My Pathway in Science and Teaching

Editor's Notes

• #13: Model by
• #18: Active faults in Japan digitized from the 1:200,000 active fault maps produced by the Research Group. Negative Correlations : Stress suddenly released of larger magnitude seismicity on interconnected faults of larger total surface Positive Correlations: Stress is gradually released by lower magnitude seismicity on smaller fault strands. Tohoku Events: July 26 event (M=6.2) were located in a positive correlation (Area III) noted to be anomalously quiescent. p for Active Faults of Japan (1991).
• #19: The study area was divided into three regional tectonic subdivisions consisting of a region of shear in the north associated with the Northern Anatolian Fault Zone (NAFZ), a region dominated by extension in the back-arc region of central Turkey, and a region of compression along the Aegean subduction zone. Seismotectonic parameters (D q and b) and geodetic strains (shear and dilatation) are shown in the table at right for each of the 25 seismic zones
• #20: Region of Strike-Slip: Over the full range: A significant positive correlation is observed between seismic clustering (D) and the Gutenberg-Richter b value along the NAFZ strike slip zone. Region of Extension: In this subdivision, seismic clustering (D 2 and D 15 ) correlate positively with dilatation (r = 0.67 and 0.73 with p = 0.02 and 0.01 respectively). The correlations suggest that increased rates of extension produce increasingly dispersed seismicity. Region of Compression: One would expect seismicity to correlate moreso with dilatation in a subduction zone. However, dilatation along the subduction zone is on average only slightly negative. Dilatation is positive in the areas to the northeast (17 nstrain/a) and negative (-29 nstrain/a) farther west along the subduction zone. This combination of positive and negative dilatation along the subduction zone is probably responsible for the lack of a more significant correlation between b and dilatation. The change of dilatation from positive to negative as one goes east to west along the subduction zone suggests a transition in plate interaction from transtensional to transpressive.
• #21: Region of Strike-Slip: Over the full range: A significant positive correlation is observed between seismic clustering (D) and the Gutenberg-Richter b value along the NAFZ strike slip zone. Region of Extension: In this subdivision, seismic clustering (D 2 and D 15 ) correlate positively with dilatation (r = 0.67 and 0.73 with p = 0.02 and 0.01 respectively). The correlations suggest that increased rates of extension produce increasingly dispersed seismicity. Region of Compression: One would expect seismicity to correlate moreso with dilatation in a subduction zone. However, dilatation along the subduction zone is on average only slightly negative. Dilatation is positive in the areas to the northeast (17 nstrain/a) and negative (-29 nstrain/a) farther west along the subduction zone. This combination of positive and negative dilatation along the subduction zone is probably responsible for the lack of a more significant correlation between b and dilatation. The change of dilatation from positive to negative as one goes east to west along the subduction zone suggests a transition in plate interaction from transtensional to transpressive.
• #25: North Boundary Fault μ : shear rigidity (~3×1010 N/m2), Hs: seismogenic layer’s thickness A: Surface area over which strain release is distributed.
• #26: The combined static stress changes caused by the summed effects of the October and December 1985 Nahanni earthquakes are shown in Figure 3c. I now examine if the subsequent 25 March 1988 SE Nahanni (Mw=6.2) and the 22 May 1988 NW Nahanni (Mw=5.0) events might have been triggered by the previous larger Nahanni earthquakes. ISC depths of the 1988 events are 10.18±2.63 km and 8.86 ± 4.39 km respectively but unpublished aftershock data [R.J. Wetmiller, personal comm., 2002] indicate that the depth for the March event is 6-8 km similar to the depths of the 1985 events. Also, the focal mechanisms of the March and May 1988 earthquakes are essentially the same (strike=170-165 degrees, dip=39-32 degrees). The aftershocks of the March 1988 earthquake and its estimated fault projection [based on the relation of moment-fault dimension relation, 18] are located on the map of combined static stress changes. The aftershock cluster of the March 1988 event seems to extend beyond the likely rupture plane and so occur on a plane activated by the 1985 events, and the March 1988 therefore was probably triggered by the previous events. Moreover, the May and March 1988 Nahanni events occur at opposite ends the 1985 fault ruptures and so are evidence of bilaterally activated along strike stress enhancements. Subsequent changes in seismicity (1985-2002) appear related to the pattern of co-seismic stress changes due to 1985 Nahanni earthquakes along their dipping planes with SE-NW ruptures (Figure 3b). A bilateral increase in stress loading is indicated Distance Along Strike by (i) the March and May 1988 mainshock locations, (ii) the larger post 1985 events occur to the south; (iii) the pattern of regional seismicity. The four largest post-December 85 events occur in the southern zone are, related to aftershocks of the 1985 Nahanni mainshocks and suggest unilateral rupture growth to the south [see Figure 4 of eg., Horner et al., 1990]. The March and May 1988 mainshocks, to the south and to the north of the 1985 events indicate a bilateral increase of seismic activity.Coulomb failure theory and variable slip models are used to calculate Coulomb stress changes for large earthquakes in the Nahanni region of Canada. Stress interactions between the Nahanni events are calculated through the dipping plane rather than flat plane since the stress change models are compared better to the aftershock data which are distributed along dip. Thus, in 1988 mainshocks of Mw=6.2 and Mw=5.2 occurred south and north of the 1985 rupture zone earthquakes possibly indicating an increase in the seismic hazard in the along-strike direction. In general, the zones of shadow and stress enhancement along fault dip and strike appear to govern the locations of the aftershocks. A previously proposed seismic gap or zone of quiescence in this region can be explained by a stress shadow zone. In contrast, aftershocks are clustered in the zones of stress enhancement. The pattern of subsequent 1988-2002 earthquake activity appears to be similar to the aftershock pattern and indicates that seismicity in the region continues to be affected by the stress changes due to the Nahanni events. Stress changes is computed on the E2 fault plane to understand the E1-E2 fault interaction than the analysis (see Figure 3c). Stress through the largest asperity of E2 in shallower depth has been largely observed to have increased while stress through the intermediate asperity, which is suggested to be center for earthquake epicenter, is partially appeared to have decreased, that may be a cause a delay of about two months for the onset time of December 23 event.
• #30: Oncel and Aydan - 2003
• #31: We analyzed seismicity in the region surrounding the Izmit Sapanca fault during a 7.4 yr period (1991–1998.4) preceding the 1999 Izmit event ( MD = 6.8 or Mw = 7.4). The study area lies in northwestern Turkey between 40.5◦ to 41◦ north latitude, and 29◦ and 31◦ east longitude. Seismic events during this time were subdivided into smaller overlapping time intervals for analysis and comparison. The correlation between b andDvaried from significantly positive to negative and back again during the analysis period. Oscillations in b-value have been reported by others (see Main & Meredith 1989; Henderson & Main 1992; Vinciguerra 2002). The results of this study reveal anomalous behaviour in the intermediate-termseismicity preceding the Izmit event. Phase III seismicity, approximately 1.5–3 yr preceding the event, remained clustered, and was characterized by a rapid rise in b from 1.6 to 2.26. Over the long-term (approximately 50 yr), fluctuations in b-value reached higher and higher peaks (Fig. 8). In western Turkey, b-value rose from 1.6 in 1974 to 2.1 in 1992 and then to 2.26 in 1998. We are missing the details of these variations from 1985 to 1992 and for the 1.5 yr immediately preceding rupture. A similar increase is observed in the yr leading up to the Coalinga earthquake (Henderson & Main 1992). Examination of data presented by Henderson & Main (1992) shows that oscillations in b-value reached their highest value about 3 months preceding final rupture. The b-value rose to maxima of 1.8 and 1.85 in 1973 and 1976, respectively, before rising to approximately 2.25 prior to the Coalinga event. We observe positive correlations between D and b when the bvalue is high and high negative correlation when the b-value is relatively low (Fig. 9). This suggests that in the Izmit area, as the probability of large earthquakes increases (lower b-value) there is a corresponding tendency for seismicity to become increasingly clustered. Concentration of maximum GPS strain along the rupture zone appears to be a long-term characteristic of the Izmit–Sapanca fault segment from 1988 to 1998, leading up to final rupture (see Fig. 1). This also corresponds to a time during which D remains close to or less than 1 (thus relatively clustered) and during which b increases. The final period of anomalous behaviour preceding the Izmit event (Phase III, Figs 9 and 11) is associated with accelerated low magnitude seismicity (increasing b-value) during which seismicity becomes more dispersed but remains relatively clustered with ( D <1). This behaviour is similar to the negative feedback process described by Henderson & Main (1992) in which strain release becomes increasingly dispersed while event magnitude drops. At Izmit, the results suggest that rupture occurs on faults with smaller and smaller surface area during this phase. Henderson & Main (1992) observe a period of positive feedback in which faults begin to coalesce leading to larger magnitude events.We do not observe this phenomenon; however, we suspect that the period of accelerated seismicity associated with Phase III eventually led to coalescence of fault surfaces and final rupture.We did not see the drop in b-value often reported to precede a major event. This drop, if it occurred, appears to have been fairly abrupt in the case of the 1999 Izmit event. Data presented by Henderson et al. (1992) for the Coalinga earthquake near Parkfield, California, indicate that this drop can be quite sudden, appearing only 2–3 months prior to rupture. The frequency of earthquake occurrence may not permit a statistically accurate short-term estimate of the b-value. In cases where the number of observed events preceding main rupture is too low to resolve the drop in b-value, cycles of accelerated low magnitude seismic activity in which b becomes anomalously high ( >2) may serve as an early warning of an impending large magnitude rupture. Analysis of microseismic data provided by increasingly dense seismic networks will shorten the period of analysis needed to identify statistically significant trends in seismic behaviour.
• #33: AIC: Akaike Information Criteria How to decrease Noise Value?
• #35: I had chance to contact with Osamu Nishizawa from Geological Survey of Japan to establish a create a Applied Seismology Laboratory at the Earth Sciences Department of KFUPM. Osamu Nishizawa-AIST
• #36: The sampling interval may be the sampling rate of the A/D convertor. In your experiments, sampling rate will be 20 nsec (50 MHz) or 50 nsec (20 MHz). 500 Hz is too slow for observing ultrasonic waves. Fluid The details of waveform measurements are mostly same as those described in Nishizawa et al. (1997, 1998). A single cycle 500 kHz sine wave (burst mode) is generated by a signal generator and then it is amplified to 100 V peak-to peak by a wide-band power amplifier. The high-voltage signal drives the wave source, PZT. The PZT then emits (send out) elastic waves, which propagate through the medium. The LDV uses a laser beam that is focused at the array point marked on a thin reflection sheet that is mounted on the sample surface (Fig. 1). The reflection sheet reflects most of the laser beam in the incident direction (Nishizawa et al., 1998). The incident beam direction is perpendicular to the major surface, and thus the observed waveform is the vertical component of the vibration. The output signal of LDV is fed to a wave memory (Compuscope, Gage A. S. Inc.), and the digitized signal is stored in a computer. To increase the signal-to-noise ratio of the waveform, the PZT is repeatedly driven by the same input signal and the waveforms are stacked. The stacking removes the incoherent high-frequency noise caused by the electronic circuit of the LDV. We stacked waveforms 1000 times ( in present study of Oncel 2000 times) and used the stacked waveform for analyses.
• #37: Seismic velocity changes due to increase the size of porosity is faster than the velocity changes due to lower porosity rocks.
• #38: Seismic velocity changes due to oil injection is observed higher (%30) as well as appeared higher porosity change (%50).
• #39: AIC: Akaike Information Criteria How to decrease Noise Value?