Focal mechanism and slip history of the 2011 M w 9.1 off the Pacific coast of Tohoku, Japan earthquake were derived rapidly from teleseismic body and surface waves. Multiple double couples (MDC) analysis was first conducted using 1-hour long period seismic waves, yielding a single double couple with a seismic moment of 5.06×10 22 N m, whose low angle nodal plane orients 199 • and dips 10 • west. Spatiotemporal rupture history was then constrained using both broadband body waves and long period seismic waves. The solution was updated twice in three days. Our preferred model, which based on the MDC fault plane, local JMA hypocenter and calibrated alignments of body and surface waves, revealed a complex rupture process. The rupture initiated slowly at a depth of 23 km. It first propagated in downdip and bilaterally directions along the subduction interface for 45 s and then broke a 80 km by 250 km near trench asperity in the up-dip direction and produced up to 60 m slip. The fault plane below the hypocenter had two more subevents, occurring in 70-95 s and 110-160 s, respectively. The total seismic moment was 5.8 × 10 22 N m. The abnormal high slip near the trench suggests a recurrence interval larger than 500 yr.

The slip history of the 2011 Mw 7.4 Sanriku‐Oki, Japan earthquake, which occurred fifty‐one hours before the Mw 9.1 Tohoku earthquake, is constrained by jointly inverting waveforms of teleseismic body waves, long period surface waves and local strong motions as well as GPS observations, after first relocating its hypocenter using a double difference approach and teleseismic P waves. The inverted results indicate that the rupture of this Sanriku‐Oki earthquake was dominated by the failure of an elliptical shape asperity, elongating roughly along the plate motion direction. The rupture initiated at the southeast corner of this asperity and propagated mainly in the west‐northwest direction with a rupture velocity of 3.1 km/s in the beginning 15 s and 1.1 km/s in the next 40 s. It released a total seismic moment of 1.6 × 1020 Nm, with 82% occurring in the first 25 s. The rupture had an average slip of 1 m and produced an average stress drop of 0.9 MPa. The Sanriku‐Oki earthquake did not break the hypocenter region of the Mw 9.1 Tohoku earthquake but slightly increased the Coulomb stress there. A correlation between the high slip region and the high Vp/Vs ratio of the overriding plate right above the plate interface has been found, which suggests the Sanriku‐Oki earthquake and its frequent predecessors might have broken a relatively weaker patch within a large strongly coupled asperity.

SUMMARY Uncertainties of earthquake finite‐fault inversions based upon strong motion data are investigated using the source inversion validation BlindTest 1 exercise of the SPICE (Seismic Wave Propagation and Imaging in Complex Media: A European Network) project, motivated by previous counterintuitive results. The distribution of slip and the shapes of asymmetric slip rate functions are simultaneously inverted by matching 10 or 33 broad‐band three‐component velocity waveforms within the period ranging from 0.02 to 2 Hz, using a finite‐fault method that carries out the waveform inversion in the wavelet domain. The effects of subfault size, data noise and the number of stations have been explored. Our results suggest: (1) Although there are inevitable discrepancies between the inverted model and the target model because of ignoring the spatial slip variations within individual subfaults, the fault slip and rise‐time distributions can be well constrained even with the data including large Gaussian noise. (2) It is crucial for source studies to develop new inversion schemes that can properly honour the frequency‐ and time‐dependent energy distribution of seismic radiation and data noise. For instance, inversions using the variance reduction function of velocity waveforms as the objective function have low sensitivities to the total seismic moment and peak slip. (3) Although the relative value of the objective function is guided in the inversion, the absolute value of the objective function cannot be used to evaluate the quality of an inverted model. (4) Because the source inversion is based on surface observations, the spatiotemporal resolution of source inversion is affected not only by the data quality but also by the earthquake itself. For vertical strike‐slip faults, the along‐strike resolution is better than that along the downdip direction.

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[1] The source model of the 2008 M w 5.4 Chino Hills, California, earthquake is constrained using near-field seismic body waves recorded by the California Integrated Seismic Network (CISN). Finite fault inversions are preformed for the two fault models based on the nodal planes derived from the CISN moment tensor solution. The northeast dipping plane (strike = 289 ; dip = 62 ), which has a similar strike as the nearby Whittier fault, is chosen as the causative fault because it fits the data significantly better. Our inversion result indicates that the majority of the Chino Hills earthquake rupture occurred in a compact area. In particular, 48% of the total seismic moment (1.6 Â 10 17 Nm) was released by the failure of a 1.8 km 2 asperity located east of the hypocenter in a short time window from 0.4 to 0.8 s after the rupture initiation. The average slip is approximately 0.5 m but the maximum slip is 1.8 m. The average rupture velocity is 1.9 km/s. The static stress drop calculated using the slip model is up to 80 MPa and the average stress drop changes from 19 to 38 MPa, depending on the average schemes. The weighted average slip velocity is 6.5 m/s for entire rupture and is 11 m/s for the east asperity. The inferred available energy and radiated energy are 8 Â 10 13 J and 2.5 Â 10 13 J, respectively. Radiation efficiency is then 0.31, which is moderately low compared with previous earthquakes but consistent with the inferred high average fracture energy density, ranging from 6.5 to 14.8 MJ/m 2 .

In retrosynthetic planning, the huge number of possible routes to synthesize a complex molecule using simple building blocks leads to a combinatorial explosion of possibilities. Even experienced chemists often have difficulty to select the most promising transformations. The current approaches rely on human-defined or machine-trained score functions which have limited chemical knowledge or use expensive estimation methods for guiding. Here we propose an experience-guided Monte Carlo tree search (EG-MCTS) to deal with this problem. Instead of rollout, we build an experience guidance network to learn knowledge from synthetic experiences during the search. Experiments on benchmark USPTO datasets show that, EG-MCTS gains significant improvement over state-of-the-art approaches both in efficiency and effectiveness. In a comparative experiment with the literature, our computer-generated routes mostly matched the reported routes. Routes designed for real drug compounds exhibit the effectiveness of EG-MCTS on assisting chemists performing retrosynthetic analysis.

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