Maximum Magnitude Estimation for An Intraplate Setting - Example: The Giles County, Virginia, Seismic Zone

1992 ◽  
Vol 63 (2) ◽  
pp. 139-152 ◽  
Author(s):  
G. A. Bollinger ◽  
M. S. Sibol ◽  
M. C. Chapman
Keyword(s):  
Magnitude Estimation ◽  
Recurrence Relations ◽  
Value Theory ◽  
Seismogenic Zone ◽  
Maximum Magnitude ◽  
Seismic Zone ◽  
Historical Earthquake ◽  
Data Bases ◽  
Source Dimensions ◽  
Global Data

Abstract The process of maximum magnitude estimation is intrinsically subjective and depends directly on the experience and judgment of the analyst. Coppersmith et al. (1987; Table 1) discuss six methods for determining the maximum magnitude earthquake for a seismogenic zone. Those include: (I) Addition of an increment to the largest historical earthquake, (II) Extrapolation of magnitude recurrence relations, (III) Use of source dimensions to estimate magnitude, (IV) Statistical approaches (application of extreme value theory and maximum likelihood techniques), (V) Strain rate or moment release rate methods, and (VI) Reference to a global data base. Each technique has associated uncertainties in its applicability to the zone under consideration as well as in the specification of the key parameters involved. Of the six techniques listed above, only the first three are applicable to the data bases presently available for intraplate areas. Application of methods I, II, and III, to the Giles County, Virginia, seismic zone leads to the following results: MS,I = 6.9 (second subscript indicating which of the six methods was used) from adding a 1.0 increment to the maximum historical earthquake known to have occurred in the zone (May 31, 1897; MMI = VIII; mb = 5.8, MS = 5.9), MS,II = 7.0 from extension of the magnitude recurrence curve for the zone to a recurrence interval of 1000 years, and MS,III = 6.5 from the average of six estimates for the fault zone area. For a single estimate of maximum magnitude, the average of the above three values MS = 6.8 or equivalently, mb = 6.3 can be used.

The interrelationship between electrical resistivity and VP/VS ratio: A novel approach to constrain the subsurface resistivity structure in data gap areas in a seismogenic zone

Geophysics ◽  
2021 ◽  
pp. 1-44
Author(s):  
Ujjal K. Borah ◽  
Prasanta K. Patro
Keyword(s):  
Electrical Resistivity ◽  
A Priori ◽  
Fault Zones ◽  
Middle Part ◽  
Seismogenic Zone ◽  
Earth Model ◽  
Seismic Zone ◽  
S Wave ◽  
Data Gap ◽  
Earthquake Zone

Large man-made water-reservoirs promote fluid diffusion and cause critically stressed fault zones underneath to trigger earthquakes. Electrical resistivity is a crucial property to investigate such fluid-filled fault zones. We, therefore, carry out magnetotelluric (MT) investigation to explore an intra-plate earthquake zone, which is related to artificial reservoir triggered seismicity. However, due to surface access restrictions, our dataset has a gap in coverage in the middle part of the study area. This data gap region coincides with the earthquake hypocenter distribution in that intra-plate earthquake zone. Therefore, it is vital to fill the data gap to get the electrical signature of the active seismic zone. To compensate for the data gap, we develop a relation that connects resistivity with the ratio of seismic P- to S-wave velocity ( VP/ VS). Utilizing this relation, we estimate a priori resistivity distribution in the data gap region from known vp/vs values during inversion to compensate for the data gap. A comparison study of the root mean square (RMS) misfits of inversion outputs (with and without data gap filled) proves the effectiveness of the established relation. The inversion outputs obtained using the established relation brings out fault signatures in the data gap region. To examine the reliability and accuracy of these fault signatures, we occupy a portion of the data gap with new MT sites. We compare the inversion output from this new setup with the inversion output obtained from the established relation and observe that the electrical signatures in both outputs are spatially correlated. Further, a synthetic test on a similar earth model establishes the credibility and robustness of the derived relation.

Interseismic stress field variations in Hjalli-Ölfus, SW Iceland

2020 ◽  
Author(s):  
Ingi Th. Bjarnason ◽  
Revathy M. Parameswaran ◽  
Bergthóra S. Thorbjarnardóttir
Keyword(s):  
Plate Boundary ◽  
Strike Slip ◽  
Seismogenic Zone ◽  
Plate Boundaries ◽  
Central Volcano ◽  
Seismic Zone ◽  
Stress Regime ◽  
Mid Atlantic Ridge ◽  
Spatio Temporal ◽  
Earthquake Sequences

<p>Western South Iceland Seismic Zone (SISZ) plate boundary lies adjacent to the Hengill central volcano. The sinistral SISZ connects the two arms of the divergent Mid-Atlantic Ridge (MAR) plate boundaries (Western and Eastern Volcanic Zones; WVZ, EVZ), while Hengill is a part of the WVZ. Seismicity in western SISZ, also known as the Hjalli-Ölfus region, closely interacts with the seismicity and magmatism in Hengill. For instance, the  4 June 1998 Mw 5.4 Hengill earthquake witnessed aftershocks that extended south to meet the Hjalli-Ölfus segment. This segment then hosted the Mw 5.1 Hjalli-Ölfus earthquake that occurred on 13 November 1998; elucidating the Hengill-Ölfus interaction. Relative relocations of earthquakes from July 1991 to December 1999 in Hjalli-Ölfus indicate that the seismogenic zone is predominant at 4-8 km depth, with 80% of the events occuring along an ~ENE-WSW trending seismic zone with lateral extension of ~12 km. The remaining occur along N-S faults, much like the observed norm of dextral faulting along the rest of the SISZ (e.g., 17 June 2000, 29 May 2008 earthquakes; Árnadottir et al., 2001; Brandsdottir et al., 2010). These relocated earthquake sequences were used to perform stress inversions within specified spatio-temporal grids. The results show that from 1994 to 1997, the western part of the Hjalli-Ölfus region exhibits an oblique normal stress regime, while the eastern part remains consistently strike-slip in nature. From mid-1997 to June 1998 western Hjalli-Ölfus shifts from an oblique normal to a strike-slip stress regime, while the eastern part maintains the strike-slip character of the SISZ. However, two months after the 4 June 1998 Hengill earthquake, the western part shifts back to an oblique normal regime, which loses a part of its normal-faulting tendency after the 13 November 1998 Hjalli-Ölfus earthquake. This variation in stress fields between two significant events on conjugately oriented prodominantly strike-slip faults is a clear example of these features influencing one another between seismic episodes. </p>

scholarly journals Present-day stress field pattern in the Vrancea seismic zone (Romania) deduced from earthquake focal mechanism inversion

2021 ◽  
Vol 64 (6) ◽  
pp. PE660
Author(s):  
Andrei Bala ◽  
Mircea Radulian ◽  
Dragos Toma-Danila
Keyword(s):  
Large Strain ◽  
Average Energy ◽  
Seismogenic Zone ◽  
Field Pattern ◽  
Seismic Zone ◽  
Depth Level ◽  
Stress Regime ◽  
Intermediate Depth ◽  
Eastern Carpathians ◽  
Earthquake Focal Mechanism

   Vrancea seismogenic zone in the South-Eastern Carpathians is characterized by localized intermediate-depth seismicity. Due to its complex geodynamics and large strain release, Vrancea represents a key element in the Carpatho-Pannonian system. Data from a recently compiled catalogue of fault plane solutions (REFMC) are inverted to evaluate stress regime in Vrancea on depth. A single predominant downdip extensive regime is obtained in all considered clusters, including the crustal layers located above the Vrancea slab. The prevalent stress regime confirms previous investigations and requires some mantle-crust coupling. The S3 principal stress is close to vertical, while S1 and S2 are horizontal, oriented perpendicularly and respectively tangentially to the Carpathians Arc bend. This configuration is present at any depth level. According to seismicity patterns, there are two main active segments in the Vrancea intermediate-depth domain, at 55 – 105 km and 105 – 180 km, both able to generate major events. The configuration of the tectonic stresses as resulted from inversion is similar in both segments. Also, high fault instability (I > 0.95) is characterizing the segments. The only notable difference is given by the friction and stress ratio parameters which drop down in the bottom segment from μ = 0.95 to μ = 0.55 and from R = 0.51 to R = 0.29. This variation is attributed to possible weakening processes activated below 100 km depth and can explain the intensification of seismicity production as earthquake rate and average energy release in the lower segment versus the upper segment. 

scholarly journals A detailed seismic zonation model for shallow earthquakes in the broader Aegean area

2013 ◽  
Vol 1 (6) ◽  
pp. 6719-6784 ◽  
Author(s):  
D. A. Vamvakaris ◽  
C. B. Papazachos ◽  
C. Papaioannou ◽  
E. M. Scordilis ◽  
G. F. Karakaisis
Keyword(s):  
Seismic Hazard ◽  
Hazard Assessment ◽  
Active Faults ◽  
Seismic Hazard Assessment ◽  
Maximum Magnitude ◽  
Seismic Zone ◽  
Seismic Zonation ◽  
Aegean Area ◽  
Seismic Zones ◽  
Shallow Earthquakes

Abstract. In the present work we present an effort to define a new seismic zonation model of area type sources for the broader Aegean area, which can be readily used for seismic hazard assessment. The definition of this model is based not only on seismicity information but incorporates all available seismotectonic and neotectonic information available for the study area, in an attempt to define zones which show not only a rather homogeneous seismicity release but also exhibit similar active faulting characteristics. For this reason, all available seismological information such as fault plane solutions and the corresponding kinematic axes have been incorporated in the analysis, as well as information about active tectonics, such as seismic and active faults. Moreover, various morphotectonic features (e.g. relief, coastline) were also considered. Finally, a revised seismic catalogue is employed and earthquake epicentres since historical times (550 BC–2008) are considered, in order to define areas of common seismotectonic characteristics, that could constitute a discrete seismic zone. A new revised model of 113 earthquake seismic zones of shallow earthquakes for the broader Aegean area is finally proposed. Using the proposed zonation model, a detailed study is performed for the catalogue completeness for the recent instrumental period. Using the defined completeness information, seismicity parameters (such as G–R values) for the 113 new seismic zones have been calculated, and their spatial distribution was also examined. The spatial variation of the obtained b values shows an excellent correlation with the geotectonic setting in the area, in good agreement with previous studies. Moreover, a quantitative estimation of seismicity is performed in terms of the mean return period, Tm, of large (M ≥ 6.0) earthquakes, as well as the most frequent maximum magnitude, Mt, for a typical time period (T = 50 yr), revealing significant spatial variations of seismicity levels within the study area. The new proposed seismic zonation model and its parameters can be readily employed for seismic hazard assessment for the broader Aegean area.

Magnitude Recurrence Relations for Colorado Earthquakes

2002 ◽  
Vol 18 (2) ◽  
pp. 233-250 ◽  
Author(s):  
Wayne A. Charlie ◽  
Raymond J. Battalora ◽  
Thomas J. Siller ◽  
Donald O. Doehring
Keyword(s):  
Recurrence Relations ◽  
Active Faults ◽  
Geological Survey ◽  
Fluid Injection ◽  
Historical Earthquake ◽  
Induced Earthquakes ◽  
Slip Rates ◽  
Probability Of Exceedance ◽  
Maximum Credible Earthquake ◽  
Significant Potential

Colorado has a significant potential for damaging earthquakes. The Colorado Geological Survey has identified 92 potentially active faults. Two faults have documented slip-rates approaching 1 mm per year. Four hundred and seventy-seven Colorado earthquakes have been felt and/or equaled or exceeded magnitude of 2.0 between 1870 and 1996. Eighty-two earthquakes have equaled or exceeded an MMI Scale of V. Colorado's largest historical earthquake, which occurred on 7 November 1882 (8 November UCT), had an estimated magnitude of 6.5 and maximum MMI of VII to VIII. Colorado's maximum credible earthquake has been estimated at 7.5 ML. In this paper we analyze independent earthquakes (foreshocks, aftershocks, and fluid-injection induced earthquakes removed) to develop magnitude-recurrence relations. Analysis of instrumentally measured earthquakes predicts that a 6.5 ML or larger earthquake occurring somewhere in Colorado has a mean recurrence interval of about 420 years. A magnitude 6.6 ML earthquake has a 10 percent Poisson's probability of exceedance in 50 years. A 7.5 ML earthquake has a 2 percent Poisson's probability of exceedance in 50 years. Colorado's magnitude-recurrence (Gutenberg-Richter) relation is log N=2.58−0.80 ML.

Maximum magnitude estimation considering the regional rupture character

2015 ◽  
Vol 19 (3) ◽  
pp. 695-719 ◽  
Author(s):  
Anbazhagan P. ◽  
Ketan Bajaj ◽  
Sayed S. R. Moustafa ◽  
Nassir S. N. Al-Arifi
Keyword(s):  
Magnitude Estimation ◽  
Maximum Magnitude
Sign in / Sign up

Export Citation Format

Share Document