Rupture Directivity Of Earthquakes Research Articles

Tsunami potential in the Makran subduction zone: Amplification effects from earthquake rupture directivity and speed

Tsunami potential in the Makran subduction zone: Amplification effects from earthquake rupture directivity and speed

An Evolutionary Shaking‐Forecast‐Based Earthquake Early Warning Method

AbstractHere we propose a methodology for Earthquake Early Warning (EEW) able to issue the alert based on the real‐time estimation of the epicentral area where a peak ground Intensity measure is expected to exceed a user‐set ground shaking level. The method provides in output a P‐wave‐based, time‐evolutive “early” shake map. It combines the peak ground velocity predictions available from the observed P‐wave amplitudes and from the region‐specific ground motion prediction equation, using progressively updated estimates of earthquake location and magnitude. The P‐wave displacement, velocity and acceleration amplitudes are jointly measured on a progressively expanded P‐wave time window while the earthquake location and magnitude are evaluated using the first P‐arrival time and displacement amplitudes at near source stations. A retrospective analysis of the 2016, Mw 6.5 Central Italy earthquake records shows that depending on the network density and spatial source coverage, the method naturally accounts for effects related to the earthquake rupture directivity and spatial variability of strong ground motion related to crustal wave propagation and site amplification. Within 1.5 s from the first alert (5.15 s after the origin time), the simulated performance of the system in predicting the event ground shaking is very high: in the 40 km‐radius area that suffered an Intensity MCS VIII–IX, 41 over 42 strong‐motion instrumented sites would have been successfully alerted, with only one false alarm. Even considering the calculated blind‐zone of 15 km radius, a 15–55 km wide annular area would have received the alert 2–14.5 s before the occurrence of the strong ground shaking. The proposed EEW method evolves with time in a way that it minimizes the missed alarms while increasing successful alarms and to a lesser extent false alarms, so it is necessary for the end‐user to accept these possibilities and account for them in a probabilistic decision scheme depending on the specific safety actuation measure to be undertaken in real‐time.

Rupture directivity and fault plane determination from analysis of rupture duration using broadband P-waves of the September 2018 M w 7.5 Palu, Indonesia earthquake

The aim of this study is to determine earthquake rupture directivity and fault plane of the 28 September 2018 M w 7.5 event in Palu, Indonesia. The data used in the current study were all acquired from broadband seismograms recorded by a network of 56 seismic stations. The method included analysis of rupture duration, where T dur was calculated using the vertical component of P-waveforms downloaded from IRIS site at http://ds.iris.edu/wilber3/find_event. For all stations involved in the T dur calculations, the largest distance between the epicenter and the corresponding station was estimated to be 40° from the azimuth station. The direction of the rupture indicated fault plane geometry of the source. The rupture directivity was found to be at azimuth 179°, in good agreement with the Palu Koro Fault azimuth. The finding implies that the direction of the earthquake rupture passed below the sea surface of Palu Bay, which could be the main source of the tsunami.

Rupture directivity, stress drop, and hypocenter migration of small earthquakes in the Yamagata-Fukushima border swarm triggered by upward pore-pressure migration after the 2011 Tohoku-Oki earthquake

We examined a relationship between rupture propagation directions and the distribution of fault strength by analyzing seismological data from the earthquake swarm on the Yamagata-Fukushima border, NE Japan. This earthquake swarm exhibits a distinct hypocenter migration behavior and was estimated to be triggered by upward fluid movement after the 2011 Tohoku-Oki earthquake. We utilized the dense nationwide seismic network in Japan to estimate apparent source time functions of >1500 small earthquakes (MJMA ≥ 2). We found clear directional dependences of the peak amplitude and the pulse-width in the apparent source time functions, suggesting the earthquake rupture directivity, for half of the earthquakes. Rupture directions mostly avoid the directions of the hypocenter migration. The difference between the microscopic and macroscopic propagations of rupture might be explained by the spatial variation in the fault strength affected by pore pressure along the fault; ruptures of each earthquake are hindered from developing toward the region with higher fault strength ahead of the pore-pressure front. Estimates of stress drop systematically increased on taking the effects of rupture directivity into account. We observed a temporal increase in stress drop from 3 MPa to 10 MPa during the pore-pressure migration.

Resolving Horizontal Rupture Directivity of Moderate Crustal Earthquake in Sparse Network With Ambient Noise Location

AbstractEarthquake rupture directivity can remove fault plane ambiguity in earthquake moment tensor solutions; thus, it is helpful to improve reliability of shake map and understanding the seismogenic processes. In this paper, we propose an algorithm to resolve the horizontal rupture directivity of moderate crustal earthquakes in two steps. The first step is to determine the two candidate fault planes from focal mechanism inversion. Then, rupture directivity is estimated via the difference between the hypocenter and the centroid location which is constrained on the candidate fault planes. Accurate centroid location is determined with ambient noise location method, in which the noise cross‐correlation functions (NCFs) provide a stable calibration for the path effects. This technique is applied to the 2011 Oklahoma earthquake, and the estimated centroid location is about 2–4 km southwest to the hypocenter, indicating that the mainshock ruptured along the 234° plane for about 4–8 km. The result is consistent with directivity estimation using a foreshock as reference event and also agrees with early aftershock distribution as well as finite fault inversion. More applications to the 2004 Parkfield earthquake and the 2014 Napa earthquake are performed to explore the effectiveness and limitation of this method. This method is helpful for determining rupture directivity of earthquakes in sparse network but requiring one or two nearby stations. Alternatively, temporary stations can be installed in the area of high seismic hazard, then a library of NCFs and path calibrations would be available for rapidly determining rupture directivity of future earthquakes.

Along-strike rupture directivity of earthquakes of the 2009 L'Aquila, central Italy, seismic sequence

Along-strike rupture directivity of earthquakes of the 2009 L'Aquila, central Italy, seismic sequence

Reply to comment by A. Douglas on ‘Systematic determination of earthquake rupture directivity and fault planes from analysis of long-periodP-wave spectra’

SUMMARY We respond to the comments by Douglas regarding our earlier paper by emphasizing that our automated method was intended to distinguish between the primary and auxiliary fault planes in earthquake focal mechanisms and does not always produce reliable results for rupture velocity and rupture length.

Comment on ‘Systematic determination of earthquake rupture directivity and fault planes from analysis of long-periodP-wave spectra’ by L. M. Warren and P. M. Shearer

SUMMARY Warren and Shearer describe a method of estimating the duration of P pulses radiated by earthquakes, on the assumption that the source is a unilateral fracture. The estimates are made in the frequency domain. The estimates obtained by Warren and Shearer for seven of the earthquakes are compared to durations estimated here in the time domain; the time-domain measurements being made on broad-band seismograms (∼0.1–4.0 Hz) derived by filtering from short-period recordings. Overall, the time-domain method indicates that the pulse duration of the earthquakes studied here range from 2.0 to 7.6 s, whereas the estimates from the results of Warren and Shearer range from 7.1 to 9.8 s. This suggests that the method of Warren and Shearer cannot resolve pulse lengths less than about 7 s. The suggestion is supported by the estimates of the duration of rupture—fault length/speed of rupture—implied by the results of Warren and Shearer. For, although the estimated fault-length ranges from 0.8 km to over 40 km most rupture durations are around 8 s.

Systematic determination of earthquake rupture directivity and fault planes from analysis of long-period P-wave spectra

Summary If an earthquake has a primarily unilateral rupture, the pulse width observed on seismograms will vary depending on the angle between the rupture direction and the takeoff vector to the station. We have developed a method to estimate the amount of pulse broadening from the spectrum and apply it to a long-period database of large, globally distributed earthquakes that occurred between 1988 and 2000. We select vertical-component P-waves at epicentral distances of 20°–98°. We compute the spectrum from a 64-s-long window around each P-wave arrival. Each spectrum is the product of source, receiver and propagation response functions as well as local source- and receiver-side effects. Since there are multiple receivers for each source and multiple sources for each receiver, we can estimate and remove the source- and receiver-side terms by stacking the appropriate P log spectra. For earthquakes deeper than ∼200 km, source effects dominate the residual spectra. We use our pulse-width estimates to determine the best rupture direction and to identify which nodal plane of the Harvard centroid moment tensor (CMT) solution is most consistent with this rupture direction for 66 events. In about 30 per cent of the cases, one of the two nodal planes produces a much better fit to the data and can be identified as the true fault plane. When results from previous studies are available for comparison, our rupture directions are usually consistent with their results, particularly for earthquakes with simple rupture histories.

Earthquake rupture dynamics frozen in exhumed ancient faults

Most of our knowledge about co-seismic rupture propagation is derived from inversion and interpretation of strong-ground-motion seismograms, laboratory experiments on rock and rock-analogue material, or inferred from theoretical and numerical elastodynamic models. However, additional information on dynamic rupture processes can be provided by direct observation of faults exhumed at the Earth's surface. Pseudotachylytes (solidified friction-induced melts) are the most certain fault-rock indicator of seismicity on ancient faults. Here we show how the asymmetry in distribution and the orientation of pseudotachylyte-filled secondary fractures around an exhumed fault can be used to reconstruct the earthquake rupture directivity, rupture velocity and fracture energy, by comparison with the theoretical dynamic stress field computed around propagating fractures. In particular, the studied natural network of pseudotachylytes is consistent with a dominant propagation direction during repeated seismic events and subsonic rupture propagation close to the Rayleigh wave velocity.

Introduction to seismology

This third edition provides a concise yet approachable introduction to seismic theory, designed as a first course for graduate students or advanced undergraduate students. It clearly explains the fundamental concepts, emphasizing intuitive understanding over lengthy derivations, and outlines the different types of seismic waves and how they can be used to resolve Earth structure and understand earthquakes. New material and updates have been added throughout, including ambient noise methods, shear-wave splitting, back-projection, migration and velocity analysis in reflection seismology, earthquake rupture directivity, and fault weakening mechanisms. A wealth of both reworked and new examples, review questions and computer-based exercises in MATLAB®/Python give students the opportunity to apply the techniques they have learned to compute results of interest and to illustrate Earth's seismic properties. More advanced sections, which are not needed to understand the other material, are flagged so that instructors or students pressed for time can skip them.