Electronic Supplement to
Behavior of Repeating Earthquake Sequences in Central California and the Implications for Subsurface Fault Creep

by D. C. Templeton, R. M. Nadeau, and R. Bürgmann

Cross section views of background seismicity and repeating earthquakes (REs)

We present cross section plots in depth, both parallel and perpendicular to, the Quien Sabe fault zone [Figure S1 and Figure S2], the Calaveras fault [Figure S3 and Figure S4], the Paicines fault [Figure S5], the San Andreas fault [Figure S6, Figure S7, and Figure S8], and the seismic structure that produced REs within the southern Coast Ranges [Figure S18 and Figure S19]. Figure S1 and Figure S2, the supplemental plots of the Quien Sabe fault zone, show how linear streaks of seismicity and a relatively simple, continuous fault plane are not requirements for the production of REs and therefore of deep fault creep. Nevertheless, on the Calaveras [Figure S4], Paicines [Figure S5], and San Andreas fault [Figure S8], REs are observed to preferentially occur along these linear streaks of seismicity. This suggests that these linear streaks of seismicity delineate collections of sub-horizontal asperities that are actively slipping, perhaps due to loading from creep in the surrounding aseismic regions.

Figure S9 shows the location of burst type REs relative to non-burst type REs and the M_w 5.1 1998 San Juan Bautista event. On the northwest portion of the San Andreas fault studied, burst type REs preferentially occur near the San Juan Bautista event or along the deeper portion of the fault (> 6.0 km). Interestingly, most of these burst type REs occurred during the strain transient associated with the San Juan Bautista slow slip event (see Figure S10 and below). It is unclear, however, if these burst type REs directly delineate the extent of the 1998 slow earthquake that occurred close to and immediately after the San Juan Bautista earthquake. On the southeast portion of the San Andreas fault, burst type REs preferentially occur along the deeper sections (> 4.5 km) of the seismogenic zone.

Timing of individual events within RE sequences

Figure S10 shows the timing of events within burst type REs along the creeping section of the San Andreas fault studied. It clearly shows that the timing of burst type REs on the northern portion of the fault was strongly influenced by the 1998 San Juan Bautista event and/or subsequent slow earthquake. Burst type REs along the southern portion of the fault, however, do not appear to be influenced by nearby larger earthquakes greater than M4.0. Thus, it appears that the only common feature between burst type REs on the northern portion of the San Andreas fault and on the southern portion are that they all preferentially occur along the deeper sections of the seismogenic zone.

Figures S11 – S17 show the timing of individual events within non-burst type RE sequences on the San Andreas fault. The locations of these sequences are shown in cross section view on Figure 8 of the main paper and Figure S8. A subset of the data shown on Figures S11 – S17 is plotted in Figure 7 of the main paper. These figures show how the influence of the 1989 Loma Prieta earthquake, which occurred approximately 30 km to the north of our study area, diminishes with distance from the epicenter. Figure S12 and Figure S13 also show the increase in RE frequency which occurred after the 1998 San Juan Bautista event in sequences up to approximately 3.5 km away from the mainshock hypocenter. As mentioned before, it is possible that these sequences may indicate the portion of the fault that slipped aseismically during the 1989 slow slip event, which was also captured by a borehole strainmeter, surface creepmeters, and a nearby continuous GPS station of the BARD network.

The timing of burst type RE sequences, which occurred in the southern Coast Ranges, is shown in Figure S20. It is seen that they are not associated with the M_w 6.5 2003 San Simeon earthquake, but it is unclear if they were influenced by a nearby M4.3 event which occurred in the same seismicity cloud as these burst type REs. No burst type or non-burst type REs were identified in the aftershock zone of the San Simeon earthquake.

Individual RE data

Table S1 provides detailed sequence information from the NCSN (Northern California Seismic Network) catalog for the 150 REs identified at the juncture of the Calaveras and San Andreas faults. Table S2 provides detailed sequence information from the NCSN catalog for the 6 REs identified within the southern Coast Ranges.

Tables

Table S1. Sequence information for REs at the juncture of the San Andreas and Calaveras faults. These include all REs plotted in Figure 3A of the main paper. The first line of each sequence defines the sequence label number, average sequence latitude, average sequence longitude, average sequence depth, median sequence magnitude, total amount of slip (cm) at sequence location, and slip rate (cm/yr) at the sequence location. The following indented lines indicate the earthquake time (YYYY.JDY.HHMMSS), earthquake latitude, earthquake longitude, earthquake depth, and earthquake magnitude for each individual event within a repeating earthquake sequence.

Table S2. Sequence information for REs within the southern Coast Ranges. These include all REs plotted in Figure 3B of the main paper. The first line of each sequence defines the sequence label number, average sequence latitude, average sequence longitude, average sequence depth, median sequence magnitude, total amount of slip (cm) at sequence location, and slip rate (cm/yr) at the sequence location. The following indented lines indicate the earthquake time (YYYY.JDY.HHMMSS), earthquake latitude, earthquake longitude, earthquake depth, and earthquake magnitude for each individual event within a repeating earthquake sequence.

Figures

Figure S1. Cross section fault parallel view of Quien Sabe fault looking from 321° azimuth. REs are plotted as colored circles and burst type REs are plotted as colored diamonds. RE labels indicate the individual sequence number corresponding to sequence numbers found in Table S1. Colors indicate the cumulative amount of slip at each sequence location over the observation period. Small grey dots are background seismicity from the hypoDD-relocated catalog of Ellsworth et al. (2000). Green triangles show the location of hypoDD-relocated earthquakes larger than M4.0. The red triangle labeled TP shows the location of the M_l 5.5 1986 Tres Piños earthquake.

Figure S2. Cross section fault perpendicular view of Quien Sabe fault looking from 51° azimuth. REs are plotted as colored circles and burst type REs are plotted as colored diamonds. RE labels indicate the individual sequence number corresponding to sequence numbers found in Table S1. Colors indicate the cumulative amount of slip at each sequence location over the observation period. Small grey dots are background seismicity from the hypoDD-relocated catalog of Ellsworth et al. (2000). Green triangles show the location of hypoDD-relocated earthquakes larger than M4.0. The red triangle labeled TP shows the location of the M_l 5.5 1986 Tres Piños earthquake.

Figure S3. Cross section fault parallel view of Calaveras fault looking from 345° azimuth. REs are plotted as colored circles and burst type REs are plotted as colored diamonds. RE labels indicate the individual sequence number corresponding to sequence numbers found in Table S1. Colors indicate the cumulative amount of slip at each sequence location over the observation period. Small grey dots are background seismicity from the hypoDD-relocated catalog of Ellsworth et al. (2000). Green triangles show the location of hypoDD-relocated earthquakes larger than M4.0. Green triangles with grey outline indicate the catalog location of earthquakes greater than M4.0 that were not included in the relocated catalog.

Figure S4. Cross section fault perpendicular view of Calaveras fault looking from 75° azimuth. REs are plotted as colored circles and burst type REs are plotted as colored diamonds. RE labels indicate the individual sequence number corresponding to sequence numbers found in Table S1. Colors indicate the cumulative amount of slip at each sequence location over the observation period. Small grey dots are background seismicity from the hypoDD-relocated catalog of Ellsworth et al. (2000). Green triangles show the location of hypoDD-relocated earthquakes larger than M4.0. Green triangles with grey outline indicate the catalog location of earthquakes greater than M4.0 that were not included in the relocated catalog.

Figure S5. Cross section fault perpendicular view of Paicines fault looking from 45° azimuth. REs are plotted as colored circles and burst type REs are plotted as colored diamonds. RE labels indicate the individual sequence number corresponding to sequence numbers found in Table S1. Colors indicate the cumulative amount of slip at each sequence location over the observation period. Small grey dots are background seismicity from the hypoDD-relocated catalog of Ellsworth et al. (2000).

Figure S6. Cross section fault parallel view of southern portion of San Andreas fault and Paicines fault looking from 313° azimuth. REs are plotted as colored circles and burst type REs are plotted as colored diamonds. Colors indicate the cumulative amount of slip at each sequence location over the observation period. Small grey dots are background seismicity from the hypoDD-relocated catalog of Ellsworth et al. (2000). Green triangles show the location of hypoDD-relocated earthquakes larger than M4.0. Green triangles with grey outline indicate the catalog location of earthquakes greater than M4.0 that were not included in the relocated catalog.

Figure S7. Cross section fault parallel view of northern portion of San Andreas fault looking from 309° azimuth. REs are plotted as colored circles and burst type REs are plotted as colored diamonds. Colors indicate the cumulative amount of slip at each sequence location over the observation period. Small grey dots are background seismicity from the hypoDD-relocated catalog of Ellsworth et al. (2000). Green triangles show the location of hypoDD-relocated earthquakes larger than M4.0. Green triangles with grey outline indicate the catalog location of earthquakes greater than M4.0 that were not included in the relocated catalog. Red triangle indicates the location of the M_w 5.1 1998 San Juan Bautista earthquake.

Figure S8. Cross section fault perpendicular view of southern portion of San Andreas fault looking from 43° azimuth. REs are plotted as colored circles and burst type REs are plotted as colored diamonds. RE labels indicate the individual sequence number corresponding to sequence numbers found in Table S1. Colors indicate the cumulative amount of slip at each sequence location over the observation period. Small grey dots are background seismicity from the hypoDD-relocated catalog of Ellsworth et al. (2000). Green triangles show the location of hypoDD-relocated earthquakes larger than M4.0. Green triangles with grey outline indicate the catalog location of earthquakes greater than M4.0 that were not included in the relocated catalog. Sections with roman numerals correspond to boxes with roman numerals in Figure 1A of the main paper.

Figure S9. Cross section fault perpendicular view of burst type REs on San Andreas fault. Burst type REs are plotted as red circles and non-burst type REs are plotted as blue circles. The location of the M_w 5.1 1989 San Juan Bautista earthquake is plotted with a green triangle.

Figure S10. Plots showing the timing of individual events within burst type REs on the San Andreas fault. X-axis is time in years. Color indicates average magnitude of events within a burst sequence. Green line labeled LP indicates time of 1989 Loma Prieta earthquake and green line labeled SJB indicates time of 1998 San Juan Bautista earthquake. A) Plot showing the occurrence of all events within burst type RE sequences on the San Andreas fault over the observation period. B) Zoom in of Figure S10A showing the occurrence of events within burst type RE sequences on the San Andreas fault for events that occurred after the 1998 San Juan Bautista earthquake.

Figure S11. Timing of non-burst type REs on the San Andreas fault for RE sequences 31 to 45. Color indicates total amount of slip at sequence location over observation period. Green line labeled LP indicates time of 1989 Loma Prieta earthquake.

Figure S12. Timing of non-burst type REs on San Andreas fault for RE sequences 46 to 62. Color indicates total amount of slip at sequence location over observation window. Green line labeled LP indicates time of 1989 Loma Prieta earthquake and red line labeled SJB indicates time of 1998 San Juan Bautista earthquake.

Figure S13. Timing of non-burst type REs on San Andreas fault for RE sequences 63 to 74. Color indicates total amount of slip at sequence location over observation window. Green line labeled LP indicates time of 1989 Loma Prieta earthquake and green line labeled SJB indicates time of 1998 San Juan Bautista earthquake.

Figure S14. Timing of non-burst type REs on San Andreas fault for RE sequences 75 to 84. Color indicates total amount of slip at sequence location over observation window. Green line labeled LP indicates time of 1989 Loma Prieta earthquake.

Figure S15. Timing of non-burst type REs on San Andreas fault for RE sequences 85 to 97. Color indicates total amount of slip at sequence location over observation window. Green line labeled LP indicates time of 1989 Loma Prieta earthquake.

Figure S16. Timing of non-burst type REs on San Andreas fault for RE sequences 98 to 112. Color indicates total amount of slip at sequence location over observation window. Green line labeled LP indicates time of 1989 Loma Preita earthquake. Vertical green lines labeled M4.7 indicate times of two nearby M4.7 earthquakes.

Figure S17. Timing of non-burst type REs on San Andreas fault for RE sequences 113 to 129. Color indicates total amount of slip at sequence location over observation window. Green line labeled LP indicates time of 1989 Loma Preita earthquake. Vertical green lines labeled M4.7 indicate times of two nearby M4.7 earthquakes.

Figure S18. Cross section view of southern Coast Ranges REs looking from 55° azimuth. Burst type REs are plotted as colored diamonds. RE labels indicate the individual sequence number corresponding to sequence numbers found in Table S2. Colors indicate the cumulative amount of slip at each sequence location over the observation period. Small grey dots are background seismicity from the NCSN catalog. Green triangles indicate the catalog location of earthquakes greater than M4.0.

Figure S19. Cross section view of southern Coast Ranges REs looking from 325° azimuth. Burst type REs are plotted as colored diamonds. RE labels indicate the individual sequence number corresponding to sequence numbers found in Table S2. Colors indicate the cumulative amount of slip at each sequence location over the observation period. Small grey dots are background seismicity from the NCSN catalog. Green triangles indicate the catalog location of earthquakes greater than M4.0.

Figure S20. Timing of burst type REs on southern Coast Ranges. Color indicates average magnitude of events within sequence. Green vertical line labeled M4.3 indicates time of nearby larger earthquake which occurred in the same seismicity cloud as the southern Coast Ranges burst type REs. Green vertical line labeled M6.5 indicates time of the M_w 6.5 2003 San Simeon earthquake which occurred on the San Andreas fault.

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