Stress drop in earthquakes

1968 ◽  
Vol 58 (1) ◽  
pp. 249-257 ◽  
Author(s):  
Chi-Yu King ◽  
Leon Knopoff
Keyword(s):  
Stress Drop ◽  
Earthquake Magnitude ◽  
Dislocation Theory ◽  
Energy Formula ◽  
Fault Trace ◽  
Fault Length

abstract A correlation is made between earthquake magnitude and parameters of fault trace on the basis of dislocation theory. For earthquakes with magnitudes M between 5.5 and 8.5, the correlation with fault length L and the maximum horizontal or vertical offset D (both in cm) is approximately log L D 2 = 2.24 M − 4.99. Combining this result with a magnitude-energy formula, it is found that the stress drop is dependent upon magnitude, with the fractional stress drop increasing with magnitude.

P-wave spectra for ML 5 foreshocks, aftershocks, and isolated earthquakes near Parkfield, California

1981 ◽  
Vol 71 (2) ◽  
pp. 423-436
Author(s):  
Willian H. Bakun ◽  
Thomas V. McEvilly
Keyword(s):  
Stress Drop ◽  
High Stress ◽  
P Wave ◽  
Wave Radiation ◽  
Focal Region ◽  
Wave Spectra ◽  
Rupture Length ◽  
Main Shocks ◽  
Relative Stress ◽  
Fault Trace

abstract Wood-Anderson seismograms recorded at Mount Hamilton (MHC, 185 km, 327°), Santa Barbara (SBC, 180 km, 158°), and Tinemaha (TIN, 240 km, 56°) provide data for comparing P-wave spectra for two immediate (17-min) foreshocks, one early (55-hr) foreshock, two aftershocks, and two “isolated” Parkfield earthquakes. All are ML 5.0 shocks with epicenters within 7 km of the common epicenter of the 1934 and 1966 Parkfield main shocks. The set of events is well suited for testing the hypothesis that foreshocks are high-stress-drop sources. Calculated stress drops are controlled by source directivity at azimuths aligned with the fault break (at MHC and SBC). P-wave radiation from the three foreshocks is focused along one fault trace azimuth, suggesting that foreshock sources are characterized by pronounced unilateral rupture expansion. At TIN, broadside to the fault where directivity has minimum effect on calculated relative stress drop, the two immediate foreshocks are higher stress-drop sources. The early foreshock is a low-to-average stress-drop source, indicating the possibility that stress concentration is a rapidly occurring phenomenon in rupture nucleation. Alternatively, the stress field is highly variable on the scale of 2 to 3 km in the focal region of an impending earthquake with a rupture length of 20 to 30 km.

Strain steps associated with earthquakes

1967 ◽  
Vol 57 (6) ◽  
pp. 1429-1444
Author(s):  
C. J. Wideman ◽  
M. W. Major
Keyword(s):  
Surface Waves ◽  
Empirical Relationship ◽  
Earthquake Magnitude ◽  
Amplitude Dependence ◽  
Wide Range ◽  
Speed Of Propagation ◽  
Fault Length ◽  
Step Amplitude

Abstract Strain steps have been observed following earthquakes ranging in magnitude from 3.0 to 8.5. An empirical relationship is derived which indicates that the magnitude, M, of the smallest earthquake from which a strain step of the order of 10−9 may be expected at a distance of Δkm is: M = 1.1 + 1.7 log ⁡ Δ 10 . Fault length is related empirically to earthquake magnitude by the equation M = 3.3 + 1.7 log ⁡ L 10 Where L is fault length in km. Comparison of these two equations shows that strains of the order of 10−9 may be expected at distances of approximately 20 fault lengths. The fault length versus magnitude equation presented is shown to be compatible with a previously published energy-magnitude relationship log ⁡ 10 E = A + 1.8 M . Strain steps are shown to have two characteristics which are similar to those of surface waves. The speed of propagation is nearly constant over a wide range of epicentral distances. Depending upon whether the travel paths are continental or oceanic, the speeds are, respectively, 3.0 ± 0.3 km/sec or near 3.6 km/sec. The strain step amplitude dependence upon distance is like R -3/2.

scholarly journals Source process of the October 12, 1992 Cairo earthquake

1999 ◽  
Vol 42 (4) ◽  
Author(s):  
H. M. Hussein
Keyword(s):  
Data Center ◽  
Stress Drop ◽  
Strike Slip ◽  
Body Waves ◽  
Source Process ◽  
Normal Faulting ◽  
Double Couple ◽  
Fault Length ◽  
Source Duration ◽  
Iris Data

Broadband body waves recorded at 12 digital seismic stations worldwide were used to study the source process of the October 12, 1992 Cairo earthquake. To study the source process of this event the P and SH waveforms from IRIS data center were inverted to double couple source using the method Kikuchi and Kanamori (1991) in which the rupture is presented by discrete subevents with various mechanisms. The best solution consists of only one event with a mechanism 270°/47°/-123° (strike/dip/slip), a normal faulting mechanism with small strike slip component. This solution is almost compatible with the previously suggested mechanisms for the same event. This event took place at a depth of 22 km. This depth explains the lack of surface faulting. The seismic moment is 7.2 ´ 10 17 Nm (Mw = 5.8) with a source duration of 4 s. The estimated fault length is about 11 km, the derived average dislocation (D) is 0.24 m, the stress drop (Ds ) is 1.85 MPa and the Orwan stress drop is 0.425 MPa.

scholarly journals From mapped faults to fault-length earthquake magnitude (FLEM): a test on Italy with methodological implications

Solid Earth ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 1555-1579 ◽  
Author(s):  
Fabio Trippetta ◽  
Patrizio Petricca ◽  
Andrea Billi ◽  
Cristiano Collettini ◽  
Marco Cuffaro ◽  
...  
Keyword(s):  
Stress Field ◽  
Strain Rate ◽  
Earthquake Magnitude ◽  
National Scale ◽  
Field Orientation ◽  
Scaling Relationships ◽  
Fault Length

Abstract. Empirical scaling relationships between fault or slip dimensions and earthquake magnitudes are often used to assess the maximum possible earthquake magnitude of a territory. Upon the assumption of the reactivability of any fault, the earthquake magnitudes derived from the surface fault length (FLEM) are compared at the national scale in Italy against catalogued magnitudes. FLEMs are obtained by considering a comprehensive fault dataset regardless of fault age, stress field orientation, strain rate, etc. In particular, (1) a comprehensive catalogue of all known faults is compiled by merging the most complete databases available; (2) FLEM is then derived from fault length; and (3) the resulting FLEMs are compared (i.e. the mathematical difference) with catalogued earthquake magnitudes. Results show that the largest FLEMs as well as the largest differences between FLEMs and catalogued magnitudes are observed for poorly constrained faults, mainly inferred from subsurface data. It is suggested that these areas have to be further characterized to better estimate fault dimension and segmentation and hence properly assess the FLEM. Where, in contrast, the knowledge of faults is geologically well constrained, the calculated FLEM is often consistent with the catalogued seismicity, with the 2σ value of the distribution of differences being 1.47 and reducing to 0.53 when considering only the Mw≥6.5 earthquakes. Our work highlights areas, in Italy, where further detailed studies on faults are required.

scholarly journals THE ATALANTI ACTIVE FAULT: RE-EVALUATION USING NEW GEOLOGICAL DATA

2004 ◽  
Vol 36 (4) ◽  
pp. 1560 ◽  
Author(s):  
Σ. B. Παυλίδης ◽  
Σ. Βαλκανιώτης ◽  
A. Γκανάς ◽  
Δ. Κεραμυδάς ◽  
Σ. Σμπόρας
Keyword(s):  
Active Fault ◽  
Active Faults ◽  
Earthquake Magnitude ◽  
Earthquake Sequence ◽  
Historical Earthquake ◽  
Geological Data ◽  
Maximum Earthquake Magnitude ◽  
Surface Ruptures ◽  
Fault Trace ◽  
Maximum Earthquake

The Northern Gulf of Evoia is a region with an intense neotectonic activity, dominated by characteristic and impressive active faults. The only fault in the region which is connected with a strong historical earthquake, is the Atalanti fault, with the well-known earthquake sequence of 1894. For an accurate mapping of the fault trace, the 1894 surface ruptures investigation and the estimation of the area's seismic hazard, there has been made a detailed geological - neotectonic investigation of the Atalanti city area. The results of this investigation show that the Atalanti fault comprises a 20- 30km long fault zone, divided in at least 4 segments: Atalanti, Kiparissi-Almyra, Tragana-Proskyna, Martino and possibly Larymna segment. The maximum earthquake magnitude is estimated in Msmax=6.8, and the recurrence interval, concerning the same magnitude, for Atalanti fault is larger than 1000 years, possibly even more than 2000 years. Paleoseismological trenching in Agios Konstantinos area excludes the connection of this fault with the earthquake sequence of 1894.

The spectral theory of seismic sources

1973 ◽  
Vol 63 (3) ◽  
pp. 1133-1144 ◽  
Author(s):  
M. J. Randall
Keyword(s):  
Spectral Theory ◽  
Stress Drop ◽  
Seismic Energy ◽  
Source Model ◽  
Earthquake Magnitude ◽  
Seismic Sources ◽  
Dislocation Model ◽  
Empirical Relationships ◽  
Aftershock Sequences ◽  
Characteristic Stress

abstract The far-field results of Brune's spectral theory are shown to be largely independent of his source model; this implies that the theory has even greater power than it seemed, but that its success in explaining the observed spectra does not in itself justify a dislocation model. Expressions are derived for seismic energy and characteristic stress which are independent of assumptions as to source model. For several models, the characteristic stress is found to be a good approximation to the stress-drop. A theoretical relationship between earthquake magnitude ML, stress-drop, and fault size is derived. This provides a means of estimating the stress-drop for earthquakes associated with aftershock sequences, using estimates of ML and fault size, and is consistent with empirical relationships between magnitude and fault size, and between seismic energy and magnitude.

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