Fault plane orientations of microearthquakes at Mt. Etna from the inversion of P-wave rise times

2010 ◽  
Vol 189 (3-4) ◽  
pp. 247-256 ◽  
Author(s):  
Salvatore de Lorenzo ◽  
Elisabetta Giampiccolo ◽  
Carmen Martinez-Arevalo ◽  
Domenico Patanè ◽  
Annalisa Romeo
Keyword(s):  
Fault Plane ◽  
P Wave ◽  
Mt Etna

Control of rupture by fault geometry during the 1966 parkfield earthquake

1981 ◽  
Vol 71 (1) ◽  
pp. 95-116 ◽  
Author(s):  
Allan G. Lindh ◽  
David M. Boore
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
San Andreas Fault ◽  
Strong Motion ◽  
P Wave ◽  
Fault Geometry ◽  
Dynamic Rupture ◽  
San Andreas ◽  
Hill Station ◽  
Parkfield Earthquake

abstract A reanalysis of the available data for the 1966 Parkfield, California, earthquake (ML=512) suggests that although the ground breakage and aftershocks extended about 40 km along the San Andreas Fault, the initial dynamic rupture was only 20 to 25 km in length. The foreshocks and the point of initiation of the main event locate at a small bend in the mapped trace of the fault. Detailed analysis of the P-wave first motions from these events at the Gold Hill station, 20 km southeast, indicates that the bend in the fault extends to depth and apparently represents a physical discontinuity on the fault plane. Other evidence suggests that this discontinuity plays an important part in the recurrence of similar magnitude 5 to 6 earthquakes at Parkfield. Analysis of the strong-motion records suggests that the rupture stopped at another discontinuity in the fault plane, an en-echelon offset near Gold Hill that lies at the boundary on the San Andreas Fault between the zone of aseismic slip and the locked zone on which the great 1857 earthquake occurred. Foreshocks to the 1857 earthquake occurred in this area (Sieh, 1978), and the epicenter of the main shock may have coincided with the offset zone. If it did, a detailed study of the geological and geophysical character of the region might be rewarding in terms of understanding how and why great earthquakes initiate where they do.

Aftershocks of the February 21, 1973 Point Mugu, California earthquake

1976 ◽  
Vol 66 (6) ◽  
pp. 1931-1952
Author(s):  
Donald J. Stierman ◽  
William L. Ellsworth
Keyword(s):  
Fault Zone ◽  
Main Shock ◽  
Fault Plane ◽  
Body Wave ◽  
P Wave ◽  
Fault System ◽  
Wave Radiation ◽  
Fault Plane Solutions ◽  
Complex Deformation ◽  
Transverse Ranges

abstract The ML 6.0 Point Mugu, California earthquake of February 21, 1973 and its aftershocks occurred within the complex fault system that bounds the southern front of the Transverse Ranges province of southern California. P-wave fault plane solutions for 51 events include reverse, strike slip and normal faulting mechanisms, indicating complex deformation within the 10-km broad fault zone. Hypocenters of 141 aftershocks fail to delineate any single fault plane clearly associated with the main shock rupture. Most aftershocks cluster in a region 5 km in diameter centered 5 km from the main shock hypocenter and well beyond the extent of fault rupture estimated from analysis of body-wave radiation. Strain release within the imbricate fault zone was controlled by slip on preexisting planes of weakness under the influence of a NE-SW compressive stress.

scholarly journals Isochronal maps at Mt. Etna volcano (Italy): a simple and reliable tool for investigating large-scale heterogeneities

1997 ◽  
Vol 40 (5) ◽  
Author(s):  
G. Patanè ◽  
C. Centamore ◽  
S. La Delfa
Keyword(s):  
Large Scale ◽  
Volcanic Edifice ◽  
P Wave ◽  
Etna Volcano ◽  
Low Velocity ◽  
Seismic Stations ◽  
Arrival Times ◽  
Mt Etna ◽  
Wave Arrival ◽  
Feeding Systems

This paper analyses twelve etnean earthquakes which occurred at various depths and recorded at least by eleven stations. The seismic stations span a wide part of the volcanic edifice; therefore each set of direct P-wave arrival times at these stations can be considered appropriate for tracing isochronal curves. Using this simple methodology and the results obtained by previous studies the authors make a reconstruction of the geometry of the bodies inside the crust beneath Mt. Etna. These bodies are interpreted as a set of cooled magmatic masses, delimited by low-velocity discontinuities which can be considered, at present, the major feeding systems of the volcano.

Earthquake/earth tide correlation and other features of the Susanville, California, earthquake sequence of June-July 1976

1980 ◽  
Vol 70 (5) ◽  
pp. 1583-1593
Author(s):  
Amy S. Mohler
Keyword(s):  
Shear Stress ◽  
Compressive Stress ◽  
Sierra Nevada ◽  
Fault Plane ◽  
Earth Tide ◽  
P Wave ◽  
First Motion ◽  
Entire Sequence ◽  
June July ◽  
Earthquake Sequences

abstract An earthquake of magnitude ML 4.5 occurred on June 20, 1976 in an area of complex faulting in northeastern California, near the intersection of the Sierra Nevada, Modoc Plateau, Cascade Range, and Basin and Range geological provinces. P-wave first motion plots for larger aftershocks of this earthquake indicate maximum and minimum compressive stress, respectively, in north-south and east-west directions, with predominantly strike-slip motion. Focal depths for these events ranged from 7 to 15 km, consistent with other earthquake sequences in the region. Origin times of more than 4,700 aftershocks for the period between June 20 and July 1 are compared with the phase of solid-earth tidal components appropriate for normal and shear stress on northeast- and northwest-trending fault planes. Based on this comparison, approximately 20 per cent more earthquakes occurred at times when the normal compressive stress on the fault plane was decreasing, and the shear stress was increasing in the sense of slip on the fault plane. This correlation may be explained by two large bursts of aftershocks that occurred at times when tidal stresses were favorable for motion on the fault plane, rather than continuous triggering of small events during the entire sequence.

The Peru-Bolivia border earthquake of August 15, 1963

1970 ◽  
Vol 60 (2) ◽  
pp. 639-646 ◽  
Author(s):  
Umesh Chandra
Keyword(s):  
Travel Time ◽  
Fault Plane ◽  
P Wave ◽  
Focal Mechanism Solution ◽  
Event Analysis ◽  
Rupture Propagation ◽  
Fault Propagation ◽  
Amplitude Data ◽  
First Motion ◽  
Deep Focus

abstract The seismograms of the deep focus Peru-Bolivia border earthquake of August 15, 1963 reveal the presence of a number of conspicuous phases occurring within 15 seconds of the first P onset. These phases cannot be explained on the basis of known travel-time curves. Accordingly, the earthquake is interpreted to have occurred in a series of jerks during the course of fault propagation, or in other words it is composed of multiple events. Only one of these events, following the first event, at which the amplitude of the recorded motion becomes suddenly very large, has been located in this study. The focal mechanism solution of this earthquake has been determined from the P wave first motion and amplitude data. Consideration of the direction of rupture propagation determined from the multiple event analysis makes it possible to identify the fault plane in the mechanism solution. The parameters of the fault plane, length and speed of rupture between the two events have been determined.

The Broach earthquake of March 23, 1970

1972 ◽  
Vol 62 (1) ◽  
pp. 47-61
Author(s):  
Harsh K. Gupta ◽  
Indra Mohan ◽  
Hari Narain
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
Geological Structure ◽  
P Wave ◽  
Field Observations ◽  
B Values ◽  
Macroseismic Effects ◽  
Godavari Valley ◽  
First Motion ◽  
Largest Aftershock

Abstract The recent seismicity of the Broach region has been studied and correlated with the regional geological structure. The macroseismic effects are briefly described. Analysis of the first motion of P-wave data indicates the plane striking N 92°E to be the fault plane as supported by field observations also. The present seismic activity is found to be similar to the recent Godavari Valley earthquake sequence of April 1970 and different from the earthquakes in the Koyna region on the basis of b values, foreshock-aftershock pattern, and the ratio of the largest aftershock to the main shock magnitude.

A source theory for complex earthquakes

1975 ◽  
Vol 65 (5) ◽  
pp. 1385-1405 ◽  
Author(s):  
R. R. Blandford
Keyword(s):  
Fault Plane ◽  
Amplitude Ratio ◽  
P Wave ◽  
Corner Frequency ◽  
Transform Faults ◽  
Shallow Earthquakes ◽  
Short Period ◽  
Wave Forms ◽  
The Moment ◽  
Third Moment

Abstract Earthquake source theories of Haskell, Brune, and Savage have been drawn upon to develop a description of an earthquake as a major slip accompanied by many smaller tensional and slip events. We find natural explanations of several previously unexplained observations, such as: Robustness of the MS: mb discriminant, P corner frequency higher than S corner frequency for shallow earthquakes, High-frequency P/S amplitude ratio higher for shallow earthquakes than previous theories predict, Increase of complexity as a function of third moment, Small mb relative to MS for transform faults. (This can also be explained by emergent short-period P wave forms or by a low-Q region underlying the source). The theory predicts that MS:mb populations of earthquakes and explosions will not converge at small magnitudes. The theory also suggests that the standard interpretations of corner-frequency measurements can provide only a lower limit to fault-plane dimensions and, in combination with the moment, only an upper limit on stress drop.

scholarly journals The contribution of the NEMO-SN1 seafloor observatory to improve the seismic locations in the Ionian Sea (Italy)

2021 ◽  
Vol 64 (Vol. 64 (2021)) ◽  
Author(s):  
Tiziana Sgroi ◽  
Graziella Barberi ◽  
Alessandro Marchetti
Keyword(s):  
Structural Model ◽  
Single Point ◽  
Oceanic Lithosphere ◽  
P Wave ◽  
Ionian Sea ◽  
Offshore Area ◽  
Crustal Earthquakes ◽  
Mt Etna ◽  
Seismogenic Structures ◽  
Seafloor Observatory

The Western Ionian Sea is characterised by an active and diffuse seismicity, directly related to the convergence of the European and African Plates and by gravitational sinking and rollback of the  oceanic lithosphere. In this area, the location of earthquakes is characterised by considerable uncertainties due to large azimuthal gaps, resulting in notable location errors. This problem was  partially overcome with the use of data recorded by NEMO-SN1 seafloor observatory (October 2002 February 2003; June 2012 - May 2013). We relocated 1130 crustal and sub-crustal earthquakes  using land network and NEMO-SN1 data. As most events occurred on Mt. Etna, we focused on 358  earthquakes in the offshore area and near the coasts of Sicily and Calabria. The use of the combined  land-marine networks has improved the earthquake locations in terms of azimuthal GAP, as well as  in horizontal and vertical errors. The comparison between locations performed with and without NEMO-SN1 data shows that differences in latitude, longitude and depths are more evident in the Western Ionian Sea and in the coast of Sicily, where values of the differences over 5 km correspond  to structural heterogeneities. The increased number of seismic stations deployed on land from 2003  to 2012 did not influence the location of events occurring offshore, where NEMO-SN1 continued to be the distinctive tool in the location process. Moreover, the new 73 focal mechanisms computed with  P-wave polarities from NEMO-SN1 and land stations are in agreement with the regional structural   model, showing a prevalent normal, normal/oblique, and strike-slip kinematics. The similarity of two   new focal solutions with the mechanisms of the main shock and aftershock of the 1990 earthquake  demonstrates that the seismic structures are still active and potentially dangerous. The P-wave travel- time residual analysis confirms the activity along the main structural alignments.  A single point of observation in the Ionian Sea can significantly improve the quality of locations, giving an opportunity to focus on the seismogenic structures responsible for the occurrence of  medium-to-high magnitude earthquakes.

Sign in / Sign up

Export Citation Format

Share Document