Total Rupture Duration Research Articles

The 26 November 2019 Mw 6.4 Albania Destructive Earthquake

AbstractWith the strong 26 November 2019 earthquake that struck western Albania, several buildings collapsed, causing 51 casualties, mainly in the areas of Durrës and Thumanë. The destruction is attributed to several factors, including strong ground motion (maximum peak ground acceleration=192 cm/s2 in Durrës), soil liquefaction, site amplification, poor building workmanship and construction quality, aging of building materials, impact on buildings of the strong 21 September 2019 Mw 5.6 foreshock, and pre-existing stress on buildings sustaining differential displacements because of soft soil conditions in their foundations. In both areas, we estimated maximum seismic intensity of VIII–IX (modified Mercalli intensity and European Macroseismic Scale 1998 scales). Fault-plane solutions indicated reverse faulting striking northwest–southeast. From regional tectonics, we assumed that the causal fault dips to east-northeast, implying that the affected area is situated at the hanging wall domain of the causative fault. Using the Non-Linear Location program algorithm and ak135 velocity model and 71 P and S phases, we manually located the mainshock hypocenter offshore, at distance of ∼17 km from Durrës and at depth of ∼22 km. Adopting this solution, a finite-fault model of space–time seismic slip was developed from the inversion of teleseismic P waveforms. Strike 345°, dip 22°, rupture velocity 2.6 km/s, and total rupture duration ∼16 s fit the data. The rupture was complex, showing one main patch at the south and a second at the north with maximum slips of ∼1.5 and ∼1 m, respectively. The rake vector at the main slip area was 99°, indicating that the thrust-type component played the most important role in the rupture process. The total seismic moment released was estimated at Mo=5.0×1018 N·m corresponding to Mw 6.4.

New Source Duration Relationships for Mexican Earthquakes: Practical Application to Stochastic Summation Methods

From the gathering of 127 source time functions (STFs) of seismic events in Mexico, relationships have been developed between the seismic moment (M0) and the total source rupture duration (τd), for normal-faulting inslab, interplate and strike-slipe mechanisms. This relationship has been explored by different authors like Furomoto and Nakanishi (J Geophys Res 88:2191–2198, 1983), Tanioka and Ruff (Seismol Res Lett 68:386–400, 1997), Singh et al. (Bull Seismol Soc Ame 90:468–482, 2000), among others; the latter authors present a similar general relationship for Mexico, considering 53 STFs and with information until 1998. In this research, complementary databases have been integrated, and the available functions updated base on recent research works about the SCARDEC method are used (Vallee et al. in Geophys J Int 184:338–358, 2011; Vallee and Douet in Phys Earth Planet Interiors 257:149–157, 2016). With the proposed expressions, it is possible to estimate reasonably, the main parameters of interest for algorithms of stochastic summation, such as the corner frequencies or stress drops in order to simulate strong ground motions, commonly used for source-rupture studies, site-amplification analysis, or for earthquake-resistant design. Besides, a new flexible model of stochastic summation is presented, which allows considering several ways to generate more realistic motions, according to the spectral behavior, both for low and for intermediate frequencies, under earthquakes with moderate and high magnitude; this model was compared with results from a two-stage alternative method considering two corner frequencies.

Fault models for the Bodrum–Kos tsunamigenic earthquake (Mw6.6) of 20 July 2017 in the east Aegean Sea

We investigate a fault model for the shallow, strong (Mw6.6) tsunamigenic earthquake of 20 July 2017 with source area in the east Aegean Sea between Bodrum peninsula (Turkey) and Kos Isl. (Greece). Fault plane solutions are consistent with the regional active tectonics indicating normal faulting striking about E–W. A relocated hypocenter of the main shock was obtained and the rupture time-space history for two alternative fault solutions dipping either to the south or to north was approached by inverting P-waves recorded at teleseismic (30°–90°) distances. In both fault solutions the seismic moment calculated corresponds to magnitude Mw = 6.6 while the earthquake had total rupture duration of less than 10 s. The maximum co-seismic slip was close to the hypocenter ∼1.6 m and ∼2.2 m for the south and north dipping faults, respectively. Close to the surface co-seismic slip of ∼0.3 m was calculated. Our analysis of Sentinel satellite InSAR images showed ground deformation fringes indicating ∼13 cm vertical displacement change between the North and South coasts of the Karaada islet. This result is in line with our preference of the south dipping fault, supported primarily by GPS displacements, regional tectonics, aftershock activity and tsunami observations, although results of InSAR inversion fit equally well both solutions.

The isolated ∼680 km deep 30 May 2015 MW 7.9 Ogasawara (Bonin) Islands earthquake

Deep-focus earthquakes, located in very high-pressure conditions 300 to 700 km below the Earth's surface within sinking slabs of relatively cold oceanic lithosphere, are mysterious phenomena. The largest recorded deep-focus earthquake (MW 7.9) in the Izu–Bonin slab struck on 30 May 2015 beneath the Ogasawara (Bonin) Islands, isolated from prior seismicity by over 100 km in depth, and followed by only a few small aftershocks. Globally, this is the deepest (680 km centroid depth) event with MW≥7.8 in the seismological record. Seismicity indicates along-strike contortion of the Izu–Bonin slab, with horizontal flattening near a depth of 550 km in the Izu region and rapid steepening to near-vertical toward the south above the location of the 2015 event. This event was exceptionally well-recorded by seismic stations around the world, allowing detailed constraints to be placed on the source process. Analyses of a large global data set of P, SH and pP seismic phases using short-period back-projection, subevent directivity, and broadband finite-fault inversion indicate that the mainshock ruptured a shallowly-dipping fault plane with patchy slip that spread over a distance of ∼40 km with a multi-stage expansion rate (∼5+ km/s down-dip initially, ∼3 km/s up-dip later). During the 17 s total rupture duration the radiated energy was ∼3.3×1016 J and the stress drop was ∼38 MPa. The radiation efficiency is moderate (0.34), intermediate to that of the 1994 Bolivia and 2013 Sea of Okhotsk MW 8.3 deep earthquakes, indicating that source processes of very large deep earthquakes sample a wide range of behavior from dissipative, more viscous failure to very brittle failure. The isolated occurrence of the event, much deeper than the apparently thermally-bounded distribution of Bonin-slab seismicity above 600 km depth, suggests that localized stress concentration associated with the pronounced deformation of the Izu–Bonin slab and proximity to the 660-km phase transition likely played a dominant role in generating this major earthquake.

Complementary slip distributions of the August 4, 2003 Mw 7.6 and November 17, 2013 Mw 7.8 South Scotia Ridge earthquakes

The South Scotia Ridge Transform (SSRT) plate boundary between the Scotia and Antarctic plates experienced large strike-slip earthquakes on August 4, 2003 (Mw 7.6) and November 17, 2013 (Mw 7.8). These events have overlapping aftershock zones, which is unusual. A 36°–45° southward dipping fault zone ruptured with left-lateral displacements in each event along the northern margin of the South Orkney micro-continent near 60°S. Slip distributions for the two events are determined using teleseismic body and surface wave recordings along with constraints from GPS ground motion recordings at station BORC on Laurie Island (South Orkney Islands), just south of the SSRT. The aftershock distributions, high-frequency back-projections, and unconstrained body wave finite-fault inversions permit significant overlap of the 2003 and 2013 slip zones; however, the GPS static displacements resolve differences in the large-slip regions of the two ruptures. The 2013 earthquake sequence along the SSRT initiated with Mw 6.1 (November 13) and Mw 6.8 (November 16) foreshocks located ∼50 km west of the mainshock hypocenter, and had aftershocks extending ∼250 km eastward. The rupture spread primarily eastward at ∼2.5 km/s with a total rupture duration of about 120 s, with two distinct patches of large-slip located northwest and northeast of the South Orkney Islands. The rupture swept past BORC, with high-rate GPS (HRGPS) ground motion recordings capturing the time-varying slip history of the faulting. Traditional GPS data require that the largest-slip region of the shorter rupture in 2003 is located in the gap NNE of BORC between the two patches that ruptured in 2013. There appears to be some overlap of lower slip regions. The complementary slip distributions comprise a relatively uniform offset along this portion of the SSRT, which is one of the most seismically active regions of the entire Antarctic plate boundary.

Source‐rupture process of the 2011 Ibaraki‐oki, Japan, earthquake (Mw 7.9) estimated from the joint inversion of strong‐motion and GPS Data: Relationship with seamount and Philippine Sea Plate

AbstractThe source‐rupture process of the 2011 Ibaraki‐oki earthquake was estimated from the joint inversion of the strong‐motion and global positioning system (GPS) data. The estimated seismic moment and maximum slip are 7.8 × 1020 Nm (Mw 7.9) and 6.3 m, respectively. The total rupture duration is approximately 30 s. The derived source model has one large slip area, which is surrounded by the subducted seamount and the northeastern edge of the Philippine Sea plate. From this model, we concluded that the rupture propagation of the 2011 Ibaraki‐oki earthquake was stopped by the seamount and the Philippine Sea plate. We also showed the possibility of the rupture of this event being the reactivation of the preexisting asperity of an event that occurred in 1923.

Source Process of the 2011 Tohoku Earthquake Estimated from the Joint Inversion of Teleseismic Body Waves and Geodetic Data Including Seafloor Observation Data: Source Model with Enhanced Reliability by Using Objectively Determined Inversion Settings

Research Article| May 01, 2013 Source Process of the 2011 Tohoku Earthquake Estimated from the Joint Inversion of Teleseismic Body Waves and Geodetic Data Including Seafloor Observation Data: Source Model with Enhanced Reliability by Using Objectively Determined Inversion Settings Hisahiko Kubo; Hisahiko Kubo Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611‐0011, Japankubo.hisahiko.26a@st.kyoto-u.ac.jp Search for other works by this author on: GSW Google Scholar Yasumaro Kakehi Yasumaro Kakehi Graduate School of Science, Kobe University, 1‐1 Rokkodai‐cho, Nada, Kobe, Hyogo 657‐8501, Japankakehi@kobe-u.ac.jp Search for other works by this author on: GSW Google Scholar Author and Article Information Hisahiko Kubo Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611‐0011, Japankubo.hisahiko.26a@st.kyoto-u.ac.jp Yasumaro Kakehi Graduate School of Science, Kobe University, 1‐1 Rokkodai‐cho, Nada, Kobe, Hyogo 657‐8501, Japankakehi@kobe-u.ac.jp Publisher: Seismological Society of America First Online: 14 Jul 2017 Online ISSN: 1943-3573 Print ISSN: 0037-1106 Bulletin of the Seismological Society of America (2013) 103 (2B): 1195–1220. https://doi.org/10.1785/0120120113 Article history First Online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Hisahiko Kubo, Yasumaro Kakehi; Source Process of the 2011 Tohoku Earthquake Estimated from the Joint Inversion of Teleseismic Body Waves and Geodetic Data Including Seafloor Observation Data: Source Model with Enhanced Reliability by Using Objectively Determined Inversion Settings. Bulletin of the Seismological Society of America 2013;; 103 (2B): 1195–1220. doi: https://doi.org/10.1785/0120120113 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract The rupture process of the 2011 Tohoku earthquake is estimated from the joint inversion of teleseismic body waves and geodetic data using multiple time‐window analysis. To enhance the reliability of the inversion solution, two important inversion‐setting parameters that control the spatiotemporal slip distribution, the maximum slip duration of each subfault (Tsd) and the propagation velocity of the first time window (Vftw), are determined by objective criteria. By performing a semblance analysis of small‐aperture seismic array data of near‐source strong motion waveforms, Tsd is determined to be 100 s. Vftw is determined to be 2.0 km/s from the matching of the teleseismic and geodetic slip models. The spatial resolution of geodetic inversion is significantly improved by using seafloor crustal deformation data in the source area in addition to the terrestrial Global Positioning System network data. The estimated seismic moment and the maximum slip are 3.4×1022 N·m (Mw=9.0) and 43 m, respectively. The total rupture duration is ∼150 s. Large slip is seen in the shallow part of the fault surface, including the hypocenter, and its spatial extent along the trench axis is ∼300 km. This model is consistent with the results of bathymetric surveys and the slip models from tsunami data. The relationships among the fault parameters of the characterized source model of the 2011 Tohoku earthquake suggest the possibility that saturation of fault width occurs for this huge earthquake.Online Material: Text S1 denotes the explanation of how the rupture propagation in the dip direction affects the estimated value of maximum slip duration (Tsd). Table S1 denotes the detailed information of the teleseismic stations. Table S2 denotes the detailed information of the terrestrial geodetic stations. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Rupture Process of 6 April 2009 L'Aquila, Italy, Mw6.3 Earthquake: a Comparison Between Apparent Source Time Function Method and Direct Wave Inversion Method

AbstractThe characteristics of two inversion techniques, the apparent source time function (ASTF) inversion technique and the direct wave (DW) inversion technique, were compared by applying them to the MW6.3 L'Aquila, Italy, earthquake for its spatio‐temporal rupture process. The ASTF results show that the earthquake consisted of two sub‐events, and the second one caused distinct Doppler effect, indicating a mainly unilateral rupture propagating southeastwards. The DW results in cases that rakes are variable and invariable were in a good agreement with the ASTF results. They all indicated that there were two slip‐concentrated patches on the fault plane. One was around the hypocenter, with the maximum slip of 1.2 m, and another was 5~10 km away from the former in the strike direction, with the maximum slip of 1.0 m. The total rupture duration is about 9.5 s, and the maximum slip‐rate reaches 0.6~0.7 m/s. It should be the quick rupture and the hanging‐wall effect that led the tremendous damage to the L'Aquila city.

The Mw 7.7 Tocopilla Earthquake of 14 November 2007 at the Southern Edge of the Northern Chile Seismic Gap: Rupture in the Deep Part of the Coupled Plate Interface

The slip distribution of the Mw 7.7 Tocopilla earthquake was obtained from the joint inversion of teleseismic and strong-motion data. Rupture occurred as underthrusting at the base of the seismically coupled plate interface, mainly between 35 and 50 km depth. From the hypocenter, located below the coast 25 km south of the town of Tocopilla, the rupture propagated 50 km northward and 100 km southward. Overall, the slip distribution was dominated by two slip patches, one near the hypo- center and the other 70 km to the south where slip reached its maximum value (3 m). An additional branch of moderate slip propagated at shallower depth toward the west near the northern tip of the Mejillones peninsula. Rupture velocity remained close to 2:8 km=sec, with a total rupture duration of 45 sec. The first 2 weeks of aftershocks located with a local seismic network display a strong correlation with the slip distri- bution. The 2007 rupture ended below the Mejillones peninsula, where the 1995 An- tofagasta rupture also ended (Ruegg et al., 1996; Delouis et al., 1997; Pritchard et al., 2006). This corroborates the role of barrier played by this structure. The downdip end of the seismically coupled zone at 50 km depth, evidenced by previous studies for the 1995 event, is also confirmed. The 2007 Tocopilla earthquake contributed only mod- erately to the rupturing of the great northern Chile seismic gap, which still has the capacity for generating a much larger underthrusting event.

Source mechanism and source parameters of May 28, 1998 earthquake, Egypt

On May 28, 1998, a moderate size earthquake of mb 5.5 occurred offshore the northwestern part of Egypt (latitude 31.45°N and longitude 27.64°E). It was widely felt in the northern part of Egypt. Being the largest well-recorded event in the area for which seismic data from the global digital network are available, it provides an excellent opportunity to study the tectonic process and present day stress field occurring along the offshore Egyptian coast. The source parameters of this event are determined using three different techniques: modeling of surface wave spectral amplitudes, regional waveform inversion, and teleseismic body waveform inversion. The results show a high-angle reverse fault mechanism generally trending NNW–SSE. The P-axis trends ENE–WSW consistently with the prevailed compression stress along the southeastern Hellenic arc and southwestern part of the Cyprean arc. This unexpected mechanism is most probably related to a positive inversion of the NW trending offshore normal faults and confirms an extension of the back thrusting effects towards the African margin. The estimated focal depth ranges from 22 to 25 km, indicating a lower crustal origin earthquake owing to deep-seated tectonics. The source time function indicates a single source with rise time and total rupture duration of 2 and 5 s, respectively. The seismic moment (Mo) and the moment magnitude (Mw) determined by the three techniques are 1.03 × 1017 Nm, 5.28; 1.24 × 1017 Nm, 5.33; and 1.68 × 1017 Nm, 5.42; respectively. The calculated fault radius, stress drop, and the average dislocation assuming a circular fault model are 7.2 km, 0.63 Mpa, and 0.11 m, respectively.

Another look at the 1993 and 1995 Gulf of Aqaba earthquakes from the analysis of teleseismic waveforms

In this work we estimated the source process and the source parameters of the 1993 and 1995 Gulf of Aqaba earthquakes. To investigate the source process of both events, we inverted the teleseismic P- and SH-waveform data using an iterative technique in which the rupture is modeled as a series of point source subevents with varying mechanisms. The main source process of the 1993 event can be explained by two subevents with essentially the same mechanism. These two subevents had different focal depths. The second subevent was about 5 s later than the first one and about 70% of the moment rate released with the second one. The total rupture duration time was about 12 s. Our solution for the 1995 Gulf of Aqaba earthquake indicated that the event consists of three subevents with various fault geometries and about 60% of the moment released by the second subevent. The first subevent occurred at a depth of 13 km, and was followed after 9 s by the second one at a depth of 11 km; the third subevent, at a depth of 9 km occurred 19 s after the second one. The total duration of the earthquake rupture process was about 18.7 s. The obtained mechanisms for the 1993 and 1995 Gulf of Aqaba earthquakes are well correlated with the structural setting of the Gulf of Aqaba.

Moment tensor inversion and source rupture process of the September 27, 2003 M S=7.9 earthquake occurred in the border area of China, Russia and Mongolia

We conducted moment tensor inversion and studied source rupture process for MS=7.9 earthquake occurred in the border area of China, Russia and Mongolia on September 27 2003, by using digital teleseismic P-wave seismograms recorded by long-period seismograph stations of the global seismic network. Considering the aftershock distribution and the tectonic settings around the epicentral area, we propose that the MS=7.9 earthquake occurred on a fault plane with the strike of 127°, the dip of 79° and the rake of 171°. The rupture process inversion result of MS=7.9 earthquake shows that the total rupture duration is about 37 s, the scalar moment tensor is M0=0.97×1020 N·m. Rupture mainly occurred on the shallow area with 110 km long and 30 km wide, the location in which the rupture initiated is not where the main rupture took place, and the area with slip greater than 0.5 m basically lies within 35 km deep middle-crust under the earth surface. The maximum static slip is 3.6 m. There are two distinct areas with slip larger than 2.0 m. We noticed that when the rupture propagated towards northwest and closed to the area around the MS=7.3 hypocenter, the slip decreased rapidly, which may indicate that the rupture process was stopped by barriers. The consistence of spatial distribution of slip on the fault plane with the distribution of aftershocks also supports that the rupture is a heterogeneous process owing to the presence of barriers.

The 2000 Tottori earthquake: A shallow earthquake with no surface rupture and slip properties controlled by depth

The Mw6.8 Tottori earthquake, Japan, does not exhibit any surface trace but was particularly well instrumented. Strong motion displacement records and GPS coseismic data are used to constrain the evolution of the slip on the fault plane in time and space. We adopt in this study a two‐plane fault geometry based on aftershock distributions and analysis of close station records. In a first step, our inversion allowed surface slip. The model obtained has a significant surface slip, which contradicts the absence of clear surface slip reported by geologists. In a second step, models with no slip at the surface (buried faults), compatible with geological observations, have been tested. The tests with different fault depths show that when slip is allowed to occur close to the surface, the fit to seismological and geodetic data is increased. These tests confirm that slip actually occurred at shallow depth. Despite the nonuniqueness of the solution, all the inverted source models show (1) a large slip amplitude patch at a depth of about 4–5 km and (2) relatively small slip in the hypocentral area. The rupture velocity is about 2750 m/s in the asperity region. The total rupture duration is about 8 s. The slip distribution seems to be controlled by the variation of fault properties with depth. Another feature that could control the rupture of this earthquake is a fault plane almost perpendicular to the main fault NW of the epicenter, which apparently inhibits further rupture propagation.

Spatial and Temporal Distribution of Slip for the 1999 Chi-Chi, Taiwan, Earthquake

We investigated the rupture process of the 1999 Chi-Chi, Taiwan, earth- quake, using high-quality near-source strong-motion records, broadband teleseismic displacement waveforms, and well-distributed Global Positioning System (GPS) data. The near-source strong-motion displacement waveforms recorded significant static offsets of up to 8 m. The teleseismic displacement records show a significant pulse with duration of about 18 to 20 sec. Taking into account the surface displacements observed along the Chelungpu fault, we considered two fault geometries: a single planar fault and a two-segment fault with a northeast-striking section near the north- ern end. Using the finite-fault model with variable slip vectors, we derived two models of the temporal and spatial slip distribution of the earthquake. The GPS data provided good surface displacement constraints for the slip-distribution determina- tion. The spatial slip distribution is generally consistent with field observations. The results for the simple fault model show a large asperity located in the region about 25 to 55 km north of the hypocenter with maximum slip of about 15 m. When we use the two-segment model, the asperity further extends to the region where the fault bends toward the northeast with a maximum slip of up to 20 m. A large amount of right-lateral slip beneath station TCU068 is necessary to explain its observed large west movement. It implies a local converging slip at the corner where the fault bends to the northeast. The slip amplitude near the hypocenter is about 3 to 6 m. The seismic moments determined from the various data sets are within the range of 2 to 4 10 27 dyne cm. Most of the slip concentrated at shallow depths (less than 10 km). The total rupture duration is about 28 sec, and the rupture velocity is 75% to 80% of the shear-wave velocity. The slip vector shows a clockwise rotation during the fault rupture. The static stress drop of the large asperity region is comparable with the dynamic stress drop, as observed directly from the slip velocity at the station near the large slip region.

Slip distribution of the 2003 Boumerdes‐Zemmouri earthquake, Algeria, from teleseismic, GPS, and coastal uplift data

Using a joint inversion of seismological waveforms and ground displacement observations, we estimate several parameters of the fault geometry and rupture process of the Mw = 6.9 May 21, 2003 Boumerdes‐Zemmouri earthquake. The relocated epicenter is considered as a known parameter. Total rupture length, rupture duration, and maximum slip are 55 km (from 3.4°E to 4.0°E), 12 s, and 3 m. The modeled south dipping reverse fault, oriented ENE‐WSW outcrops a few km offshore which is consistent with the absence of observed surface rupture inland. Two shallow and relatively localized slip zones are found, on both sides of the hypocenter. To the SW, between Boumerdes and Zemmouri, slip is concentrated between 11 and 2 km depth. To the NE, between Zemmouri and Dellys, slip is concentrated between 6 km depth and the sea floor. Various resolution tests indicate that our model is well constrained by the available data, and help understanding which data constrains each parameter of the model.

Analysis of the 2001 Geiyo, Japan, earthquake using high‐density strong ground motion data: Detailed rupture process of a slab earthquake in a medium with a large velocity contrast

Detailed rupture process of the 2001 Geiyo, Japan, earthquake (Mw = 6.8), which is a slab earthquake in the Philippine Sea slab, is investigated from the inversion of strong motion waveforms. In the inversion, a realistic curved fault model is assumed, and the one‐dimensional underground structure models considering the deep slab structure and the shallow surface layers are used. The estimated seismic moment and the maximum slip are 2.1 × 1019 N m and 2.4 m, respectively. The total rupture duration is ∼10 s. The obtained rupture process is very complex. The rupture changed gradually from a normal fault type into a more strike‐slip type during its propagation. The slip distribution is heterogeneous, and the rupture area extends over both of the slab oceanic crust and the slab oceanic mantle. In the medium of the source area, there exists a large velocity contrast at the slab oceanic crust‐mantle boundary. The largest slip is seen in the low‐velocity (low‐rigidity) oceanic crust. It is reasonable from the viewpoint of rupture dynamics that large slip occurs in the low‐rigidity layer, which is easier to deform. Thus the obtained slip model suggests that the rupture process of the 2001 Geiyo earthquake was strongly influenced by the heterogeneity of the background medium.

Source Time Function and Duration of Mexican Earthquakes

We have compiled source-time functions (STFs) of 54 Mexican earthquakes (3.0 ≤ M ≤ 8). The depth, H , of 48 of these earthquakes lies between 10 and 50 km. The STFs of 43 earthquakes were determined from local and regional strong-motion and/or broadband recordings. For the rest of the events, the STFs were taken from published analysis of teleseismic body waves, or from the University of Michigan Source-Time Function catalog. If available, the seismic moments were taken from the analysis of teleseismic body waves; if not, as was often the case for earthquakes with M ≤ 5.5, they were estimated from the local recordings themselves. From the STF of each earthquake we have measured pulse duration of each subevent (τp), total rupture duration (τt), and rise time (τr), along with their respective seismic moments. The data fit the relation \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(M\_{0}{/}{\tau}\_{\mathrm{p}}^{3}{\sim}6.7{\times}10^{23}\) \end{document} dyne cm/s3. This relation is similar to that reported for deeper earthquakes (mostly in the 50 to 125 km depth range) in the Kanto district of Japan. The pulse duration of Mexican and Kanto earthquakes, scaled to a seismic moment of 1026 dyne cm, τps, is about 5 s, nearly independent of depth for 10 ≤ H ≤ 125 km. We compliment these two data sets with those for California (H ≤ 20 km) and for deep earthquakes ( H ≥ 100 km). When viewed over the entire depth range, the total rupture duration (τt) is related to M by log τt = (0.363 ± 0.008) log M - 8.58 (±0.190), and the duration, within the scatter of the data, appears to be independent of depth. When the data are examined in smaller subsets, as has been done by several authors, certain trends manifest themselves. For example, the pulse and the total duration of deep earthquakes ( H ≥ 100 km) scales as \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(M_{0}^{0.16}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(M_{0}^{0.25}\) \end{document}, respectively, and the moment-scaled pulse and total duration decreases by about 20% between 100 and 600 km depth. This decrease is much less than that reported previously. Furthermore, an earlier finding of fast rise times for very deep earthquakes is not substantiated by the recent data. Thus, the anomaly in the duration of the deep earthquakes, as compared to the shallow ones, appears to be smaller than previously suspected. Manuscript received 15 June 1999.

経験的グリーン関数法による1993年北海道南西沖地震の破壊過程

We investigated the rupture process of the 1993 Hokkaido-Nansei-Oki earthquake (MJMA=7.8) using the broad-band strong motion seismograms recorded at Tomari which is located about 260km distant from the epicenter. We determined the rupture model employing the empirical Green function method in which the waveform of a main shock is synthesized from the waveform of an aftershock. We used the aftershock (MJMA=6.0) that occurred near the main shock epicenter about three hours later. The observed waveforms are best fitted to the synthetics produced for the rupture model involving two major events which ruptured at a time interval of 31-34 seconds. The first event is located near the epicenter and the second event is located near the Okushiri island, about 70km south of the first event. The fault sizes of the two events are both 40×20km2, which are small as compared with the overall area of the aftershock distribution. The total rupture duration is 43-46 seconds. It appears likely that the seismic energy was not released uniformely from the entire aftershock area. The present rupture model is consistent with the previous results obtained from the waveform inversions of teleseismic and strong motion data, suggesting the validity of the empirical Green function method and its usefulness for investigating the rupture process of large earthquakes.

Application of seismogram synthesis to the study of earthquake source from strong motion records

We present the results of an analysis of the Michoacan and Landers earthquakes to constrain the kinematic description of the rupture process. The example of the Michoacan earthquake shows that a crack type model is better a dislocation model to describe the displacement in the vicinity of the fault. We also show that this in contradiction with the fact that the faulting appears to be a complex process. We attribute this complexity to instabilities in crack growth. The June 28, Landers earthquake offers an exceptional opportunity to apply a new inversion technique to a major strike slip event. We model the rupture evolution including local differences in slip durations and variations in rupture velocity. The slip distribution shows that this event consists of a series of regions of high slip (sub-events) separated by regions of relative low slip. Our inversion favors the hypothesis that the duration of the slip at each point is of the order of the duration of the rupture of each sub-event and is consistent with a crack type process occurring during each sub-event. For such a large earthquake, the slip duration is however smaller than the total rupture duration.

Spatial and temporal distribution of slip for the 1992 Landers, California, earthquake

AbstractWe have determined a source rupture model for the 1992 Landers earthquake (MW 7.2) compatible with multiple data sets, spanning a frequency range from zero to 0.5 Hz. Geodetic survey displacements, near-field and regional strong motions, broadband teleseismic waveforms, and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface. Our fault parameterization involves a variable-slip, multiple-segment, finite-fault model which treats the diverse data sets in a self-consistent manner, allowing them to be inverted both independently and in unison. The high-quality data available for the Landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern. In all models, consistent features include the following: (1) similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 × 1026 dyne-cm (seismic potency of 2.3 to 2.7 km3); (2) very heterogeneous, unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km, though slip is limited to shallower regions in some areas; (3) a total rupture duration of 24 sec and an average rupture velocity of 2.7 km/sec; and (4) substantial variations of slip with depth relative to measured surface offsets. The extended rupture length and duration of the Landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter-duration, strike-slip events. Our imaging allows visualization of the rupture evolution, including local differences in slip durations and variations in rupture velocity. Rupture velocity decreases markedly at shallow depths, as well as near regions of slip transfer from one fault segment to the next, as rupture propagates northwestward along the multiply segmented fault length. The rupture front slows as it reaches the northern limit of the Johnson Valley/Landers faults where slip is transferred to the southern Homestead Valley fault; an abrupt acceleration is apparent following the transfer. This process is repeated, and is more pronounced, as slip is again passed from the northern Homestead Valley fault to the Emerson fault. Although the largest surface offsets were observed at the northern end of the rupture, our modeling indicates that substantial rupture was also relatively shallow (less than 10 km) in this region.