortical neurons in vitro and reduced brain injury as well as functional impairment in mice submitted to middle cerebral artery occlusion. Likewise, miR-124 induced enhanced neurovascular remodeling leading to increased angioneurogenesis 8 weeks post-stroke. While REST abundance increased upon stroke, the increase was prevented by miR-124 despite a so far unknown negative feedback loop between miR-124 and REST. Rather, miR-124 decreased the expression of the deubiquitinating enzyme Usp14, which has two conserved miR-124-binding sites in the 3'UTR of its mRNA, and thereby mediated reduced REST levels. The down-regulation of REST by miR-124 was also mimicked by the Usp14 inhibitor IU-1, suggesting that miR-124 promotes neuronal survival under ischemic conditions via Usp14-dependent REST degradation. Ectopic miR-124 expression, therefore, appears as an attractive and novel tool in stroke treatment, mediating neuroprotection via a hitherto unknown mechanism that involves Usp14-dependent REST degradation. PMID:23754622

  5. Focal mechanism determinations of earthquakes along the North Anatolian fault, beneath the Sea of Marmara and the Aegean Sea

    NASA Astrophysics Data System (ADS)

    Nakano, Masaru; Citak, Seckin; Kalafat, Doğan

    2015-09-01

    We determined the centroid moment tensor (CMT) solutions of earthquakes that occurred along the North Anatolian fault (NAF) beneath the Sea of Marmara and the Aegean Sea, using data obtained from Turkey's broad-band seismograph network. The CMT solution of the 2014 Aegean Sea earthquake ( Mw 6.9) represents a strike-slip fault, consistent with the geometry of the NAF, and the source-time function indicates that this event comprised several distinct subevents. Each subevent is considered to have ruptured a different fault segment. This observation indicates the existence of a mechanical barrier, namely a NAF segment boundary, at the hypocenter. CMT solutions of background seismicity beneath the Aegean Sea represent strike-slip or normal faulting along the NAF or its branch faults. The tensional axes of these events are oriented northeast-southwest, indicating a transtensional tectonic regime. Beneath the Sea of Marmara, the CMT solutions represent mostly strike-slip faulting, consistent with the motion of the NAF, but we identified a normal fault event with a tensional axis parallel to the strike of the NAF. This mechanism indicates that a pull-apart basin, marking a segment boundary of the NAF, is developing there. Because ruptures of a fault system and large earthquake magnitudes are strongly controlled by the fault system geometry and fault length, mapping fault segments along NAF can help to improve the accuracy of scenarios developed for future disastrous earthquakes in the Marmara region.

  6. Application example: Preliminary Results of ISOLA use to find moment tensor solutions and centroid depth applied to aftershocks of Mw=8.8 February 27 2010, Maule Earthquake

    NASA Astrophysics Data System (ADS)

    Nacif, S. V.; Sanchez, M. A.

    2013-05-01

    We selected seven aftershocks from Maule earthquake between 33.5°S to 35°S from May to September to find single source inversion. The data were provided by XY Chile Ramp Experiment* which was deployed after great Maule earthquake. Waveform data are from 13 broad band stations chosen from the 58 broad band stations deployed by IRIS-PASCAL from April to September 2010. Stations are placed above the normal subduction section south of ~33.5°S. Events were located with an iterative software called Hypocenter using one dimensional local model, obtained above for the forearc region between 33°S to 35°S. We used ISOLA which is a fortran code with a Matlab interface to obtain moment tensors solutions, optimum position and time of the subevents. Values depth obtained by a grid search of centroid position show range values which are compatibles with the interplate seismogenic zone. Double-Couple focal mechanism solutions (Figure 1) show 4 thrust events which can be associated with that zone. However, only one of them has strike, dip and rake of 358°, 27° and 101 respectively, appropriate to be expected for interplate seismogenic zone. On the other hand, the other 3 events show strike and normal double-couple focal mechanism solutions (Figure 1). This last topic makes association to those events to the contact of the Nazca and South American plate difficult. Nevertheless, in a first stage, their depths may allow possibility of an origin there. * The facilities of the IRIS Data Management System, and specifically the IRIS Data Management Center, were used for access to waveform, metadata or products required in this study. The IRIS DMS is funded through the National Science Foundation and specifically the GEO Directorate through the Instrumentation and Facilities Program of the National Science Foundation under Cooperative Agreement EAR-0552316. Some activities of are supported by the National Science Foundation EarthScope Program under Cooperative Agreement EAR-0733069

  7. Spatial stress variations in the aftershock sequence following the 2008 M6 earthquake doublet in the South Iceland Seismic Zone

    NASA Astrophysics Data System (ADS)

    Hensch, M.; Árnadóttir, Th.; Lund, B.; Brandsdóttir, B.

    2012-04-01

    The South Iceland Seismic Zone (SISZ) is an approximately 80 km wide E-W transform zone, bridging the offset between the Eastern Volcanic Zone and the Hengill triple junction to the west. The plate motion is accommodated in the brittle crust by faulting on many N-S trending right-lateral strike-slip faults of 2-5 km separation. Major sequences of large earthquakes (M>6) has occurred repeatedly in the SISZ since the settlement in Iceland more than thousand years ago. On 29th May 2008, two M6 earthquakes hit the western part of the SISZ on two adjacent N-S faults within a few seconds. The intense aftershock sequence was recorded by the permanent Icelandic SIL network and a promptly installed temporary network of 11 portable seismometers in the source region. The network located thousands of aftershocks during the following days, illuminating a 12-17 km long region along both major fault ruptures as well as several smaller parallel faults along a diffuse E-W trending region west of the mainshock area without any preceding main rupture. This episode is suggested to be the continuation of an earthquake sequence which started with two M6.5 and several M5-6 events in June 2000. The time delay between the 2000 and 2008 events could be due to an inflation episode in Hengill during 1993-1998, that potentially locked N-S strike slip faults in the western part of the SISZ. Around 300 focal solutions for aftershocks have been derived by analyzing P-wave polarities, showing predominantly strike-slip movements with occasional normal faulting components (unstable P-axis direction), which suggests an extensional stress regime as their driving force. A subsequent stress inversion of four different aftershock clusters reveals slight variations of the directions of the average σ3 axes. While for both southern clusters, including the E-W cluster, the σ3 axes are rather elongated perpendicular to the overall plate spreading axis, they are more northerly trending for shallower clusters

  8. The SOUTHERN PUNA Seismic Experiment: Shape of the Subducting Nazca Plate, Areas of Concentrated Mantle and Crustal Earthquakes, and Crustal Focal Mechanisms

    NASA Astrophysics Data System (ADS)

    Mulcahy, P.; Chen, C.; Kay, S. M.; Brown, L. D.; Alvarado, P. M.; Sandvol, E. A.; Heit, B.; Yuan, X.

    2010-12-01

    younger dome complex northeast of Ojos del Salado. Thirteen new focal mechanisms were calculated showing mainly strike slip and thrust faulting solutions on the plateau and an east-west compressional direction consistent with the only previous existing focal mechanism in Chinn and Isacks (1988). Overall, the shallow hypocenter depths and apparent stress orientation of local crustal earthquakes indicate that the southern Puna crust is hot and currently under compression.

  9. Modeling of Kashmir Aftershock Decay Based on Static Coulomb Stress Changes and Laboratory-Derived Rate-and-State Dependent Friction Law

    NASA Astrophysics Data System (ADS)

    Javed, F.; Hainzl, S.; Aoudia, A.; Qaisar, M.

    2016-05-01

    We model the spatial and temporal evolution of October 8, 2005 Kashmir earthquake's aftershock activity using the rate-and-state dependent friction model incorporating uncertainties in computed coseismic stress perturbations. We estimated the best possible value for frictional resistance " Aσ n", background seismicity rate " r" and coefficient of stress variation "CV" using maximum log-likelihood method. For the whole Kashmir earthquake sequence, we measure a frictional resistance Aσ n ~ 0.0185 MPa, r ~ 20 M3.7+ events/year and CV = 0.94 ± 0.01. The spatial and temporal forecasted seismicity rate of modeled aftershocks fits well with the spatial and temporal distribution of observed aftershocks that occurred in the regions with positive static stress changes as well as in the apparent stress shadow region. To quantify the effect of secondary aftershock triggering, we have re-run the estimations for 100 stochastically declustered catalogs showing that the effect of aftershock-induced secondary stress changes is obviously minor compared to the overall uncertainties, and that the stress variability related to uncertain slip model inversions and receiver mechanisms remains the major factor to provide a reasonable data fit.

  10. Exploring aftershock properties with depth using Bayesian statistics

    NASA Astrophysics Data System (ADS)

    Narteau, Clement; Shebalin, Peter; Holschneider, Matthias

    2013-04-01

    Stress magnitudes and frictional faulting properties vary with depth and may strongly affect earthquake statistics. Nevertheless, if the Anderson faulting theory may be used to define the relative stress magnitudes, it remains extremely difficult to observe significant variations of earthquake properties from the top to the bottom of the seismogenic layer. Here, we concentrate on aftershock sequences in normal, strike-slip and reverse faulting regimes to isolate specific temporal properties of this major relaxation process with respect to depth. More exactly, we use Bayesian statistics of the Modified Omori Law to characterize the exponent p of the power-law aftershock decay rate and the duration c of the early stage of aftershock activity that does not fit with this power-law regime. Preliminary results show that the c-value decreases with depth without any significant variation of the p-value. Then, we infer the duration of a non power-law aftershock decay rate over short times can be related to the level of stress in the seismogenic crust.

  11. Preparation phase and consequences of a large earthquake: insights from foreshocks and aftershocks of the 2014 Mw 8.1 Iquique earthquake, Chile

    NASA Astrophysics Data System (ADS)

    Cesca, Simone; Grigoli, Francesco; Heimann, Sebastian; Dahm, Torsten

    2015-04-01

    The April 1, 2014, Mw 8.1 Iquique earthquake in Northern Chile, was preceded by an anomalous, extensive preparation phase. The precursor seismicity at the ruptured slab segment was observed sporadically several months before the main shock, with a significant increment in seismicity rates and observed magnitudes in the last three weeks before the main shock. The large dataset of regional recordings helped us to investigate the role of such precursor activity, comparing foreshock and aftershock seismicity to test models of rupture preparation and models of strain and stress rotation during an earthquake. We used full waveforms techniques to locate events, map the seismicity rate, derive source parameters, and assess spatiotemporal stress changes. Results indicate that the spatial distributions of foreshocks delineated the shallower part of the rupture areas of the main shock and its largest aftershock, and is well matching the spatial extension of the aftershocks. During the foreshock sequence, seismicity spatially is mainly localized in two clusters, separated by a region of high locking. The ruptures of mainshock and largest aftershock nucleate within these clusters and propagate to the locked region; the aftershocks are again localized in correspondence to the original spatial clusters, and the central region is locked again. More than 300 moment tensor inversions were performed, down to Mw 4.0, most of them corresponding to almost pure double couple thrust mechanisms, with a geometry consistent with the slab orientation. No significant differences are observed among thrust mechanisms in different areas, nor among thrust foreshocks and aftershocks. However, a new family of normal fault mechanisms appears after the main shock, likely affecting the shallow wedge structure in consequence of the increased extensional stress in this region. We infer a stress rotation after the main shock, as proposed for recent larger thrust earthquakes, which suggests that the April

  12. Analysis of the Petatlan aftershocks: Numbers, energy release, and asperities

    NASA Astrophysics Data System (ADS)

    ValdéS, Carlos; Meyer, Robert P.; ZuñIga, Ramón; Havskov, Jens; Singh, Shri K.

    1982-10-01

    The Petatlan earthquake of March 14, 1979 (Ms = 7.6), occurred between the Middle America trench and the Mexican coast, 15 km southwest of Petatlan, Guerrero, Mexico. From seismograms recorded on smoked paper, FM, and digital tapes, we have identified 255 aftershocks with coda lengths greater than 60 s that occurred 11 hours to 36 days after the main shock. Based on these events, the aftershock epicentral area defined during the period between 11 and 60 hours was about 2000 km2; between 11 hours and 6 days it was about 2400 km2. Although the area grew to 6060 km2 in 36 days, most of the activity was still confined within the area defined after 6 days. This suggests that the smaller aftershock area might represent an asperity. The distribution of events and energy release per unit area confirm the existence of heterogeneity in the aftershock area. Thus our data support the concept of an inhomogeneous rupture area that includes an asperity, as suggested by Chael and Stewart (1982) to account for the differences they computed for the body and surface wave moments from WWSSN data. However, the combination of the moments Reichle et al. (1982) report for body and surface waves from IDA data and the rupture areas reported in this paper results in a solution that is most physically realizable in terms of stress drop and slip. We calculate stress drops of 5 and 15 bars, the former for the average over the entire area, the latter for the asperity, and an average slip of 60 cm for the entire area and 120 cm for the asperity. These values for slip are 30% and 60%, respectively, of the convergence of the Cocos plate relative to the North America plate during the 36-year period between the last two major earthquakes in the Petatlan area. Hypocenters of the aftershocks define a zone about 25 km thick, dipping 15° with an azimuth of N20°E, which is perpendicular to the Middle America trench. Most aftershocks are below the main shock. The b value estimated for aftershocks in the

  13. The 29 September 2009 Samoa Islands Tsunami: Simulations Based on the First Focal Mechanism Solutions and Implications on Tsunami Early Warning Strategies

    NASA Astrophysics Data System (ADS)

    Tonini, Roberto; Armigliato, Alberto; Tinti, Stefano

    2011-06-01

    The tsunamigenic earthquake (Mw = 8.1) that occurred on 29 September 2009 at 17:48 UTC offshore of the Samoa archipelago east of the Tonga trench represents an example of the so-called "outer-rise" earthquakes. The areas most affected were the south coasts of Western and American Samoa, where almost 200 people were killed and run-up heights were measured in excess of 5 m at several locations along the coast. Moreover, tide gauge records showed a maximum peak-to-peak height of about 3.5 m near Pago Pago (American Samoa) and of 1.5 m offshore of Apia (Western Samoa). In this work, different fault models based on the focal mechanism solutions proposed by Global CMT and by USGS immediately after the 2009 Samoan earthquake are tested by comparing the near-field recorded signals (three offshore DART buoys and two coastal tide gauges) and the synthetic signals provided by the numerical simulations. The analysis points out that there are lights and shadows, in the sense that none of the computed tsunamis agrees satisfactorily with all the considered signals, although some of them reproduce some of the records quite well. This "partial agreement" and "partial disagreement" are analysed in the perspective of tsunami forecast and of Tsunami Early Warning System strategy.

  14. Source Fault of the Dec.26, 2003 Bam Earthquake (Mw6.5) in Southeastern Iran Inferred From Aftershock Observation Data by Temporal High-Sensitive-Seismograph Network

    NASA Astrophysics Data System (ADS)

    Suzuki, S.; Matsushima, T.; Ito, Y.; Hosseini, S. K.; Nakamura, T.; Arash, J.; Sadeghi, H.; Maleki, M.; Aghda, F.

    2004-05-01

    The Bam earthquake occurred in southeastern Iran at 05:26 A.M.(local time) on December 26, 2003 (epicenter: 29.010N, 58.266E, Mo=6.6x10**18Nm, Mw=6.5; ref.1). The earthquake had strike-slip mechanism (strike=175, dip=85, slip=153; ref.2) and source parameters (focal depth=4km, fault dimension=20kmx15km, Dmax=1.0m, stress drop=3.7MPa; ref.2). The earthquake struck the ancient city of Bam and killed more than 40,000 people. It shows that one third of about 120,000 in population in and around Bam city were killed. The main reason of such a big damage may be caused by weak adobe and brick houses; even so, the damage was too much big. We, therefore, are researching other cause of such a big damage. Taking instruments from Japan for this aim we installed 9 high sensitive seismographs and one accelerograph in and around Bam city on February 6-8, 2004. And we observed aftershocks and continue during one month. Reading P and S arriving times of about 100 aftershocks occurring from February 6 to 10, we determined those preliminary hypocenters and magnitudes. Those epicenters (errors<500m) distribute mainly from northeastern Bam city to south direction with about 20km length. It means that the fault of the main shock passed just under eastern half of Bam city where most of houses and buildings were heavily damaged. This fault is about 4 km away west from Bam fault which is presented in geological map (ref.3). A north-south vertical cross-section of the hypocentral distribution (maybe errors < 1km) shows that most of their depths are shallower than 14km and a seismic gap exists in the laterally middle part of their distribution and shallower than 6 km in depth. The shallow seismic gap may correspond to a main fracture zone as shown in the slip distribution figure proposed by Yamanaka (ref.2). This main fracture occurring shallower than about 6 km in depth must be one of causes of the big damage in Bam. (Reference) ref1:USGS,http://neic.usgs.gov/neis/FM/, ref 2: ERI, U. Tokyo

  15. Routine estimate of focal depths for moderate and small earthquakes by modelling regional depth phase sPmP in eastern Canada

    NASA Astrophysics Data System (ADS)

    Ma, S.; Peci, V.; Adams, J.; McCormack, D.

    2003-04-01

    from sP-P arrival times and/or depths of aftershocks for moderate earthquakes in western Quebec (WQU), and (2) to depths from Pg, Sg arrival times for earthquakes in Charlevoix (CHV) which lies under a dense network and has a reasonable crustal model. In all cases the differences are 2 km or less. We conclude that if sPmP and reference phase Pg or PmP are correctly recognized, and a reasonable crustal model is available, the error in focal depth is around 2 km. As the focal depth estimate is model-dependent, the better the crustal model is, the more accurate the focal depth. The focal mechanism used to calculate synthetics does not cause large errors in focal depth, as it does not severely change arrival times. To date, we have roughly analyzed the sPmP phases for about 80 earthquakes from 1995 to 2002 with mN >= 2.8 in WQU and for about 10 in CHV. Estimated focal depths range from about 5 km to over 30 km.

  16. Source mechanisms of the 2009 seismic sequence in the northwest of New Guinea Island, Indonesia

    NASA Astrophysics Data System (ADS)

    Nakano, M.; Kumagai, H.; Yamashina, T.; Inoue, H.; Sunarjo

    2009-12-01

    On January 3rd, 2009 (UTC), large earthquakes successively occurred around the Bird's Head peninsula, northwest of New Guinea Island, Indonesia. The first earthquake (Mw=7.6) occurred on 19:43 (UTC). The second event (Mw=7.4) occurred about three hours later (22:33 UTC) at about 100 km east of the first one. Tsunamis with heights of several tens cm caused by these events were observed in Japan. North of the Bird's Head peninsula, the Pacific plate is subducting below New Guinea Island along the Manokwari trough. The seismic activity along the Manokwari trough is not well known. To clarify the seismic activity along this trough is important for the disaster mitigation in New Guinea Island as well as tsunami hazards in the coastal regions along the Pacific Ocean. We investigated the source mechanisms of the earthquakes that occurred in the seismic sequence. We used data from the broadband seismograph network in Indonesia. Using the waveform inversion method of Nakano et al. (2008, GJI), we obtained the following results. The first earthquake was located 15 km below the northern shore of the Bird's Head peninsula. Its moment magnitude (Mw) and rupture duration (T) were estimated as 7.6 and 24 s, respectively. The focal mechanism showed a reverse-type fault with the compression axis oriented to NS. The second earthquake was located about 70 km east of the first one, with a depth of 10 km. Mw and T were estimated as 7.4 and 32 s, respectively. The focal mechanism was similar to that of the first event. Since the rupture durations of these events are comparable to typical durations for events of these magnitudes, these events were not tsunami earthquakes. We also applied the waveform inversion analysis to aftershocks. We obtained source parameters for about 30 earthquakes that occurred until the end of May, 2009. The aftershocks mostly aligned on a plane dipping to the south. This plane may represent the Pacific plate subducting along the Manokwari trough. The source

  17. Observational Constraints from Waveform Relocated Southern California Seismicity and Refined Focal Mechanisms for Synthesizing Heterogeneities in Fault Zone Properties and Signatures of Seismic Rupture

    NASA Astrophysics Data System (ADS)

    Hauksson, E.; Yang, W.; Shearer, P. M.

    2012-12-01

    To study relationships between fault zones and seismic ruptures, we analyze the waveform relocated (1981 to 2011) catalog of more than 500,000 earthquakes, and 170,000 refined focal mechanisms. This seismicity, with five mainshocks of M>6.5, reflects regional tectonics and other crustal deformation processes as well as the physical properties of major fault zones. The plate boundary is expressed as a system of late Quaternary faults or principal slip zones (PSZs) that accommodate major earthquakes, with numerous adjacent smaller slip surfaces. The plate-tectonic strain loading causes the largest earthquakes along the PSZs, moderate-sized events in their immediate vicinity, and small earthquakes across the region. To determine properties of individual faults, we measure the hypocentral distance to the nearest PSZ. We assign geophysical parameters such as heat flow and shear or dilatation strain rates to each hypocenter. To analyze fault ruptures, we use stress drop values for ~60,000 events as well as focal mechanisms. Geometrical complexities, variations in the state of stress, and variability in rheology result in heterogeneities in fault zone properties, which may affect the different stages of major rupture along the PSZs. We analyze our data to investigate seismogenic thickness and fault zone width as well as source processes. We find that the seismicity rate is a function of location, with the rate dying off exponentially with distance from the PSZ. The distance decay is similar to the decay per kilometer of depth in the rate of earthquakes below 5 km. About 80% of the small earthquakes are located within 5 km of a PSZ. For small earthquakes, stress drops increase in size with distance away from the PSZs. The magnitude distribution near the PSZs suggests that large earthquakes are more common close to the PSZs, and they are more likely to occur at greater depth than small earthquakes. In contrast, small quakes can occur at any geographical location. Similarly

  18. Stress adjustment revealed by seismicity and earthquake focal mechanisms in northeast China before and after the 2011 Tohoku-Oki earthquake

    NASA Astrophysics Data System (ADS)

    Yu, Hongyu; Zhao, Li; Liu, Yajing; Ning, Jieyuan; Chen, Qi-Fu; Lin, Jian

    2016-01-01

    In order to understand the influence of the March 11, 2011, MW 9.0 Tohoku-Oki earthquake on regional-scale seismicity, we study the seismicity rate and focal mechanism solutions (FMSs) of earthquakes in northeast China (NEC) before and after the megathrust event. Broadband seismic waveforms from 270 permanent and temporary stations are used to invert for the moment tensors of 69 earthquakes between 2009 and 2013 in the NEC. Our results show that there are distinct changes in seismicity rate on major NEC faults before and after the 2011 Tohoku-Oki event although the seismic moment rate of the whole region remains roughly constant. In comparison to a wide distribution of earthquakes before the Tohoku-Oki event, FMSs of crustal earthquakes in the NEC after the megathrust event can be categorized into two groups: strike-slip events with E-W compression and normal-faulting events with N-S extension. Stress field inversions before and after the Tohoku-Oki event suggest that the variations in seismicity and FMSs are due to a minor adjustment of regional stress state imposed by the megathrust event, which is further confirmed by static Coulomb stress change calculations. Mantle-depth seismicity is also influenced by the megathrust event, possibly via a down-dip transfer of compressional stress along the subducting plate, as manifested by the absence of moderate-sized mantle-depth earthquakes (~ MW 4-5) between May 2011 and April 2013 and the occurrence of deep-focus events with P axes along the dip direction of the subducting Pacific Plate in E-W vertical cross-sectional view and in WNW-ESE direction in map view.

  19. Fault structure and kinematics of the Long Valley Caldera region, California, revealed by high-accuracy earthquake hypocenters and focal mechanism stress inversions

    USGS Publications Warehouse

    Prejean, S.; Ellsworth, W.; Zoback, M.; Waldhauser, F.

    2002-01-01

    We have determined high-resolution hypocenters for 45,000+ earthquakes that occurred between 1980 and 2000 in the Long Valley caldera area using a double-difference earthquake location algorithm and routinely determined arrival times. The locations reveal numerous discrete fault planes in the southern caldera and adjacent Sierra Nevada block (SNB). Intracaldera faults include a series of east/west-striking right-lateral strike-slip faults beneath the caldera's south moat and a series of more northerly striking strike-slip/normal faults beneath the caldera's resurgent dome. Seismicity in the SNB south of the caldera is confined to a crustal block bounded on the west by an east-dipping oblique normal fault and on the east by the Hilton Creek fault. Two NE-striking left-lateral strike-slip faults are responsible for most seismicity within this block. To understand better the stresses driving seismicity, we performed stress inversions using focal mechanisms with 50 or more first motions. This analysis reveals that the least principal stress direction systematically rotates across the studied region, from NE to SW in the caldera's south moat to WNW-ESE in Round Valley, 25 km to the SE. Because WNW-ESE extension is characteristic of the western boundary of the Basin and Range province, caldera area stresses appear to be locally perturbed. This stress perturbation does not seem to result from magma chamber inflation but may be related to the significant (???20 km) left step in the locus of extension along the Sierra Nevada/Basin and Range province boundary. This implies that regional-scale tectonic processes are driving seismic deformation in the Long Valley caldera.

  20. Imaging active faulting in a region of distributed deformation from the joint clustering of focal mechanisms and hypocentres: Application to the Azores-western Mediterranean region

    NASA Astrophysics Data System (ADS)

    Custódio, Susana; Lima, Vânia; Vales, Dina; Cesca, Simone; Carrilho, Fernando

    2016-04-01

    The matching between linear trends of hypocentres and fault planes indicated by focal mechanisms (FMs) is frequently used to infer the location and geometry of active faults. This practice works well in regions of fast lithospheric deformation, where earthquake patterns are clear and major structures accommodate the bulk of deformation, but typically fails in regions of slow and distributed deformation. We present a new joint FM and hypocentre cluster algorithm that is able to detect systematically the consistency between hypocentre lineations and FMs, even in regions of distributed deformation. We apply the method to the Azores-western Mediterranean region, with particular emphasis on western Iberia. The analysis relies on a compilation of hypocentres and FMs taken from regional and global earthquake catalogues, academic theses and technical reports, complemented by new FMs for western Iberia. The joint clustering algorithm images both well-known and new seismo-tectonic features. The Azores triple junction is characterised by FMs with vertical pressure (P) axes, in good agreement with the divergent setting, and the Iberian domain is characterised by NW-SE oriented P axes, indicating a response of the lithosphere to the ongoing oblique convergence between Nubia and Eurasia. Several earthquakes remain unclustered in the western Mediterranean domain, which may indicate a response to local stresses. The major regions of consistent faulting that we identify are the mid-Atlantic ridge, the Terceira rift, the Trans-Alboran shear zone and the north coast of Algeria. In addition, other smaller earthquake clusters present a good match between epicentre lineations and FM fault planes. These clusters may signal single active faults or wide zones of distributed but consistent faulting. Mainland Portugal is dominated by strike-slip earthquakes with fault planes coincident with the predominant NNE-SSW and WNW-ESE oriented earthquake lineations. Clusters offshore SW Iberia are

  1. Spatial variation of present-day stress field and tectonic regime in Tunisia and surroundings from formal inversion of focal mechanisms: Geodynamic implications for central Mediterranean

    NASA Astrophysics Data System (ADS)

    Soumaya, A.; Ben Ayed, N.; Delvaux, D.; Ghanmi, M.; Zargouni, F.; Khayati Ammar, H.; Kadri, A.

    2015-12-01

    We compiled 123 focal mechanisms from various sources for Tunisia and adjacent regions up toSicily, to image the current stress field in the Maghrebides chain (from Tunisia to Sicily) and its foreland. Stressinversion of all the available data provides a first-order stress field with a N150°E horizontal compression(SHmax) and a transpressional tectonic regime, but the obtained stress tensor poorly fit to the data set.Weseparated them into regional subsets (boxes) in function of their geographical proximity, kinematicregime, homogeneity of kinematic orientations, and tectonic setting. Their respective inversion evidencessecond- and third-order spatial variations in tectonic regime and horizontal stress directions. The stressfield gradually changes from compression in the Maghrebides thrust belt to transpression and strike slipin the Atlassic and Pelagian foreland, respectively, where preexisting NW-SE to E-W deep faults systemare reactivated. This spatial variation of the sismotectonic stress field and tectonic regime is consistentwith the neotectonic stress field determined by others from fault slip data. The major Slab Transfer EdgePropagator faults (i.e., North-South Axis-Hammamet relay and Malte Escarpment), which laterally delimitthe subducting slabs, play an active role in second- and third-order lateral variations of the tectonicregime and stress field orientations over the Tunisian/Sicilian domain. The past and current tectonicdeformations and kinematics of the central Mediterranean are subordinately guided by the plateconvergence (i.e., Africa-Eurasia), controlled or influenced by lateral slab migration/segmentation andby deep dynamics such as lithosphere-mantle interaction.

  2. The 29th September Samoa Islands tsunami: preliminary simulations based on the first focal mechanisms hypotheses and implications of uncertainties in tsunami early warning strategies

    NASA Astrophysics Data System (ADS)

    Tonini, R.; Pagnoni, G.; Armigliato, A.; Tinti, S.

    2009-12-01

    At 6:48 AM local time (17:48 UTC time) a strong earthquake of magnitude Mw=8.0 occurred less than 200 km south of the Samoa Islands (Western Samoa and American Samoa), triggering a tsunami that was detected by several tide gauges located all around the source area. The areas most affected were the south coasts of Western and American Samoa, where almost 200 persons were killed and run-up heights were measured in excess of 5 meters on several locations along the coast and and the tide gauges reached a maximum peak-to-peak height of about 3 meters near Pago-Pago (American Samoa) and 1.5 meters in front of Apia (Western Samoa) The existence of many tide gauge records is important to support the investigation of the source mechanism. The epicenter of this earthquake is located very close to the point where the Tonga trench turns its direction from northward to westward. Here the Pacific plate moves westward beneath the Australia plate, determining a subduction zone along the north-oriented segment of the trench and a transform zone along the west-oriented segment. The epicenter location in this complex tectonic context makes identifying the fault mechanism responsible for the tsunami generation a non-trivial task. The goal of this preliminary work is testing different fault models based on the focal mechanism solution proposed by USGS, CMT and EMSC for this earthquake, through the comparison between the tide gauge records and the synthetic signals provided by the numerical simulations, and possibly suggesting new source solutions trying to reproduce as better as possible the tsunami recordings. The numerical simulations are computed by means of the UBO-TSUFD code, developed and maintained by the Tsunami Research Team of the University of Bologna, Italy. The code solves the linear and non-linear shallow water equations and can compute inundation inland. Furthermore the computational domain can be split in grids of different space resolution in order to have more

  3. Spatial correlation of aftershock locations and on-fault main shock properties

    NASA Astrophysics Data System (ADS)

    Woessner, J.; Schorlemmer, D.; Wiemer, S.; Mai, P. M.

    2006-08-01

    We quantify the correlation between spatial patterns of aftershock hypocenter locations and the distribution of coseismic slip and stress drop on a main shock fault plane using two nonstandard statistical tests. Test T1 evaluates if aftershock hypocenters are located in low-slip regions (hypothesis H1), test T2 evaluates if aftershock hypocenters occur in regions of increased shear stress (hypothesis H2). In the tests, we seek to reject the null hypotheses H0: Aftershock hypocenters are not correlated with (1) low-slip regions or (2) regions of increased shear stress, respectively. We tested the hypotheses on four strike-slip events for which multiple earthquake catalogs and multiple finite fault source models of varying accuracy exist. Because we want to retain earthquake clustering as the fundamental feature of aftershock seismicity, we generate slip distributions using a random spatial field model and derive the stress drop distributions instead of generating seismicity catalogs. We account for uncertainties in the aftershock locations by simulating them within their location error bounds. Our findings imply that aftershocks are preferentially located in regions of low-slip (u ≤ ?umax) and of increased shear stress (Δσ < 0). In particular, the correlation is more significant for relocated than for general network aftershock catalogs. However, the results show that stress drop patterns provide less information content on aftershock locations. This implies that static shear stress change of the main shock may not be the governing process for aftershock genesis.

  4. Disease aftershocks - The health effects of natural disasters

    USGS Publications Warehouse

    Guptill, S.C.

    2001-01-01

    While the initial activity of a natural disaster event may directly injure or kill a number of people, it is possible that a significant number of individuals will be affected by disease outbreaks that occur after the first effects of the disaster have passed. Coupling the epidemiologist's knowledge of disease outbreaks with geographic information systems and remote sensing technology could help natural disaster relief workers to prevent additional victims from disease aftershocks.

  5. Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines

    NASA Astrophysics Data System (ADS)

    Gibbons, Steven J.; Kværna, Tormod; Harris, David B.; Dodge, Douglas A.

    2016-04-01

    Aftershock sequences following very large earthquakes present enormous challenges to near-realtime generation of seismic bulletins. The increase in analyst resources needed to relocate an inflated number of events is compounded by failures of phase association algorithms and a significant deterioration in the quality of underlying fully automatic event bulletins. Current processing pipelines were designed a generation ago and, due to computational limitations of the time, are usually limited to single passes over the raw data. With current processing capability, multiple passes over the data are feasible. Processing the raw data at each station currently generates parametric data streams which are then scanned by a phase association algorithm to form event hypotheses. We consider the scenario where a large earthquake has occurred and propose to define a region of likely aftershock activity in which events are detected and accurately located using a separate specially targeted semi-automatic process. This effort may focus on so-called pattern detectors, but here we demonstrate a more general grid search algorithm which may cover wider source regions without requiring waveform similarity. Given many well-located aftershocks within our source region, we may remove all associated phases from the original detection lists prior to a new iteration of the phase association algorithm. We provide a proof-of-concept example for the 2015 Gorkha sequence, Nepal, recorded on seismic arrays of the International Monitoring System. Even with very conservative conditions for defining event hypotheses within the aftershock source region, we can automatically remove over half of the original detections which could have been generated by Nepal earthquakes and reduce the likelihood of false associations and spurious event hypotheses. Further reductions in the number of detections in the parametric data streams are likely using correlation and subspace detectors and/or empirical matched

  6. High-Resolution Low Power, Intergrated Aftershock and Microzonation System

    NASA Astrophysics Data System (ADS)

    Zimakov, L.; Passmore, P.

    2012-04-01

    Refraction Technology, Inc. has developed a self-contained, fully integrated Aftershock System, model 160-03, providing the customer simple and quick deployment during aftershock emergency mobilization and microzonation studies. The 160-03 has no external cables or peripheral equipment for command/control and operation in the field. The 160-03 contains three major components integrated in one case: a) 24-bit resolution state-of-the art low power ADC with CPU and Lid interconnect boards; b) power source; and c) three component 2 Hz sensors (two horizontals and one vertical), and built-in ±4g accelerometer. Optionally, the 1 Hz sensors can be built-in the 160-03 system at the customer's request. The self-contained rechargeable battery pack provides power autonomy up to 7 days during data acquisition at 200 sps on continuous three weak motion and triggered three strong motion recording channels. For longer power autonomy, the 160-03 Aftershock System battery pack can be charged from an external source (solar power system). The data in the field is recorded to a built-in swappable USB flash drive. The 160-03 configuration is fixed based on a configuration file stored on the system. The detailed specifications and performance are presented and discussed

  7. The 20th April 2005 Koryakia earthquake (Russia): a case of study for its aftershock seismic sequence

    NASA Astrophysics Data System (ADS)

    Caccamo, D.; Barbieri, L. M.; Lagana, C.; Francesco, P.; D'Amico, S.

    2009-12-01

    Even if the Koryakia earthquake (April 20, 2005 at 23:25:02-UTC) occurred in sparsely populated northeastern Russia about 40 people were injured and the several villages were destroyed. Some buildings and water supply systems were badly damaged as well. The Koryakia earthquake occurred in north-northeast of the Kamchatka Peninsula. The earthquake was in a complicated geological setting where the configuration and interaction of the tectonic plates between northeastern Asia and northwestern North America are still poorly understood. The aim of this paper is to study the Koryakia seismic sequence trough the application of the Delta/Sigma method (PEPI - Caccamo et al. 2005) and using data coming from the USGS data-bank. Using this method is possible to observe statistically significant anomalies in the temporal decay of seismic sequence before the occurrence of a large aftershock. The Delta/Sigma analysis show some anomalies in the temporal decay a few days before the occurrence of large aftershock. They possibly are not random fluctuations but probably could be considered as precursors. Fractal geometry is sometimes important to better explain the mechanisms of seismicity and so it could be useful to analyze the behavior of aftershocks occurrence. In this paper a fractal analysis od the seismic sequence was performed investigating the box-counting dimension (D0) and the correlation dimension (D2).

  8. Preliminary Double-Difference Relocations of Bhuj Aftershocks

    NASA Astrophysics Data System (ADS)

    Raphael, A. J.; Bodin, P.; Horton, S.; Gomberg, J.

    2001-12-01

    The Mw=7.7 Bhuj earthquake of 26 January, 2001 in Gujarat, India, was a scientifically important earthquake that took place in a rather poorly instrumented region. Lack of nearby mainshock recordings and lack of surface rupture preclude the calculation of a high-resolution picture of the mainshock rupture processes like those presented for other recent large, better instrumented earthquakes. This is particularly vexing because, given its history of infrequent moderate-to-large earthquakes and its setting within a continental plate interior, the Bhuj earthquake might provide important insights for other high-consequence-but-low-occurrence-rate regions such as the central US. Fortunately we do have excellent recordings of numerous aftershocks on a temporary network of 8 portable seismographs. In order to constrain rupture complexity, we are computing high-resolution relative relocations of aftershocks using HypoDD, the double-difference algorithm of Waldhauser and Ellsworth \\(BSSA, 2000\\) to look for aftershock patterns that may reflect rupture characteristics. We are currently using a subset of all of the aftershocks that have been analyzed \\(P and S phases recorded on at least 4 stations\\) which consists of nearly 1000 events. This subset is less than half of all the data, and more events are being added as they are analyzed. Our preliminary results show concentrated patches of relocated aftershocks that dip to the south between 6 and 37 km deep. Strong clusters appear to illuminate the lateral edges of a rupture, with a NE trending cluster at the eastern side and a NW trending cluster at the western side, both plunging southward. The central part of the apparent rupture, which coincides with teleseismic estimates of maximum slip, appears to be relatively quiescent. We have not up to this point used waveform cross-correlation to provide relative arrival timing, but feel this may be appropriate for subsets of the overall data set. We also note the presence of

  9. Comprehensive analysis of the deviatoric stress field from focal mechanisms and slip-line field from conjugate linear seismicity clusters in southern California

    NASA Astrophysics Data System (ADS)

    Yang, W.; Hauksson, E.

    2011-12-01

    We analyze the spatial and temporal variations of the deviatoric stress field and the geometric properties of conjugate linear seismicity clusters in the southern California region using earthquake data recorded by the SCSN from 1981 to 2011. Using a data set with approximate 179,000 high quality focal mechanisms that were determined from P first motions and S/P amplitude ratios, we invert for the variation in the stress field in time and space using several methods. The inversion results match with results from prior studies with a predominant north-south to northnortheast orientation of maximum horizontal stress, but our results reveal the stress field at a higher level of resolution because we use a larger data set than was available before. The results show that the stress field exhibits minimal regional temporal variations, but some variations exist in small areas close to large mainshocks. Similarly, localized depth variations in the stress field suggest the possible existence of vertical strain partitioning. We determine a data set with approximate 8,000 seismicity clusters using waveform cross-correlation and a clustering method. We calculate the geometrical properties of the clusters, such as orientation, area, and concentration. Pairs of conjugate linear clusters exist across southern California. The angles between conjugate linear clusters in the direction of maximum shortening range from 80 [deg] to 160 [deg], with a median value of 120 [deg] and a mode value of 115 [deg]. The bisection of conjugate linear clusters in the direction of maximum shortening generally matches with the maximum horizontal stress orientation, which implies a relation between orientation of the stress field and the orientation of clusters. For clusters located close to the San Andreas Fault (SAF), the strike of one of the conjugate cluster in a pair is often parallel to the local strike of the SAF, and the conjugate angle is relatively large. Also, the conjugate angles are large

  10. Study of the Potential Earthquake Risk in the Western United States by the LURR Method Based on the Seismic Catalogue, Fault Geometry and Focal Mechanisms

    NASA Astrophysics Data System (ADS)

    Zhang, Yongxian; Yikilmaz, M. Burak; Rundle, John B.; Yin, Xiangchu; Liu, Yue; Zhang, Langping; Wang, Zijin

    2015-08-01

    Based on the load/unload response ratio (LURR) theory, spatial and temporal variation of Y/ Y c (value of LURR/critical value of LURR under 90 % confidence) in the western United States and its adjacent area (31°-44°N, -128° to -112°E) during the period from 1980 to 2011 was studied. The selected study area was zoned into 20 sub-regions, in each of which the fault geometry and the focal mechanisms were very similar such that the stress fields were almost uniform. The loading and unloading periods were determined by calculating perturbations in the Coulomb failure stress in each sub-regions induced by earth tides. Earthquakes occurring in these sub-regions were identified as a loading or unloading type, and the response rate was chosen as the Benioff strain that can be calculated from earthquake magnitude M. With a time window of 1 year, a time moving step of 1 month, a space window of a circle region with a radius of 100 km, and a space moving step of 0.5° latitudinally and longitudinally, snapshots of the evolution of Y/ Y c were generated. Scanning results show that obvious Y/ Y c anomalies can be detected near the epicenter of all big earthquakes larger than M6.5 in regions with reasonable seismic monitoring abilities. They also show Y/ Y c anomalies occurred several years prior to the big earthquakes and the lasting time of the anomaly is from one year to several years. For some LURR anomalous regions, however, no earthquakes occurred. According to the characteristics of LURR anomalies, two regions with a high risk of big earthquakes were detected. One is between the northern region of the Bay Area and the Mendocino triple junction (38°-40°N, -124° to -122°E) and the other is between Lake Tahoe and Mono Lake (37.5°-39.5°N, -120° to -118°E) along the border of California and Nevada.

  11. SCARDEC: a new technique for the rapid determination of seismic moment magnitude, focal mechanism and source time functions for large earthquakes using body-wave deconvolution

    NASA Astrophysics Data System (ADS)

    Vallée, M.; Charléty, J.; Ferreira, A. M. G.; Delouis, B.; Vergoz, J.

    2011-01-01

    the source parameters retrieved using the SCARDEC method explain the observed surface waves as well as the Global CMT parameters, thus confirming the existing trade-off. For some well-instrumented earthquakes, our results are also supported by independent studies based on local geodetic or strong motion data. This study is mainly focused on moment determination. However, the SCARDEC method also informs us about the focal mechanism and source depth, and can be a starting point to study systematically the complexity of the STF.

  12. Leading aftershocks and cascades: two possible stress release processes after a main shock

    NASA Astrophysics Data System (ADS)

    Monterrubio, Marisol; Martinez, Maria-Dolors; Lana, Xavier

    2010-05-01

    Three series of aftershocks in Southern California, associated with the main shocks of Landers (1992), Northridge (1994) and Hector Mine (1999), are interpreted as the superposition of a lasting relaxation stress process and numerous short episodes of sudden stress release. The set of aftershocks belonging to the lasting process are designed as leading aftershocks and its rate decays with time, fitting well to the classical Omori's law. The remaining aftershocks are assigned to the different episodes characterised by sudden release of stresses, each of them being designed as a cascade. Cascades are characterised by four basic properties. First, the number of aftershocks belonging to a cascade is submitted to remarkable time fluctuations. Nevertheless, it is observed a positive trend in the number of aftershocks with respect to the elapsed time measured since the origin time of the main event. Second, the rate for aftershocks belonging to a cascade can be assumed constant. Third, a power law quantifies the rate for every cascade, with the elapsed time since the main event to the beginning of the cascade being the argument of this power law. Fourth, the validity of the Gutemberg-Richter law is preserved both for the set of leading aftershocks as for the set of tremors associated to cascades. Given that the number of available aftershocks for the three seismic crisis is very high (exceeding 10,000 tremors), a detailed analysis of cascades is available.

  13. Non extensive statistical physics properties of the 2003 (Mw6.2), Lefkada, Ionian island Greece, aftershock sequence

    NASA Astrophysics Data System (ADS)

    Vallianatos, F.; Karakostas, V.; Papadimitriou, E.

    2012-04-01

    On 14 August 2003, Lefkada Island (Central Ionian) was affected by an Mw=6.2 earthquake. Due to a dense temporary seismic network that operating immediately after the main shock occurrence, hundreds of aftershocks were recorded and located with high precision whereas relocation of the main shock and early strong aftershocks became also feasible. Thus, the spatio-temporal distribution of aftershocks onto the main and the neighboring fault segments was investigated in detail enabling the recognition of four distinctive seismicity clusters separated by less active patches. The aftershock spatiotemporal properties studied here using the concept of Non-Extensive Statistical Physics (NESP). The cumulative distribution functions of the inter-event times and the inter-event distances are estimated for the data set in each seismicity cluster and the analysis results to a value of the statistical thermodynamic qT and qD parameters for each cluster, where qT varies from 1.15 to 1.47 and qD from 0.5 to 0.77 for the interevent times and distances distributions respectively. These values confirm the complexity and non-additivity of the spatiotemporal evolution of seismicity and the usefulness of NESP in investigating such phenomena. The temporal structure is also discussed using the complementary to NESP approach of superstatistics, which is based on a superposition of ordinary local equilibrium statistical mechanics. The result indicates that the temporal evolution of the Lefkada aftershock sequence in clusters A, B and C governed by very low number of degrees of freedom while D is less organized seismicity structure with a much higher number of degrees of freedom. Acknowledgments. This work was supported in part by the THALES Program of the Ministry of Education of Greece and the European Union in the framework of the project entitled "Integrated understanding of Seismicity, using innovative Methodologies of Fracture mechanics along with Earthquake and non extensive

  14. Focal neurological deficits

    MedlinePlus

    A focal neurologic deficit is a problem with nerve, spinal cord, or brain function. It affects a specific ... of the back, neck, or head Electromyogram (EMG)/ nerve conduction velocities (NCV) MRI of the back, neck, or head Spinal tap

  15. Partial (focal) seizure

    MedlinePlus

    ... Jacksonian seizure; Seizure - partial (focal); Temporal lobe seizure; Epilepsy - partial seizures ... Abou-Khalil BW, Gallagher MJ, Macdonald RL. Epilepsies. In: Daroff RB, ... 6th ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 67. ...

  16. Partial (focal) seizure

    MedlinePlus

    ... Jacksonian seizure; Seizure - partial (focal); Temporal lobe seizure; Epilepsy - partial seizures ... Abou-Khalil BW, Gallagher MJ, Macdonald RL. Epilepsies. In: Daroff ... Practice . 7th ed. Philadelphia, PA: Elsevier; 2016:chap 101. ...

  17. A Non-Extensive Statistical Physics View in the Spatiotemporal Properties of the 2003 (Mw6.2) Lefkada, Ionian Island Greece, Aftershock Sequence

    NASA Astrophysics Data System (ADS)

    Vallianatos, F.; Karakostas, V.; Papadimitriou, E.

    2014-07-01

    Investigation of the spatiotemporal properties of the 2003 Lefkada seismic sequence is performed through non-extensive statistical physics. Information on highly accurate aftershock source parameters became feasible from the recordings of a portable digital seismological network that was installed and operated in the study area, during the evolution of the seismic sequence. Thus, the spatiotemporal distribution of aftershocks onto the main and neighboring fault segments was investigated in detail, enabling the recognition of four distinctive seismicity clusters separated by less active patches. The aftershock spatiotemporal properties are studied here, using the ideas of non-extensive statistical physics (NESP). The cumulative distribution functions of the inter-event times and the inter-event distances are presented using the data set in each seismicity cluster, and the analysis results in values for the statistical thermodynamic q T and q D parameters for each cluster, where q T varies from 1.16 to 1.47 and q D from 0.42 to 0.77 for the inter-event times and distances distributions, respectively. These values confirm the complexity and non-additivity of the spatiotemporal evolution of seismicity, and the applicability of the NESP approach in investigating aftershocks sequence. The temporal pattern is discussed using the closely connected to NESP approach of superstatistics, which is based on a superposition of ordinary local equilibrium statistical mechanics. The result indicates that the temporal evolution of the Lefkada aftershock sequence in clusters A, B and C is governed by very low number of degrees of freedom, while D is a less organized seismicity structure with a much higher number of degrees of freedom.

  18. Anomalous stress diffusion, Omori's law and Continuous Time Random Walk in the 2010 Efpalion aftershock sequence (Corinth rift, Greece)

    NASA Astrophysics Data System (ADS)

    Michas, Georgios; Vallianatos, Filippos; Karakostas, Vassilios; Papadimitriou, Eleftheria; Sammonds, Peter

    2014-05-01

    result that is in accordance to earthquake triggering in global scale (Huc and Main, 2003) and aftershocks diffusion in California (Helmstetter et al., 2003). While other mechanisms may be plausible, the results indicate that anomalous stress transfer due to the occurrence of the two major events control the migration of the aftershock activity, activating different fault segments and having strong implications for the seismic hazard of the area. Acknowledgments. G. Michas wishes to acknowledge the partial financial support from the Greek State Scholarships Foundation (IKY). This work has been accomplished in the framework of the postgraduate program and co-funded through the action "Program for scholarships provision I.K.Y. through the procedure of personal evaluation for the 2011-2012 academic year" from resources of the educational program "Education and Life Learning" of the European Social Register and NSRF 2007- 2013. References Ganas, A., Chousianitis, K., Batsi, E., Kolligri, M., Agalos, A., Chouliaras, G., Makropoulos, K. (2013). The January 2010 Efpalion earthquakes (Gulf of Corinth, central Greece): Earthquake interactions and blind normal faulting. J. of Seism., 17(2), 465-484. Helmstetter, A., Ouillon, G., Sornette, D. (2003). Are aftershocks of large California earthquakes diffusing? J. of Geophys. Res. B, 108(10), 2483. Huc, M., Main, I. G. (2003). Anomalous stress diffusion in earthquake triggering: Correlation length, time dependence, and directionality. J. of Geophys. Res. B, 108(7), 2324. Karakostas, V., Karagianni, E., Paradisopoulou, P. (2012). Space-time analysis, faulting and triggering of the 2010 earthquake doublet in western Corinth gulf. Nat.Haz., 63(2), 1181-1202. Metzler, R., Klafter, J. (2000). The random walk's guide to anomalous diffusion: a fractional dynamics approach. Physics Reports, 339, 1-77. Michas, G., Vallianatos, F., Sammonds, P. (2013). Non-extensivity and long-range correlations in the earthquake activity at the West Corinth

  19. Largest Aftershocks of Megathrust Earthquakes in the World

    NASA Astrophysics Data System (ADS)

    Koyama, J.; Tsuzuki, M.

    2012-12-01

    The 2011 Tohoku-oki megathrust earthquake of Mw9.0 induced the earthquake activity in high level all over Japan. It included not only earthquakes near active faults but also volcanic earthquakes. Although we have observed tens of thousands of aftershocks, yet we do not know which is the largest aftershock of the 2011 megathrust. There occurred several megathrust earthquakes worldwide in the last one hundred years, which are almost the same size or larger than the 2011 megathrust. We have studied their largest aftershocks based on our new hypothesis of along-dip double segmentation (ADDS) and along-strike single segmentation (ASSS). ADDS in the Tohoku-oki region along the Japan trench is characterized by the apparent absence of earthquakes in the trench-ward segments as opposed to the Japan Island-ward segments that have repeated small earthquakes of up to Mw8 class. In contrast, the 1960 Chile and the 2010 Maule megathrusts are characterized by ASSS with the weak seismic activity before the main event everywhere in the subduction zone. The difference between these two types of seismic segmentations would be that strongly coupled areas of trench-ward segments give rise to ADDS, whereas almost 100% coupled areas of shallow-parts of subduction zones give rise to ASSS. In other words, the phenomenon of a seismic gap can be identified for an ASSS megathrust, where as a doughnut pattern of seismic activity appears prior to a main ADDS event. In summary, most of the largest aftershocks of ADDS megathrusts are earthquakes of outer-rise(outer trench-slope) normal faultings, where there occur two types, dip-slip and strike-slip, depending on the structure of subducting oceanic plates. The 1933 Sanriku-oki Mw8.6 (the 1896 Meiji-Sanriku M~8.5) and the 2011 Tohoku-oki Mw7.7 (the 2011 Tohoku-oki Mw9.0) are the former and the 1987 Off Alaska Mw7.8 (the 1964 Alaska Mw9.2) and the 2012 Sumatra Mw8.6 (the 2004 Sumatra-Andaman Mw9.3) are the latter. Those of ASSS megathrusts occurred

  20. SNAP focal plane

    SciTech Connect

    Lampton, Michael L.; Kim, A.; Akerlof, C.W.; Aldering, G.; Amanullah, R.; Astier, P.; Barrelet, E.; Bebek, C.; Bergstrom, L.; Berkovitz, J.; Bernstein, G.; Bester, M.; Bonissent, A.; Bower, C.; Carithers Jr., W.C.; Commins, E.D.; Day, C.; Deustua, S.E.; DiGennaro,R.; Ealet, A.; Ellis, R.S.; Eriksson, M.; Fruchter, A.; Genat, J.-F.; Goldhaber, G.; Goobar, A.; Groom, D.; Harris, S.E.; Harvey, P.R.; Heetderks, H.D.; Holland, S.E.; Huterer, D.; Karcher, A.; Kolbe, W.; Krieger, B.; Lafever, R.; Lamoureux, J.; Levi, M.E.; Levin, D.S.; Linder,E.V.; Loken, S.C.; Malina, R.; Massey, R.; McKay, T.; McKee, S.P.; Miquel, R.; Mortsell, E.; Mostek, N.; Mufson, S.; Musser, J.; Nugent, P.; Oluseyi, H.; Pain, R.; Palaio, N.; Pankow, D.; Perlmutter, S.; Pratt, R.; Prieto, E.; Refregier, A.; Rhodes, J.; Robinson, K.; Roe, N.; Sholl, M.; Schubnell, M.; Smadja, G.; Smoot, G.; Spadafora, A.; Tarle, G.; Tomasch,A.; von der Lippe, H.; Vincent, R.; Walder, J.-P.; Wang, G.

    2002-07-29

    The proposed SuperNova/Acceleration Probe (SNAP) mission will have a two-meter class telescope delivering diffraction-limited images to an instrumented 0.7 square-degree field sensitive in the visible and near-infrared wavelength regime. We describe the requirements for the instrument suite and the evolution of the focal plane design to the present concept in which all the instrumentation--visible and near-infrared imagers, spectrograph, and star guiders--share one common focal plane.

  1. What Controls the Duration of Aftershocks, and Why It Matters for Probabilistic Seismic Hazard Assessment

    NASA Astrophysics Data System (ADS)

    Stein, R. S.; Toda, S.

    2014-12-01

    A fundamental problem confronting hazard modelers in slowly deforming regions such as the central and eastern United States, Australia, and inner Honshu, is whether the current seismicity represents the steady state earthquake potential, or is instead a decaying potential associated with past mainshocks. If the current seismicity were composed of long-lived aftershock sequences, it might then be anti-correlated with the next large earthquakes. While aftershock productivity is known to be a property of the mainshock magnitude, aftershock duration (the time until the aftershock rate decays to the pre-mainshock rate) should, according to rate/state friction theory of Dieterich[1994], be inversely proportional to the fault stressing rate. If so, slowly deforming regions would be expected to sustain long aftershock sequences. Most tests have supported the Dieterich hypothesis, but use ambiguous proxies for the fault stressing rate, such as the mainshock recurrence interval. Here we test the hypothesis by examining off-fault aftershocks of the 2011 M=9 Tohoku-oki rupture up to 250 km from the source, as well as near-fault aftershocks of six large Japanese mainshocks, sampling a range of receiver faults, from thrusts slipping 80 mm/yr, to normal faults slipping 0.1 mm/yr. We find that aftershock sequences lasted a month on the fastest-slipping faults, have durations of 10-100 years on faults slipping 1-10 mm/yr, and are projected to persist for at least 200 years on the slowest faults. Although the Omori decay exponent for short and long sequences is similar, the very different background rates account for the duration differences. If the stressing rate is generally proportional to fault slip rate, then aftershock durations indeed support the Dieterich hypothesis. The test means that the hazard associated with aftershocks depends on local tectonic conditions rather than on the mainshock magnitude alone. Because declustering approaches do not remove such long

  2. Recent Experiences in Aftershock Hazard Modelling in New Zealand

    NASA Astrophysics Data System (ADS)

    Gerstenberger, M.; Rhoades, D. A.; McVerry, G.; Christophersen, A.; Bannister, S. C.; Fry, B.; Potter, S.

    2014-12-01

    The occurrence of several sequences of earthquakes in New Zealand in the last few years has meant that GNS Science has gained significant recent experience in aftershock hazard and forecasting. First was the Canterbury sequence of events which began in 2010 and included the destructive Christchurch earthquake of February, 2011. This sequence is occurring in what was a moderate-to-low hazard region of the National Seismic Hazard Model (NSHM): the model on which the building design standards are based. With the expectation that the sequence would produce a 50-year hazard estimate in exceedance of the existing building standard, we developed a time-dependent model that combined short-term (STEP & ETAS) and longer-term (EEPAS) clustering with time-independent models. This forecast was combined with the NSHM to produce a forecast of the hazard for the next 50 years. This has been used to revise building design standards for the region and has contributed to planning of the rebuilding of Christchurch in multiple aspects. An important contribution to this model comes from the inclusion of EEPAS, which allows for clustering on the scale of decades. EEPAS is based on three empirical regressions that relate the magnitudes, times of occurrence, and locations of major earthquakes to regional precursory scale increases in the magnitude and rate of occurrence of minor earthquakes. A second important contribution comes from the long-term rate to which seismicity is expected to return in 50-years. With little seismicity in the region in historical times, a controlling factor in the rate is whether-or-not it is based on a declustered catalog. This epistemic uncertainty in the model was allowed for by using forecasts from both declustered and non-declustered catalogs. With two additional moderate sequences in the capital region of New Zealand in the last year, we have continued to refine our forecasting techniques, including the use of potential scenarios based on the aftershock

  3. Statistical estimation of the duration of aftershock sequences

    NASA Astrophysics Data System (ADS)

    Hainzl, S.; Christophersen, A.; Rhoades, D.; Harte, D.

    2016-05-01

    It is well known that large earthquakes generally trigger aftershock sequences. However, the duration of those sequences is unclear due to the gradual power-law decay with time. The triggering time is assumed to be infinite in the epidemic type aftershock sequence (ETAS) model, a widely used statistical model to describe clustering phenomena in observed earthquake catalogues. This assumption leads to the constraint that the power-law exponent p of the Omori-Utsu decay has to be larger than one to avoid supercritical conditions with accelerating seismic activity on long timescales. In contrast, seismicity models based on rate- and state-dependent friction observed in laboratory experiments predict p ≤ 1 and a finite triggering time scaling inversely to the tectonic stressing rate. To investigate this conflict, we analyse an ETAS model with finite triggering times, which allow smaller values of p. We use synthetic earthquake sequences to show that the assumption of infinite triggering times can lead to a significant bias in the maximum likelihood estimates of the ETAS parameters. Furthermore, it is shown that the triggering time can be reasonably estimated using real earthquake catalogue data, although the uncertainties are large. The analysis of real earthquake catalogues indicates mainly finite triggering times in the order of 100 days to 10 years with a weak negative correlation to the background rate, in agreement with expectations of the rate- and state-friction model. The triggering time is not the same as the apparent duration, which is the time period in which aftershocks dominate the seismicity. The apparent duration is shown to be strongly dependent on the mainshock magnitude and the level of background activity. It can be much shorter than the triggering time. Finally, we perform forward simulations to estimate the effective forecasting period, which is the time period following a mainshock, in which ETAS simulations can improve rate estimates after the

  4. A kinetic model for RNA-interference of focal adhesions

    PubMed Central

    2013-01-01

    Background Focal adhesions are integrin-based cell-matrix contacts that transduce and integrate mechanical and biochemical cues from the environment. They develop from smaller and more numerous focal complexes under the influence of mechanical force and are key elements for many physiological and disease-related processes, including wound healing and metastasis. More than 150 different proteins localize to focal adhesions and have been systematically classified in the adhesome project (http://www.adhesome.org). First RNAi-screens have been performed for focal adhesions and the effect of knockdown of many of these components on the number, size, shape and location of focal adhesions has been reported. Results We have developed a kinetic model for RNA interference of focal adhesions which represents some of its main elements: a spatially layered structure, signaling through the small GTPases Rac and Rho, and maturation from focal complexes to focal adhesions under force. The response to force is described by two complementary scenarios corresponding to slip and catch bond behavior, respectively. Using estimated and literature values for the model parameters, three time scales of the dynamics of RNAi-influenced focal adhesions are identified: a sub-minute time scale for the assembly of focal complexes, a sub-hour time scale for the maturation to focal adhesions, and a time scale of days that controls the siRNA-mediated knockdown. Our model shows bistability between states dominated by focal complexes and focal adhesions, respectively. Catch bonding strongly extends the range of stability of the state dominated by focal adhesions. A sensitivity analysis predicts that knockdown of focal adhesion components is more efficient for focal adhesions with slip bonds or if the system is in a state dominated by focal complexes. Knockdown of Rho leads to an increase of focal complexes. Conclusions The suggested model provides a kinetic description of the effect of RNA

  5. Fast characterization of moment magnitude and focal mechanism in the context of tsunami warning in the NEAM region : W-phase and PDFM2 algorithms.

    NASA Astrophysics Data System (ADS)

    Schindelé, François; Roch, Julien; Duperray, Pierre; Reymond, Dominique

    2016-04-01

    Over past centuries, several large earthquakes (Mw ≥ 7.5) have been reported in the North East Atlantic and Mediterranenan sea (NEAM) region. Most of the tsunami potential seismic sources in the NEAM region, however, are in a magnitude range of 6.5 ≤ Mw ≤ 7.5 (e.g. tsunami triggered by the earthquake of Boumerdes in 2003 of Mw = 6.9). The CENALT (CENtre d'ALerte aux Tsunamis) in operation since 2012 as the French National Tsunami Warning Centre (NTWC) and Candidate Tsunami Service Provider (CTSP) has to issue warning messages within 15 minutes of the earthquake origin time. The warning level is currently based on a decision matrix depending on the magnitude, and the location of the hypocenter. Two seismic source inversion methods are implemented at CENALT: the W-phase algorithm, based on the so-called W-phase and PDFM2 algorithm , based on the surface waves and first P wave motions. They both give accurate moment magnitude and focal magnitude respectively in 10 min and 20 min. The results of the Mw magnitude, focal depth and type of fault (reverse, normal, strike-slip) are the most relevant parameters used to issue tsunami warnings. In this context, we assess the W-phase and PDFM2 methods with 29 events of magnitude Mw ≥ 5.8 for the period 2010-2015 in the NEAM region. Results with 10 and 20 min for the W-phase algorithm and with 20 and 30 min for the PDFM2 algorithm are compared to the Global Centroid Moment Tensor catalog. The W-phase and PDFM2 methods gives accurate results respectively in 10 min and 20 min. This work is funded by project ASTARTE -- Assessment, Strategy And Risk Reduction for Tsunamis in Europe - FP7-ENV2013 6.4-3, Grant 603839

  6. The Use of Explosion Aftershock Probabilities for Planning and Deployment of Seismic Aftershock Monitoring System for an On-site Inspection

    NASA Astrophysics Data System (ADS)

    Labak, P.; Ford, S. R.; Sweeney, J. J.; Smith, A. T.; Spivak, A.

    2011-12-01

    One of four elements of CTBT verification regime is On-site inspection (OSI). Since the sole purpose of an OSI shall be to clarify whether a nuclear weapon test explosion or any other nuclear explosion has been carried out, inspection activities can be conducted and techniques used in order to collect facts to support findings provided in inspection reports. Passive seismological monitoring, realized by the seismic aftershock monitoring (SAMS) is one of the treaty allowed techniques during an OSI. Effective planning and deployment of SAMS during the early stages of an OSI is required due to the nature of possible events recorded and due to the treaty related constrains on size of inspection area, size of inspection team and length of an inspection. A method, which may help in planning the SAMS deployment is presented. An estimate of aftershock activity due to a theoretical underground nuclear explosion is produced using a simple aftershock rate model (Ford and Walter, 2010). The model is developed with data from the Nevada Test Site and Semipalatinsk Test Site, which we take to represent soft- and hard-rock testing environments, respectively. Estimates of expected magnitude and number of aftershocks are calculated using the models for different testing and inspection scenarios. These estimates can help to plan the SAMS deployment for an OSI by giving a probabilistic assessment of potential aftershocks in the Inspection Area (IA). The aftershock assessment combined with an estimate of the background seismicity in the IA and an empirically-derived map of threshold magnitude for the SAMS network could aid the OSI team in reporting. We tested the hard-rock model to a scenario similar to the 2008 Integrated Field Exercise 2008 deployment in Kazakhstan and produce an estimate of possible recorded aftershock activity.

  7. Aftershock Statistics of the 1999 Chi-Chi, Taiwan Earthquake and the Concept of Omori Times

    NASA Astrophysics Data System (ADS)

    Lee, Ya-Ting; Turcotte, Donald L.; Rundle, John B.; Chen, Chien-Chih

    2013-01-01

    In this paper we consider the statistics of the aftershock sequence of the m = 7.65 20 September 1999 Chi-Chi, Taiwan earthquake. We first consider the frequency-magnitude statistics. We find good agreement with Gutenberg-Richter scaling but find that the aftershock level is anomalously high. This level is quantified using the difference in magnitude between the main shock and the largest inferred aftershock {{Updelta}}m^{ *}. Typically, {{Updelta}}m^{ *} is in the range 0.8-1.5, but for the Chi-Chi earthquake the value is {{Updelta}}m^{ *} = 0.03. We suggest that this may be due to an aseismic slow-earthquake component of rupture. We next consider the decay rate of aftershock activity following the earthquake. The rates are well approximated by the modified Omori's law. We show that the distribution of interoccurrence times between aftershocks follow a nonhomogeneous Poisson process. We introduce the concept of Omori times to study the merging of the aftershock activity with the background seismicity. The Omori time is defined to be the mean interoccurrence time over a fixed number of aftershocks.

  8. Aftershocks illuninate the 2011 Mineral, Virginia, earthquake causative fault zone and nearby active faults

    USGS Publications Warehouse

    Horton, Jr., J. Wright; Shah, Anjana K.; McNamara, Daniel E.; Snyder, Stephen L.; Carter, Aina M

    2015-01-01

    Deployment of temporary seismic stations after the 2011 Mineral, Virginia (USA), earthquake produced a well-recorded aftershock sequence. The majority of aftershocks are in a tabular cluster that delineates the previously unknown Quail fault zone. Quail fault zone aftershocks range from ~3 to 8 km in depth and are in a 1-km-thick zone striking ~036° and dipping ~50°SE, consistent with a 028°, 50°SE main-shock nodal plane having mostly reverse slip. This cluster extends ~10 km along strike. The Quail fault zone projects to the surface in gneiss of the Ordovician Chopawamsic Formation just southeast of the Ordovician–Silurian Ellisville Granodiorite pluton tail. The following three clusters of shallow (<3 km) aftershocks illuminate other faults. (1) An elongate cluster of early aftershocks, ~10 km east of the Quail fault zone, extends 8 km from Fredericks Hall, strikes ~035°–039°, and appears to be roughly vertical. The Fredericks Hall fault may be a strand or splay of the older Lakeside fault zone, which to the south spans a width of several kilometers. (2) A cluster of later aftershocks ~3 km northeast of Cuckoo delineates a fault near the eastern contact of the Ordovician Quantico Formation. (3) An elongate cluster of late aftershocks ~1 km northwest of the Quail fault zone aftershock cluster delineates the northwest fault (described herein), which is temporally distinct, dips more steeply, and has a more northeastward strike. Some aftershock-illuminated faults coincide with preexisting units or structures evident from radiometric anomalies, suggesting tectonic inheritance or reactivation.

  9. Maximal radius of the aftershock zone in earthquake networks

    NASA Astrophysics Data System (ADS)

    Mezentsev, A. Yu.; Hayakawa, M.

    2009-09-01

    In this paper, several seismoactive regions were investigated (Japan, Southern California and two tectonically distinct Japanese subregions) and structural seismic constants were estimated for each region. Using the method for seismic clustering detection proposed by Baiesi and Paczuski [M. Baiesi, M. Paczuski, Phys. Rev. E 69 (2004) 066106; M. Baiesi, M. Paczuski, Nonlin. Proc. Geophys. (2005) 1607-7946], we obtained the equation of the aftershock zone (AZ). It was shown that the consideration of a finite velocity of seismic signal leads to the natural appearance of maximal possible radius of the AZ. We obtained the equation of maximal radius of the AZ as a function of the magnitude of the main event and estimated its values for each region.

  10. A random effects epidemic-type aftershock sequence model.

    PubMed

    Lin, Feng-Chang

    2011-04-01

    We consider an extension of the temporal epidemic-type aftershock sequence (ETAS) model with random effects as a special case of a well-known doubly stochastic self-exciting point process. The new model arises from a deterministic function that is randomly scaled by a nonnegative random variable, which is unobservable but assumed to follow either positive stable or one-parameter gamma distribution with unit mean. Both random effects models are of interest although the one-parameter gamma random effects model is more popular when modeling associated survival times. Our estimation is based on the maximum likelihood approach with marginalized intensity. The methods are shown to perform well in simulation experiments. When applied to an earthquake sequence on the east coast of Taiwan, the extended model with positive stable random effects provides a better model fit, compared to the original ETAS model and the extended model with one-parameter gamma random effects. PMID:24039322

  11. Mechanics of Multifault Earthquake Ruptures

    NASA Astrophysics Data System (ADS)

    Fletcher, J. M.; Oskin, M. E.; Teran, O.

    2015-12-01

    The 2010 El Mayor-Cucapah earthquake of magnitude Mw 7.2 produced the most complex rupture ever documented on the Pacific-North American plate margin, and the network of high- and low-angle faults activated in the event record systematic changes in kinematics with fault orientation. Individual faults have a broad and continuous spectrum of slip sense ranging from endmember dextral strike slip to normal slip, and even faults with thrust sense of dip slip were commonly observed in the aftershock sequence. Patterns of coseismic slip are consistent with three-dimensional constrictional strain and show that integrated transtensional shearing can be accommodated in a single earthquake. Stress inversions of coseismic surface rupture and aftershock focal mechanisms define two coaxial, but permuted stress states. The maximum (σ1) and intermediate (σ2) principal stresses are close in magnitude, but flip orientations due to topography- and density-controlled gradients in lithostatic load along the length of the rupture. Although most large earthquakes throughout the world activate slip on multiple faults, the mechanical conditions of their genesis remain poorly understood. Our work attempts to answer several key questions. 1) Why do complex fault systems exist? They must do something that simple, optimally-oriented fault systems cannot because the two types of faults are commonly located in close proximity. 2) How are faults with diverse orientations and slip senses prepared throughout the interseismic period to fail spontaneously together in a single earthquake? 3) Can a single stress state produce multi-fault failure? 4) Are variations in pore pressure, friction and cohesion required to produce simultaneous rupture? 5) How is the fabric of surface rupture affected by variations in orientation, kinematics, total geologic slip and fault zone architecture?

  12. A New Hybrid STEP/Coulomb model for Aftershock Forecasting

    NASA Astrophysics Data System (ADS)

    Steacy, S.; Jimenez, A.; Gerstenberger, M.

    2014-12-01

    Aftershock forecasting models tend to fall into two classes - purely statistical approaches based on clustering, b-value, and the Omori-Utsu law; and Coulomb rate-state models which relate the forecast increase in rate to the magnitude of the Coulomb stress change. Recently, hybrid models combining physical and statistical forecasts have begun to be developed, for example by Bach and Hainzl (2012) and Steacy et al. (2013). The latter approach combined Coulomb stress patterns with the STEP (short-term earthquake probability) model by redistributing expected rate from areas with decreased stress to regions where the stress had increased. The chosen 'Coulomb Redistribution Parameter' (CRP) was 0.93, based on California earthquakes, which meant that 93% of the total rate was expected to occur where the stress had increased. The model was tested against the Canterbury sequence and the main result was that the new model performed at least as well as, and often better than, STEP when tested against retrospective data but that STEP was generally better in pseudo-prospective tests that involved data actually available within the first 10 days of each event of interest. The authors suggested that the major reason for this discrepancy was uncertainty in the slip models and, particularly, in the geometries of the faults involved in each complex major event. Here we develop a variant of the STEP/Coulomb model in which the CRP varies based on the percentage of aftershocks that occur in the positively stressed areas during the forecast learning period. We find that this variant significantly outperforms both STEP and the previous hybrid model in almost all cases, even when the input Coulomb model is quite poor. Our results suggest that this approach might be more useful than Coulomb rate-state when the underlying slip model is not well constrained due to the dependence of that method on the magnitude of the Coulomb stress change.

  13. A Quantitative Test for the Spatial Relationship Between Aftershock Distributions and Mainshock Rupture Properties

    NASA Astrophysics Data System (ADS)

    Woessner, J.; Ripperger, J.; Mai, M. P.; Wiemer, S.

    2004-12-01

    Correlating the properties of the mainshock rupture with the location of corresponding aftershocks may provide insight into the relationship between mainshock-induced static stress changes and aftershock occurrence. In this study, we develop a rigorous statistical test to quantify the spatial pattern of aftershock locations with the corresponding distributions of coseismic slip and stress-drop. Well-located aftershock hypocenters are projected onto the mainshock fault plane and coseismic slip and stress drop values are interpolated to their respective location. The null hypothesis H0 for the applied test statistic is: Aftershock hypocenters are randomly distributed on the mainshock fault plane and are not correlated with mainshock properties. Because we want to maintain spatial earthquake clustering as one of the important observed features of seismicity, we synthesize slip distributions using a random spatial field model from which we then compute the respective stress-drop distributions. For each simulation of earthquake slip, we compute the test statistic for the slip and stress-drop distribution, testing whether or not an apparent correlation between mainshock properties and aftershock locations exists. Uncertainties in the aftershock locations are accounted for by simulating a thousand catalogues for which we randomize the location of the aftershocks within their given location error bounds. We then determine the number of aftershocks in low-slip or negative stress-drop regions for simulated slip distributions, and compare those to the measurements obtained for finite-source slip inversions. We apply the test to crustal earthquakes in California and Japan. If possible, we use different source models and earthquake catalogues with varying accuracy to investigate the dependence of the test results on, for example, the location uncertainties of aftershocks. Contrary to the visual impression, we find that for some strike-slip earthquakes or segments of the

  14. Cumulative Coulomb Stress Triggering as an Explanation for the Canterbury (New Zealand) Aftershock Sequence: Initial Conditions Are Everything?

    NASA Astrophysics Data System (ADS)

    Bebbington, Mark; Harte, David; Williams, Charles

    2016-01-01

    Using 2 years of aftershock data and three fault-plane solutions for each of the initial M7.1 Darfield earthquake and the larger (M >6) aftershocks, we conduct a detailed examination of Coulomb stress transfer in the Canterbury 2010-2011 earthquake sequence. Moment tensor solutions exist for 283 of the events with M ≥ 3.6, while 713 other events of M ≥ 3.6 have only hypocentre and magnitude information available. We look at various methods for deciding between the two possible mechanisms for the 283 events with moment tensor solutions, including conformation to observed surface faulting, and maximum ΔCFF transfer from the Darfield main shock. For the remaining events, imputation methods for the mechanism including nearest-neighbour, kernel smoothing, and optimal plane methods are considered. Fault length, width, and depth are arrived at via a suite of scaling relations. A large (50-70 %) proportion of the faults considered were calculated to have initial loading in excess of the final stress drop. The majority of faults that accumulated positive ΔCFF during the sequence were `encouraged' by the main shock failure, but, on the other hand, of the faults that failed during the sequence, more than 50 % of faults appeared to have accumulated a negative ΔCFF from all preceding failures during the sequence. These results were qualitatively insensitive to any of the factors considered. We conclude that there is much unknown about how Coulomb stress triggering works in practice.

  15. A non-extensive statistical physics view to the spatiotemporal properties of the June 1995, Aigion earthquake (M6.2) aftershock sequence (West Corinth rift, Greece)

    NASA Astrophysics Data System (ADS)

    Vallianatos, Filippos; Michas, Giorgos; Papadakis, Giorgos; Sammonds, Peter

    2012-06-01

    In the present study, the spatiotemporal properties of the Aigion earthquake (15 June 1995) aftershock sequence are being studied using the concept of non-extensive statistical physics (NESP). The cumulative distribution functions of the inter-event times and the inter-event distances are being estimated for the data set which is assumed to be complete and the analysis yielded the thermodynamic q parameter to be qT = 1.58 and q r = 0.53 for the two distributions, respectively. The results fit rather well to the inter-event distances and times distributions, implying the complexity of the spatiotemporal properties of seismicity and the usefulness of NESP in investigating such phenomena. The temporal structure is also being discussed using the complementary to NESP approach of superstatistics, which is based on a superposition of ordinary local equilibrium statistical mechanics. The result indicates that very low degrees of freedom describe the temporal evolution of the Aigion earthquake aftershock seismicity.

  16. The M w6.7 12 October 2013 western Hellenic Arc main shock and its aftershock sequence: implications for the slab properties

    NASA Astrophysics Data System (ADS)

    Papadimitriou, Eleftheria; Karakostas, Vassilis; Mesimeri, Maria; Vallianatos, Filippos

    2016-01-01

    The 12 October 2013 M w6.7 earthquake offshore Crete Island is one of the few strong earthquakes to have occurred in the last few decades in the southwestern part of the Hellenic subduction zone (HSZ), providing the opportunity to evaluate characteristics of the descending slab. The HSZ has experienced several strong (M ≥ 7.0) earthquakes in historical times with the largest one being the 365 AD, M w = 8.4 earthquake, the largest known ever occurred in the Mediterranean region. The 2013 main shock occurred in close proximity with the 365 event, on an interplate thrust fault at a depth of 26 km, onto the coupled part of the overriding and descending plates. GCMT solution shows a slightly oblique (rake = 130°) thrust faulting with downdip compression on a nearly horizontal (dip = 3°) northeast-dipping fault plane with strike (340°) parallel to the subduction front, with the compression axis being oriented in the direction of plate convergence. The subduction interface can be more clearly resolved with the integration of aftershock locations and CMT solution. For this scope, the aftershocks were relocated after obtaining a v p/v s ratio equal to 1.76, a one-dimensional velocity model and time delays that approximate the velocity structure of the study area, and the employment of double-difference technique for both phase pick data and cross-correlation differential times. The first-day relocated seismicity, alike aftershocks in the first 2 months, shows activation of an area at the upper part of the descending slab, with most activity being concentrated between 13 and 27 km, where the main shock is also encompassed. Aftershocks are rare near to the main shock, implying homogeneous slip on a large patch of the rupture plane. Based on the aftershock distribution, the size of the activated area estimated is about 24 km long and 17 km wide. Coulomb stress changes resolved for transpressive motion reveal negligible off-fault aftershock triggering, evidencing a

  17. Hybrid Extrinsic Silicon Focal Plane Architecture

    NASA Astrophysics Data System (ADS)

    Pommerrenig, D. H.; Meinhardt, T.; Lowe, J.

    1981-02-01

    Large-area focal planes require mechanical assembly techniques which must be compatible with optical alignment, minimum deadspace, and cryogenic requirements in order to achieve optimum performance. Hybrid extrinsic silicon has been found particularly suitable for such an application. It will be shown that by choosing a large-area extrinsic silicon detector array which is hybrid-mated to a multiplicity of multiplexers a very cost-effective and high-density focal plane module can be assembled. Other advantages of this approach are inherent optical alignment and excellent performance.

  18. Forecasting Aftershocks from Multiple Earthquakes: Lessons from the Mw=7.3 2015 Nepal Earthquake

    NASA Astrophysics Data System (ADS)

    Jiménez, Abigail; NicBhloscaidh, Mairéad; McCloskey, John

    2016-04-01

    The Omori decay of aftershocks is often perturbed by large secondary events which present particular, but not uncommon, challenges to aftershock forecasting. The Mw = 7.8, 25 April 2015, Gorkha, Nepal earthquake was followed on 12 May by the Mw = 7.3 Kodari earthquake, superimposed its own aftershocks on the Gorkha sequence, immediately invalidating forecasts made by single-mainshock forecasting methods. The complexity of the Gorkha rupture process, where the hypocentre and moment centroid were separated by some 75 km, provided an insurmountable challenge for other standard forecasting methods. Here, we report several modifications of existing algorithms, which were developed in response to the complexity of this sequence and which appear to provide a more general framework for the robust and dependable forecasting of aftershock probabilities. We suggest that these methods may be operationalised to provide a scientific underpinning for an evidence-based management system for post-earthquake crises.

  19. Focal Venous Hypertension as a Pathophysiologic Mechanism for Tissue Hypertrophy, Port-Wine Stains, the Sturge-Weber Syndrome, and Related Disorders: Proof of Concept with Novel Hypothesis for Underlying Etiological Cause (An American Ophthalmological Society Thesis)

    PubMed Central

    Parsa, Cameron F.

    2013-01-01

    Purpose: To provide an in-depth re-examination of assumed causes of tissue hypertrophy, port-wine stains, and the Sturge-Weber, Cobb, Klippel-Trénaunay, and related syndromes to support an alternative unifying pathophysiologic mechanism of venous dysplasia producing focal venous hypertension with attendant tissue responses; to provide proof of concept with new patient data; to propose a novel etiological hypothesis for the venous dysplasia in these syndromes and find supportive evidence. Methods: Data from 20 patients with port-wine stains and corneal pachymetry readings was collected prospectively by the author in an institutional referral-based practice. The literature was searched using MEDLINE, and articles and textbooks were obtained from the bibliographies of these publications. Results: Newly obtained dermatologic, corneal pachymetry, fundus ophthalmoscopic, ocular and orbital venous Doppler ultrasonography, and magnetic resonance imaging findings in patients with the Sturge-Weber syndrome or isolated port-wine stains, along with published data, reveal diffusely thickened tissues and neural atrophy in all areas associated with venous congestion. Conclusions: Contrary to traditional understanding, signs and symptoms in the Sturge-Weber and related syndromes, including both congenital and acquired port-wine stains, are shown to arise from effects of localized primary venous dysplasia or acquired venous obstruction rather than neural dysfunction, differentiating these syndromes from actual phacomatoses. Effects of focal venous hypertension are transmitted to nearby areas via compensatory collateral venous channels in the above conditions, as in the Parkes Weber syndrome. A novel underlying etiology—prenatal venous thrombo-occlusion—is proposed to be responsible for the absence of veins with persistence and enlargement of collateral circulatory pathways with data in the literature backing this offshoot hypothesis. The mechanism for isolated pathologic

  20. Characterization of the time-dependent strain field at seismogenic depths using first-motion focal mechanisms: Observations of large-scale decadal variations in stress along the San Andrea fault system

    USGS Publications Warehouse

    Sipkin, S.A.; Silver, P.G.

    2003-01-01

    We present a method for summing moment tensors derived from first-motion focal mechanisms to study temporal dependence in features of the subsurface regional strain field. Time-dependent processes are inferred by comparing mechanisms summed over differing time periods. We apply this methodology to seismogenic zones in central and southern California using focal mechanisms produced by the Northern and Southern California Seismograph Networks for events during 1980-1999. We find a consistent pattern in both the style of deformation (strike-slip versus compressional) and seismicity rate across the entire region. If these temporal variations are causally related, it suggests a temporal change in the regional-scale stress field. One change consistent with the observations is a rotation in the regional maximum horizontal compressive stress direction, followed by a reversal to the original direction. Depending upon the dominant style of deformation locally, this change in orientation of the regional stress will tend to either enhance or hinder deformation. The mode of enhanced deformation can range from increased microseismicity and creep to major earthquakes. We hypothesize that these temporal changes in the regional stress field are the result of subtle changes in apparent relative plate motion between the Pacific and North American plates, perhaps due to long-range postseismic stress diffusion. Others have hypothesized that small changes in plate motion over thousands of years, and/or over decades, are responsible for changes in the style of deformation in southern California. We propose that such changes, over the course of just a few years, also affect the style of deformation.

  1. Three Ingredients for Improved Global Aftershock Forecasts: Tectonic Region, Time-Dependent Catalog Incompleteness, and Inter-Sequence Variability

    NASA Astrophysics Data System (ADS)

    Page, M. T.; Hardebeck, J.; Felzer, K. R.; Michael, A. J.; van der Elst, N.

    2015-12-01

    Following a large earthquake, seismic hazard can be orders of magnitude higher than the long-term average as a result of aftershock triggering. Due to this heightened hazard, there is a demand from emergency managers and the public for rapid, authoritative, and reliable aftershock forecasts. In the past, USGS aftershock forecasts following large, global earthquakes have been released on an ad-hoc basis with inconsistent methods, and in some cases, aftershock parameters adapted from California. To remedy this, we are currently developing an automated aftershock product that will generate more accurate forecasts based on the Reasenberg and Jones (Science, 1989) method. To better capture spatial variations in aftershock productivity and decay, we estimate regional aftershock parameters for sequences within the Garcia et al. (BSSA, 2012) tectonic regions. We find that regional variations for mean aftershock productivity exceed a factor of 10. The Reasenberg and Jones method combines modified-Omori aftershock decay, Utsu productivity scaling, and the Gutenberg-Richter magnitude distribution. We additionally account for a time-dependent magnitude of completeness following large events in the catalog. We generalize the Helmstetter et al. (2005) equation for short-term aftershock incompleteness and solve for incompleteness levels in the global NEIC catalog following large mainshocks. In addition to estimating average sequence parameters within regions, we quantify the inter-sequence parameter variability. This allows for a more complete quantification of the forecast uncertainties and Bayesian updating of the forecast as sequence-specific information becomes available.

  2. Quantifying Early Aftershock Activity of the 2004 Mid Niigata Prefecture Earthquake (Mw6.6)

    NASA Astrophysics Data System (ADS)

    Enescu, B.; Mori, J.; Miyazawa, M.

    2006-12-01

    We analyse the early aftershock activity of the 2004 Mid Niigata earthquake, using both earthquake catalog data and continuous waveform recordings. The frequency-magnitude distribution analysis of the Japan Meteorological Agency (JMA) catalog shows that the magnitude of completeness of the aftershocks changes from values around 5.0, immediately after the mainshock, to about 1.8, twelve hours later. Such a large incompleteness of early events can bias significantly the estimation of aftershock rates. To better determine the temporal pattern of aftershocks in the first minutes after the Niigata earthquake, we analyse the continuous seismograms recorded at six Hi-Net (High Sensitivity Seismograph Network) stations located close to the aftershock distribution. Clear aftershocks can be seen from about 35 sec. after the mainshock. We use events which are both identified on the filtered waveforms and are listed in the JMA catalogue, to calibrate an amplitude-magnitude relation. We estimate that the events picked on the waveforms recorded at two seismic stations (NGOH and YNTH), situated on opposite sides of the aftershock distribution, are complete above a threshold magnitude of 3.4. The c-value determined by taking these events into account is about 0.003 days (4.3 min). Statistical tests demonstrate that a small, but non-zero, c-value is a reliable result. We also analyse the decay with time of the moment release rates of the aftershocks in the JMA catalog, since these rates should be much less influenced by the missing small events. The moment rates follow a power-law time dependence from a few minutes to months after the mainshock. We finally show that the rate-and-state dependent friction law or stress corrosion could explain well our findings.

  3. Correlating Aftershock Hypocenters With On-fault Main Shock Properties: Introducing Non-standard Statistical Tests

    NASA Astrophysics Data System (ADS)

    Woessner, J.; Schorlemmer, D.; Wiemer, S.; Mai, P. M.

    2005-12-01

    Quantitatively correlating properties of finite-fault source models with hypocenters of aftershocks may provide new insight in the relationship between either slip or static stress change distributions and aftershock occurrence. We present advanced non-standard statistical test approaches to evaluate the test hypotheses (1) if aftershocks are preferentially located in areas of low slip and (2) if aftershocks are located in increased shear stress against the null hypothesis: aftershocks are located randomly on the fault plane. By using multiple test approaches, we investigate possible pitfalls and the information content of statistical testing. To perform the tests, we use earthquakes for which multiple finite-fault source models and earthquake catalogs of varying accuracy exist. The aftershock hypocenters are projected onto the main-shock rupture plane and uncertainties are accounted for by simulating hypocenter locations in the given error bounds. For the statistical tests, we retain the spatial clustering of earthquakes as the most important observed features of seismicity and synthesize random slip distributions with different approaches: first, using standard statistical methods that randomize the obtained finite-fault source model values and second, using a random spatial field model. We then determine the number of aftershocks in low-slip or increased shear-stress regions for simulated slip distributions, and compare those to the measurements obtained for finite-source slip inversions. We apply the tests to prominent earthquakes in California and Japan and find statistical significant evidence that aftershocks are preferentially located in low-slip regions. The tests, however, show a lower significance for the correlation with the shear-stress distribution, but are in general agreement with the expectations of the asperity model. Tests using the hypocenters of relocated catalogs show higher significances.

  4. Investigations of Periodic Disturbances on Seismic Aftershock Recordings

    NASA Astrophysics Data System (ADS)

    Liebsch, Mattes; Gorschlüter, Felix; Knoop, Jan-Frederik; Altmann, Jürgen

    2013-04-01

    The Comprehensive Nuclear Test-Ban Treaty Organisation (CTBTO) runs the International Monitoring System (IMS) to detect possible violations of the treaty. The seismic sensors of the IMS are set up to detect every underground explosion with a yield of 1 kT TNT equivalent or even better everywhere on the world. Under consideration of all IMS data the hypocentre of a large underground explosion is located within an area of about 1000 sq km. To verify if it was a violation of the Test-Ban Treaty the CTBTO (after CTBT entry into force) is allowed to carry out an on-site inspection (OSI) in the area of suspicion. During an OSI the hypocentre is to be located much more precisely; for this a local seismic aftershock monitoring system (SAMS) can be installed to detect small seismic events caused as a consequence of the explosion, such as relaxation of the rock around the cavity. However the magnitude of these aftershock signals is extremely weak. Other difficulties arise from other seismic signals in the inspection area, for example caused by vehicles of the inspectors, from coupling of airborne signals to the ground, or even by intended attempts to disturb the OSI. While the aftershock signals have a pulsed shape, man-made seismic signals (primarily created by engines) usually show periodic characteristics and thus are representable as a sum of sine functions and their harmonics. A mathematical expression for the Hann-windowed discrete Fourier transform of the underlying sine is used to characterise every such disturbance by the amplitude, frequency and phase. The contributions of these sines are computed and subtracted from the complex spectrum sequentially. Synthetic sines superposed to real signals, orders of magnitude stronger than the latter, can be removed successfully. Removal of periodic content from the signals of a helicopter overflight reduces the amplitude by a factor 3.3 when the frequencies are approximately constant. To reduce or prevent disturbing seismic

  5. An Explosion Aftershock Model with Application to On-Site Inspection

    NASA Astrophysics Data System (ADS)

    Ford, Sean R.; Labak, Peter

    2016-01-01

    An estimate of aftershock activity due to a theoretical underground nuclear explosion is produced using an aftershock rate model. The model is developed with data from the Nevada National Security Site, formerly known as the Nevada Test Site, and the Semipalatinsk Test Site, which we take to represent soft-rock and hard-rock testing environments, respectively. Estimates of expected magnitude and number of aftershocks are calculated using the models for different testing and inspection scenarios. These estimates can help inform the Seismic Aftershock Monitoring System (SAMS) deployment in a potential Comprehensive Test Ban Treaty On-Site Inspection (OSI), by giving the OSI team a probabilistic assessment of potential aftershocks in the Inspection Area (IA). The aftershock assessment, combined with an estimate of the background seismicity in the IA and an empirically derived map of threshold magnitude for the SAMS network, could aid the OSI team in reporting. We apply the hard-rock model to a M5 event and combine it with the very sensitive detection threshold for OSI sensors to show that tens of events per day are expected up to a month after an explosion measured several kilometers away.

  6. Forecasting aftershock activity: 1. Adaptive estimates based on the Omori and Gutenberg-Richter laws

    NASA Astrophysics Data System (ADS)

    Baranov, S. V.; Shebalin, P. N.

    2016-05-01

    The method for forecasting the intensity of the aftershock processes after strong earthquakes in different magnitude intervals is considered. The method is based on the joint use of the time model of the aftershock process and the Gutenberg-Richter law. The time model serves for estimating the intensity of the aftershock flow with a magnitude larger than or equal to the magnitude of completeness. The Gutenberg-Richter law is used for magnitude scaling. The suggested approach implements successive refinement of the parameters of both components of the method, which is the main novelty distinguishing it from the previous ones. This approach, to a significant extent, takes into account the variations in the parameters of the frequency-magnitude distribution, which often show themselves by the decreasing fraction of stronger aftershocks with time. Testing the method on eight aftershock sequences in the regions with different patterns of seismicity demonstrates the high probability of successful forecasts. The suggested technique can be employed in seismological monitoring centers for forecasting the aftershock activity of a strong earthquake based on the results of operational processing.

  7. Rupture processes of the 2015 Mw 7.9 Gorkha earthquake and its Mw 7.3 aftershock and their implications on the seismic risk

    NASA Astrophysics Data System (ADS)

    Liu, Chengli; Zheng, Yong; Wang, Rongjiang; Shan, Bin; Xie, Zujun; Xiong, Xiong; Ge, Can

    2016-07-01

    The rupture processes of the 2015 April 25 Gorkha earthquake and its strongest aftershock occurred on May 12 in Nepal are investigated by joint inversion of seismological and geodetic data. Synthetic test shows that the sedimentary layers in the source region play an important role in the rupture process inversion. Our optimized model of the mainshock shows that the rupture has a unilateral propagation pattern. The dominant mechanism is pure thrust with maximum slip of 5.8 m, the rupture scale extends ~ 60 km along dip and ~ 150 km along strike, and the largest static stress change is ~ 7.6 MPa. The total seismic moment is 7.87 × 1020 N m, equivalent to Mw 7.9. Most seismic moment was released within 80 s and the majority seismic moment was released at the first 40 s. The rupture propagated in main slip asperity with a velocity of ~ 3.0 km/s. The strong aftershock magnitude is about Mw 7.3, and the peak slip is about 5.0 m, close to the peak slip of the mainshock. Moreover, the slips of the mainshock and the aftershocks are in good complementary, suggesting a triggering relationship between them. Considering the strain accumulation, the Gorkha earthquake ruptured only part of the seismic gap alone, thus still poses high earthquake risk, especially in the west side of the mainshock rupture zone.

  8. Aftershock Records in the Kathmandu Valley of the 2015 Gorkha, Nepal, Earthquake

    NASA Astrophysics Data System (ADS)

    Shigefuji, M.; Takai, N.; Sasatani, T.; Bijukchhen, S.; Ichiyanagi, M.; Rajaure, S.; Dhital, M. R.

    2015-12-01

    The devastating earthquake, named the Gorkha Earthquake, was followed by a series of aftershocks: more than 350 of them greater than M 4 and four aftershock greater than M 6. The rupture of main shock originating 80 km NW of capital Kathmandu propagated towards east. The ensuing aftershock activities are concentrated in the eastern part of the rupture area. The aftershock of Mw 6.6 occurred about half an hour later at epicentre near to that of the main shock. The other three large aftershocks however, were originated in the eastern extreme of the rupture zone. The aftershock of Mw 7.3 that occurred on 12th May 2015 brought about more damages to infrastructures already vulnerable due to the main shock. To understand the site effect of the Kathmandu valley structure, we installed continuous recording accelerometers in four different parts of the valley. Four stations were installed along a west-to-east profile of the valley at KTP (Kirtipur; hill top), TVU (Kirtipur; hill side), PTN (Patan) and THM (Thimi). The surface S-wave velocity of the KTP site was over 700 cm s-1, but for each of the other three sites it was less than 200 cm s-1. These velocities are consistent with the geological formations; KTP is above hard rock, and TVU, PTN and THM are over the lake sediment of the valley. It is normal for the amplitude of earthquake motion to be larger in areas lying above sedimentary soil than in areas above hard rock, and these motions can be amplified further by certain deep underground structures. To know deep underground structure using with aftershock records, we installed more four instruments in the Kathmandu basin after main shock. We analysed the strong-motion data of these five aftershocks recorded in the eight strong-motion accelerometers. The station of KTP is considered as reference site to compare the effect of sediments on the earthquake waves. The large aftershocks all have highest Peak Ground Velocity (PGV) at TVU and the station of KTP showed the least

  9. Aftershock communication during the Canterbury Earthquakes, New Zealand: implications for response and recovery in the built environment

    USGS Publications Warehouse

    Julia Becker; Wein, Anne; Sally Potter; Emma Doyle; Ratliff, Jamie L.

    2015-01-01

    On 4 September 2010, a Mw7.1 earthquake occurred in Canterbury, New Zealand. Following the initial earthquake, an aftershock sequence was initiated, with the most significant aftershock being a Mw6.3 earthquake occurring on 22 February 2011. This aftershock caused severe damage to the city of Christchurch and building failures that killed 185 people. During the aftershock sequence it became evident that effective communication of aftershock information (e.g., history and forecasts) was imperative to assist with decision making during the response and recovery phases of the disaster, as well as preparedness for future aftershock events. As a consequence, a joint JCDR-USGS research project was initiated to investigate: • How aftershock information was communicated to organisations and to the public; • How people interpreted that information; • What people did in response to receiving that information; • What information people did and did not need; and • What decision-making challenges were encountered relating to aftershocks. Research was conducted by undertaking focus group meetings and interviews with a range of information providers and users, including scientists and science advisors, emergency managers and responders, engineers, communication officers, businesses, critical infrastructure operators, elected officials, and the public. The interviews and focus group meetings were recorded and transcribed, and key themes were identified. This paper focuses on the aftershock information needs for decision-making about the built environment post-earthquake, including those involved in response (e.g., for building assessment and management), recovery/reduction (e.g., the development of new building standards), and readiness (e.g. between aftershocks). The research has found that the communication of aftershock information varies with time, is contextual, and is affected by interactions among roles, by other information, and by decision objectives. A number

  10. Delayed Triggering of Early Aftershocks by Multiple Waves Circling the Earth

    NASA Astrophysics Data System (ADS)

    Sullivan, B.; Peng, Z.

    2011-12-01

    It is well known that direct surface waves of large earthquakes are capable of triggering shallow earthquakes and deep tremor at long-range distances. Recent studies have shown that multiple surface waves circling the earth could also remotely trigger microearthquakes [Peng et al., 2011]. However, it is still not clear whether multiple surface waves returning back to the mainshock epicenters could also trigger/modulate aftershock activities. Here we conduct a study to search for evidence of such triggering by systematically examining aftershock activities of 20 magnitude-8-or-higher earthquakes since 1990 that are capable of producing surface waves circling the globe repeatedly. We compute the magnitude of completeness for each sequence, and stack all the sequences together to compute the seismicity and moment rates by sliding data windows. The sequences are also shuffled randomly and these rates are compared to the actual data as well as synthetic aftershock sequences to estimate the statistical significance of the results. We also compare them with varying stacks of magnitude 7-8 earthquakes to better understand the possible biases that could be introduced by our rate calculation method. Our preliminary results suggest that there is some moderate increase of early aftershock activity after a few hours when the surface waves return to the epicentral region. However, we could not completely rule out the possibility that such an increase is purely due to random fluctuations of aftershocks or caused by missing aftershocks in the first few hours after the mainshock. We plan to examine continuous waveform data of selected sequences to obtain a better understanding of the multiple surface waves and aftershock activity.

  11. Statistical monitoring of aftershock sequences: a case study of the 2015 Mw7.8 Gorkha, Nepal, earthquake

    NASA Astrophysics Data System (ADS)

    Ogata, Yosihiko; Tsuruoka, Hiroshi

    2016-03-01

    Early forecasting of aftershocks has become realistic and practical because of real-time detection of hypocenters. This study illustrates a statistical procedure for monitoring aftershock sequences to detect anomalies to increase the probability gain of a significantly large aftershock or even an earthquake larger than the main shock. In particular, a significant lowering (relative quiescence) in aftershock activity below the level predicted by the Omori-Utsu formula or the epidemic-type aftershock sequence model is sometimes followed by a large earthquake in a neighboring region. As an example, we detected significant lowering relative to the modeled rate after approximately 1.7 days after the main shock in the aftershock sequence of the Mw7.8 Gorkha, Nepal, earthquake of April 25, 2015. The relative quiescence lasted until the May 12, 2015, M7.3 Kodari earthquake that occurred at the eastern end of the primary aftershock zone. Space-time plots including the transformed time can indicate the local places where aftershock activity lowers (the seismicity shadow). Thus, the relative quiescence can be hypothesized to be related to stress shadowing caused by probable slow slips. In addition, the aftershock productivity of the M7.3 Kodari earthquake is approximately twice as large as that of the M7.8 main shock.

  12. Seismological evidence of an active footwall shortcut thrust in the Northern Itoigawa-Shizuoka Tectonic Line derived by the aftershock sequence of the 2014 M 6.7 Northern Nagano earthquake

    NASA Astrophysics Data System (ADS)

    Panayotopoulos, Yannis; Hirata, Naoshi; Hashima, Akinori; Iwasaki, Takaya; Sakai, Shin'ichi; Sato, Hiroshi

    2016-06-01

    A destructive M 6.7 earthquake struck Northern Nagano prefecture on November 22, 2014. The main shock occurred on the Kamishiro fault segment of the northern Itoigawa-Shizuoka Tectonic Line (ISTL). We used data recorded at 41 stations of the local seismographic network in order to locate 2118 earthquakes that occurred between November 18 and November 30, 2014. To estimate hypocenters, we assigned low Vp models to stations within the Northern Fossa Magna (NFM) basin thus accounting for large lateral crustal heterogeneities across the Kamishiro fault. In order to further improve accuracy, the final hypocenter locations were recalculated inside a 3D velocity model using the double-difference method. We used the aftershock activity distribution and focal mechanism solutions of major events in order to estimate the source fault area of the main shock. Our analysis suggests that the shallow part of the source fault corresponds to the surface trace of the Kamishiro fault and dips 30°-45° SE, while the deeper part of the source fault corresponds to the downdip portion of the Otari-Nakayama fault, a high angle fault dipping 50°-65° SE that formed during the opening of the NFM basin in the Miocene. Along its surface trace the Otari-Nakayama fault has been inactive during the late Quaternary. We verified the validity of our model by calculating surface deformation using a simple homogeneous elastic half-space model and comparing it to observed surface deformation from satellite interferometry, assuming large coseismic slip in the areas of low seismicity and small coseismic slip in the areas of high seismicity. Shallowing of the source fault from 50°-65° to 30°-45° in the upper 4 km, in the areas where both surface fault traces are visible, is a result of footwall shortcut thrusting by the Kamishiro fault off the Otari-Nakayama fault.

  13. Seismicity and seismogenic structures of Central Apennines (Italy): constraints on the present-day stress field from focal mechanisms - The SLAM (Seismicity of Lazio-Abruzzo and Molise) project

    NASA Astrophysics Data System (ADS)

    Frepoli, Alberto; Battista Cimini, Giovanni; De Gori, Pasquale; De Luca, Gaetano; Marchetti, Alessandro; Montuori, Caterina; Pagliuca, Nicola

    2016-04-01

    We present new results for the microseismic activity in the Central Apennines recorded from a total of 81seismic stations. The large number of recording sites derives from the combination of temporary and permanent seismic networks operating in the study region. Between January 2009 and October 2013 we recorded 6923 earthquakes with local magnitudes ML ranging from 0.1 to 4.8. We located hypocentres by using a refined 1D crustal velocity model. The majority of the hypocenters are located beneath the axes of the Apenninic chain, while the seismic activity observed along the peri-Tyrrhenian margin is lower. The seismicity extends to a depth of 32 km; the hypocentral depth distribution exhibits a pronounced peak of seismic energy release in the depth range between 8 and 20 km. During the observation period we recorded two major seismic swarms and one seismic sequence in the Marsica-Sorano area in which we have had the largest detected magnitude (ML = 4.8). Fault plane solutions for a total of 600 earthquakes were derived from P-polarities. This new data set consists of a number of focal plane solutions that is about four times the data so far available for regional stress field study. The majority of the focal mechanisms show predominantly normal fault solutions. T-axis trends are oriented NE-SW confirming that the area is in extension. We also derived the azimuths of the principal stress axes by inverting the fault plane solutions and calculated the direction of the maximum horizontal stress, which is mainly sub-vertical oriented. The study region has been historically affected by many strong earthquakes, some of them very destructive. This work can give an important contribution to the seismic hazard assessment in an area densely populated as the city of Rome which is distant around 60 km from the main seismogenic structures of Central Apennine.

  14. Explanation of temporal clustering of tsunami sources using the epidemic-type aftershock sequence model

    USGS Publications Warehouse

    Geist, Eric L.

    2014-01-01

    Temporal clustering of tsunami sources is examined in terms of a branching process model. It previously was observed that there are more short interevent times between consecutive tsunami sources than expected from a stationary Poisson process. The epidemic‐type aftershock sequence (ETAS) branching process model is fitted to tsunami catalog events, using the earthquake magnitude of the causative event from the Centennial and Global Centroid Moment Tensor (CMT) catalogs and tsunami sizes above a completeness level as a mark to indicate that a tsunami was generated. The ETAS parameters are estimated using the maximum‐likelihood method. The interevent distribution associated with the ETAS model provides a better fit to the data than the Poisson model or other temporal clustering models. When tsunamigenic conditions (magnitude threshold, submarine location, dip‐slip mechanism) are applied to the Global CMT catalog, ETAS parameters are obtained that are consistent with those estimated from the tsunami catalog. In particular, the dip‐slip condition appears to result in a near zero magnitude effect for triggered tsunami sources. The overall consistency between results from the tsunami catalog and that from the earthquake catalog under tsunamigenic conditions indicates that ETAS models based on seismicity can provide the structure for understanding patterns of tsunami source occurrence. The fractional rate of triggered tsunami sources on a global basis is approximately 14%.

  15. Chapter D. The Loma Prieta, California, Earthquake of October 17, 1989 - Aftershocks and Postseismic Effects

    USGS Publications Warehouse

    Reasenberg, Paul A., (Edited By)

    1997-01-01

    While the damaging effects of the earthquake represent a significant social setback and economic loss, the geophysical effects have produced a wealth of data that have provided important insights into the structure and mechanics of the San Andreas Fault system. Generally, the period after a large earthquake is vitally important to monitor. During this part of the seismic cycle, the primary fault and the surrounding faults, rock bodies, and crustal fluids rapidly readjust in response to the earthquake's sudden movement. Geophysical measurements made at this time can provide unique information about fundamental properties of the fault zone, including its state of stress and the geometry and frictional/rheological properties of the faults within it. Because postseismic readjustments are rapid compared with corresponding changes occurring in the preseismic period, the amount and rate of information that is available during the postseismic period is relatively high. From a geophysical viewpoint, the occurrence of the Loma Prieta earthquake in a section of the San Andreas fault zone that is surrounded by multiple and extensive geophysical monitoring networks has produced nothing less than a scientific bonanza. The reports assembled in this chapter collectively examine available geophysical observations made before and after the earthquake and model the earthquake's principal postseismic effects. The chapter covers four broad categories of postseismic effect: (1) aftershocks; (2) postseismic fault movements; (3) postseismic surface deformation; and (4) changes in electrical conductivity and crustal fluids.

  16. Reduced Mechanical Stretch Induces Enhanced Endothelin B Receptor-Mediated Contractility via Activation of Focal Adhesion Kinase and Extracellular Regulated Kinase 1/2 in Cerebral Arteries from Rat.

    PubMed

    Spray, Stine; Rasmussen, Marianne N P; Skovsted, Gry F; Warfvinge, Karin; Sheykhzade, Majid; Edvinsson, Lars

    2016-07-01

    Cerebral ischaemia results in enhanced endothelin B (ETB ) receptor-mediated contraction and receptor protein expression in the affected cerebrovascular smooth muscle cells (SMC). Organ culture of cerebral arteries is a method to induce similar alterations in ETB receptor expression. We suggest that rapid and sustained reduction in wall tension/stretch is a possible trigger mechanism for this vascular remodelling. Isolated rat middle cerebral artery (MCA) segments were incubated in a wire myograph with or without mechanical stretch, prior to assessment of their contractile response to the selective ETB receptor agonist sarafotoxin 6c. The involvement of extracellular regulated kinase (ERK) 1/2 and focal adhesion kinase (FAK) was studied by their specific inhibitors U0126 and PF-228, respectively. Compared with their stretched counterparts, unstretched MCA segments showed a significantly increased ETB receptor-mediated contractile response after 12 hr of incubation, which was attenuated by either U0126 or PF-228. The functionally increased ETB -mediated contractility could be attributed to two different mechanisms: (i) a difference in ETB receptor localization from primarily endothelial expression to SMC expression and (ii) an increased calcium sensitivity of the SMCs due to an increased expression of the calcium channel transient receptor potential canonical 1. Collectively, our results present a possible mechanism linking lack of vessel wall stretch/tension to changes in ETB receptor-mediated contractility via triggering of an early mechanosensitive signalling pathway involving ERK1/2 and FAK signalling. A mechanism likely to be an initiating factor for the increased ETB receptor-mediated contractility found after cerebral ischaemia. PMID:26781487

  17. Sensory-motor integration in focal dystonia.

    PubMed

    Avanzino, Laura; Tinazzi, Michele; Ionta, Silvio; Fiorio, Mirta

    2015-12-01

    Traditional definitions of focal dystonia point to its motor component, mainly affecting planning and execution of voluntary movements. However, focal dystonia is tightly linked also to sensory dysfunction. Accurate motor control requires an optimal processing of afferent inputs from different sensory systems, in particular visual and somatosensory (e.g., touch and proprioception). Several experimental studies indicate that sensory-motor integration - the process through which sensory information is used to plan, execute, and monitor movements - is impaired in focal dystonia. The neural degenerations associated with these alterations affect not only the basal ganglia-thalamic-frontal cortex loop, but also the parietal cortex and cerebellum. The present review outlines the experimental studies describing impaired sensory-motor integration in focal dystonia, establishes their relationship with changes in specific neural mechanisms, and provides new insight towards the implementation of novel intervention protocols. Based on the reviewed state-of-the-art evidence, the theoretical framework summarized in the present article will not only result in a better understanding of the pathophysiology of dystonia, but it will also lead to the development of new rehabilitation strategies. PMID:26164472

  18. Experimental investigation of MRgHIFU sonication with interleaved electronic and mechanical displacement of the focal point for transrectal prostate application

    NASA Astrophysics Data System (ADS)

    Petrusca, Lorena; Ngo, Jacqueline; Brasset, Lucie; Blanc, Emmanuel; Murillo, Adriana; Auboiroux, Vincent; Cotton, François; Chapelon, Jean-Yves; Salomir, Rares

    2012-08-01

    High intensity focused ultrasound (HIFU) under MRI guidance may provide minimally invasive treatment for localized prostate cancer. In this study, ex vivo and in vivo experiments were performed using a prostate-dedicated endorectal phased array (16 circular elements arranged on a truncated spherical cap of radius 60 mm) and a translation-rotation mechanical actuator in order to evaluate the lesion formation and the potential interest of dual-modality (electronic and mechanical) interleaved displacement of the focus for volumetric sonication paradigms. Different sonication sequences, including elementary lesions, line scan, slice sweeping and volume sonications, were investigated with a clinical 1.5 T MR scanner. Two orthogonal planes (axial and sagittal) were simultaneously monitored using rapid MR thermometry (PRFS method) and the temperature and thermal dose maps were displayed in real time. No RF interferences were detected in MR acquisition during sonications. The shape of the thermal lesions in vivo was examined at day 5 post-treatment by MRI follow-up (T2w sequence and Gd-T1w-TFE) and postmortem histological analysis. This study suggests that electronic displacement of the focus (along the ultrasound propagation axis) interleaved with mechanical X-Z translations and rotation around B0 can be a suitable modality to treat patient-specific sizes and shapes of a pathologic tissue. The electronic displacement of focus (achieved in less than 0.1 s) is an order of magnitude faster than the mechanical motion of the HIFU device (1 s latency). As an example, for an in vivo volumetric sonication with foci between 32 and 47 mm (7 successive line scans, 11 lines/slice, 4 foci/line) with applied powers between 17.4 and 39.1 Wac, a total duration of sonication of 408.1 s was required to ablate a volume of approximately 5.7 cm3 (semi-chronic lesion measured at day 5), while the maximum temperature elevation reached was 30 °C. While electronic focusing is necessary to speed

  19. Combined Scanning Transmission Electron Microscopy Tilt- and Focal Series

    SciTech Connect

    Dahmen, Tim; Baudoin, Jean-Pierre G; Lupini, Andrew R; Kubel, Christian; Slusallek, Phillip; De Jonge, Niels

    2014-01-01

    In this study, a combined tilt- and focal series is proposed as a new recording scheme for high-angle annular dark-field scanning transmission electron microscopy (STEM) tomography. Three-dimensional (3D) data were acquired by mechanically tilting the specimen, and recording a through-focal series at each tilt direction. The sample was a whole-mount macrophage cell with embedded gold nanoparticles. The tilt focal algebraic reconstruction technique (TF-ART) is introduced as a new algorithm to reconstruct tomograms from such combined tilt- and focal series. The feasibility of TF-ART was demonstrated by 3D reconstruction of the experimental 3D data. The results were compared with a conventional STEM tilt series of a similar sample. The combined tilt- and focal series led to smaller missing wedge artifacts, and a higher axial resolution than obtained for the STEM tilt series, thus improving on one of the main issues of tilt series-based electron tomography.

  20. Aftershock locations and rupture characteristics of the 2006 May 27, Yogyakarta-Indonesia earthquake

    NASA Astrophysics Data System (ADS)

    Irwan, M.; Ando, M.; Kimata, F.; Tadokoro, K.; Nakamichi, H.; Muto, D.; Okuda, T.; Hasanuddin, A.; Mipi A., K.; Setyadji, B.; Andreas, H.; Gamal, M.; Arif, R.

    2006-12-01

    A strong earthquake (M6.3) rocked the Bantul district, south of Yogyakarta Special Province (DIY) on the morningof May 27, 2006. We installed a temporary array of 6 seismographs to record aftershocks of the earthquake. The area of aftershocks, which may be interpreted as mainshock ruptured area has dimensions of about 25 km length and 20 km width, in the N48E direction. At depth the seismicity mainly concentrated between 5 to 15 km. The distribution of aftershock does not appear to come very close to the surface. There is no obvious surface evidence of causative fault in this area, though we find many crack and fissures that seem to have produced by the strong ground motion. We used the orientation and size of the fault determined from our aftershock results to carry out an inversion of teleseismic data for the slip distribution. We used broad- band seismograms of the IRIS network with epicentral distances between 30 and 90 degrees. We assume a single fault plane, strike 48 degree and dip 80 degree, which is inferred from the aftershock distribution. The total seismic moment is 0.369 x 10(19) Nm with maximum slip 0.4 meters. The asperity is located about 5 km away southwest of USGS estimated epicenter. Although the distances from the seismic source to heavily damaged areas Bantul and Klaten are 10 to 50 km, soft sedimentary soil likely to have generated very damaging motions within the area.

  1. Generalized Omori-Utsu law for aftershock sequences in southern California

    NASA Astrophysics Data System (ADS)

    Davidsen, J.; Gu, C.; Baiesi, M.

    2015-05-01

    We investigate the validity of a proposed generalized Omori-Utsu law for the aftershock sequences for the Landers, Hector Mine, Northridge and Superstition Hills earthquakes, the four largest events in the southern California catalogue we analyse. This law unifies three of the most prominent empirical laws of statistical seismology-the Gutenberg-Richter law, the Omori-Utsu law, and a generalized version of Båth's law-in a formula casting the parameters in the Omori-Utsu law as a function of the lower magnitude cutoff mc for the aftershocks considered. By applying a recently established general procedure for identifying aftershocks, we confirm that the generalized Omori-Utsu law provides a good approximation for the observed rates overall. In particular, we provide convincing evidence that the characteristic time c is not constant but a genuine function of mc, which cannot be attributed to short-term aftershock incompleteness. However, the estimation of the specific parameters is somewhat sensitive to the aftershock selection method used. This includes c(mc), which has important implications for inferring the underlying stress field.

  2. Analysing the 1811-1812 New Madrid earthquakes with recent instrumentally recorded aftershocks

    USGS Publications Warehouse

    Mueller, K.; Hough, S.E.; Bilham, R.

    2004-01-01

    Although dynamic stress changes associated with the passage of seismic waves are thought to trigger earthquakes at great distances, more than 60 per cent of all aftershocks appear to be triggered by static stress changes within two rupture lengths of a mainshock. The observed distribution of aftershocks may thus be used to infer details of mainshock rupture geometry. Aftershocks following large mid-continental earthquakes, where background stressing rates are low, are known to persist for centuries, and models based on rate-and-state friction laws provide theoretical support for this inference. Most past studies of the New Madrid earthquake sequence have indeed assumed ongoing microseismicity to be a continuing aftershock sequence. Here we use instrumentally recorded aftershock locations and models of elastic stress change to develop a kinematically consistent rupture scenario for three of the four largest earthquakes of the 1811-1812 New Madrid sequence. Our results suggest that these three events occurred on two contiguous faults, producing lobes of increased stress near fault intersections and end points, in areas where present-day microearthquakes have been hitherto interpreted as evidence of primary mainshock rupture. We infer that the remaining New Madrid mainshock may have occurred more than 200 km north of this region in the Wabash Valley of southern Indiana and Illinois-an area that contains abundant modern microseismicity, and where substantial liquefaction was documented by historic accounts. Our results suggest that future large midplate earthquake sequences may extend over a much broader region than previously suspected.

  3. Analysing the 1811-1812 New Madrid earthquakes with recent instrumentally recorded aftershocks.

    PubMed

    Mueller, Karl; Hough, Susan E; Bilham, Roger

    2004-05-20

    Although dynamic stress changes associated with the passage of seismic waves are thought to trigger earthquakes at great distances, more than 60 per cent of all aftershocks appear to be triggered by static stress changes within two rupture lengths of a mainshock. The observed distribution of aftershocks may thus be used to infer details of mainshock rupture geometry. Aftershocks following large mid-continental earthquakes, where background stressing rates are low, are known to persist for centuries, and models based on rate-and-state friction laws provide theoretical support for this inference. Most past studies of the New Madrid earthquake sequence have indeed assumed ongoing microseismicity to be a continuing aftershock sequence. Here we use instrumentally recorded aftershock locations and models of elastic stress change to develop a kinematically consistent rupture scenario for three of the four largest earthquakes of the 1811-1812 New Madrid sequence. Our results suggest that these three events occurred on two contiguous faults, producing lobes of increased stress near fault intersections and end points, in areas where present-day microearthquakes have been hitherto interpreted as evidence of primary mainshock rupture. We infer that the remaining New Madrid mainshock may have occurred more than 200 km north of this region in the Wabash Valley of southern Indiana and Illinois--an area that contains abundant modern microseismicity, and where substantial liquefaction was documented by historic accounts. Our results suggest that future large mid-plate earthquake sequences may extend over a much broader region than previously suspected. PMID:15152249

  4. Decay of aftershock density with distance does not indicate triggering by dynamic stress

    USGS Publications Warehouse

    Richards-Dinger, K.; Stein, R.S.; Toda, S.

    2010-01-01

    Resolving whether static or dynamic stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard. Felzer and Brodsky examined the distance distribution of earthquakes occurring in the first five minutes after 2 ≤ M  M  M ≥ 2 aftershocks showed a uniform power-law decay with slope −1.35 out to 50 km from the mainshocks. From this they argued that the distance decay could be explained only by dynamic triggering. Here we propose an alternative explanation for the decay, and subject their hypothesis to a series of tests, none of which it passes. At distances more than 300 m from the 2 ≤  M< 3 mainshocks, the seismicity decay 5 min before the mainshocks is indistinguishable from the decay five minutes afterwards, indicating that the mainshocks have no effect at distances outside their static triggering range. Omori temporal decay, the fundamental signature of aftershocks, is absent at distances exceeding 10 km from the mainshocks. Finally, the distance decay is found among aftershocks that occur before the arrival of the seismic wave front from the mainshock, which violates causality. We argue that Felzer and Brodsky implicitly assume that the first of two independent aftershocks along a fault rupture triggers the second, and that the first of two shocks in a creep- or intrusion-driven swarm triggers the second, when this need not be the case.

  5. When and where the aftershock activity was depressed: Contrasting decay patterns of the proximate large earthquakes in southern California

    USGS Publications Warehouse

    Ogata, Y.; Jones, L.M.; Toda, S.

    2003-01-01

    Seismic quiescence has attracted attention as a possible precursor to a large earthquake. However, sensitive detection of quiescence requires accurate modeling of normal aftershock activity. We apply the epidemic-type aftershock sequence (ETAS) model that is a natural extension of the modified Omori formula for aftershock decay, allowing further clusters (secondary aftershocks) within an aftershock sequence. The Hector Mine aftershock activity has been normal, relative to the decay predicted by the ETAS model during the 14 months of available data. In contrast, although the aftershock sequence of the 1992 Landers earthquake (M = 7.3), including the 1992 Big Bear earthquake (M = 6.4) and its aftershocks, fits very well to the ETAS up until about 6 months after the main shock, the activity showed clear lowering relative to the modeled rate (relative quiescence) and lasted nearly 7 years, leading up to the Hector Mine earthquake (M = 7.1) in 1999. Specifically, the relative quiescence occurred only in the shallow aftershock activity, down to depths of 5-6 km. The sequence of deeper events showed clear, normal aftershock activity well fitted to the ETAS throughout the whole period. We argue several physical explanations for these results. Among them, we strongly suspect aseismic slips within the Hector Mine rupture source that could inhibit the crustal relaxation process within "shadow zones" of the Coulomb's failure stress change. Furthermore, the aftershock activity of the 1992 Joshua Tree earthquake (M = 6.1) sharply lowered in the same day of the main shock, which can be explained by a similar scenario.

  6. Investigation of the high-frequency attenuation parameter, κ (kappa), from aftershocks of the 2010 Mw 8.8 Maule, Chile earthquake

    USGS Publications Warehouse

    Neighbors, Corrie; Liao, E. J.; Cochran, Elizabeth S.; Funning, G. J.; Chung, A. I.; Lawrence, J. F.; Christensen, C. M.; Miller, M.; Belmonte, A.; Sepulveda, H. H. Andrés

    2014-01-01

    The Bío Bío region of Chile experienced a vigorous aftershock sequence following the 2010 February 27 Mw 8.8 Maule earthquake. The immediate aftershock sequence was captured by two temporary seismic deployments: the Quake Catcher Network Rapid Aftershock Mobilization Program (QCN RAMP) and the Incorporated Research Institutions for Seismology CHile Aftershock Mobilization Program (IRIS CHAMP). Here, we use moderate to large aftershocks (ML ≥ 4.0) occurring between 2010 March 1 and June 30 recorded by QCN RAMP and IRIS CHAMP stations to determine the spectral decay parameter, kappa (κ). First, we compare waveforms and κ estimates from the lower-resolution QCN stations to the IRIS CHAMP stations to ensure the QCN data are of sufficient quality. We find that QCN stations provide reasonable estimates of κ in comparison to traditional seismic sensors and provide valuable additional observations of local ground motion variation. Using data from both deployments, we investigate the variation in κ for the region to determine if κ is influenced primarily by local geological structure, path attenuation, or source properties (e.g. magnitude, mechanism and depth). Estimates of κ for the Bío Bío region range from 0.0022 to 0.0704 s with a mean of 0.0295 s and are in good agreement with κ values previously reported for similar tectonic environments. κ correlates with epicentral distance and, to a lesser degree, with source magnitude. We find little to no correlation between the site kappa, κ0, and mapped geology, although we were only able to compare the data to a low-resolution map of surficial geology. These results support an increasing number of studies that suggest κobservations can be attributed to a combination of source, path and site properties; additionally, measured κ are often highly scattered making it difficult to separate the contribution from each of these factors. Thus, our results suggest that contributions from the site

  7. Investigation of the high-frequency attenuation parameter, κ (kappa), from aftershocks of the 2010 Mw 8.8 Maule, Chile earthquake

    NASA Astrophysics Data System (ADS)

    Neighbors, C.; Liao, E. J.; Cochran, E. S.; Funning, G. J.; Chung, A. I.; Lawrence, J. F.; Christensen, C.; Miller, M.; Belmonte, A.; Andrés Sepulveda, H. H.

    2015-01-01

    The Bío Bío region of Chile experienced a vigorous aftershock sequence following the 2010 February 27 Mw 8.8 Maule earthquake. The immediate aftershock sequence was captured by two temporary seismic deployments: the Quake Catcher Network Rapid Aftershock Mobilization Program (QCN RAMP) and the Incorporated Research Institutions for Seismology CHile Aftershock Mobilization Program (IRIS CHAMP). Here, we use moderate to large aftershocks (ML ≥ 4.0) occurring between 2010 March 1 and June 30 recorded by QCN RAMP and IRIS CHAMP stations to determine the spectral decay parameter, kappa (κ). First, we compare waveforms and κ estimates from the lower-resolution QCN stations to the IRIS CHAMP stations to ensure the QCN data are of sufficient quality. We find that QCN stations provide reasonable estimates of κ in comparison to traditional seismic sensors and provide valuable additional observations of local ground motion variation. Using data from both deployments, we investigate the variation in κ for the region to determine if κ is influenced primarily by local geological structure, path attenuation, or source properties (e.g. magnitude, mechanism and depth). Estimates of κ for the Bío Bío region range from 0.0022 to 0.0704 s with a mean of 0.0295 s and are in good agreement with κ values previously reported for similar tectonic environments. κ correlates with epicentral distance and, to a lesser degree, with source magnitude. We find little to no correlation between the site kappa, κ0, and mapped geology, although we were only able to compare the data to a low-resolution map of surficial geology. These results support an increasing number of studies that suggest κ observations can be attributed to a combination of source, path and site properties; additionally, measured κ are often highly scattered making it difficult to separate the contribution from each of these factors. Thus, our results suggest that contributions from the site, path and source

  8. Insights into induced earthquakes and aftershock activity with in-situ measurements of seismic velocity variations in an active underground mine

    NASA Astrophysics Data System (ADS)

    Brenguier, F.; Olivier, G.; Campillo, M.; Roux, P.; Shapiro, N.; Lynch, R.

    2015-12-01

    The behaviour of the crust shortly after large earthquakes has been the subject of numerous studies, but many co- and post-seismic processes remain poorly understood. Damage and healing of the bulk rock mass, post-seismic deformation and the mechanisms of earthquake triggering are still not well understood. These processes are important to properly model and understand the behaviour of faults and earthquake cycles.In this presentation, we will show how in-situ measurements of seismic velocity variations have given new insights into these co- and post-seismic processes. An experiment was performed where a blast was detonated in a tunnel in an underground mine, while seismic velocity variations were accurately (0.005 %) measured with ambient seismic noise correlations. Additionally, aftershock activity was examined and the influence of the removal of a piece of solid rock was estimated with elastic static stress modelling. The majority of the aftershocks were delayed with respect to the passing of the dynamic waves from the blast, while the locations of the aftershocks appeared clustered and not homogeneously spread around the blast location. A significant velocity drop is visible during the time of the blast, which is interpreted as co-seismic damage and plastic deformation. These non-elastic effects are healed by the confining stresses over a period of 5 days until the seismic velocity converges to a new baseline level. The instantaneous weakening and gradual healing observed from the velocity variations are qualitatively similar to results reported in laboratory studies. The change in the baseline level of the seismic velocity before and after the blast indicate a change in the static stress that is comparable to the results of elastic static stress modelling. The differences between the elastic model predictions and the seismic velocity variations could be due to zones of fractured rock, indicated by the spatial clustering of the aftershocks, that are not

  9. Recombinant Tissue Plasminogen Activator Induces Neurological Side Effects Independent on Thrombolysis in Mechanical Animal Models of Focal Cerebral Infarction: A Systematic Review and Meta-Analysis

    PubMed Central

    Wei, You-Dong; Liu, Yi-Yun; Ren, Yi-Fei; Liang, Zi-Hong; Wang, Hai-Yang; Zhao, Li-Bo; Xie, Peng

    2016-01-01

    Background and Purpose Recombinant tissue plasminogen activator (rtPA) is the only effective drug approved by US FDA to treat ischemic stroke, and it contains pleiotropic effects besides thrombolysis. We performed a meta-analysis to clarify effect of tissue plasminogen activator (tPA) on cerebral infarction besides its thrombolysis property in mechanical animal stroke. Methods Relevant studies were identified by two reviewers after searching online databases, including Pubmed, Embase, and ScienceDirect, from 1979 to 2016. We identified 6, 65, 17, 12, 16, 12 and 13 comparisons reporting effect of endogenous tPA on infarction volume and effects of rtPA on infarction volume, blood-brain barrier, brain edema, intracerebral hemorrhage, neurological function and mortality rate in all 47 included studies. Standardized mean differences for continuous measures and risk ratio for dichotomous measures were calculated to assess the effects of endogenous tPA and rtPA on cerebral infarction in animals. The quality of included studies was assessed using the Stroke Therapy Academic Industry Roundtable score. Subgroup analysis, meta-regression and sensitivity analysis were performed to explore sources of heterogeneity. Funnel plot, Trim and Fill method and Egger’s test were obtained to detect publication bias. Results We found that both endogenous tPA and rtPA had not enlarged infarction volume, or deteriorated neurological function. However, rtPA would disrupt blood-brain barrier, aggravate brain edema, induce intracerebral hemorrhage and increase mortality rate. Conclusions This meta-analysis reveals rtPA can lead to neurological side effects besides thrombolysis in mechanical animal stroke, which may account for clinical exacerbation for stroke patients that do not achieve vascular recanalization with rtPA. PMID:27387385

  10. Mosaic Focal Plane Development

    NASA Astrophysics Data System (ADS)

    Mason, David L.; Horner, Scott D.; Aamodt, Earl K.

    2002-12-01

    Advances in systems engineering, applied sciences, and manufacturing technologies have enabled the development of large ground based and spaced based astronomical instruments having a large Field of View (FOV) to capture a large portion of the universe in a single image. A larger FOV can be accomplished using light weighted optical elements, improved support structures, and the development of mosaic Focal Plane Assemblies (mFPA). A mFPA designed for astronomy can use multiple Charged Coupled Devices (CCD) mounted onto a single camera baseplate integrated at the instrument plane of focus. Examples of current, or proposed, missions utilizing mFPA technology include FAME, GEST, Kepler, GAIA, LSST, and SNAP. The development of a mFPA mandates tighter control on the design trades, component development, CCD characterization, component integration, and performance verification testing. This paper addresses the capability Lockheed Martin Space Systems Company's (LMSSC) Advanced Technology Center (ATC) has developed to perform CCD characterization, mFPA assembly and alignment, and mFPA system level testing.

  11. Mosaic Focal Plane Development

    NASA Astrophysics Data System (ADS)

    Mason, D.; Horner, S.; Aamodt, E.

    Advances in manufacturing and applied sciences have enabled the development of large ground and spaced based astronomical instruments having a Field of View (FOV) large enough to capture a large portion of the universe in a single image. A large FOV can be accomplished using light weighted optics, improved structures, and the development of mosaic Focal Plane Assemblies (mFPAs). A mFPA comprises multiple Charged Coupled Devices (CCD) mounted onto a single baseplate integrated at the focus plane of the instrument. Examples of current, or proposed, missions utilizing mFPA technology include FAME, GEST, Kepler, GAIA, LSST, and SNAP. The development of a mFPA mandates tight control on the design trades of component development, CCD definition and characterization, component integration, and performance verification testing. This paper addresses the results of the Lockheed Martin Space Systems Company (LMSSC), Advanced Technology Center (ATC) developed mFPA. The design trades and performance characterization are services provided by the LMSSC ATC but not detailed in this paper.

  12. Lancang—Gengma Earthquake: A Preliminary Report on the November 6, 1988, Event and Its Aftershocks

    NASA Astrophysics Data System (ADS)

    Chen, Yuntai; Wu, Francis T.

    On November 6, 1988, two earthquakes with magnitude >7 occurred within 15 minutes in southwestern Yunnan Province, China, near the Burmese border. The aftershock series in the next six weeks included three earthquakes with magnitude >6.0. Rapid deployment of accelerographs enabled us to record a large number of aftershocks, including two Ms >6 events, at near-source distances.At 130314.5 UT on November 6 an earthquake with Ms = 7.6 (U.S. Geological Survey Ms = 7.3) occurred 40 km northwest of Lancang (Figure 1). Thirteen minutes later another large event with Ms = 7.2 (USGS Ms 6.4) occurred 60 km north-northwest of the first shock. By December 20 more than 600 aftershocks with Ms >3 had occurred.

  13. Focal Mechanism of a Catastrophic Earthquake of the Last Rococo Period (1783) in Southern Italy Retrieved by Inverting Historical Information on Damage

    NASA Astrophysics Data System (ADS)

    Sirovich, L.; Pettenati, F.

    2007-05-01

    Using geophysical inversion to discover the fault source of a blind earthquake, that took place before the invention of the seismograph, seemed impossible. We demonstrated that sometimes it is possible using our simplified KF model (Sirovich, 1996) through automatic genetic inversion (Gentile et al., 2004 in BSSA; Sirovich and Pettenati, 2004 in JGR), and determined it conclusively by treating the Coalinga 1983, Loma Prieta 1989, and Northridge 1994 earthquakes (Pettenati and Sirovich, 2007 in BSSA). KF is able to simulate the body-wave radiation from a linear source, and eleven source parameters are retrieved: the three nucleation coordinates, the fault-plane solution, the seismic moment, the rupture velocities and lengths along-strike and anti-strike, the shear wave velocity in the half-space. To find the minima on the hypersurface of the residuals in the multi-parameter model space, we use a genetic process with niching since we have already shown that the problem is bimodal for pure dip-slip mechanisms. The objective function of the nonlinear inversion is the sum of the squared residuals (calculated-minus-observed intensity at all sites). Here, we use the very good intensity data provided in the MCS scale by the INGV of Italy for the M 6.9 earthquake of Feb. 5, 1783 (see the Italian intensity data bank on http:emidius.mi.ingv.it/DOM/consultazione.html). The data of 1783 were created by seismologists and historians who interpreted the reports of the time and many other historical sources. Given the limitations of the KF approach, we limited our inversion to a square area of 200 by 200 km around the most heavily damaged zone. 341 surveyed towns and hamlets received intensity degrees by INGV (we discarded 6 of them as statistical outliers according to the classical Chauvenet method). Thus, 335 data were inverted. The match between experimental and synthetic isoseismals is really noteworthy. The found mechanism is almost pure dip-slip and, thus, the problem is

  14. Aftershock source imaging using reverse time migration of data from the dense AIDA array deployed after the 2011 Virginia earthquake

    NASA Astrophysics Data System (ADS)

    Wang, K.; Davenport, K. K.; Hole, J. A.; Chapman, M. C.; Quiros, D. A.; Brown, L. D.

    2013-12-01

    Reverse time migration has previously been used to back-project energy recorded by dense arrays to the source region of large subduction-zone earthquakes. The results have illuminated energy release as a function of time and space on the fault surface, improving our understanding of rupture processes. We apply reverse time migration to data from a dense local aftershock array to image magnitude <0 to 3.7 events. AIDA (Aftershock Imaging with Dense Arrays) recorded aftershocks of the August 23, 2011, magnitude 5.8 earthquake in Louisa County, Virginia. AIDA deployed 201 stations in three phases to record wavefields at 200-400 m spacing to reduce spatial aliasing and to lower the event detection threshold. Aftershocks recorded by AIDA were reverse-time migrated in a velocity model created by aftershock travel-time tomography. An aftershock with a magnitude less than 0 was successfully imaged as a point source with a resolution of <200 m. Slip propagation was successfully imaged for a magnitude 3.7 aftershock, propagating 200-300 m shallower and southward. Both P and S-wave data were independently migrated, with similar results. The method is being applied to automatically detect and locate tiny events with low signal-to-noise ratio. Tests show that the images are limited by insufficient temporal sampling and predictable migration artifacts caused by the station geometry. Future aftershock deployments can improve these conditions.

  15. GIS-based 3D visualization of the Mw 7.7, 2007, Tocopilla aftershocks

    NASA Astrophysics Data System (ADS)

    Eggert, S.; Sobiesiak, M.; Altenbrunn, K.

    2009-12-01

    The November 14, 2007 Mw 7.7 earthquake nucleated on the west coast of northern Chile about 40 km east of the city of Tocopilla. It took place in the southern part of a large seismic gap, the Iquique subduction zone segment which is supposed to be at the end of its seismic cycle. The Tocopilla fault plane appears to be the northern continuation of the Mw 8.0, 1995 Antofagasta earthquake. We present a complex 3D model of the rupture area including first hypocenter localizations of aftershocks following the event. The data was recorded during a mission of the German Task Force for Earthquakes after the 2007 Tocopilla earthquake. The seismic stations were recording the aftershocks from November 2007 until May 2008. In general, subduction zones have a complex structure where most of the volumes examined are characterized by strong variations in physical and material parameters. Therefore, 3D representation of the geophysical and geological conditions to be found are of great importance to understand such a subduction environment. We start with a two-dimensional visualization of the geological and geophysical setting. In a second step, we use GIS as a three-dimensional modeling tool which gives us the possibility to visualize the complex geophysical processes. One can easily add and delete data and focus on the information one needs. This allows us to investigate the aftershock distribution along the subducting slab and identify clear structures and clusters within the data set. Furthermore we combine the 2007 Tocopilla data set with the 1995 Antofagasta aftershocks which provides a new, three-dimensional insight into the segment boundary of these two events. Analyzing the aftershock sequence with a GIS-based model will not only help to visualize the setting but also be the base for various calculations and further explorations of the complex structures. Aftershocks following the 1995 Antofagasta earthquake and the 2007 Tocopilla earthquake

  16. Spatial and temporal analysis of the Mw 7.7, 2007, Tocopilla aftershock sequence

    NASA Astrophysics Data System (ADS)

    Eggert, Silke; Sobiesiak, Monika

    2010-05-01

    On 14 November 2007, 15:40:51 UTC a large Mw 7.7 earthquake occurred in the region of Tocopilla in Northern Chile. The epicenter is located at 22.30°S, 69.89°W, ~ 35 km south east of the city of Tocopilla and 160 km north of Antofagasta (earthquake location by GEOFON network). The earthquake took place in the southern part of the Northern Chile seismic gap which is supposed to be at the end of its seismic cycle. Currently, the gap is spanning the rupture area of the Mw=9 1877 Iquique event, a region which is now unbroken for almost 150 years. Therefore, the 2007 Tocopilla earthquake is the first large event that occurred inside the Northern Chile seismic gap since 1877. We present a study of the spatial and temporal distribution of the aftershock activity following the 2007 Tocopilla event using the frequency-magnitude distribution and other parameters. Studying this aftershock sequence will provide closer insight into the fault dimension of this subduction zone earthquake and the tectonic setting of the region. The distribution of aftershocks into depth shows that the majority of the hypocenters are located along the subduction interface, reaching down to ~ 50 km depth. In the western part, the aftershock sequence splits into two branches, one heading towards the trench, the other bending into the crust in front of the Mejillones Peninsula. In the epicentral horizontal, we observe a concentration of aftershocks around the northern part of the Mejillones Peninsula and along the coast up to the Río Loa. This leads to the conclusion that the shallow part in the north west did probably not break during the event. The spatial density of aftershocks shows two offshore patches north-east of the peninsula. Analyzing the spatio-temporal distribution of our aftershock data set, we can see that the fault rupture propagated towards the south west with a fault plane of about 150 km length. These observations are consistent with first results by other studies. Our

  17. DETERMINATION OF ELASTIC WAVE VELOCITY AND RELATIVE HYPOCENTER LOCATIONS USING REFRACTED WAVES. II. APPLICATION TO THE HAICHENG, CHINA, AFTERSHOCK SEQUENCE.

    USGS Publications Warehouse

    Shedlock, Kaye M.; Jones, Lucile M.; Ma, Xiufang

    1985-01-01

    The authors located the aftershocks of the February 4, 1975 Haicheng, China, aftershock sequence using an arrival time difference (ATD) simultaneous inversion method for determining the near-source (in situ) velocity and the location of the aftershocks with respect to a master event. The aftershocks define a diffuse zone, 70 km multiplied by 25 km, trending west-northwest, perpendicular to the major structural trend of the region. The main shock and most of the large aftershocks have strike-slip fault plane solutions. The preferred fault plane strikes west-northwest, and the inferred sense of motion is left-lateral. The entire Haicheng earthauake sequence appears to have been the response of an intensely faulted range boundary to a primarily east-west crustal compression and/or north-south extension.

  18. Syntelencephaly associated with connected transhemispheric cleft of focal cortical dysplasia.

    PubMed

    Fujimoto, S; Togari, H; Banno, T; Wada, Y

    1999-05-01

    The authors report a female with syntelencephaly associated with a connected transhemispheric cleft of focal cortical dysplasia. Syntelencephaly is a rare anomaly characterized by fusion of the hemispheres in the posterior frontal and parietal regions and is considered a new variant of holoprosencephaly. Cranial magnetic resonance imaging of the patient revealed syntelencephaly associated with bilateral fused clefts of focal cortical dysplasia without the pial-ependymal seam, which was regarded as an incomplete type of schizencephaly. The underlying mechanism is discussed. PMID:10371387

  19. Optimally oriented ``fault-valve'' thrusts: Evidence for aftershock-related fluid pressure pulses?

    NASA Astrophysics Data System (ADS)

    Micklethwaite, S.

    2008-04-01

    A thrust-vein network from the Triumph gold deposit, Western Australia, is explained in terms of an extremely high rate of fluid-pressure increase, prior to failure, relative to the rate of stress increase. The thrust fault is a small-displacement fault characterized by a thick, fault-parallel shear vein, plus multiple low-angle extension veins, with orientations that demonstrate the thrust was optimally oriented relative to the locally imposed crustal stresses. Large extension veins have irregular margins, are dominantly composed of coarse milky quartz with no obvious laminations or solid inclusion trails, and are regularly spaced along the thrust (1-2 m). The fault-vein geometries indicate the Triumph thrust is a rare candidate for "fault-valve" failure of an optimally oriented thrust, and it is possible the structure formed in a small number of failure events, during load weakening of the thrust. An analysis using the Coulomb criterion shows that load weakening of a thrust occurs when fluid pressure increases relative to tectonic stress by a factor dependent on the orientation of the thrust. Thrust and reverse faults in dry crust load strengthen prior to failure, but the poroelastic behavior of sealed, fluid-saturated crust is enough to induce load weakening in compressive environments; thus poroelastic load weakening is expected to be an important failure mechanism in hydrothermal environments. However, in the case of the Triumph thrust, dilatant shear failure necessitates a fluid pressure increase which is an order of magnitude larger still. The observations and results are consistent with a pulse of high fluid pressure migrating up through fault or fracture networks that have elevated permeability relative to the wall rock, under conditions of transiently low differential stress. Fluid pressure differences resulted between the fault and wall rock, leading to extension fracture and fault failure. Such conditions may occur when adjacent large earthquakes induce

  20. Propagation of Coulomb stress uncertainties in physics-based aftershock models

    NASA Astrophysics Data System (ADS)

    Cattania, Camilla; Hainzl, Sebastian; Wang, Lifeng; Roth, Frank; Enescu, Bogdan

    2014-10-01

    Stress transfer between earthquakes is recognized as a fundamental mechanism governing aftershock sequences. A common approach to relate stress changes to seismicity rate changes is the rate-and-state constitutive law developed by Dieterich: these elements are the foundation of Coulomb-rate-and-state (CRS) models. Despite the successes of Coulomb hypothesis and of the rate-and-state formulation, such models perform worse than statistical models in an operational forecasting context: one reason is that Coulomb stress is subject to large uncertainties and intrinsic spatial heterogeneity. In this study, we characterize the uncertainties in Coulomb stress inherited from different physical quantities and assess their effect on CRS models. We use a Monte Carlo method and focus on the following aspects: the existence of multiple receiver faults; the stress heterogeneity within grid cells, due to their finite size; and errors inherited from the coseismic slip model. We study two well-recorded sequences from different tectonic settings: the Mw = 6.0 Parkfield and the Mw= 9.0 Tohoku earthquakes. We find that the existence of multiple receiver faults is the most important source of intrinsic stress heterogeneity, and CRS models perform significantly better when this variability is taken into account. The choice of slip model also generates large uncertainties. We construct an ensemble model based on published slip models and find that it outperforms individual models. Our findings highlight the importance of identifying sources of errors and quantifying confidence boundaries in the forecasts; moreover, we demonstrate that consideration of stress heterogeneity and epistemic uncertainty has the potential to improve the performance of operational forecasting models.

  1. Aftershock seismicity and Tectonic Setting of the 16 September 2015 Mw 8.3 Illapel earthquake

    NASA Astrophysics Data System (ADS)

    Lange, Dietrich; Geersen, Jacob; Barrientos, Sergio; Moreno, Marcos; Grevemeyer, Ingo; Contreras-Reyes, Eduardo; Kopp, Heidrun

    2016-04-01

    Powerful subduction zone earthquakes rupture thousands of square kilometers along continental margins but at certain locations earthquake rupture terminates. On 16 September 2015 the Mw. 8.3 Illapel earthquake ruptured a 200 km long stretch of the Central Chilean subduction zone, triggering a tsunami and causing significant damage. Here we analyze the spatial pattern of coseismic rupture and the temporal and spatial pattern of local seismicity for aftershocks and foreshocks in relation to the tectonic setting in the earthquake area. Aftershock seismicity surrounds the rupture area in lateral and downdip direction. For the first 24 hours following the mainshock we observe aftershock migration to both lateral directions with velocities of approximately 2.5 and 5 km/h. At the southern earthquake boundary aftershocks cluster around individual subducted seamounts located on the prolongation of the downthrusting Juan Fernández Ridge indicating stress transfer from the main rupture area. In the northern part of the rupture area a deeper band of local seismicity is observed indicating an alternation of seismic to aseismic behavior of the plate interface in downdip direction. This aseismic region at ~30 km depth that is also observed before the Illapel 2015 earthquake is likely controlled by the intersection of the continental Moho with the subducting slab.

  2. Statistical properties of aftershock rate decay: Implications for the assessment of continuing activity

    NASA Astrophysics Data System (ADS)

    Adamaki, Aggeliki; Papadimitriou, Eleftheria; Tsaklidis, George; Karakostas, Vassilios

    2011-08-01

    Aftershock rates seem to follow a power law decay, but the assessment of the aftershock frequency immediately after an earthquake, as well as during the evolution of a seismic excitation remains a demand for the imminent seismic hazard. The purpose of this work is to study the temporal distribution of triggered earthquakes in short time scales following a strong event, and thus a multiple seismic sequence was chosen for this purpose. Statistical models are applied to the 1981 Corinth Gulf sequence, comprising three strong (M = 6.7, M = 6.5, and M = 6.3) events between 24 February and 4 March. The non-homogeneous Poisson process outperforms the simple Poisson process in order to model the aftershock sequence, whereas the Weibull process is more appropriate to capture the features of the short-term behavior, but not the most proper for describing the seismicity in long term. The aftershock data defines a smooth curve of the declining rate and a long-tail theoretical model is more appropriate to fit the data than a rapidly declining exponential function, as supported by the quantitative results derived from the survival function. An autoregressive model is also applied to the seismic sequence, shedding more light on the stationarity of the time series.

  3. Aftershocks and Omori's law in a modified Carlson-Langer model with nonlinear viscoelasticity

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Hidetsugu; Okamura, Kazuki

    2015-05-01

    A modified Carlson-Langer model for earthquakes is proposed, which includes nonlinear viscoelasticity. Several aftershocks are generated after the main shock owing to the damping of the additional viscoelastic force. Both the Gutenberg-Richter law and Omori's law are reproduced in a numerical simulation of the modified Carlson-Langer model on a critical percolation cluster of a square lattice.

  4. The 1886-1889 aftershocks of the Charleston, South Carolina, Earthquake: A Widespread burst of seismicity

    NASA Astrophysics Data System (ADS)

    Seeber, L.; Armbruster, J. G.

    1987-03-01

    A systematic search of contemporary newspapers in South Carolina, North Carolina, Georgia and eastern Tennessee during the 1886-1889 (inclusive) aftershock sequence of the August 31, 1886 earthquake near Charleston, South Carolina has provided more than 3000 intensity reports for 522 earthquakes as compared to 144 previously known earthquakes for the same period. Of these 144 events, 138 were felt in Charleston/Summerville and had been assigned epicenters in that area. In contrast the new data provide 112 well-constrained macroseismic epicenters. The 1886-1889 seismicity is characterized by a linear relation between log frequency and magnitude with a slope b≈1, a temporal decay of earthquake frequency proportional to time-1, and a low level of seismicity prior to the main shock. These are frequently observed characteristics of aftershock sequences. By 1889, the level of seismicity had decreased more than 2 orders of magnitude, reaching approximately the current level in the same area. The 1886-1889 epicenters delineate a large aftershock zone that extends northwest about 250 km across Appalachian strike from the coast into the Piedmont and at least 100 km along strike near the Fall Line of South Carolina and Georgia. An abrupt change in stress and/or effective strength is required over this zone. If this change can only occur in the near field of a single fault dislocation, this fault must be larger horizontally than the thickness of the seismogenic zone by an order of magnitude and must be shallow dipping. The correlation between the area of intensity VIII in the main shock with the area of large aftershocks is consistent with this hypothesis. The lack of a major fault affecting the post-Upper Jurassic onlap sediments also favors a shallow dipping active fault, possibly a Paleozoic-Mesozoic southeasterly dipping fault or detachment that may outcrop northwest of the aftershock zone. The 1886-1889 aftershocks occupy the same area as the South Carolina

  5. 2008 Little Andaman aftershock: Genetic linkages with the subducting 90°E ridge and 2004 Sumatra-Andaman earthquake

    NASA Astrophysics Data System (ADS)

    Catherine, J. K.; Gahalaut, V. K.; Ambikapathy, A.; Kundu, Bhaskar; Subrahmanyam, C.; Jade, S.; Bansal, Amit; Chadha, R. K.; Narsaiah, M.; Premkishore, L.; Gupta, D. C.

    2009-12-01

    We analyse the June 27, 2008 Little Andaman aftershock (Mw 6.6) of December 26, 2004 Sumatra-Andaman earthquake (Mw 9.2) that occurred near the trench in the subducting India plate beneath the Sunda Plate. Unlike majority of the other aftershocks in the frontal arc, the Little Andaman aftershock and its own aftershocks occurred through normal slip on the north-south oriented steep planes. We use the coseismic and ongoing postseismic deformation due to the 2004 Sumatra-Andaman earthquake at a GPS site nearest to the Little Andaman aftershock and compute changes in the Coulomb stresses due to the coseismic slip and postseismic afterslip. The Coulomb stress on the Little Andaman aftershock fault plane progressively increased since the 2004 Sumatra-Andaman earthquake which probably led to the occurrence of the Little Andaman aftershock on the pre-existing N-S oriented strike-slip steep planes of the subducting 90°E ridge that were reactivated through normal slip.

  6. Three Dimensional P Wave Velocity Model for the Crust Containing Aftershocks of the Bhuj, India Earthquake

    NASA Astrophysics Data System (ADS)

    Powell, C. A.; Vlahovic, G.; Bodin, P.; Horton, S.

    2001-12-01

    A three-dimensional P wave velocity model has been constructed for the crust in the vicinity of the Mw=7.7 January 26th Bhuj, India earthquake using aftershock data obtained by CERI away teams. Aftershocks were recorded by 8 portable, digital K2 seismographs (the MAEC/ISTAR network) and by a continuously recording Guralp CMG40TD broad-band seismometer. Station spacing is roughly 30 km. The network was in place for 18 days and recorded ground motions from about 2000 aftershocks located within about 100 km of all stations. The 3-D velocity model is based upon an initial subset of 461 earthquakes with 2848 P wave arrivals. The initial 1-D velocity model was determined using VELEST and the 3-D model was determined using the nonlinear travel time tomography method of Benz et al. [1996]. Block size was set at 2 by 2 by 2 km. A 45% reduction in RMS travel time residuals was obtained after 10 iterations holding hypocenters fixed. We imaged velocity anomalies in the range -2 to 4%. Low velocities were found in the upper 6 km and the anomalies follow surface features such as the Rann of Kutch. High velocity features were imaged at depth and are associated with the aftershock hypocenters. High crustal velocities are present at depths exceeding 20 km with the exception of the crust below the Rann of Kutch. The imaged velocity anomaly pattern does not change when different starting models are used and when hypocenters are relocated using P wave arrivals only. The analysis will be extended to an expanded data set of 941 aftershocks.

  7. Effects of Aftershock Declustering in Risk Modeling: Case Study of a Subduction Sequence in Mexico

    NASA Astrophysics Data System (ADS)

    Kane, D. L.; Nyst, M.

    2014-12-01

    Earthquake hazard and risk models often assume that earthquake rates can be represented by a stationary Poisson process, and that aftershocks observed in historical seismicity catalogs represent a deviation from stationarity that must be corrected before earthquake rates are estimated. Algorithms for classifying individual earthquakes as independent mainshocks or as aftershocks vary widely, and analysis of a single catalog can produce considerably different earthquake rates depending on the declustering method implemented. As these rates are propagated through hazard and risk models, the modeled results will vary due to the assumptions implied by these choices. In particular, the removal of large aftershocks following a mainshock may lead to an underestimation of the rate of damaging earthquakes and potential damage due to a large aftershock may be excluded from the model. We present a case study based on the 1907 - 1911 sequence of nine 6.9 <= Mw <= 7.9 earthquakes along the Cocos - North American plate subduction boundary in Mexico in order to illustrate the variability in risk under various declustering approaches. Previous studies have suggested that subduction zone earthquakes in Mexico tend to occur in clusters, and this particular sequence includes events that would be labeled as aftershocks in some declustering approaches yet are large enough to produce significant damage. We model the ground motion for each event, determine damage ratios using modern exposure data, and then compare the variability in the modeled damage from using the full catalog or one of several declustered catalogs containing only "independent" events. We also consider the effects of progressive damage caused by each subsequent event and how this might increase or decrease the total losses expected from this sequence.

  8. Statistical Variability and Tokunaga Branching of Aftershock Sequences Utilizing BASS Model Simulations

    NASA Astrophysics Data System (ADS)

    Yoder, Mark R.; Van Aalsburg, Jordan; Turcotte, Donald L.; Abaimov, Sergey G.; Rundle, John B.

    2013-01-01

    Aftershock statistics provide a wealth of data that can be used to better understand earthquake physics. Aftershocks satisfy scale-invariant Gutenberg-Richter (GR) frequency-magnitude statistics. They also satisfy Omori's law for power-law seismicity rate decay and Båth's law for maximum-magnitude scaling. The branching aftershock sequence (BASS) model, which is the scale-invariant limit of the epidemic-type aftershock sequence model (ETAS), uses these scaling laws to generate synthetic aftershock sequences. One objective of this paper is to show that the branching process in these models satisfies Tokunaga branching statistics. Tokunaga branching statistics were originally developed for drainage networks and have been subsequently shown to be valid in many other applications associated with complex phenomena. Specifically, these are characteristic of a universality class in statistical physics associated with diffusion-limited aggregation. We first present a deterministic version of the BASS model and show that it satisfies the Tokunaga side-branching statistics. We then show that a fully stochastic BASS simulation gives similar results. We also study foreshock statistics using our BASS simulations. We show that the frequency-magnitude statistics in BASS simulations scale as the exponential of the magnitude difference between the mainshock and the foreshock, inverse GR scaling. We also show that the rate of foreshock occurrence in BASS simulations decays inversely with the time difference between foreshock and mainshock, an inverse Omori scaling. Both inverse scaling laws have been previously introduced empirically to explain observed foreshock statistics. Observations have demonstrated both of these scaling relations to be valid, consistent with our simulations. ETAS simulations, in general, do not generate Båth's law and do not generate inverse GR scaling.

  9. Decay of aftershock density with distance does not indicate triggering by dynamic stress.

    PubMed

    Richards-Dinger, Keith; Stein, Ross S; Toda, Shinji

    2010-09-30

    Resolving whether static or dynamic stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard. Felzer and Brodsky examined the distance distribution of earthquakes occurring in the first five minutes after 2 ≤ M < 3 and 3 ≤ M < 4 mainshocks and found that their magnitude M ≥ 2 aftershocks showed a uniform power-law decay with slope -1.35 out to 50 km from the mainshocks. From this they argued that the distance decay could be explained only by dynamic triggering. Here we propose an alternative explanation for the decay, and subject their hypothesis to a series of tests, none of which it passes. At distances more than 300 m from the 2 ≤ M < 3 mainshocks, the seismicity decay 5 min before the mainshocks is indistinguishable from the decay five minutes afterwards, indicating that the mainshocks have no effect at distances outside their static triggering range. Omori temporal decay, the fundamental signature of aftershocks, is absent at distances exceeding 10 km from the mainshocks. Finally, the distance decay is found among aftershocks that occur before the arrival of the seismic wave front from the mainshock, which violates causality. We argue that Felzer and Brodsky implicitly assume that the first of two independent aftershocks along a fault rupture triggers the second, and that the first of two shocks in a creep- or intrusion-driven swarm triggers the second, when this need not be the case. PMID:20882015

  10. Precise Measurement of Effective Focal Length

    NASA Technical Reports Server (NTRS)

    Wise, T. D.; Young, J. B.

    1983-01-01

    Computerized instrument measures effective focal lengths to 0.01 percent accuracy. Laser interferometers measure mirror angle and stage coordinate y in instrument for accurate measurment of focal properties of optical systems. Operates under computer control to measure effective focal length, focal surface shape, modulation transfer function, and astigmatism.

  11. Perverted head shaking nystagmus in focal pontine infarction.

    PubMed

    Kim, Hyun-Ah; Lee, Hyung; Sohn, Sung-Il; Kim, Ji Soo; Baloh, Robert W

    2011-02-15

    Although several papers have been published on perverted head shaking nystagmus (PHSN) associated with focal brainstem or cerebellar lesion, there are no reports of a focal pontine infarct that causes PHSN. We report a patient with focal pontine infarction who presented with sustained dizziness, limb dysmetria on the left extremity, decreased sensations to position and vibration of the left extremity, and gait imbalance. Only vestibular abnormality was downbeat nystagmus after vigorous head shakings. The maximum slow phase velocity of PHSN was 26°/s, and its duration was about 20s. This is the first report of PHSN associated with focal pontine infarction. Crossed ventral tegmental tract and velocity storage mechanism of vestibulocerebellum might be related on PHSN in this case. PMID:21146834

  12. Focal Adhesion Kinase-Dependent Regulation of Adhesive Force Involves Vinculin Recruitment to Focal Adhesions

    PubMed Central

    Hanks, Steven K.; García, Andrés J.

    2016-01-01

    Background information Focal adhesion kinase (FAK), an essential non-receptor tyrosine kinase, plays pivotal roles in migratory responses, adhesive signaling, and mechanotransduction. FAK-dependent regulation of cell migration involves focal adhesion turnover dynamics as well as actin cytoskeleton polymerization and lamellipodia protrusion. Whereas roles for FAK in migratory and mechanosensing responses have been established, the contributions of FAK to the generation of adhesive forces are not well understood. Results Using FAK-null cells expressing wild-type and mutant FAK under an inducible tetracycline promoter, we analyzed the role of FAK in the generation of steady-state adhesive forces using micropatterned substrates and a hydrodynamic adhesion assay. FAK expression reduced steady-state strength by 30% compared to FAK-null cells. FAK expression reduced vinculin localization to focal adhesions by 35% independently from changes in integrin binding and localization of talin and paxillin. RNAi knockdown of vinculin abrogated the FAK-dependent differences in adhesive force. FAK-dependent changes in vinculin localization and adhesive force were confirmed in human primary fibroblasts with FAK knocked down by RNAi. The autophosphorylation Y397 and kinase domain Y576/Y577 sites were differentially required for FAK-mediated adhesive responses. Conclusions We demonstrate that FAK reduces steady-state adhesion strength by modulating vinculin recruitment to focal adhesions. These findings provide insights into the role of FAK in mechanical interactions between a cell and the extracellular matrix. PMID:19883375

  13. Thermomechanical architecture of the VIS focal plane for Euclid

    NASA Astrophysics Data System (ADS)

    Martignac, Jérôme; Carty, Michaël.; Tourette, Thierry; Bachet, Damien; Berthé, Michel; Augueres, Jean-Louis; Amiaux, Jérôme; Fontignie, Jean; Horeau, Benoît; Renaud, Diana; Pottinger, Sabrina; Denniston, James; Winter, Berend; Guttridge, Phillip; Cole, Richard; Cropper, Mark; Niemi, Sami; Coker, John; Hunt, Thomas

    2014-08-01

    One of the main challenges for current and near future space experiments is the increase of focal plane complexity in terms of amount of pixels. In the frame work of the ESA Euclid mission to be launched in 2020, the Euclid Consortium is developing an extremely large and stable focal plane for the VIS instrument. CEA has developed the thermomechanical architecture of that Focal Plane taking into account all the very stringent performance and mission related requirements. The VIS Focal Plane Assembly integrates 36 CCDs (operated at 150K) connected to their front end electronics (operated at 280K) as to obtain one of the largest focal plane (˜0.6 billion pixels) ever built for space application after the GAIA one. The CCDs are CCD273 type specially designed and provided by the e2v company under ESA contract, front end electronics is studied and provided by MSSL. In this paper we first recall the specific requirements that have driven the overall architecture of the VIS-FPA and especially the solutions proposed to cope with the scientific needs of an extremely stable focal plane, both mechanically and thermally. The mechanical structure based on SiC material used for the cold sub assembly supporting the CCDs is detailed. We describe also the modular architecture concept that we have selected taking into account AIT-AIV and programmatic constraints.

  14. Implications of spatial and temporal development of the aftershock sequence for the Mw 8.3 June 9, 1994 Deep Bolivian Earthquake

    NASA Astrophysics Data System (ADS)

    Myers, Stephen C.; Wallace, Terry C.; Beck, Susan L.; Silver, Paul G.; Zandt, George; Vandecar, John; Minaya, Estela

    On June 9, 1994 the Mw 8.3 Bolivia earthquake (636 km depth) occurred in a region which had not experienced significant, deep seismicity for at least 30 years. The mainshock and aftershocks were recorded in Bolivia on the BANJO and SEDA broadband seismic arrays and on the San Calixto Network. We used the joint hypocenter determination method to determine the relative location of the aftershocks. We have identified no foreshocks and 89 aftershocks (m > 2.2) for the 20-day period following the mainshock. The frequency of aftershock occurrence decreased rapidly, with only one or two aftershocks per day occuring after day two. The temporal decay of aftershock activity is similar to shallow aftershock sequences, but the number of aftershocks is two orders of magnitude less. Additionally, a mb ∼6, apparently triggered earthquake occurred just 10 minutes after the mainshock about 330 km east-southeast of the mainshock at a depth of 671 km. The aftershock sequence occurred north and east of the mainshock and extends to a depth of 665 km. The aftershocks define a slab striking N68°W and dipping 45°NE. The strike, dip, and location of the aftershock zone are consistent with this seismicity being confined within the downward extension of the subducted Nazca plate. The location and orientation of the aftershock sequence indicate that the subducted Nazca plate bends between the NNW striking zone of deep seismicity in western Brazil and the N-S striking zone of seismicity in central Bolivia. A tear in the deep slab is not necessitated by the data. A subset of the aftershock hypocenters cluster along a subhorizontal plane near the depth of the mainshock, favoring a horizontal fault plane. The horizontal dimensions of the mainshock [Beck et al., this issue; Silver et al., 1995] and slab defined by the aftershocks are approximately equal, indicating that the mainshock ruptured through the slab.

  15. Sex prevalence of focal dystonias.

    PubMed Central

    Soland, V L; Bhatia, K P; Marsden, C D

    1996-01-01

    The sex prevalence of idiopathic focal dystonia is reported from a data base review of all patients seen at the National Hospital of Neurology, Queen Square and King's College, London up to 1993. There was a higher prevalence of females to males in all categories of focal dystonia involving the craniocervical region. The female to male ratio for cranial dystonia was 1.92:1 (P < 0.01) and 1.6:1 (P < 0.001) for spasmodic torticollis. On the other hand, twice as many men than women had writer's cramp (M:F = 2.0:1, P < 0.01). At present, there is no clear explanation to account for this differences in the sex prevalence of different types of focal dystonia. PMID:8708656

  16. Continuously variable focal length lens

    DOEpatents

    Adams, Bernhard W; Chollet, Matthieu C

    2013-12-17

    A material preferably in crystal form having a low atomic number such as beryllium (Z=4) provides for the focusing of x-rays in a continuously variable manner. The material is provided with plural spaced curvilinear, optically matched slots and/or recesses through which an x-ray beam is directed. The focal length of the material may be decreased or increased by increasing or decreasing, respectively, the number of slots (or recesses) through which the x-ray beam is directed, while fine tuning of the focal length is accomplished by rotation of the material so as to change the path length of the x-ray beam through the aligned cylindrical slows. X-ray analysis of a fixed point in a solid material may be performed by scanning the energy of the x-ray beam while rotating the material to maintain the beam's focal point at a fixed point in the specimen undergoing analysis.

  17. Seismotectonics of the April-May 2015 Nepal earthquakes: An assessment based on the aftershock patterns, surface effects and deformational characteristics

    NASA Astrophysics Data System (ADS)

    Parameswaran, Revathy M.; Natarajan, Thulasiraman; Rajendran, Kusala; Rajendran, C. P.; Mallick, Rishav; Wood, Matthew; Lekhak, Harish C.

    2015-11-01

    Occurrence of the April 25, 2015 (Mw 7.8) earthquake near Gorkha, central Nepal, and another one that followed on May 12 (Mw 7.3), located ∼140 km to its east, provides an exceptional opportunity to understand some new facets of Himalayan earthquakes. Here we attempt to assess the seismotectonics of these earthquakes based on the deformational field generated by these events, along with the spatial and temporal characteristics of their aftershocks. When integrated with some of the post-earthquake field observations, including the localization of damage and surface deformation, it became obvious that although the mainshock slip was mostly limited to the Main Himalayan Thrust (MHT), the rupture did not propagate to the Main Frontal Thrust (MFT). Field evidence, supported by the available InSAR imagery of the deformation field, suggests that a component of slip could have emerged through a previously identified out-of-sequence thrust/active thrust in the region that parallels the Main Central Thrust (MCT), known in the literature as a co-linear physiographic transitional zone called PT2. Termination of the first rupture, triggering of the second large earthquake, and distribution of aftershocks are also spatially constrained by the eastern extremity of PT2. Mechanism of the 2015 sequence demonstrates that the out-of-sequence thrusts may accommodate part of the slip, an aspect that needs to be considered in the current understanding of the mechanism of earthquakes originating on the MHT.

  18. A Fluid-driven Earthquake Cycle, Omori's Law, and Fluid-driven Aftershocks

    NASA Astrophysics Data System (ADS)

    Miller, S. A.

    2015-12-01

    Few models exist that predict the Omori's Law of aftershock rate decay, with rate-state friction the only physically-based model. ETAS is a probabilistic model of cascading failures, and is sometimes used to infer rate-state frictional properties. However, the (perhaps dominant) role of fluids in the earthquake process is being increasingly realised, so a fluid-based physical model for Omori's Law should be available. In this talk, I present an hypothesis for a fluid-driven earthquake cycle where dehydration and decarbonization at depth provides continuous sources of buoyant high pressure fluids that must eventually make their way back to the surface. The natural pathway for fluid escape is along plate boundaries, where in the ductile regime high pressure fluids likely play an integral role in episodic tremor and slow slip earthquakes. At shallower levels, high pressure fluids pool at the base of seismogenic zones, with the reservoir expanding in scale through the earthquake cycle. Late in the cycle, these fluids can invade and degrade the strength of the brittle crust and contribute to earthquake nucleation. The mainshock opens permeable networks that provide escape pathways for high pressure fluids and generate aftershocks along these flow paths, while creating new pathways by the aftershocks themselves. Thermally activated precipitation then seals up these pathways, returning the system to a low-permeability environment and effective seal during the subsequent tectonic stress buildup. I find that the multiplicative effect of an exponential dependence of permeability on the effective normal stress coupled with an Arrhenius-type, thermally activated exponential reduction in permeability results in Omori's Law. I simulate this scenario using a very simple model that combines non-linear diffusion and a step-wise increase in permeability when a Mohr Coulomb failure condition is met, and allow permeability to decrease as an exponential function in time. I show very

  19. A generalized law for aftershock rates in a damage rheology model

    NASA Astrophysics Data System (ADS)

    Ben Zion, Y.; Lyakhovsky, V.

    2003-12-01

    Aftershocks are the response of a damaged rock surrounding large earthquake ruptures to the stress perturbations produced by the large events. Lyakhovsky et al. [JGR, 1997] developed a damage rheology model that provides a quantitative treatment for macroscopic effects of evolving distributed cracking with local density represented by a state variable a. The equation for damage evolution, based on the balance equations of energy and entropy and generalization of linear elasticity, accounts for both degradation and healing as a function of the existing strain tensor and material properties that may be constrained by lab data (rate coefficients and ratio of strain invariants separating states of degradation and healing). Analyses of stress-strain and acoustic emission laboratory data during deformation leading to brittle failure indicate further [Liu et al., AGU, F01; Hamiel et al., this meeting] that the fit between model predictions and observations improves if we also incorporate gradual accumulation of a non-reversible deformation with a rate proportional to the rate of damage increase. For analysis of aftershocks, we consider the relaxation process of a material following the application of a strain step associated with the occurrence of a mainshock. The coupled differential equations governing the damage evolution and stress relaxation can be written in non-dimensional form by scaling the elastic stress to its initial value and the time to characteristic time of damage evolution td. With this, the system behavior is controlled by a single non-dimensional ratio R = td/tM representing the ratio between the damage time scale to the Maxwell relaxation time tM. For very small R there is no relaxation and the response consists of constant rate of damage increase until failure. For very large R there is rapid relaxation without significant change to the level of damage. For intermediate cases the equations are strongly coupled and nonlinear. The analytical solution

  20. Hurricane Irene's Impacts on the Aftershock Sequence of the 2011 Mw5.8 Virginia Earthquake

    NASA Astrophysics Data System (ADS)

    Meng, X.; Peng, Z.; Yang, H.; Allman, S.

    2013-12-01

    Recent studies have shown that typhoon could trigger shallow slow-slip events in Taiwan. However, it is unclear whether such extreme weather events could affect the occurrence of regular earthquakes as well. A good opportunity to test this hypothesis occurred in 2011 when an Mw 5.8 earthquake struck Louisa County, Virginia. This event ruptured a shallow, reverse fault. Roughly 5 days later, hurricane Irene struck the coast of Norfolk, Virginia, which is near the epicentral region of the Virginia mainshock. Because aftershocks listed in the ANSS catalog were incomplete immediately after the main shock, it is very difficult to find the genuine correlation between the seismicity rate changes and hurricane Irene. Hence, we use a recently developed waveform matched filter technique to scan through the continuous seismic data to detect small aftershocks that are previously unidentified. A mixture of 7 temporary stations from the IRIS Ramp deployment and 8 temporary stations deployed by Virginia Tech is used. The temporary stations were set up between 24 to 72 hours following the main shock around its immediate vicinity, which provides us a unique dataset recording the majority aftershock sequence of an intraplate earthquake. We us 80 aftershocks identified by Chapman [2013] as template events and scan through the continuous data from 23 August 2011 through 10 September 2011. So far, we have detected 704 events using a threshold of 12 times the median absolute deviation (MAD), which is ~25 times more than listed in the ANSS catalog. The aftershock rate generally decayed with time as predicted by the Omori's law. A statistically significant increase of seismicity rate is found when hurricane Irene passed by the epicentral region. A possible explanation is that the atmosphere pressure drop unloaded the surface, which brought the reverse faults closer to failure. However, we also identified similar fluctuations of seismicity rate changes at other times. Hence, it is still

  1. Shear Wave Splitting Analysis of Aftershocks of the 2013 Mw6.6 Lushan Earthquake, China

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Zhang, H.

    2013-12-01

    Shear wave splits into faster and slower shear waves that are nearly perpendicular when it travels through an anisotropic medium. There are two important parameters of shear wave splitting, one is the fast polarization direction of the fast shear wave and the other one is the time delay of the slow shear wave. The mechanisms for anisotropy in the upper crust can be divided into two categories. The first category is stress-induced anisotropy related to alignment of cracks in response to the in situ stress field. The second category is structural anisotropy associated with aligned planar features such as fault zone fabrics, sedimentary bedding planes and aligned minerals. We can characterize anisotropy around fault zone by shear wave splitting analysis. We used cross-correlation method for the shear wave splitting analysis. Since the faster shear wave and the slower shear wave are from the same source, they will correlate well after the time delay correction. We rotated two horizontal seismograms at a 10 increment of azimuth α from 00 to 1800. For each α, the cross-correlation coefficients between the two orthogonal seismograms are calculated for a range of time delays τ. When the absolute value of cross-correlation coefficient reaches a maximum, the corresponding values of α and τ are chosen as the fast polarization direction of the faster shear wave and the time delay of the slower shear wave, respectively. We chose 200 aftershocks observed at a temporary array consisting of 29 stations in the Lushan region. Shear wave arrivals were first picked for setting up the time window for the shear wave splitting analysis using the cross-correlation method. Because these 200 events are shallower than 20km, we can infer that the shear wave splitting is caused by crustal anisotropy. The rose diagram of the fast polarization directions of the fast shear waves showed two major directions. One is nearly parallel to the south-north trending fault system in this region, and

  2. Focal weakness following herpes zoster.

    PubMed Central

    Cockerell, O C; Ormerod, I E

    1993-01-01

    Three patients presented with focal weakness of an arm which followed segmental herpes zoster affecting the same limb. Neurophysiological investigations suggest that the site of the lesion lay at the root, plexus, or peripheral nerve level. This reflects the various ways in which the virus may affect the peripheral nervous system. PMID:8410022

  3. Real-time forecast of aftershocks from a single seismic station signal

    NASA Astrophysics Data System (ADS)

    Lippiello, E.; Cirillo, A.; Godano, G.; Papadimitriou, E.; Karakostas, V.

    2016-06-01

    The evaluation of seismic hazard in the hours following large earthquakes is strongly affected by biases due to difficulties in determining earthquake location. This leads to the huge incompleteness of instrumental catalogs. Here we show that if, on the one hand, the overlap of aftershock coda waves hides many small events, on the other hand, it leads to a well-determined empirical law controlling the decay of the amplitude of the seismic signal at a given site. The fitting parameters of this law can be related to those controlling the temporal decay of the aftershock number, and it is then possible to obtain short-term postseismic occurrence probability from a single recorded seismic signal. We therefore present a novel procedure which, without requiring earthquake location, produces more accurate and almost real-time forecast, in a site of interest, directly from the signal of a seismic station installed at that site.

  4. The aftershock sequence of the 2015 April 25 Gorkha-Nepal earthquake

    NASA Astrophysics Data System (ADS)

    Adhikari, L. B.; Gautam, U. P.; Koirala, B. P.; Bhattarai, M.; Kandel, T.; Gupta, R. M.; Timsina, C.; Maharjan, N.; Maharjan, K.; Dahal, T.; Hoste-Colomer, R.; Cano, Y.; Dandine, M.; Guilhem, A.; Merrer, S.; Roudil, P.; Bollinger, L.

    2015-12-01

    The M 7.8 2015 April 25 Gorkha earthquake devastated the mountainous southern rim of the High Himalayan range in central Nepal. The main shock was followed by 553 earthquakes of local magnitude greater than 4.0 within the first 45 days. In this study, we present and qualify the bulletin of the permanent National Seismological Centre network to determine the spatio-temporal distribution of the aftershocks. The Gorkha sequence defines a ˜140-km-long ESE trending structure, parallel to the mountain range, abutting on the presumed extension of the rupture plane of the 1934 M 8.4 earthquake. In addition, we observe a second seismicity belt located southward, under the Kathmandu basin and in the northern part of the Mahabarat range. Many aftershocks of the Gorkha earthquake sequence have been felt by the 3 millions inhabitants of the Kathmandu valley.

  5. Aftershocks of the December 7, 2012 intraplate doublet near the Japan Trench axis

    NASA Astrophysics Data System (ADS)

    Obana, Koichiro; Kodaira, Shuichi; Nakamura, Yasuyuki; Sato, Takeshi; Fujie, Gou; Takahashi, Tsutomu; Yamamoto, Yojiro

    2014-12-01

    On December 7, 2012, a pair of large Mw 7.2 intraplate earthquakes occurred near the Japan Trench axis off Miyagi, northeast Japan. This doublet consisted of a deep reverse-faulting event followed by a shallow normal-faulting event. Aftershock observations using conventional and newly developed ultra-deep ocean bottom seismographs in the trench axis area showed that the shallow normal-faulting event occurred in the subducting Pacific plate just landward of the trench axis. The shallow normal-faulting aftershock activity indicated that in-plate tension in the incoming/subducting Pacific plate extends to a depth of at least 30 km, which is deeper than before the 2011 Tohoku-Oki earthquake, whereas in-plate compression occurs at depths of more than 50 km. Hence, we concluded that the neutral plane of the in-plate stress is located between depths of 30 and 50 km near the trench axis.

  6. Aftershocks of the 2010 Mw 7.2 El Mayor-Cucapah earthquake revealcomplex faulting in the Yuha Desert, California

    USGS Publications Warehouse

    Kroll, K.; Cochran, Elizabeth S.; Richards-Dinger, K.; Sumy, Danielle

    2013-01-01

    We detect and precisely locate over 9500 aftershocks that occurred in the Yuha Desert region during a 2 month period following the 4 April 2010 Mw 7.2 El Mayor-Cucapah (EMC) earthquake. Events are relocated using a series of absolute and relative relocation procedures that include Hypoinverse, Velest, and hypoDD. Location errors are reduced to ~40 m horizontally and ~120 m vertically.Aftershock locations reveal a complex pattern of faulting with en echelon fault segments trending toward the northwest, approximately parallel to the North American-Pacific plate boundary and en echelon, conjugate features trending to the northeast. The relocated seismicity is highly correlated with published surface mapping of faults that experienced triggered surface slip in response to the EMC main shock. Aftershocks occurred between 2 km and 11 km depths, consistent with previous studies of seismogenic thickness in the region. Three-dimensional analysis reveals individual and intersecting fault planes that are limited in their along-strike length. These fault planes remain distinct structures at depth, indicative of conjugate faulting, and do not appear to coalesce onto a throughgoing fault segment. We observe a complex spatiotemporal migration of aftershocks, with seismicity that jumps between individual fault segments that are active for only a few days to weeks. Aftershock rates are roughly consistent with the expected earthquake production rates of Dieterich (1994). The conjugate pattern of faulting and nonuniform aftershock migration patterns suggest that strain in the Yuha Desert is being accommodated in a complex manner.

  7. Aftershock seismicity and tectonic setting of the 16 September 2015 Mw 8.3 Illapel earthquake, Central Chile

    NASA Astrophysics Data System (ADS)

    Lange, Dietrich; Geersen, Jacob; Barrientos, Sergio; Moreno, Marcos; Grevemeyer, Ingo; Contreras-Reyes, Eduardo; Kopp, Heidrun

    2016-06-01

    Powerful subduction zone earthquakes rupture thousands of square kilometers along continental margins but at certain locations earthquake rupture terminates. To date detailed knowledge of the parameters that govern seismic rupture and aftershocks is still incomplete. On 16 September 2015 the Mw. 8.3 Illapel earthquake ruptured a 200 km long stretch of the Central Chilean subduction zone, triggering a tsunami and causing significant damage. Here we analyze the temporal and spatial pattern of the co-seismic rupture and aftershocks in relation to the tectonic setting in the earthquake area. Aftershocks cluster around the area of maximum coseismic slip, in particular in lateral and downdip direction. During the first 24 hours after the mainshock, aftershocks migrated in both lateral directions with velocities of approximately 2.5 and 5 km/h. At the southern rupture boundary aftershocks cluster around individual subducted seamounts that are related to the downthrusting Juan Fernández Ridge. In the northern part of the rupture area aftershocks separate into an upper cluster (above 25 km depth) and a lower cluster (below 35 km depth). This dual seismic-aseismic transition in downdip direction is also observed in the interseismic period suggesting that it may represent a persistent feature for the Central Chilean subduction zone.

  8. Aftershock seismicity and tectonic setting of the 2015 September 16 Mw 8.3 Illapel earthquake, Central Chile

    NASA Astrophysics Data System (ADS)

    Lange, Dietrich; Geersen, Jacob; Barrientos, Sergio; Moreno, Marcos; Grevemeyer, Ingo; Contreras-Reyes, Eduardo; Kopp, Heidrun

    2016-08-01

    Powerful subduction zone earthquakes rupture thousands of square kilometres along continental margins but at certain locations earthquake rupture terminates. To date, detailed knowledge of the parameters that govern seismic rupture and aftershocks is still incomplete. On 2015 September 16, the Mw 8.3 Illapel earthquake ruptured a 200 km long stretch of the Central Chilean subduction zone, triggering a tsunami and causing significant damage. Here, we analyse the temporal and spatial pattern of the coseismic rupture and aftershocks in relation to the tectonic setting in the earthquake area. Aftershocks cluster around the area of maximum coseismic slip, in particular in lateral and downdip direction. During the first 24 hr after the main shock, aftershocks migrated in both lateral directions with velocities of approximately 2.5 and 5 km hr-1. At the southern rupture boundary, aftershocks cluster around individual subducted seamounts that are related to the downthrusting Juan Fernández Ridge. In the northern part of the rupture area, aftershocks separate into an upper cluster (above 25 km depth) and a lower cluster (below 35 km depth). This dual seismic-aseismic transition in downdip direction is also observed in the interseismic period suggesting that it may represent a persistent feature for the Central Chilean subduction zone.

  9. Evolution of the vigorous 2006 swarm in Zakynthos (Greece) and probabilities for strong aftershocks occurrence

    NASA Astrophysics Data System (ADS)

    Papadimitriou, Eleftheria; Gospodinov, Dragomir; Karakostas, Vassilis; Astiopoulos, Anastasios

    2013-04-01

    A multiplet of moderate-magnitude earthquakes (5.1 ≤ M ≤ 5.6) took place in Zakynthos Island and offshore area (central Ionian Islands, Greece) in April 2006. The activity in the first month occupied an area of almost 35 km long, striking roughly NNW-SSE, whereas aftershocks continued for several months, decaying with time but persisting at the same place. The properties of the activated structure were investigated with accurate relocated data and the available fault plane solutions of some of the stronger events. Both the distribution of seismicity and fault plane solutions show that thrusting with strike-slip motions are both present in high-angle fault segments. The segmentation of the activated structure could be attributed to the faulting complexity inherited from the regional compressive tectonics. Investigation of the spatial and temporal behavior of seismicity revealed possible triggering of adjacent fault segments that may fail individually, thus preventing coalescence in a large main rupture. In an attempt to forecast occurrence probabilities of six of the strong events ( M w ≥ 5.0), estimations were performed following the restricted epidemic-type aftershock sequence model, applied to data samples before each one of these strong events. Stochastic modeling was also used to identify "quiescence" periods before the examined aftershocks. In two out of the six cases, real aftershock rate did decrease before the next strong shock compared to the modeled one. The latter results reveal that rate decrease is not a clear precursor of strong shocks in the swarm and no quantitative information, suitable to supply probability gain, could be extracted from the data.

  10. Urban seismology - Northridge aftershocks recorded by multi-scale arrays of portable digital seismographs

    USGS Publications Warehouse

    Meremonte, M.; Frankel, A.; Cranswick, E.; Carver, D.; Worley, D.

    1996-01-01

    We deployed portable digital seismographs in the San Fernando Valley (SFV), the Los Angeles basin (LAB), and surrounding hills to record aftershocks of the 17 January 1994 Northridge California earthquake. The purpose of the deployment was to investigate factors relevant to seismic zonation in urban areas, such as site amplification, sedimentary basin effects, and the variability of ground motion over short baselines. We placed seismographs at 47 sites (not all concurrently) and recorded about 290 earthquakes with magnitudes up to 5.1 at five stations or more. We deployed widely spaced stations for profiles across the San Fernando Valley, as well as five dense arrays (apertures of 200 to 500 m) in areas of high damage, such as the collapsed Interstate 10 overpass, Sherman Oaks, and the collapsed parking garage at CalState Northridge. Aftershock data analysis indicates a correlation of site amplification with mainshock damage. We found several cases where the site amplification depended on the azimuth of the aftershock, possibly indicating focusing from basin structures. For the parking garage array, we found large ground-motion variabilities (a factor of 2) over 200-m distances for sites on the same mapped soil unit. Array analysis of the aftershock seismograms demonstrates that sizable arrivals after the direct 5 waves consist of surface waves traveling from the same azimuth as that of the epicenter. These surface waves increase the duration of motions and can have frequencies as high as about 4 Hz. For the events studied here, we do not observe large arrivals reflected from the southern edge of the San Fernando Valley.

  11. Long aftershock sequences within continents and implications for earthquake hazard assessment.

    PubMed

    Stein, Seth; Liu, Mian

    2009-11-01

    One of the most powerful features of plate tectonics is that the known plate motions give insight into both the locations and average recurrence interval of future large earthquakes on plate boundaries. Plate tectonics gives no insight, however, into where and when earthquakes will occur within plates, because the interiors of ideal plates should not deform. As a result, within plate interiors, assessments of earthquake hazards rely heavily on the assumption that the locations of small earthquakes shown by the short historical record reflect continuing deformation that will cause future large earthquakes. Here, however, we show that many of these recent earthquakes are probably aftershocks of large earthquakes that occurred hundreds of years ago. We present a simple model predicting that the length of aftershock sequences varies inversely with the rate at which faults are loaded. Aftershock sequences within the slowly deforming continents are predicted to be significantly longer than the decade typically observed at rapidly loaded plate boundaries. These predictions are in accord with observations. So the common practice of treating continental earthquakes as steady-state seismicity overestimates the hazard in presently active areas and underestimates it elsewhere. PMID:19890328

  12. Can current New Madrid seismicity be explained as a decaying aftershock sequence?

    NASA Astrophysics Data System (ADS)

    Page, M. T.; Hough, S. E.; Felzer, K. R.

    2012-12-01

    It has been suggested that continuing seismicity in the New Madrid, central U.S. region is primarily composed of the continuing long-lived aftershock sequence of the 1811-1812 sequence, and thus cannot be taken as an indication of present-day strain accrual in the region. We examine historical and instrumental seismicity in the New Madrid region to determine if such a model is feasible given 1) the observed protracted nature of past New Madrid sequences, with multiple mainshocks with apparently similar magnitudes; 2) the rate of historically documented early aftershocks from the 1811-1812 sequence; and 3) plausible mainshock magnitudes and aftershock-productivity parameters. We use ETAS modeling to search for sub-critical sets of direct Omori parameters that are consistent with all of these datasets, given a realistic consideration of their uncertainties, and current seismicity in the region. The results of this work will help to determine whether or not future sequences are likely to be clusters of events like those in the past, a key issue for earthquake response planning.

  13. Main shock and aftershock records of the 1999 Izmit and Duzce, Turkey earthquakes

    USGS Publications Warehouse

    Celebi, M.; Akkar, Sinan; Gulerce, U.; Sanli, A.; Bundock, H.; Salkin, A.

    2001-01-01

    The August 17, 1999 Izmit (Turkey) earthquake (Mw=7.4) will be remembered as one of the largest earthquakes of recent times that affected a large urban environment (U.S. Geological Survey, 1999). This significant event was followed by many significant aftershocks and another main event (Mw=7.2) that occurred on November 12, 1999 near Duzce (Turkey). The shaking that caused the widespread damage and destruction was recorded by a handful of accelerographs (~30) in the earthquake area operated by different networks. The characteristics of these records show that the recorded peak accelerations, shown in Figure 1, even those from near field stations, are smaller than expected (Çelebi, 1999, 2000). Following this main event, several organizations from Turkey, Japan, France and the USA deployed temporary accelerographs and other aftershock recording hardware. Thus, the number of recording stations in the earthquake affected area was quadrupled (~130). As a result, as seen in Figure 2, smaller magnitude aftershocks yielded larger peak accelerations, indicating that because of the sparse networks, recording of larger motions during the main shock of August 17, 1999 were possibly missed.

  14. Earthquake statistics, spatiotemporal distribution of foci and source mechanisms - a key to understanding of the West Bohemia/Vogtland earthquake swarms

    NASA Astrophysics Data System (ADS)

    Horálek, Josef; Čermáková, Hana; Fischer, Tomáš

    2016-04-01

    Earthquake swarms are sequences of numerous events closely clustered in space and time and do not have a single dominant mainshock. A few of the largest events in a swarm reach similar magnitudes and usually occur throughout the course of the earthquake sequence. These attributes differentiate earthquake swarms from ordinary mainshock-aftershock sequences. Earthquake swarms occur worldwide, in diverse geological units. The swarms typically accompany volcanic activity at margins of the tectonic plate but also occur in intracontinental areas where strain from tectonic-plate movement is small. The origin of earthquake swarms is still unclear. The swarms typically occur at the plate margins but also in intracontinental areas. West Bohemia-Vogtland represents one of the most active intraplate earthquake-swarm areas in Europe. It is characterised by a frequent reoccurrence of ML < 4.0 swarms and by high activity of crustal fluids. West Bohemia-Vogtland is one of the most active intraplate earthquake-swarm areas in Europe which also exhibits high activity of crustal fluids. The Nový Kostel focal zone (NK) dominates the recent seismicity, there were swarms in 1997, 2000, 2008 and 20011, and a striking non-swarm activity (mainshock-aftershock sequences) up to magnitude ML= 4.5 in May to August 2014. The swarms and the 2014 mainshock-aftershock sequences are located close to each other at depths between 6 and 13 km. The frequency-magnitude distributions of all the swarms show bimodal-like character: the most events obey the b-value = 1.0 distribution, but a group of the largest events depart significantly from it. All the ML > 2.8 swarm events are located in a few dense clusters which implies step by step rupturing of one or a few asperities during the individual swarms. The source mechanism patters (moment-tensor description, MT) of the individual swarms indicate several families of the mechanisms, which fit well geometry of respective fault segments. MTs of the most

  15. MRI of Focal Liver Lesions.

    PubMed

    Albiin, Nils

    2012-05-01

    Magnetic resonance imaging, MRI has more advantages than ultrasound, computed tomography, CT, positron emission tomography, PET, or any other imaging modality in diagnosing focal hepatic masses. With a combination of basic T1 and T2 weighted sequences, diffusion weighted imaging, DWI, and hepatobiliary gadolinium contrast agents, that is gadobenate dimeglumine (Gd-BOPTA) and gadoxetic acid (Gd-EOB), most liver lesions can be adequately diagnosed. Benign lesions, as cyst, hemangioma, focal nodular hyperplasia, FNH or adenoma, can be distinguished from malignant lesions. In a non-cirrhotic liver, the most common malignant lesions are metastases which may be hypovascular or hypervascular. In the cirrhotic liver hepatocellular carcinoma, HCC, is of considerable importance. Besides, intrahepatic cholangiocarcinoma and other less common malignancies has to be assessed. In this review, the techniques and typical MRI features are presented as well as the new algorithm issued by American Association for the Study of the Liver Diseases (AASLD). PMID:23049491

  16. Variable focal length deformable mirror

    DOEpatents

    Headley, Daniel; Ramsey, Marc; Schwarz, Jens

    2007-06-12

    A variable focal length deformable mirror has an inner ring and an outer ring that simply support and push axially on opposite sides of a mirror plate. The resulting variable clamping force deforms the mirror plate to provide a parabolic mirror shape. The rings are parallel planar sections of a single paraboloid and can provide an on-axis focus, if the rings are circular, or an off-axis focus, if the rings are elliptical. The focal length of the deformable mirror can be varied by changing the variable clamping force. The deformable mirror can generally be used in any application requiring the focusing or defocusing of light, including with both coherent and incoherent light sources.

  17. Spatial/Temporal interdependence of aftershocks following the 10/31/2001 M5.1 Anza Earthquake

    NASA Astrophysics Data System (ADS)

    Kilb, D.; Martynov, V.; Vernon, F. L.

    2004-12-01

    On 10/31/2001, a M5.1 earthquake occurred in the middle of the ANZA network (7 24-bit broadband stations were within 20 km of the epicenter) that spans the San Jacinto fault zone in southern California. A high pass filter (f > 1.0 Hz) was used to identify seismic arrival times of the aftershocks and in turn determine the aftershock locations. In this way, we cataloged 599 events (0< M < 2.5) in the initial 2 hours of this sequence and 4500 aftershocks within the first 2 months, complete to M ≈ 0.0. Here, we study three different temporal/spatial features found in these data. (1) Initially we suspected earthquakes within the region of the mainshock had a bimodal distribution of earthquake magnitudes (peaks at M=0.1 and M=1.5); however, we found this distribution was an artifact of the spatial recording capabilities of small magnitude aftershocks. (2) In the original aftershock locations we found two linear voids in seismicity (trends ˜N45W and ˜N45E) in the primary aftershock cluster forming an X pattern. This is not likely caused by the number of significant digits in the location algorithm because these voids do not follow individual latitude or longitude lines, nor is this likely due to recording inaccuracies because the network coverage of the region is more than optimal. We are investigating other causes of these voids. (3) In the broadband data, we found only one detectable aftershock in the first 2 minutes of the continuous waveforms; yet on the short period records at one of the closest stations, TRO, we can identify an additional event at 15 seconds into the sequence. To quantify our detection capabilities, we estimate when aftershocks of different magnitudes can be identified within the mainshock coda. We are fairly confident that \\> M 1.5 events 45 seconds or longer after the mainshock should be detectable, which suggests that the lack of seismicity in the 45 second-2.0 minute range is potentially real. This non-zero lag-time between the mainshock

  18. Tomographic velocity model for the aftershock region of the 2001 Gujarat, India earthquake

    NASA Astrophysics Data System (ADS)

    Negishi, H.; Kumar, S.; Mori, J. J.; Sato, T.; Bodin, P.; Rastogi, B.

    2002-12-01

    A tomographic inversion was applied to the aftershock data collected after the January 26, 2001 Bhuj earthquake (Ms 7.9, Mw 7.7), which occurred on a south dipping (~50 degrees) reverse fault in the state of Gujarat in western India. We used high quality arrivals from 8,374 P and 7,994 S waves of 1404 aftershocks recorded on 27 digital stations from temporary seismic arrays setup by the India-Japan team; NGRI, India; and CERI, Memphis Univ., USA, following the Bhuj main shock. First, we used the Joint Hypocenters Determination Method for obtaining relocated hypocenters and a one-dimensional Vp and Vs velocity model, and then the resultant hypocenters and 1-D velocity model were used as the initial parameters for a 3-D tomographic inversion. The tomography technique is based on a grid-modeling method by Zhao et al. . Vp, Vs and hypocenters are determined simultaneously. We tried to use the Cross-Validation Technique for determining an optimum model in the seismic tomography. This approach has been applied to other tomographic studies to investigate the quantitative fluctuation range of velocity perturbations . Significant variations in the velocity (up to 6%) and Poisson's ratio (up to 8%) are revealed in the aftershock area. It seems that the aftershock distribution corresponds to the boundary between high and low velocity heterogeneities. Small values of Vp/Vs are generally found at depths of 10 to 35 km, i.e. the depth range of aftershock distribution. However, the deeper region below the hypocenter of the mainshock, at depths of 35 to 45 km, is characterized by relatively high values of Vp/Vs and low values of Vs. This anomaly may be due to a weak fractured and fluid filled rock matrix, which might have contributed to triggering this earthquake. This earthquake occurred on a relatively deep and steeply dipping fault with a large stress drop . Theoretically it is difficult to slip steep faults, especially in the lower crust. Our tomographic investigation provides

  19. An Improved Source-Scanning Algorithm for Locating Earthquake Clusters or Aftershock Sequences

    NASA Astrophysics Data System (ADS)

    Liao, Y.; Kao, H.; Hsu, S.

    2010-12-01

    The Source-scanning Algorithm (SSA) was originally introduced in 2004 to locate non-volcanic tremors. Its application was later expanded to the identification of earthquake rupture planes and the near-real-time detection and monitoring of landslides and mud/debris flows. In this study, we further improve SSA for the purpose of locating earthquake clusters or aftershock sequences when only a limited number of waveform observations are available. The main improvements include the application of a ground motion analyzer to separate P and S waves, the automatic determination of resolution based on the grid size and time step of the scanning process, and a modified brightness function to utilize constraints from multiple phases. Specifically, the improved SSA (named as ISSA) addresses two major issues related to locating earthquake clusters/aftershocks. The first one is the massive amount of both time and labour to locate a large number of seismic events manually. And the second one is to efficiently and correctly identify the same phase across the entire recording array when multiple events occur closely in time and space. To test the robustness of ISSA, we generate synthetic waveforms consisting of 3 separated events such that individual P and S phases arrive at different stations in different order, thus making correct phase picking nearly impossible. Using these very complicated waveforms as the input, the ISSA scans all model space for possible combination of time and location for the existence of seismic sources. The scanning results successfully associate various phases from each event at all stations, and correctly recover the input. To further demonstrate the advantage of ISSA, we apply it to the waveform data collected by a temporary OBS array for the aftershock sequence of an offshore earthquake southwest of Taiwan. The overall signal-to-noise ratio is inadequate for locating small events; and the precise arrival times of P and S phases are difficult to

  20. [Focal liver lesion, incidental finding].

    PubMed

    Dietrich, C F; Jenssen, C

    2012-10-01

    The differential diagnosis of incidentally found Focal Liver Lesions (FLL) is complex. Screening procedures so far are only defined for patients with liver cirrhosis. Characterization of a FLL begins as soon as it is detected. Taking patients history and thorough clinical examination are essential. An imaging procedure that is used to detect liver masses should also allow the examiner to determine whether the lesion is benign or malignant. Conventional B-mode US and colour Doppler imaging are effective at detecting and characterizing typical liver cysts and calcifications. Laboratory data, computed tomography, magnetic resonance imaging and imaging guided liver biopsy are complementary methods.Contrast Enhanced Ultrasound (CEUS) is a well established diagnostic imaging technique for a variety of indications and applications. One of the most important applications is in the liver where it is frequently a first-line technique for the detection and diagnosis (characterization) of focal liver lesions (FLL). In this setting the accurate differentiation of benign from malignant lesions is critical to ensure the patient undergoes the appropriate therapeutic option. This has been documented in recently published guidelines, in particular in terms of the enhancement patterns of the most common FLL hemangioma, focal nodular hyperplasia hepatocellular adenoma and their differentiation from malignant lesions. In this article the role of CEUS in the characterization of incidentally found FLL is described. PMID:23033169

  1. Persistent Focal Behavior and Physical Activity Performance

    ERIC Educational Resources Information Center

    Erfle, Stephen E.

    2014-01-01

    This article examines the proclivity and performance attributes of focal students across time and activities using data from 9,345 students. Three systematic focal behavior partitions are examined: Across activities, across time, and across activities and time. A student's performance is focal if it ends in 0 or 5 for push-ups and 0 for…

  2. Characterization of the KATRIN Focal Plane Detector

    NASA Astrophysics Data System (ADS)

    Bodine, Laura; Leber, Michelle; Myers, Allan; Tolich, Kazumi; Vandevender, Brent; Wall, Brandon

    2008-10-01

    The Karlsruhe Tritium Neutrino (KATRIN) Experiment is a next generation tritium beta decay experiment designed to measure directly the electron neutrino mass with a sensitivity of 0.2 eV. In the experiment, electrons from tritium decay of a gaseous source are magnetically guided through analyzing solenoidal retarding electrostatic spectrometers and detected via a focal plane detector. The focal plane detector is a 90mm diameter, 500 micron thick monolithic silicon pin-diode array with 148 pixels. The diode contacts have a titanium nitride overlayer and are connected to preamplifiers via an array of spring-loaded pogo pins. This novel connection scheme minimizes backgrounds from radioactive materials near the detector, facilitates characterization and replacement of the detector wafer, but requires a unique mounting design. The force of the pins strains the silicon, possibly altering the detector properties and performance. Results on the mechanical, thermal and electrical performance of a prototype detector under stress from pogo pin readouts will be presented.

  3. Ultrasound elastographic techniques in focal liver lesions

    PubMed Central

    Conti, Clara Benedetta; Cavalcoli, Federica; Fraquelli, Mirella; Conte, Dario; Massironi, Sara

    2016-01-01

    Elastographic techniques are new ultrasound-based imaging techniques developed to estimate tissue deformability/stiffness. Several ultrasound elastographic approaches have been developed, such as static elastography, transient elastography and acoustic radiation force imaging methods, which include point shear wave and shear wave imaging elastography. The application of these methods in clinical practice aims at estimating the mechanical tissues properties. One of the main settings for the application of these tools has been liver stiffness assessment in chronic liver disease, which has been studied mainly using transient elastography. Another field of application for these techniques is the assessment of focal lesions, detected by ultrasound in organs such as pancreas, prostate, breast, thyroid, lymph nodes. Considering the frequency and importance of the detection of focal liver lesions through routine ultrasound, some studies have also aimed to assess the role that elestography can play in studying the stiffness of different types of liver lesions, in order to predict their nature and thus offer valuable non-invasive methods for the diagnosis of liver masses. PMID:26973405

  4. Focal embolic cerebral ischemia in the rat

    PubMed Central

    Zhang, Li; Zhang, Rui Lan; Jiang, Quan; Ding, Guangliang; Chopp, Michael; Zhang, Zheng Gang

    2015-01-01

    Animal models of focal cerebral ischemia are well accepted for investigating the pathogenesis and potential treatment strategies for human stroke. Occlusion of the middle cerebral artery (MCA) with an endovascular filament is a widely used model to induce focal cerebral ischemia. However, this model is not amenable to thrombolytic therapies. As thrombolysis with recombinant tissue plasminogen activator (rtPA) is a standard of care within 4.5 hours of human stroke onset, suitable animal models that mimic cellular and molecular mechanisms of thrombosis and thrombolysis of stroke are required. By occluding the MCA with a fibrin-rich allogeneic clot, we have developed an embolic model of MCA occlusion in the rat, which recapitulates the key components of thrombotic development and of thrombolytic therapy of rtPA observed from human ischemic stroke. The surgical procedures of our model can be typically completed within approximately 30 min and are highly adaptable to other strains of rats as well as mice for both genders. Thus, this model provides a powerful tool for translational stroke research. PMID:25741989

  5. Poldip2 controls vascular smooth muscle cell migration by regulating focal adhesion turnover and force polarization

    PubMed Central

    Datla, Srinivasa Raju; McGrail, Daniel J.; Vukelic, Sasa; Huff, Lauren P.; Lyle, Alicia N.; Pounkova, Lily; Lee, Minyoung; Seidel-Rogol, Bonnie; Khalil, Mazen K.; Hilenski, Lula L.; Terada, Lance S.; Dawson, Michelle R.; Lassègue, Bernard

    2014-01-01

    Polymerase-δ-interacting protein 2 (Poldip2) interacts with NADPH oxidase 4 (Nox4) and regulates migration; however, the precise underlying mechanisms are unclear. Here, we investigated the role of Poldip2 in focal adhesion turnover, as well as traction force generation and polarization. Poldip2 overexpression (AdPoldip2) in vascular smooth muscle cells (VSMCs) impairs PDGF-induced migration and induces a characteristic phenotype of long cytoplasmic extensions. AdPoldip2 also prevents the decrease in spreading and increased aspect ratio observed in response to PDGF and slightly impairs cell contraction. Moreover, AdPoldip2 blocks focal adhesion dissolution and sustains H2O2 levels in focal adhesions, whereas Poldip2 knockdown (siPoldip2) significantly decreases the number of focal adhesions. RhoA activity is unchanged when focal adhesion dissolution is stimulated in control cells but increases in AdPoldip2-treated cells. Inhibition of RhoA blocks Poldip2-mediated attenuation of focal adhesion dissolution, and overexpression of RhoA or focal adhesion kinase (FAK) reverses the loss of focal adhesions induced by siPoldip2, indicating that RhoA and FAK mediate the effect of Poldip2 on focal adhesions. Nox4 silencing prevents focal adhesion stabilization by AdPoldip2 and induces a phenotype similar to siPoldip2, suggesting a role for Nox4 in Poldip2-induced focal adhesion stability. As a consequence of impaired focal adhesion turnover, PDGF-treated AdPoldip2 cells are unable to reduce and polarize traction forces, a necessary first step in migration. These results implicate Poldip2 in VSMC migration via regulation of focal adhesion turnover and traction force generation in a Nox4/RhoA/FAK-dependent manner. PMID:25063792

  6. Poldip2 controls vascular smooth muscle cell migration by regulating focal adhesion turnover and force polarization.

    PubMed

    Datla, Srinivasa Raju; McGrail, Daniel J; Vukelic, Sasa; Huff, Lauren P; Lyle, Alicia N; Pounkova, Lily; Lee, Minyoung; Seidel-Rogol, Bonnie; Khalil, Mazen K; Hilenski, Lula L; Terada, Lance S; Dawson, Michelle R; Lassègue, Bernard; Griendling, Kathy K

    2014-10-01

    Polymerase-δ-interacting protein 2 (Poldip2) interacts with NADPH oxidase 4 (Nox4) and regulates migration; however, the precise underlying mechanisms are unclear. Here, we investigated the role of Poldip2 in focal adhesion turnover, as well as traction force generation and polarization. Poldip2 overexpression (AdPoldip2) in vascular smooth muscle cells (VSMCs) impairs PDGF-induced migration and induces a characteristic phenotype of long cytoplasmic extensions. AdPoldip2 also prevents the decrease in spreading and increased aspect ratio observed in response to PDGF and slightly impairs cell contraction. Moreover, AdPoldip2 blocks focal adhesion dissolution and sustains H2O2 levels in focal adhesions, whereas Poldip2 knockdown (siPoldip2) significantly decreases the number of focal adhesions. RhoA activity is unchanged when focal adhesion dissolution is stimulated in control cells but increases in AdPoldip2-treated cells. Inhibition of RhoA blocks Poldip2-mediated attenuation of focal adhesion dissolution, and overexpression of RhoA or focal adhesion kinase (FAK) reverses the loss of focal adhesions induced by siPoldip2, indicating that RhoA and FAK mediate the effect of Poldip2 on focal adhesions. Nox4 silencing prevents focal adhesion stabilization by AdPoldip2 and induces a phenotype similar to siPoldip2, suggesting a role for Nox4 in Poldip2-induced focal adhesion stability. As a consequence of impaired focal adhesion turnover, PDGF-treated AdPoldip2 cells are unable to reduce and polarize traction forces, a necessary first step in migration. These results implicate Poldip2 in VSMC migration via regulation of focal adhesion turnover and traction force generation in a Nox4/RhoA/FAK-dependent manner. PMID:25063792

  7. Variable-focal lens using electroactive polymer actuator

    NASA Astrophysics Data System (ADS)

    Vunder, V.; Punning, A.; Aabloo, A.

    2011-03-01

    The paper describes a simple and cost-effective design and fabrication process of a liquid-filled variable-focal lens. The lens was made of soft polymer material, its shape and curvature can be controlled by hydraulic pressure. An electroactive polymer is used as an actuator. A carbon-polymer composite (CPC) was used. The device is composed of elastic membrane upon a circular lens chamber, a reservoir of liquid, and a channel between them. It was made of three layers of polydimethylsiloxane (PDMS), bonded using the partial curing technique. The channels and reservoir were filled with incompressible liquid after curing process. A CPC actuator was mechanically attached to reservoir to compress or decompress the liquid. Squeezing the liquid between the reservoir and the lens chamber will push the membrane inward or outward resulting in the change of the shape of the lens and alteration of its focal length. Depending on the pressure the lens can be plano-convex or plano-concave or even switch between the two configurations. With only a few minor modifications it is possible to fabricate bi-convex and bi-concave lenses. The lens with a 1 mm diameter and the focal length from infinity to 17 mm is reported. The 5x15mm CPC actuator with the working voltage of only up to +/-2.5 V was capable to alter the focal length within the full range of the focal length in 10 seconds.

  8. The Focal Surface of the JEM-EUSO Instrument

    SciTech Connect

    Kawasaki, Y.; Casolino, M.; Gorodetzky, P.; Santangelo, A.; Ricci, M.; Kajino, F.; Ebisuzaki, T.

    2011-09-22

    The Extreme Universe Space Observatory on JEM/EF (JEM-EUSO) is a space mission to study extremely high-energy cosmic rays. The JEM-EUSO instrument is a wide-angle refractive telescope in the near-ultraviolet wavelength region which will be mounted to the International Space Station. Its goal is to measure time-resolved fluorescence images of extensive air showers in the atmosphere. In this paper we describe in detail the main features and technological aspects of the focal surface of the instrument. The JEM-EUSO focal surface is a spherically curved surface, with an area of about 4.5m{sup 2}. The focal surface detector is made of more than 5,000 multi-anode photomultipliers (MAPMTs). Current baseline is Hamamatsu R11265-03-M64. The approach to the focal surface detector is highly modular. Photo-Detector-Modules (PDM) are the basic units that drive the mechanical structure and data acquisition. Each PDM consists of 9 Elementary Cells (ECs). The EC, which is the basic unit of the MAPMT support structure and of the front-end electronics, contains 4 units of MAPMTs. In total, about 1,200 ECs or about 150 PDMs are arranged on the whole of the focal surface of JEM-EUSO.

  9. SNAP Satellite Focal Plane Development

    SciTech Connect

    Bebek, C.; Akerlof, C.; Aldering, G.; Amanullah, R.; Astier, P.; Baltay, C.; Barrelet, E.; Basa, S.; Bercovitz, J.; Bergstrom, L.; Berstein, G.P.; Bester, M.; Bohlin, R.; Bonissent, A.; Bower, C.; Campbell, M.; Carithers, W.; Commins, E.; Day, C.; Deustua, S.; DiGennaro, R.; Ealet, A.; Ellis, R.; Emmett, W.; Eriksson, M.; Fouchez,D.; Fruchter, A.; Genat, J-F.; Goldhaber, G.; Goobar, A.; Groom, D.; Heetderks, H.; Holland, S.; Huterer, D.; Johnson, W.; Kadel, R.; Karcher,A.; Kim, A.; Kolbe, W.; Lafever, R.; Lamoureaux, J.; Lampton, M.; Lefevre, O.; Levi, M.; Levin, D.; Linder, E.; Loken, S.; Malina, R.; Mazure, A.; McKay, T.; McKee, S.; Miquel, R.; Morgan, N.; Mortsell, E.; Mostek, N.; Mufson, S.; Musser, J.; Roe, N.; Nugent, P.; Oluseyi, H.; Pain, R.; Palaio, N.; Pankow, D.; Perlmutter, S.; Prieto, E.; Rabinowitz,D.; Refregier, A.; Rhodes, J.; Schubnell, M.; Sholl, M.; Smadja, G.; Smith, R.; Smoot, G.; Snyder, J.; Spadafora, A.; Szymkowiak, A.; Tarle,G.; Taylor, K.; Tilquin, A.; Tomasch, A.; Vincent, D.; von der Lippe, H.; Walder, J-P.; Wang, G.

    2003-07-07

    The proposed SuperNova/Acceleration Probe (SNAP) mission will have a two-meter class telescope delivering diffraction-limited images to an instrumented 0.7 square degree field in the visible and near-infrared wavelength regime. The requirements for the instrument suite and the present configuration of the focal plane concept are presented. A two year R&D phase, largely supported by the Department of Energy, is just beginning. We describe the development activities that are taking place to advance our preparedness for mission proposal in the areas of detectors and electronics.

  10. Decreased subcortical cholinergic arousal in focal seizures

    PubMed Central

    Motelow, Joshua E.; Li, Wei; Zhan, Qiong; Mishra, Asht M.; Sachdev, Robert N. S.; Liu, Geoffrey; Gummadavelli, Abhijeet; Zayyad, Zaina; Lee, Hyun Seung; Chu, Victoria; Andrews, John P.; Englot, Dario J.; Herman, Peter; Sanganahalli, Basavaraju G.; Hyder, Fahmeed; Blumenfeld, Hal

    2015-01-01

    SUMMARY Impaired consciousness in temporal lobe seizures has a major negative impact on quality of life. The prevailing view holds that this disorder impairs consciousness by seizure spread to the bilateral temporal lobes. We propose instead that seizures invade subcortical regions and depress arousal, causing impairment through decreases rather than through increases in activity. Using functional magnetic resonance imaging in a rodent model, we found increased activity in regions known to depress cortical function including lateral septum and anterior hypothalamus. Importantly, we found suppression of intralaminar thalamic and brainstem arousal systems and suppression of the cortex. At a cellular level, we found reduced firing of identified cholinergic neurons in the brainstem pedunculopontine tegmental nucleus and basal forebrain. Finally, we used enzyme-based amperometry to demonstrate reduced cholinergic neurotransmission in both cortex and thalamus. Decreased subcortical arousal is a novel mechanism for loss of consciousness in focal temporal lobe seizures. PMID:25654258

  11. Design of large aperture focal plane shutter

    NASA Astrophysics Data System (ADS)

    Hu, Jia-wen; Ma, Wen-li; Huang, Jin-long

    2012-09-01

    To satisfy the requirement of large telescope, a large aperture focal plane shutter with aperture size of φ200mm was researched and designed to realize, which could be started and stopped in a relative short time with precise position, and also the blades could open and close at the same time at any orientation. Timing-belts and stepper motors were adopted as the drive mechanism. Velocity and position of the stepper motors were controlled by the PWM pulse generated by DSP. Exponential curve is applied to control the velocity of the stepper motors to make the shutter start and stop in a short time. The closing/open time of shutter is 0.2s, which meets the performance requirements of large telescope properly.

  12. Estimating seismic site response in Christchurch City (New Zealand) from dense low-cost aftershock arrays

    USGS Publications Warehouse

    Kaiser, Anna E.; Benites, Rafael A.; Chung, Angela I.; Haines, A. John; Cochran, Elizabeth S.; Fry, Bill

    2011-01-01

    The Mw 7.1 September 2010 Darfield earthquake, New Zealand, produced widespread damage and liquefaction ~40 km from the epicentre in Christchurch city. It was followed by the even more destructive Mw 6.2 February 2011 Christchurch aftershock directly beneath the city’s southern suburbs. Seismic data recorded during the two large events suggest that site effects contributed to the variations in ground motion observed throughout Christchurch city. We use densely-spaced aftershock recordings of the Darfield earthquake to investigate variations in local seismic site response within the Christchurch urban area. Following the Darfield main shock we deployed a temporary array of ~180 low-cost 14-bit MEMS accelerometers linked to the global Quake-Catcher Network (QCN). These instruments provided dense station coverage (spacing ~2 km) to complement existing New Zealand national network strong motion stations (GeoNet) within Christchurch city. Well-constrained standard spectral ratios were derived for GeoNet stations using a reference station on Miocene basalt rock in the south of the city. For noisier QCN stations, the method was adapted to find a maximum likelihood estimate of spectral ratio amplitude taking into account the variance of noise at the respective stations. Spectral ratios for QCN stations are similar to nearby GeoNet stations when the maximum likelihood method is used. Our study suggests dense low-cost accelerometer aftershock arrays can provide useful information on local-scale ground motion properties for use in microzonation. Preliminary results indicate higher amplifications north of the city centre and strong high-frequency amplification in the small, shallower basin of Heathcote Valley.

  13. An Autonomous System for Grouping Events in a Developing Aftershock Sequence

    SciTech Connect

    Harris, D. B.; Dodge, D. A.

    2011-03-22

    We describe a prototype detection framework that automatically clusters events in real time from a rapidly unfolding aftershock sequence. We use the fact that many aftershocks are repetitive, producing similar waveforms. By clustering events based on correlation measures of waveform similarity, the number of independent event instances that must be examined in detail by analysts may be reduced. Our system processes array data and acquires waveform templates with a short-term average (STA)/long-term average (LTA) detector operating on a beam directed at the P phases of the aftershock sequence. The templates are used to create correlation-type (subspace) detectors that sweep the subsequent data stream for occurrences of the same waveform pattern. Events are clustered by association with a particular detector. Hundreds of subspace detectors can run in this framework a hundred times faster than in real time. Nonetheless, to check the growth in the number of detectors, the framework pauses periodically and reclusters detections to reduce the number of event groups. These groups define new subspace detectors that replace the older generation of detectors. Because low-magnitude occurrences of a particular signal template may be missed by the STA/LTA detector, we advocate restarting the framework from the beginning of the sequence periodically to reprocess the entire data stream with the existing detectors. We tested the framework on 10 days of data from the Nevada Seismic Array (NVAR) covering the 2003 San Simeon earthquake. One hundred eighty-four automatically generated detectors produced 676 detections resulting in a potential reduction in analyst workload of up to 73%.

  14. Hemodynamics of focal choroidal excavations.

    PubMed

    Soma, Ryoko; Moriyama, Muka; Ohno-Matsui, Kyoko

    2015-04-01

    The purpose of this study was to investigate the hemodynamics of focal choroidal excavations (FCEs). Four eyes of four patients with a FCE were studied. Indocyanine green angiography (ICGA), laser speckle flowgraphy (LSFG), optical coherence tomography (OCT), and multi-focal electroretinography (mfERG) were performed to investigate the choroidal hemodynamics and the morphological and functional changes. The mean depth of the FCE determined by OCT was 222.5 ± 49.5 μm with a range of 164-272 μm. In one case, subretinal fluid was observed in the excavation, and in three cases, subretinal fluid was not observed. ICGA showed hypofluorescence, and laser flowgraphy (LSFG) showed decreased choroidal blood flow at the excavation in all cases. Three cases were symptomatic, and the amplitudes of the mfERGs were reduced. FCEs cause a decrease of choroidal blood flow. In three of four cases, the mfERGs were depressed over the FCEs leading to symptoms. PMID:25626897

  15. Rewritable photochromic focal plane masks

    NASA Astrophysics Data System (ADS)

    Molinari, Emilio; Bertarelli, Chiara; Bianco, Andrea; Bortoletto, Fabio; Conconi, Paolo; Crimi, Giuseppe; Gallazzi, Maria C.; Giro, Enrico; Lucotti, Andrea; Pernechele, Claudio; Zerbi, Filippo M.; Zerbi, Giuseppe

    2003-02-01

    The application of organic photochromic materials in astronomy is opening new possibilities which we are investigating in order to design innovative devices for future instrumentation. The photochromic property of transparent/opaque transition (although in a limited wavelength range) and the changes in intrinsic refractive index have led our studies to application in astronomic spectrographs, both as focal plane mask (for MOS application) and as dispersive elements (volume phase holographic gratings, VPHG), respectively. In both cases the possibility to write and erase devices with suitable irradiation has revealed a new perspective for non-disposable and fully customizable items for spectroscopy. Pursuing this goal we have synthesized a series of novel photochromic materials belonging to the diarylethenes. They fulfill the requirements of thermal stability and fatigue resistance necessary to build functional devices. Prototypes of high contrast focal plane mask working in the H-alpha spectral region have been manufactured and characterized both in laboratory and with the AFOSC camera at Asiago telescope (1.8 m). A custom writing robot (ARATRO) which, taking imaging frames and with the aid of interactive mask design software and ad hoc control electronics, is able to write MOS masks, has been constructed. The design of the MOS masks allow the fitting in the AFOSC slit wheel. The overall set-up is ready for the sky tests.

  16. Geotechnical effects of the 2015 magnitude 7.8 Gorkha, Nepal, earthquake and aftershocks

    USGS Publications Warehouse

    Moss, Robb E S; Thompson, Eric; Kieffer, D Scott; Tiwari, Binod; Hashash, Youssef M A; Acharya, Indra; Adhikari, Basanta; Asimaki, Domniki; Clahan, Kevin B.; Collins, Brian D.; Dahal, Sachindra; Jibson, Randall W.; Khadka, Diwakar; Macdonald, Amy; Madugo, Chris L M; Mason, H Benjamin; Pehlivan, Menzer; Rayamajhi, Deepak; Uprety, Sital

    2015-01-01

    This article summarizes the geotechnical effects of the 25 April 2015 M 7.8 Gorkha, Nepal, earthquake and aftershocks, as documented by a reconnaissance team that undertook