TABLE S1. CATALOG OF DETECTED EVENTS. Depth (km) M D C? 07/26/11 01:02:

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Justin Morton
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1 GSA Data Repository Templates/ Catalogs* Seamount Events Supplementary material for Newly detected earthquakes in Cascadia subduction zone linked to seamount subduction and deformed upper plate by Morton, Bilek and Rowe Date Time (UTC) Latitude ( ) TABLE S1. CATALOG OF DETECTED EVENTS Longitude ( ) Depth (km) M D Num. of Picks Azimuthal C? 07/26/11 01:02: Gap ( ) Dist. to nearest station tt RMS 07/26/11 01:02: T, Tr 08/24/11 08:21: /21/11 04:49: S 11/28/11 00:27: /23/11 02:11: /23/11 03:42: /12/12 07:07: /08/12 10:25: T, Tr, S 03/12/12 11:37: /12/12 11:51: /13/12 22:19: /17/12 22:17: /19/12 13:34: /20/12 08:30: T, Tr, S 03/20/12 08:43: T, Tr, S 03/20/12 09:28: (s) ERH (km) ERZ # (km)

2 03/20/12 09:35: /20/12 09:47: /20/12 10:14: /20/12 10:36: /22/12 00:58: /22/12 06:34: /22/12 09:26: /23/12 12:53: /23/12 14:15: /24/12 17:11: /25/12 04:50: /26/12 00:01: T, S 03/26/12 00:15: /26/12 05:35: /26/12 13:02: /02/12 13:53: /05/12 23:05: /17/12 17:35: /17/12 17:36: S 04/22/12 09:18: /24/12 18:08: /24/12 23:27: /25/12 00:59: /28/12 06:29: /06/12 23:43:

3 05/12/12 14:18: /12/12 14:21: /15/12 21:16: C, S 05/17/12 13:30: C, S 05/17/12 19:51: /17/12 19:52: /17/12 19:57: /17/12 19:58: /17/12 22:05: /17/12 22:36: /26/12 10:40: /03/12 17:39: C, S 06/03/12 17:46: /03/12 17:47: /03/12 19:01: S 06/04/12 11:43: /21/12 15:57: /13/12 07:06: /14/12 01:57: /18/12 05:31: /07/12 17:15: /14/12 13:37: T, Tr, S 01/25/13 00:41: /25/13 01:34: /25/13 02:01:

4 T, Tr, S 01/25/13 03:43: /25/13 03:50: T, Tr, S 01/25/13 04:27: /25/13 04:49: /25/13 04:53: /25/13 06:11: /25/13 08:39: /25/13 08:39: T, Tr, S 01/25/13 08:58: /25/13 18:47: T 03/06/13 15:01: /10/13 04:43: T 04/18/13 08:32: /06/13 18:02: T 07/22/13 05:24: /23/13 17:47: S 11/02/13 13:21: /20/13 15:35: /27/13 02:18: /02/14 17:57: /25/14 05:57: /04/14 02:08: /04/14 02:08: /14/14 07:53: T 08/19/14 08:50:

5 09/28/14 18:51: /28/14 19:00: /30/14 11:02: /27/14 07:40: T, S 10/27/14 07:41: /27/14 07:45: /27/14 07:55: /27/14 16:00: /02/14 08:37: /06/14 04:15: S 11/19/14 09:01: /29/14 16:54: /29/14 18:34: /13/15 12:19: /18/15 02:55: T, S 04/19/15 00:57: /24/15 11:00: /11/15 03:19: /11/15 04:00: /21/15 02:42: T, Tr, S 06/25/15 20:25: /26/15 01:24: /26/15 01:24: /26/15 03:35: /26/15 05:44:

6 06/26/15 09:49: /26/15 09:55: /26/15 10:13: /26/15 11:02: T, Tr, S 06/26/15 13:29: /26/15 18:01: /26/15 18:38: /26/15 19:03: /26/15 19:46: /26/15 19:47: /27/15 13:06: /27/15 20:28: /27/15 22:33: /27/15 23:28: /28/15 00:13: /28/15 00:31: /28/15 01:46: /28/15 02:07: /28/15 02:41: /28/15 02:41: /28/15 04:05: /28/15 05:20: /28/15 11:59: /28/15 15:50: /29/15 11:44:

7 06/29/15 11:50: T, S 06/30/15 03:40: /05/15 03:06: /05/15 03:20: T, S 07/22/15 02:37: /27/15 04:52: /29/15 00:55: Northern Cluster Events 10/11/11 19:54: /29/11 00:51: /29/11 11:27: T, S 12/20/11 00:00: /20/11 00:01: /20/11 01:24: S 12/20/11 10:48: /07/12 21:10: /07/12 21:10: /13/12 02:51: /17/12 16:40: /04/12 05:23: /06/12 18:08: /16/12 06:47: S 04/17/12 01:46: /17/12 03:43: /17/12 07:25:

8 S 04/17/12 15:41: T, S 04/18/12 07:33: T, Tr, S 04/18/12 15:21: /18/12 15:24: /18/12 15:25: /18/12 15:58: /18/12 18:00: S 04/18/12 22:30: /19/12 20:50: /19/12 20:50: /09/12 15:34: /11/12 12:31: /11/12 12:37: /11/12 13:13: /14/12 19:02: /23/12 20:02: /22/12 14:32: /28/12 01:28: T 06/28/12 19:35: C 06/30/12 16:43: /30/12 18:36: /02/12 17:11: /02/12 05:57: /04/12 05:12: /08/12 12:04:

9 T 08/29/12 07:54: /29/12 08:00: T 08/29/12 08:05: /29/12 08:52: /31/12 10:36: /26/12 02:19: /04/12 04:50: /04/12 04:51: T 10/04/12 05:07: /04/12 05:34: /09/12 04:39: T, S 10/10/12 23:26: /06/12 03:29: /19/12 04:27: /24/12 08:26: /24/12 08:27: /24/12 08:28: /04/13 03:26: /12/13 01:41: /05/13 08:04: /19/13 16:48: /16/13 11:32: /18/13 05:06: /18/13 09:55: /22/13 11:01:

10 05/29/13 22:17: /06/13 09:39: /07/13 13:37: /22/15 08:24: /22/15 08:50: /22/15 09:23: Non-Cluster Events C 08/03/11 08:14: C 08/03/11 23:15: C 08/04/11 20:01: C 08/06/11 07:06: /06/11 09:48: C 08/22/11 11:07: C 08/24/11 19:29: C 08/27/11 18:35: /31/11 16:07: C 09/30/11 03:15: T 10/03/11 00:52: /24/11 18:45: /28/11 13:29: /10/11 08:20: /11/11 22:46: /14/11 05:47: /14/11 09:16: C 11/20/11 17:41:

11 12/18/11 09:05: T 12/28/11 14:24: /29/11 21:36: /31/11 11:02: /02/12 23:37: /11/12 08:41: C 01/14/12 17:58: /14/12 18:26: S 01/14/12 21:26: /18/12 14:37: /01/12 09:12: /04/12 22:01: /05/12 08:59: /13/12 16:55: C 02/15/12 08:12: C 02/24/12 07:55: S 03/03/12 12:22: /08/12 21:20: C 03/18/12 18:48: /23/12 22:56: /25/12 14:19: C 03/26/12 13:16: C 04/05/12 14:37: C 04/08/12 13:36: C 04/08/12 13:42:

12 C 04/08/12 14:42: C 04/08/12 17:16: /16/12 22:26: /02/12 08:52: C 05/28/12 03:40: /08/12 00:24: C 06/15/12 14:25: C 06/16/12 05:14: C 06/23/12 18:08: C 06/27/12 06:29: C 07/10/12 13:58: /20/12 20:54: /20/12 11:49: /25/12 21:23: /30/12 00:15: C 09/08/12 04:57: /17/12 01:59: C, S 09/22/12 20:15: /26/12 02:19: /03/12 03:25: /09/12 13:56: /04/13 14:53: /02/13 15:53: /10/13 21:08: /02/13 20:29:

13 09/15/13 23:36: /16/13 04:03: C 12/15/13 18:20: C 01/16/14 15:38: C 01/24/14 13:53: C 02/25/14 23:03: /25/14 23:04: /13/14 21:53: C 05/16/14 09:23: /01/15 14:58: /01/15 11:32: /22/15 21:58: /01/15 21:07: *T indicates an event was used as a template for scanning; C indicates the event is in the regional catalogs but was not used for scanning; Tr indicates an event that was also in the catalogs of Tréhu et al. (2015; 2018); S indicates an event that was also in the catalog of Stone et al. (2018) M D is duration magnitude. ERH indicates horizontal location error. # ERZ indicates vertical location error.

14 Figure DR1. Vertical component seismograms for one of the largest (MD 3.15) seamount events, occurring on 27 October, 2014 at 07:41:40.28 UTC. Seismograms are labeled by station name, with corresponding IRIS DMC network code and filter used. Direct P, S and duration picks used for location and magnitude estimation are shown. Sixteen of the stations have duration picks that are outside the shown time window.

15 Magnetically imaged, accreted Siletz Terrane, Wells, Vp/Vs = 1.77 Vp/Vs = X Vp/Vs = 1.85 Orwell Lines, Gerdom et al., 2000 Orwell Lines, Tréhu et al., 2015 Vp/Vs = 1.78 X X X Orwell Velocity Models, Tréhu et al., D Model Locations Figure DR2. Map of CSZ margin with regions colored by the extent of an applied velocity model. Regions were chosen to account for along-strike heterogeneity and to incorporate numerous velocity lines from multiple studies, as well as to account for differences where the crystalline Siletz terrane is present. One-dimensional velocity models are chosen from a series of seismic profile studies (Locations of 1-D models indicated by black squares) and include the ORWELL-1 and ORWELL-3 velocity models presented in Tréhu et al. (2015). Vp/Vs values used are noted by their corresponding 1-D model locations. Solid colored regions indicate where a single velocity model is applied; dashed lines indicate the extent of transition zones between single-model regions, where a mix of models is applied (Klein, 2002). Magnitude From Other Sources Depth (km) From Other Sources Depth (km) (This Study) Duration Magnitude (This Study) Seamount Events, Comparison with PNSN Seamount Events, Comparison with Stone et al., 2018 Seamount Events, Comparison with Tréhu et al., 2015 & 2018 Northern Cluster, Comparison with PNSN Northern Cluster, Comparison with Stone et al., 2018 Northern Cluster, Comparison with Tréhu et al., 2015 & Figure DR3. Comparison of common event depths (left) and magnitudes (right) determined from this study with those determined by other studies (Tréhu et al. 2015; 2018; Stone et al., 2018) and the regional Pacific Northwest Seismic Network (PNSN). For comparison with the Stone et al. (2018) catalog, we use 1-D velocity models from some of the same studies along the margin, but exact 1-D model locations and extent of where they are applied differ, as well as the models used for the Juan de Fuca plate and on land. Similarly, the 1-D velocity models used by PNSN differ from those we use, and the extents of where they are applied differ from those we determined.

16 S-wave Arrival Time - P-wave Arrival Time (s) Seamount Cluster Vp/Vs = P-wave Travel Time (s) P-wave Travel Time (s) Northern Cluster Vp/Vs = 1.76 J25B NEWO J26C J18B J18D HEBO J10D J11D J25A M09B HYSB1 M07A J33A MONO J27D M11B J25C I02D MPO RNO COR 10 I03D G03D J34A J25D HYS14 J33B J33C COR 00 J27B KMO M08C BABR J17D J26A J34C J19D J41A M08A FC03D J26D JEDS J19B J10B J11B Figure DR4. Wadati diagrams for the seamount (left) and northern (right) clusters with pick-based Vp/Vs ratios. Symbols correspond to direct P- and S-wave picks on a given station. Linear arrival time (P or S) vs. S-P time behavior is expected for well-picked arrival times and is evident for our events. No event in the set has all station picks as outliers, indicating that the few outliers present are issues with individual station picks (although they appear acceptable) rather than issues with the location of the event.

17 Maximum Amplitude (Counts) BABR I02D I03D J19B J25A Seamount Cluster J25D J27D J33B JEDS M07A 106 M08A M09B NEWO MPO RNO Maximum Amplitude (Counts) BABR G03D I02D J25A J25B Northern Cluster J33A J33B JEDS M07A M08A RNO Duration Magnitude Duration Magnitude km km Longitudinal Distance from Seamount Magnetic Anomaly Center (km) km Depth (km) 10 Latitudinal Distance from Gravity Anomaly Center (km) Latitudinal Distance from Seamount Magnetic Anomaly Center (km) Figure DR5. Comparison of determined duration magnitudes with the maximum amplitude of stations that contributed to magnitude determination for seamount (left) and northern (right) clusters. The maximum amplitude was chosen between the direct P-wave arrival and signal duration picks. Only stations with 10 or more duration picks during the time period are shown Longitudinal Distance from Gravity Anomaly Center (km) 25 Figure DR6. Focal mechanisms determined for events in the seamount (left) and northern (right) clusters using the FocMec program (Snoke, 2003), colored by event depth. Events with multiple possible mechanism solutions show all solutions boxed together. Gray shaded regions are the M2 seamount magnetic anomaly (left) and G2 gravity anomaly (right). Colored vertical lines are the depth contours of the plate interface of Gerdom et al. (2000). Mechanisms with bold outlines (left) are consistent with the pattern predicted by the upper plate deformation model of seamount subduction (Dominguez et al., 1998; Wang and Bilek, 2011; 2014).

18 REFERENCES CITED Dominguez, S., Lallemand, S.E., Malavieille, J., and von Huene, R., 1998, Upper plate deformation associated with seamount subduction: Tectonophysics, v. 293, p Gerdom, M., Tréhu, A.M., Flueh, E.R., and Klaeschen, D., 2000, The continental margin off oregon from seismic investigations: Tectonophysics, v. 329, p , doi: /S (00) Klein, F.W., 2002, HYPOINVERSE-2000: a Fortran Program to Solve for Earthquake Locations and Magnitudes: U.S. Geological Survey Open-File Report Snoke, J. A. (2003), FOCMEC: FOcal MEChanism determinations: International Handbook of Earthquake and Engineering Seismology (W. H. K. Lee, H. Kanamori, P.C. Jennings, and C. Kisslinger, eds.), Academic Press, San Diego (Part B: and accompanying CD). Stone, I., Vidale, J.E., Han, S., and Roland, E., 2018, Catalog of off-shore seismicity in Cascadia: Insights into the regional distribution of microseismicity and its relation to subduction processes: Journal of Geophysical Research: Solid Earth, v. 123, p. 1 12, doi: /2017JB Tréhu, A.M., Braunmiller, J., and Davis, E., 2015, Seismicity of the Central Cascadia Continental Margin near 44.5 N: A Decadal View: Seismological Research Letters, v. 86, no. 3, p , doi: / Tréhu, A.M., Wilcock, W.S.D., Hilmo, R., Bodin, P., Connolly, J., Roland, E.C., and Braunmiller, J., 2018, The Role of the Ocean Observatories Initiative of the Cascadia Subduction Zone: Oceanography, v. 31, no. 1, p , doi: /oceanog Wells, R.E., Weaver, C.S., and Blakely, R.J., 1998, Fore-arc migration in Cascadia and its neotectonic significance: Geology, v. 26, no. 8, p , doi: / (1998). Wang, K., and Bilek, S.L., 2011, Do subducting seamounts generate or stop large earthquakes? Geology, v. 39, no. 9, p , doi: /G

19 Wang, K., and Bilek, S.L., 2014, Invited review paper: Fault creep caused by subduction of rough seafloor relief: Tectonophysics, v. 610, p. 1 24, doi: /j.tecto

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